% Embree: High Performance Ray Tracing Kernels 2.17.1 % Intel Corporation
Embree is a collection of high-performance ray tracing kernels, developed at Intel. The target user of Embree are graphics application engineers that want to improve the performance of their application by leveraging the optimized ray tracing kernels of Embree. The kernels are optimized for photo-realistic rendering on the latest Intel® processors with support for SSE, AVX, AVX2, and AVX-512. Embree supports runtime code selection to choose the traversal and build algorithms that best matches the instruction set of your CPU. We recommend using Embree through its API to get the highest benefit from future improvements. Embree is released as Open Source under the Apache 2.0 license.
Embree supports applications written with the Intel SPMD Program Compiler (ISPC, https://ispc.github.io/) by also providing an ISPC interface to the core ray tracing algorithms. This makes it possible to write a renderer in ISPC that leverages SSE, AVX, AVX2, and AVX-512 without any code change. ISPC also supports runtime code selection, thus ISPC will select the best code path for your application, while Embree selects the optimal code path for the ray tracing algorithms.
Embree contains algorithms optimized for incoherent workloads (e.g. Monte Carlo ray tracing algorithms) and coherent workloads (e.g. primary visibility and hard shadow rays). For standard CPUs, the single-ray traversal kernels in Embree provide the best performance for incoherent workloads and are very easy to integrate into existing rendering applications. For AVX-512 enabled machines, a renderer written in ISPC using the default hybrid ray/packet traversal algorithms have shown to perform best, but requires writing the renderer in ISPC. In general for coherent workloads, ISPC outperforms the single ray mode on each platform. Embree also supports dynamic scenes by implementing high performance two-level spatial index structure construction algorithms.
In addition to the ray tracing kernels, Embree provides some tutorials to demonstrate how to use the [Embree API]. The example photorealistic renderer that was originally included in the Embree kernel package is now available in a separate GIT repository (see [Embree Example Renderer]).
Embree supports Windows (32-bit and 64-bit), Linux (64-bit) and Mac OS X (64-bit). The code compiles with the Intel Compiler, GCC, Clang and the Microsoft Compiler.
Using the Intel Compiler improves performance by approximately 10%. Performance also varies across different operating systems, with Linux typically performing best as it supports transparently transitioning to 2MB pages.
Embree is optimized for Intel CPUs supporting SSE, AVX, AVX2, and AVX-512 instructions, and requires at least a CPU with support for SSE2. Contributing to Embree
To contribute code to the Embree repository you need to sign a Contributor License Agreement (CLA). Individuals need to fill out the [Individual Contributor License Agreement (ICLA)]. Corporations need to fill out the [Corporate Contributor License Agreement (CCLA)] and each employee that wants to contribute has to fill out an [Individual Contributor License Agreement (ICLA)]. Please follow the instructions of the CLA forms to send them.
If you encounter bugs please report them via Embree's GitHub Issue Tracker.
For questions please write us at embree_support@intel.com.
To receive notifications of updates and new features of Embree please subscribe to the Embree mailing list.
This software is based in part on the work of the Independent JPEG Group.
You can install the Embree library using the Windows MSI installer
embree-2.17.1-x64.msi. This
will install the 64-bit Embree version by default in Program Files\Intel\Embree v2.17.1 x64.
You have to set the path to the bin folders manually to your PATH
environment variable for applications to find Embree.
To compile applications with Embree using CMake please have a look at
the find_embree tutorial. To compile this tutorial, you need to set
the embree_DIR CMake variable of this tutorial to Program Files\Intel\Embree v2.17.1 x64.
To uninstall Embree again open Programs and Features by clicking the
Start button, clicking Control Panel, clicking Programs, and
then clicking Programs and Features. Select Embree 2.17.1 x64 and uninstall it.
Embree is also delivered as a ZIP file
embree-2.17.1.x64.windows.zip. After
unpacking this ZIP file you should set the path to the lib folder
manually to your PATH environment variable for applications to find
Embree. To compile applications with Embree you also have to set the
Include Directories path in Visual Studio to the include folder of
the Embree installation.
If you plan to ship Embree with your application, best use the Embree version from this ZIP file.
Uncompress the 'tar.gz' file embree-2.17.1.x86_64.rpm.tar.gz to obtain the individual RPM files:
tar xzf embree-2.17.1.x86_64.rpm.tar.gz
To install the Embree using the RPM packages on your Linux system type the following:
sudo rpm --install embree-lib-2.17.1-1.x86_64.rpm
sudo rpm --install embree-devel-2.17.1-1.noarch.rpm
sudo rpm --install embree-examples-2.17.1-1.x86_64.rpm
You also have to install the Intel® Threading Building Blocks (TBB)
using yum:
sudo yum install tbb.x86_64 tbb-devel.x86_64
On Debian-based Linux distributions you first need to convert the RPM
filed into DEB files using the alien tool:
sudo apt-get install alien dpkg-dev debhelper build-essential
sudo alien embree-lib-2.17.1-1.x86_64.rpm
sudo alien embree-devel-2.17.1-1.noarch.rpm
sudo alien embree-examples-2.17.1-1.x86_64.rpm
sudo dpkg -i embree-devel_2.17.1-2_all.deb
sudo dpkg -i embree-examples_2.17.1-2_amd64.deb
sudo dpkg -i embree-lib_2.17.1-2_amd64.deb
Also install the Intel® Threading Building Blocks (TBB) using apt-get:
sudo apt-get install libtbb-dev
Alternatively you can download the latest TBB version from
https://www.threadingbuildingblocks.org/download
and set the LD_LIBRARY_PATH environment variable to point
to the TBB library.
Note that the Embree RPMs are linked against the TBB version coming with CentOS. This older TBB version is missing some features required to get optimal build performance and does not support building of scenes lazily during rendering. To get a full featured Embree please install using the tar.gz files, which always ship with the latest TBB version.
Under Linux Embree is installed by default in the /usr/lib64 and
/usr/include directories. This way applications will find Embree
automatically. The Embree tutorials are installed into the
/usr/bin/embree2 folder. Specify the full path to
the tutorials to start them.
To uninstall Embree again just execute the following:
sudo rpm --erase embree-lib-2.17.1-1.x86_64
sudo rpm --erase embree-devel-2.17.1-1.noarch
sudo rpm --erase embree-examples-2.17.1-1.x86_64
The Linux version of Embree is also delivered as a tar.gz file
embree-2.17.1.x86_64.linux.tar.gz. Unpack
this file using tar and source the provided embree-vars.sh (if you
are using the bash shell) or embree-vars.csh (if you are using the
C shell) to setup the environment properly:
tar xzf embree-2.17.1.x64.linux.tar.gz
source embree-2.17.1.x64.linux/embree-vars.sh
If you want to ship Embree with your application best use the Embree version provided through the tar.gz file.
We recommend adding a relative RPATH to your application that points
to the location Embree (and TBB) can be found, e.g. $ORIGIN/../lib.
To install the Embree library on your Mac OS X system use the
provided package installer inside
embree-2.17.1.x86_64.dmg. This
will install Embree by default into /opt/local/lib and
/opt/local/include directories. The Embree tutorials are installed
into the /Applications/Embree2 folder.
You also have to install the Intel® Threading Building Blocks (TBB) using MacPorts:
sudo port install tbb
Alternatively you can download the latest TBB version from
https://www.threadingbuildingblocks.org/download
and set the DYLD_LIBRARY_PATH environment variable to point
to the TBB library.
To uninstall Embree again execute the uninstaller script
/Applications/Embree2/uninstall.command.
The Mac OS X version of Embree is also delivered as a tar.gz file
embree-2.17.1.x86_64.macosx.tar.gz. Unpack
this file using tar and source the provided embree-vars.sh (if you
are using the bash shell) or embree-vars.csh (if you are using the
C shell) to setup the environment properly:
tar xzf embree-2.17.1.x64.macosx.tar.gz
source embree-2.17.1.x64.macosx/embree-vars.sh
If you want to ship Embree with your application please use the Embree
library of the provided tar.gz file. The library name of that Embree
library is of the form @rpath/libembree.2.dylib
(and similar also for the included TBB library). This ensures that you
can add a relative RPATH to your application that points to the location
Embree (and TBB) can be found, e.g. @loader_path/../lib.
The precompiled Embree library uses the multi-target mode of ISPC. For your ISPC application to properly link against Embree you also have to enable this mode. You can do this by specifying multiple targets when compiling your application with ISPC, e.g.:
ispc --target sse2,sse4,avx,avx2 -o code.o code.ispc
We recommend to use CMake to build Embree. Do not enable fast-math optimization, these might break Embree.
To compile Embree you need a modern C++ compiler that supports C++11.
Embree is tested with Intel® Compiler 17.0 (Update 1), Intel®
Compiler 16.0 (Update 1), Clang 3.8.0 (supports AVX2), Clang 4.0.0
(supports AVX512) and GCC
5.4.0. If the GCC that comes with your Fedora/Red Hat/CentOS
distribution is too old then you can run the provided script
scripts/install_linux_gcc.sh to locally install a recent GCC into
$HOME/devtools-2.
Embree supports to use the Intel® Threading Building Blocks (TBB) as
tasking system. For performance and flexibility reasons we recommend
to use Embree with the Intel® Threading Building Blocks (TBB) and best
also use TBB inside your application. Optionally you can disable TBB
in Embree through the EMBREE_TASKING_SYSTEM CMake variable.
Embree supports the Intel® SPMD Program Compiler (ISPC), which allows
straight forward parallelization of an entire renderer. If you do not
want to use ISPC then you can disable EMBREE_ISPC_SUPPORT in
CMake. Otherwise, download and install the ISPC binaries (we have
tested ISPC version 1.9.1) from
ispc.github.io. After
installation, put the path to ispc permanently into your PATH
environment variable or you need to correctly set the
ISPC_EXECUTABLE variable during CMake configuration.
You additionally have to install CMake 2.8.11 or higher and the developer version of GLUT.
Under Mac OS X, all these dependencies can be installed using MacPorts:
sudo port install cmake tbb freeglut
Depending on your Linux distribution you can install these dependencies
using yum or apt-get. Some of these packages might already be
installed or might have slightly different names.
Type the following to install the dependencies using yum:
sudo yum install cmake.x86_64
sudo yum install tbb.x86_64 tbb-devel.x86_64
sudo yum install freeglut.x86_64 freeglut-devel.x86_64
sudo yum install libXmu.x86_64 libXi.x86_64
sudo yum install libXmu-devel.x86_64 libXi-devel.x86_64
Type the following to install the dependencies using apt-get:
sudo apt-get install cmake-curses-gui
sudo apt-get install libtbb-dev
sudo apt-get install freeglut3-dev
sudo apt-get install libxmu-dev libxi-dev
Finally you can compile Embree using CMake. Create a build directory
inside the Embree root directory and execute ccmake .. inside this
build directory.
mkdir build
cd build
ccmake ..
Per default CMake will use the compilers specified with the CC and
CXX environment variables. Should you want to use a different
compiler, run cmake first and set the CMAKE_CXX_COMPILER and
CMAKE_C_COMPILER variables to the desired compiler. For example, to
use the Intel® Compiler instead of the default GCC on most Linux machines
(g++ and gcc) execute
cmake -DCMAKE_CXX_COMPILER=icpc -DCMAKE_C_COMPILER=icc ..
Similarly, to use Clang set the variables to clang++ and clang,
respectively. Note that the compiler variables cannot be changed anymore
after the first run of cmake or ccmake.
Running ccmake will open a dialog where you can perform various
configurations as described below in [CMake Configuration]. After having
configured Embree, press c (for configure) and g (for generate) to
generate a Makefile and leave the configuration. The code can be
compiled by executing make.
make
The executables will be generated inside the build folder. We recommend
to finally install the Embree library and header files on your
system. Therefore set the CMAKE_INSTALL_PREFIX to /usr in cmake
and type:
sudo make install
If you keep the default CMAKE_INSTALL_PREFIX of /usr/local then
you have to make sure the path /usr/local/lib is in your
LD_LIBRARY_PATH.
You can also uninstall Embree again by executing:
sudo make uninstall
If you cannot install Embree on your system (e.g. when you don't have
administrator rights) you need to add embree_root_directory/build to
your LD_LIBRARY_PATH.
Embree is tested under Windows using the Visual Studio 2017, Visual Studio 2015 (Update 1) compiler (Win32 and x64), Visual Studio 2013 (Update 5) compiler (Win32 and x64), Intel® Compiler 17.0 (Update 1) (Win32 and x64), Intel® Compiler 16.0 (Update 1) (Win32 and x64), and Clang 3.9 (Win32 and x64). Using the Visual Studio 2015 compiler, Visual Studio 2013 compiler, Intel® Compiler, and Clang you can compile Embree for AVX2. To compile Embree for AVX-512 you have to use the Intel® Compiler.
Embree supports to use the Intel® Threading Building Blocks (TBB) as
tasking system. For performance and flexibility reasons we recommend
to use Embree with the Intel® Threading Building Blocks (TBB) and best
also use TBB inside your application. Optionally you can disable TBB
in Embree through the EMBREE_TASKING_SYSTEM CMake variable.
Embree will either find the Intel® Threading Building Blocks (TBB)
installation that comes with the Intel® Compiler, or you can install the
binary distribution of TBB directly from
www.threadingbuildingblocks.org
into a folder named tbb into your Embree root directory. You also have
to make sure that the libraries tbb.dll and tbb_malloc.dll can be found when
executing your Embree applications, e.g. by putting the path to these
libraries into your PATH environment variable.
Embree supports the Intel® SPMD Program Compiler (ISPC), which allows
straight forward parallelization of an entire renderer. When
installing ISPC make sure to download an ISPC version from
ispc.github.io that is
compatible with your Visual Studio version. There are two ISPC
versions, one for Visual Studio 2013 and earlier, and one for Visual
Studio 2015 and later. When using the wrong ISPC version you will get
link errors. After installation, put the path to ispc.exe
permanently into your PATH environment variable or you need to
correctly set the ISPC_EXECUTABLE variable during CMake
configuration. We have tested ISPC version 1.9.1. If you do not want
to use ISPC then you can disable EMBREE_ISPC_SUPPORT in CMake.
You additionally have to install CMake (version 2.8.11 or higher). Note that you need a native Windows CMake installation, because CMake under Cygwin cannot generate solution files for Visual Studio.
Run cmake-gui, browse to the Embree sources, set the build directory
and click Configure. Now you can select the Generator, e.g. "Visual
Studio 12 2013" for a 32-bit build or "Visual Studio 12 2013 Win64"
for a 64-bit build.
To use a different compile than the Microsoft Visual C++ compiler, you additionally need to specify the proper compiler toolset through the option "Optional toolset to use (-T parameter)". E.g. to use Clang for compilation set the toolset to "LLVM-vs2013", to use the Intel® Compiler 2017 for compilation set the toolset to "Intel C++ Compiler 17.0".
Do not change the toolset manually in a solution file (neither through the project properties dialog, nor through the "Use Intel Compiler" project context menu), as then some compiler specific command line options cannot get set by CMake.
Most configuration parameters described in the [CMake Configuration] can be set under Windows as well. Finally, click "Generate" to create the Visual Studio solution files.
Option Description Default
CMAKE_CONFIGURATION_TYPE List of generated Debug;Release;RelWithDebInfo configurations.
USE_STATIC_RUNTIME Use the static OFF version of the C/C++ runtime library.
: Windows-specific CMake build options for Embree.
Use the generated Visual Studio solution file embree2.sln to compile
the project. To build Embree with support for the AVX2 instruction set
you need at least Visual Studio 2013 (Update 4).
We recommend enabling syntax highlighting for the .ispc source and
.isph header files. To do so open Visual Studio, go to Tools ⇒
Options ⇒ Text Editor ⇒ File Extension and add the isph and ispc
extension for the "Microsoft Visual C++" editor.
Embree can also be configured and built without the IDE using the Visual Studio command prompt:
cd path\to\embree
mkdir build
cd build
cmake -G "Visual Studio 12 2013 Win64" ..
cmake --build . --config Release
To use to the Intel® Compiler set the proper toolset, e.g. for Intel Compiler 17.0:
cmake -G "Visual Studio 12 2013 Win64" -T "Intel C++ Compiler 17.0" ..
cmake --build . --config Release
You can also build only some projects with the --target switch.
Additional parameters after "--" will be passed to msbuild. For
example, to build the Embree library in parallel use
cmake --build . --config Release --target embree -- /m
The default CMake configuration in the configuration dialog should be appropriate for most usages. The following table describes all parameters that can be configured in CMake:
Option Description Default
CMAKE_BUILD_TYPE Can be used to switch between Release Debug mode (Debug), Release mode (Release), and Release mode with enabled assertions and debug symbols (RelWithDebInfo).
EMBREE_STACK_PROTECTOR Enables protection of return OFF address from buffer overwrites.
EMBREE_ISPC_SUPPORT Enables ISPC support of Embree. ON
EMBREE_STATIC_LIB Builds Embree as a static OFF library. When using the statically compiled Embree library, you have to define ENABLE_STATIC_LIB before including rtcore.h in your application.
EMBREE_IGNORE_CMAKE_CXX_FLAGS When enabled Embree ignores ON default CMAKE_CXX_FLAGS.
EMBREE_TUTORIALS Enables build of Embree ON tutorials.
EMBREE_BACKFACE_CULLING Enables backface culling, i.e. OFF only surfaces facing a ray can be hit.
EMBREE_INTERSECTION_FILTER Enables the intersection filter ON feature.
EMBREE_INTERSECTION_FILTER Restore previous hit when ON _RESTORE ignoring hits.
EMBREE_RAY_MASK Enables the ray masking feature. OFF
EMBREE_RAY_PACKETS Enables ray packet support. ON
EMBREE_IGNORE_INVALID_RAYS Makes code robust against the OFF risk of full-tree traversals caused by invalid rays (e.g. rays containing INF/NaN as origins).
EMBREE_TASKING_SYSTEM Chooses between Intel® Threading TBB Building Blocks (TBB) or an internal tasking system (INTERNAL).
EMBREE_MAX_ISA Select highest supported ISA AVX2 (SSE2, SSE4.2, AVX, AVX2, AVX512KNL, AVX512SKX, or NONE). When set to NONE the EMBREE_ISA_* variables can be used to enable ISAs individually.
EMBREE_ISA_SSE2 Enables SSE2 when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_ISA_SSE42 Enables SSE4.2 when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_ISA_AVX Enables AVX when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_ISA_AVX2 Enables AVX2 when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_ISA_AVX512KNL Enables AVX-512 for Xeon Phi when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_ISA_AVX512SKX Enables AVX-512 for Skylake when OFF EMBREE_MAX_ISA is set to NONE.
EMBREE_GEOMETRY_TRIANGLES Enables support for triangle ON geometries.
EMBREE_GEOMETRY_QUADS Enables support for quad ON geometries.
EMBREE_GEOMETRY_LINES Enables support for line ON geometries.
EMBREE_GEOMETRY_HAIR Enables support for hair ON geometries.
EMBREE_GEOMETRY_SUBDIV Enables support for subdiv ON geometries.
EMBREE_GEOMETRY_USER Enables support for user ON geometries.
EMBREE_NATIVE_SPLINE_BASIS Specifies the spline basis BEZIER Embree uses internally for its calculations. Hair and curves using this basis can be rendered directly, others are converted.
: CMake build options for Embree.
When using the statically compiled Embree library, you have to define ENABLE_STATIC_LIB before including rtcore.h in your application. Further multiple static libraries are generated for the different ISAs selected (e.g. embree2.a, embree2_sse42.a, embree2_avx.a, embree2_avx2.a, embree2_avx512knl.a, embree2_avx512skx.a). You have to link these libraries in increasing ISA order (the order shown in the example). Embree API
The Embree API is a low level ray tracing API that supports defining
and committing of geometry and performing ray queries of different
types. Static and dynamic scenes are supported, that may contain
triangle geometries, quad geometries, line segment geometries, hair
geometries, analytic bezier curves, subdivision meshes, instanced
geometries, and user defined geometries. For each geometry type
multi-segment motion blur is supported, including support for
transformation motion blur of instances. Supported ray queries are,
finding the closest scene intersection along a ray, and testing a ray
segment for any intersection with the scene. Single rays, as well as
packets of rays in a struct of array layout can be used for packet
sizes of 1, 4, 8, and 16 rays. Using the ray stream interface a stream
of an arbitrary number M of ray packets of arbitrary size N can be
processed. Filter callback functions are supported, that get invoked
for every intersection encountered during traversal.
The Embree API exists in a C++ and ISPC version. This document
describes the C++ version of the API, the ISPC version is almost
identical. The only differences are that the ISPC version needs some
ISPC specific uniform type modifiers, and has special functions that
operate on ray packets of the native SIMD size the ISPC code is
compiled for.
Embree supports two modes for a scene, the normal mode and stream mode, which require different ray queries and callbacks to be
used. The normal mode is the default, but we will switch entirely to
the ray stream mode in a later release.
The user is supposed to include the embree2/rtcore.h, and the
embree2/rtcore_ray.h file, but none of the other header files. If
using the ISPC version of the API, the user should include
embree2/rtcore.isph and embree2/rtcore_ray.isph.
#include <embree2/rtcore.h>
#include <embree2/rtcore_ray.h>
All API calls carry the prefix rtc which stands for ray
tracing core. Embree supports a device concept, which allows
different components of the application to use the API without
interfering with each other. You have to create at least one Embree
device through the rtcNewDevice call. Before the application exits
it should delete all devices by invoking
rtcDeleteDevice. An application typically creates a single device
only, and should create only a small number of devices.
RTCDevice device = rtcNewDevice(NULL);
...
rtcDeleteDevice(device);
It is strongly recommended to have the Flush to Zero and Denormals are Zero mode of the MXCSR control and status register enabled for
each thread before calling the rtcIntersect and rtcOccluded
functions. Otherwise, under some circumstances special handling of
denormalized floating point numbers can significantly reduce
application and Embree performance. When using Embree together with
the Intel® Threading Building Blocks, it is sufficient to execute the
following code at the beginning of the application main thread (before
the creation of the tbb::task_scheduler_init object):
#include <xmmintrin.h>
#include <pmmintrin.h>
...
_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON);
_MM_SET_DENORMALS_ZERO_MODE(_MM_DENORMALS_ZERO_ON);
Embree processes some implementation specific configuration from the following locations in the specified order:
- configuration string passed to the
rtcNewDevicefunction .embree2file in the application folder.embree2file in the home folder
Settings performed later overwrite previous settings. This way the
configuration for the application can be changed globally (either
through the rtcNewDevice call or through the .embree2 file in the
application folder) and each user has the option to modify the
configuration to fit its needs. Configuration files can be ignored by
the application by passing ignore_config_files=1 to rtcNewDevice.
API calls that access geometries are only thread safe as long as different geometries are accessed. Accesses to one geometry have to get sequenced by the application. All other API calls are thread safe. The API calls are re-entrant, it is thus safe to trace new rays and create new geometry when intersecting a user defined object.
Each user thread has its own error flag per device. If an error occurs
when invoking some API function, this flag is set to an error code if it
stores no previous error. The rtcDeviceGetError function reads and returns
the currently stored error and clears the error flag again.
Possible error codes returned by rtcDeviceGetError are:
Error Code Description
RTC_NO_ERROR No error occurred.
RTC_UNKNOWN_ERROR An unknown error has occurred.
RTC_INVALID_ARGUMENT An invalid argument was specified.
RTC_INVALID_OPERATION The operation is not allowed for the specified object.
RTC_OUT_OF_MEMORY There is not enough memory left to complete the operation.
RTC_UNSUPPORTED_CPU The CPU is not supported as it does not support SSE2.
RTC_CANCELLED The operation got cancelled by an Memory Monitor Callback or Progress Monitor Callback function.
: Return values of rtcDeviceGetError.
When the device construction fails rtcNewDevice returns NULL as
device. To detect the error code of a such a failed device
construction pass NULL as device to the rtcDeviceGetError
function. For all other invokations of rtcDeviceGetError a proper
device pointer has to get specified.
Using the rtcDeviceSetErrorFunction2 call, it is also possible to
set a callback function that is called whenever an error occurs for a
device.
typedef void (*RTCErrorFunc2)(void* userPtr, const RTCError, const char* str);
void rtcDeviceSetErrorFunction2(RTCDevice, RTCErrorFunc2, void* userPtr);
When invoked, the registered callback function gets passed a user
defined pointer userPtr, the error code code, as well as some
string str that describes the error further. Passing NULL as
function pointer to rtcDeviceSetErrorFunction2 disables the set
callback function again. The previously described error flags are also
set if an error callback function is present.
Arrays and buffers passed to Embree in most cases have strict alignment and padding requirements to facilitate efficient SIMD processing. The required alignment and padding vary between 16 and 64 bytes, depending on the actual function and data type.
A scene is a container for a set of geometries of potentially different
types. A scene is created using the rtcDeviceNewScene function call, and
destroyed using the rtcDeleteScene function call. Two types of scenes
are supported, dynamic and static scenes. Different flags specify the
type of scene to create and the type of ray query operations that can
later be performed on the scene. The following example creates a scene
that supports dynamic updates and the single ray rtcIntersect and
rtcOccluded calls.
RTCScene scene = rtcDeviceNewScene(device, RTC_SCENE_DYNAMIC, RTC_INTERSECT1);
...
rtcDeleteScene(scene);
Using the following scene flags the user can select between creating a static or dynamic scene.
Scene Flag Description
RTC_SCENE_STATIC Scene is optimized for static geometry. RTC_SCENE_DYNAMIC Scene is optimized for dynamic geometry.
: Dynamic type flags for rtcDeviceNewScene.
A dynamic scene is created by invoking rtcDeviceNewScene with the
RTC_SCENE_DYNAMIC flag. Different geometries can now be created
inside that scene. Geometries are enabled by default. Once the scene
geometry is specified, an rtcCommit call will finish the scene
description and trigger building of internal data structures. After
the rtcCommit call it is safe to perform ray queries of the type
specified at scene construction time. Geometries can get disabled
(rtcDisable call), enabled again (rtcEnable call), and deleted
(rtcDeleteGeometry call). Geometries can also get modified,
including their vertex and index arrays. After the modification of
some geometry, rtcUpdate or rtcUpdateBuffer has to get called for
that geometry to specify which buffers got modified. Each modified
buffer can be specified separately using the rtcUpdateBuffer
function. In contrast the rtcUpdate function simply tags each buffer
of some geometry as modified. If geometries got enabled, disabled,
deleted, or modified an rtcCommit call has to get invoked before
performing any ray queries for the scene, otherwise the effect of the
ray query is undefined. During an rtcCommit call modifications to
the scene are not allowed.
A static scene is created by the rtcDeviceNewScene call with the
RTC_SCENE_STATIC flag. Geometries can only get created, enabled,
disabled and modified until the first rtcCommit call. After the
rtcCommit call, each access to any geometry of that static scene is
invalid. Geometries that got created inside a static scene can only
get deleted by deleting the entire scene.
The modification of geometry, building of hierarchies using
rtcCommit, and tracing of rays have always to happen separately,
never at the same time.
Embree silently ignores primitives that would cause numerical issues, e.g. primitives containing NaNs, INFs, or values greater than 1.844E18f.
The following flags can be used to tune the used acceleration structure. These flags are only hints and may be ignored by the implementation.
Scene Flag Description
RTC_SCENE_COMPACT Creates a compact data structure and avoids algorithms that consume much memory.
RTC_SCENE_COHERENT Optimize for coherent rays (e.g. primary rays).
RTC_SCENE_INCOHERENT Optimize for in-coherent rays (e.g. diffuse reflection rays).
RTC_SCENE_HIGH_QUALITY Build higher quality spatial data structures.
: Acceleration structure flags for rtcDeviceNewScene.
The following flags can be used to tune the traversal algorithm that is used by Embree. These flags are only hints and may be ignored by the implementation.
Scene Flag Description
RTC_SCENE_ROBUST Avoid optimizations that reduce arithmetic accuracy.
: Traversal algorithm flags for rtcDeviceNewScene.
The second argument of the rtcDeviceNewScene function are algorithm flags,
that allow to specify which ray queries are required by the application.
Calling a ray query API function for a scene that is different to the
ones specified at scene creation time is not allowed. Further, the
application should only pass ray query requirements that are really
needed, to give Embree most freedom in choosing the best algorithm. E.g.
in case Embree implements no packet traversers for some highly optimized
data structure for single rays, then this data structure cannot be used
if the user enables any ray packet query.
Algorithm Flag Description
RTC_INTERSECT1 Enables the rtcIntersect and rtcOccluded
functions (single ray interface) for this scene.
RTC_INTERSECT4 Enables the rtcIntersect4 and rtcOccluded4
functions (4-wide packet interface) for this scene.
RTC_INTERSECT8 Enables the rtcIntersect8 and rtcOccluded8
functions (8-wide packet interface) for this scene.
RTC_INTERSECT16 Enables the rtcIntersect16 and rtcOccluded16
functions (16-wide packet interface) for this
scene.
RTC_INTERSECT_STREAM Enables the rtcIntersect1M, rtcOccluded1M,
rtcIntersect1Mp, rtcOccluded1Mp,
rtcIntersectNM, rtcOccludedNM,
rtcIntersectNp, and rtcOccludedNp
functions for this scene.
RTC_INTERPOLATE Enables the rtcInterpolate and rtcInterpolateN
interpolation functions.
: Enabled algorithm flags for rtcDeviceNewScene.
Embree supports two modes for a scene, the normal mode and stream mode. These modes mainly differ in the kind of callbacks invoked and
how rays are extended with user data. The normal mode is enabled by
default, the ray stream mode can be enabled using the
RTC_INTERSECT_STREAM algorithm flag for a scene. Only in ray stream
mode, the stream API functions rtcIntersect1M, rtcIntersect1Mp,
rtcIntersectNM, and rtcIntersectNp as well as their occlusion
variants can be used.
The scene bounding box can get read by the function
rtcGetBounds(RTCScene scene, RTCBounds& bounds_o). This function
will write the AABB of the scene to bounds_o. Time varying bounds
can be obtained usin the rtcGetLinearBounds(RTCScene scene, RTCBounds* bounds_o) function. This function will write two AABBs to
bounds_o. Linearly interpolating these bounds to a specific time t
yields bounds that bound the geometry at that time. Invoking these
functions is only valid when all scene changes got committed using
rtcCommit.
Geometries are always contained in the scene they are created in. Each
geometry is assigned an integer ID at creation time, which is unique
for that scene. The current version of the API supports triangle
meshes (rtcNewTriangleMesh2), quad meshes (rtcNewQuadMesh2),
Catmull-Clark subdivision surfaces (rtcNewSubdivisionMesh2), curve
geometries (rtcNewBezierCurveGeometry2), hair geometries
(rtcNewBezierHairGeometry2), single level instances of other scenes
(rtcNewInstance3), and user defined geometries
(rtcNewUserGeometry3). The API is designed in a way that easily
allows adding new geometry types in later releases.
The application can manage geometry IDs itself, or let Embree allocate
geometry IDs. Therefore all geometry creation functions have a
geomID parameter. This parameter can be set to
RTC_INVALID_GEOMETRY_ID to let Embree allocate a geometry ID
(default) or to some geometry ID allocated by the application.
If the application allocates a geometry ID, then this geometry ID has to be unused in the scene, otherwise the creation of the geometry will fail. Further, the geometry IDs allocated by the application should be compact, as Embree internally created a vector which size is equal to the largest geometry ID used. Creating very large geometry IDs for small scenes would thus cause a memory consumption and performance overhead.
If Embree allocates a geometry ID then the following properties hold. For dynamic scenes, all IDs are assigned sequentially, starting from 0, as long as no geometry got deleted. If geometries got deleted, the implementation will reuse IDs later on in an implementation dependent way. Consequently sequential assignment is no longer guaranteed, but a compact range of IDs. These rules allow the application to manage a dynamic array to efficiently map from geometry IDs to its own geometry representation. For static scenes, geometry IDs are assigned sequentially starting at 0. This allows the application to use a fixed size array to map from geometry IDs to its own geometry representation.
Alternatively the application can also use the void rtcSetUserData (RTCScene scene, unsigned geomID, void* ptr) function to set a user
data pointer ptr to its own geometry representation, and later read
out this pointer again using the void* rtcGetUserData (RTCScene scene, unsigned geomID) function.
The following geometry flags can be specified at construction time of geometries:
Geometry Flag Description
RTC_GEOMETRY_STATIC The geometry is considered static and should get modified rarely by the application. This flag has to get used in static scenes.
RTC_GEOMETRY_DEFORMABLE The geometry is considered to deform in a coherent way, e.g. a skinned character. The connectivity of the geometry has to stay constant, thus modifying the index array is not allowed. The implementation is free to choose a BVH refitting approach for handling meshes tagged with that flag.
RTC_GEOMETRY_DYNAMIC The geometry is considered highly dynamic and changes frequently, possibly in an unstructured way. Embree will rebuild data structures from scratch for this type of geometry.
: Flags for the creation of new geometries.
Triangle meshes are created using the rtcNewTriangleMesh2 function
call, and potentially deleted using the rtcDeleteGeometry function
call.
The number of triangles, number of vertices, and optionally the number of time steps for multi-segment motion blur have to get specified at construction time of the mesh. The user can also specify additional flags that choose the strategy to handle that mesh in dynamic scenes. The following example demonstrates how to create a triangle mesh without motion blur:
unsigned geomID = rtcNewTriangleMesh2(scene, geomFlags,
numTriangles, numVertices, 1);
The triangle indices can be set by mapping and writing to the index
buffer (RTC_INDEX_BUFFER) and the triangle vertices can be set by
mapping and writing into the vertex buffer (RTC_VERTEX_BUFFER). The
index buffer contains an array of three 32-bit indices, while the
vertex buffer contains an array of three float values. The vertex
buffer can be at most 16GB large. When the vertex buffer is managed
internally the stride between vertices is 16 bytes. For multi segment
motion blur, for each time step a vertex buffer has to be specified,
and all these buffers have to have the same stride. All buffers have
to get unmapped before an rtcCommit call to the scene.
struct Vertex { float x, y, z, a; };
struct Triangle { int v0, v1, v2; };
Vertex* vertices = (Vertex*) rtcMapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
// fill vertices here
rtcUnmapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
Triangle* triangles = (Triangle*) rtcMapBuffer(scene, geomID, RTC_INDEX_BUFFER);
// fill triangle indices here
rtcUnmapBuffer(scene, geomID, RTC_INDEX_BUFFER);
Also see tutorial [Triangle Geometry] for an example of how to create triangle meshes.
The parametrization of a triangle uses the first vertex p0 as base
point, and the vector p1 - p0 as u-direction and p2 - p0 as
v-direction. The following picture additionally illustrates the
direction the geometry normal is pointing into.
![][imgTriangleUV]
Some texture coordinates t0,t1,t2 can be linearly interpolated over
the triangle the following way:
t_uv = (1-u-v)*t0 + u*t1 + v*t2
Quad meshes are created using the rtcNewQuadMesh2 function
call, and potentially deleted using the rtcDeleteGeometry function
call.
The number of quads, number of vertices, and optionally the number of time steps for multi-segment motion blur have to get specified at construction time of the mesh. The user can also specify additional flags that choose the strategy to handle that mesh in dynamic scenes. The following example demonstrates how to create a quad mesh without motion blur:
unsigned geomID = rtcNewQuadMesh2(scene, geomFlags,
numQuads, numVertices, 1);
The quad indices can be set by mapping and writing to the index buffer
(RTC_INDEX_BUFFER) and the quad vertices can be set by mapping and
writing into the vertex buffer (RTC_VERTEX_BUFFER). The index buffer
contains an array of four 32-bit indices, while the vertex buffer
contains an array of three float values. The vertex buffer can be at
most 16GB large. When the vertex buffer is managed internally the
stride between vertices is 16 bytes. For multi segment motion blur,
for each time step a vertex buffer has to be specified, and all these
buffers have to have the same stride. All buffers have to get unmapped
before an rtcCommit call to the scene.
struct Vertex { float x, y, z, a; };
struct Quad { int v0, v1, v2, v3; };
Vertex* vertices = (Vertex*) rtcMapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
// fill vertices here
rtcUnmapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
Quad* quads = (Quad*) rtcMapBuffer(scene, geomID, RTC_INDEX_BUFFER);
// fill quad indices here
rtcUnmapBuffer(scene, geomID, RTC_INDEX_BUFFER);
A quad is internally handled as a pair of two triangles v0,v1,v3 and
v2,v3,v1, with the u'/v' coordinates of the second triangle
corrected by u = 1-u' and v = 1-v' to produce a quad
parametrization where u and v go from 0 to 1.
To encode a triangle as a quad just replicate the last triangle vertex
(v0,v1,v2 -> v0,v1,v2,v2). This way the quad mesh can be used to
represent a mixed mesh which contains triangles and quads.
Catmull-Clark subdivision surfaces for meshes consisting of faces of up to 15 vertices (e.g. triangles, quadrilateral, pentagons, etc.) are supported, including support for edge creases, vertex creases, holes, non-manifold geometry, and face-varying interpolation.
A subdivision surface is created using the rtcNewSubdivisionMesh2
function call, and deleted again using the rtcDeleteGeometry
function call.
unsigned rtcNewSubdivisionMesh2(RTCScene scene,
RTCGeometryFlags flags,
size_t numFaces,
size_t numEdges,
size_t numVertices,
size_t numEdgeCreases,
size_t numVertexCreases,
size_t numCorners,
size_t numHoles,
size_t numTimeSteps,
unsigned int geomID);
The number of faces (numFaces), edges/indices (numEdges), vertices
(numVertices), edge creases (numEdgeCreases), vertex creases
(numVertexCreases), holes (numHoles), and time steps
(numTimeSteps) have to get specified at construction time.
The following buffers have to get setup by the application: the face
buffer (RTC_FACE_BUFFER) contains the number edges/indices (3 to 15) of
each of the numFaces faces, the index buffer (RTC_INDEX_BUFFER)
contains multiple (3 to 15) 32-bit vertex indices for each face and
numEdges indices in total, the vertex buffer (RTC_VERTEX_BUFFER)
stores numVertices vertices as single precision x, y, z floating
point coordinates aligned to 16 bytes. The value of the 4th float used
for alignment can be arbitrary.
Optionally the application may fill additional index buffers if
multiple topologies are required for face-varying interpolation. The
standard vertex buffers RTC_VERTEX_BUFFER are always bound to the
geometry topology (topology 0) thus use RTC_INDEX_BUFFER0. Data
interpolation may use different topologies as described later.
Optionally, the application can setup the hole buffer (RTC_HOLE_BUFFER)
with numHoles many 32-bit indices of faces that should be considered
non-existing in all topologies.
Optionally, the application can fill the level buffer
(RTC_LEVEL_BUFFER) with a tessellation rate for each or the edges of
each face, making a total of numEdges values. The tessellation level
is a positive floating point value, that specifies how many quads
along the edge should get generated during tessellation. If no level
buffer is specified a level of 1 is used. The maximally supported edge
level is 4096 and larger levels get clamped to that value. Note that
some edge may be shared between (typically 2) faces. To guarantee a
watertight tessellation, the level of these shared edges has to be
exactly identical. A uniform tessellation rate for an entire
subdivision mesh can be set by using the
rtcSetTessellationRate(RTCScene scene, unsigned geomID, float rate)
function. The existance of a level buffer has preference over the
uniform tessellation rate.
Optionally, the application can fill the sparse edge crease buffers to
make some edges appear sharper. The edge crease index buffer
(RTC_EDGE_CREASE_INDEX_BUFFER) contains numEdgeCreases many pairs
of 32-bit vertex indices that specify unoriented edges in the
geometry topology. The edge crease weight buffer
(RTC_EDGE_CREASE_WEIGHT_BUFFER) stores for each of theses crease
edges a positive floating point weight. The larger this weight, the
sharper the edge. Specifying a weight of infinity is supported and
marks an edge as infinitely sharp. Storing an edge multiple times with
the same crease weight is allowed, but has lower performance. Storing
an edge multiple times with different crease weights results in
undefined behavior. For a stored edge (i,j), the reverse direction
edges (j,i) does not have to get stored, as both are considered the
same edge. Edge crease features are specified for the geomtetry
topology, but copied to all other topologies automatically.
Optionally, the application can fill the sparse vertex crease buffers
to make some vertices appear sharper. The vertex crease index buffer
(RTC_VERTEX_CREASE_INDEX_BUFFER), contains numVertexCreases many
32-bit vertex indices to specify a set of vertices from the geometry
topology. The vertex crease weight buffer
(RTC_VERTEX_CREASE_WEIGHT_BUFFER) specifies for each of these
vertices a positive floating point weight. The larger this weight, the
sharper the vertex. Specifying a weight of infinity is supported and
makes the vertex infinitely sharp. Storing a vertex multiple times
with the same crease weight is allowed, but has lower
performance. Storing a vertex multiple times with different crease
weights results in undefined behavior. Vertex crease features are
specified for the geomtetry topology, but copied to all other
topologies automatically.
Faces with 3 to 15 vertices are supported (triangles, quadrilateral, pentagons, etc).
The user can also specify a geometry mask and additional flags that choose the strategy to handle that subdivision mesh in dynamic scenes.
The implementation of subdivision surfaces uses an internal software cache, which can get configured to some desired size (see [Configuring Embree]).
The parametrization of a regular quadrilateral uses the first vertex p0 as
base point, and the vector p1 - p0 as u-direction and p3 - p0 as
v-direction. The following picture additionally illustrates the
direction the geometry normal is pointing into.
![][imgQuadUV]
Some texture coordinates t0,t1,t2,t3 can be bi-linearly
interpolated over the quadrilateral the following way:
t_uv = (1-v)((1-u)*t0 + u*t1) + v*((1-u)*t3 + u*t2)
The parametrization for all other face types where the number of vertices is not equal to 4, have a special parametrization where the n'th quadrilateral (that would be obtained by a single subdivision step) and the local hit location inside this quadrilateral are encoded in the UV coordinates. The following piece of code extracts the sub-patch ID i and UVs of this subpatch:
const unsigned l = floorf(0.5f*U);
const unsigned h = floorf(0.5f*V);
const unsigned i = 4*h+l;
const float u = 2.0f*fracf(0.5f*U)-0.5f;
const float v = 2.0f*fracf(0.5f*V)-0.5f;
This encoding allows local subpatch UVs to be in the range
[-0.5,1.5[ thus negative subpatch UVs can get passed to
rtcInterpolate to sample subpatches slightly out of bounds.
This can be useful to calculate derivatives using finite
differences if required. The encoding further has the property
that you can just move some value du (or dv) on a subpatch by
adding du (or dv) to the special UV encoding as long as you
are not falling out of the [-0.5,1.5[ range. Further, derivatives
calculated using finite differences are compatible
with derivatives calculated using rtcInterpolate when using the
standard formula:
dF(u)/du = (F(u+du)-F(u))/du
To smoothly interpolate texture coordinates over the subdivision
surface we recommend using the rtcInterpolate function, which will
apply the standard subdivision rules for interpolation and
automatically take care of the special UV encoding for
non-quadrilaterals.
Face-varying interpolation is supported through multiple topologies per subdivision mesh and binding such topologies to user vertex buffers to interpolate. This way texture coordinates may use a different topology with additional boundaries to construct separate UV regions inside one subdivision mesh.
Each such topology consists of an index buffer and subdivision
mode. Up to 16 topologies are supported, with corresponding index
buffers RTC_INDEX_BUFFER0+i, with i in the range 0 to 15.
Each of the 16 supported user vertex buffers
RTC_USER_VERTEX_BUFFER0+j (j in the range 0 to 15) can be assigned
to some topology using the rtcSetIndexBuffer call:
void rtcSetIndexBuffer(RTCScene scene, unsigned geomID,
RTCBufferType vertexBuffer, RTCBufferType indexBuffer);
The face buffer (RTC_FACE_BUFFER) is shared between all topologies,
which means that the n'th primitive always has the same number of
vertices (e.g. being a triangle or a quad) for each topology. However,
the indices of the topologies themselves may be different.
The subdivision modes can be used to force linear interpolation for some parts of the subdivision mesh.
Boundary Mode Description
RTC_SUBDIV_NO_BOUNDARY Boundary patches are ignored. This way each rendered patch has a full set of control vertices.
RTC_SUBDIV_SMOOTH_BOUNDARY The sequence of boundary control points are used to generate a smooth B-spline boundary curve (default mode).
RTC_SUBDIV_PIN_CORNERS Corner vertices are pinned to their location during subdivision.
RTC_SUBDIV_PIN_BOUNDARY All vertices at the border are pinned to their location during subdivision. This way the boundary is interpolated linearly.
RTC_SUBDIV_PIN_ALL All vertices at the border are binned to their location during subdivision. This way all patches are linearly interpolated.
: Subdivision modes supported by Embree.
These modes can be set to each topology separately using the
rtcSetSubdivisionMode API call with the following signature:
void rtcSetSubdivisionMode(RTCScene scene, unsigned geomID,
unsigned topologyID, RTCSubdivisionMode mode);
These modes are typically used to interpolate face-varying data
properly. E.g. the topology used to interpolate texture coordinaces
are typically assigned the RTC_SUBDIV_PIN_BOUNDARY mode, to also map
texels at the border of the texture to the mesh.
Also see tutorial [Subdivision Geometry] for an example of how to create subdivision surfaces.
Line segments are supported to render hair geometry. A line segment consists of a start and end point, and start and end radius. Individual line segments are considered to be subpixel sized which allows the implementation to approximate the intersection calculation. This in particular means that zooming onto one line segment might show geometric artifacts.
Line segments are created using the rtcNewLineSegments2 function
call, and potentially deleted using the rtcDeleteGeometry function
call.
The number of line segments, the number of vertices, and optionally the number of time steps for multi-segment motion blur have to get specified at construction time of the line segment geometry.
The segment indices can be set by mapping and writing to the index buffer
(RTC_INDEX_BUFFER) and the vertices can be set by mapping and
writing into the vertex buffer (RTC_VERTEX_BUFFER). In case of
motion blur, the vertex buffers (RTC_VERTEX_BUFFER0+t) have to get
filled for each time step t.
The index buffer contains an array of 32-bit indices pointing to the
ID of the first of two vertices, while the vertex buffer
stores all control points in the form of a single precision position
and radius stored in x, y, z, r order in memory. The
radii have to be greater or equal zero. All buffers have to get
unmapped before an rtcCommit call to the scene.
The intersection with the line segment primitive stores the parametric
hit location along the line segment as u-coordinate (range v is always set to zero). The geometry normal Ng is filled with the
the tangent, i.e. the vector from start to end vertex.
Like for triangle meshes, the user can also specify a geometry mask and additional flags that choose the strategy to handle that mesh in dynamic scenes.
The following example demonstrates how to create some line segment geometry:
unsigned geomID = rtcNewLineSegments2(scene, geomFlags, numCurves,
numVertices, 1);
struct Vertex { float x, y, z, r; };
Vertex* vertices = (Vertex*) rtcMapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
// fill vertices here
rtcUnmapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
int* curves = (int*) rtcMapBuffer(scene, geomID, RTC_INDEX_BUFFER);
// fill indices here
rtcUnmapBuffer(scene, geomID, RTC_INDEX_BUFFER);
Hair geometries are supported, which consist of multiple hairs represented as cubic spline curves with varying radius per control point. As spline basis we currently support Bézier splines and B-splines. Individual hairs are considered to be subpixel sized which allows the implementation to approximate the intersection calculation. This in particular means that zooming onto one hair might show geometric artifacts.
Hair geometries are created using the rtcNewBezierHairGeometry2 or
rtcNewBSplineHairGeometry2 function call, and potentially deleted
using the rtcDeleteGeometry function call.
The number of hair curves, the number of vertices, and optionally the number of time steps for multi-segment motion blur have to get specified at construction time of the hair geometry.
The curve indices can be set by mapping and writing to the index
buffer (RTC_INDEX_BUFFER) and the control vertices can be set by
mapping and writing into the vertex buffer (RTC_VERTEX_BUFFER). In
case of motion blur, the vertex buffers RTC_VERTEX_BUFFER0+t have to
get filled for each time step.
The index buffer contains an array of 32-bit indices pointing to the
ID of the first of four control vertices, while the vertex buffer
stores all control points in the form of a single precision position
and radius stored in x, y, z, r order in memory. The hair
radii have to be greater or equal zero. All buffers have to get
unmapped before an rtcCommit call to the scene.
The intersection with the hair primitive stores the parametric hit
location along the hair as u-coordinate (range 0 to +1), and the
normalized distance as the v-coordinate (range -1 to +1). The
geometry normal Ng is filled with the the tangent of the bezier
curve at the hit location on the curve (dPdu).
The implementation may choose to subdivide the Bézier curve into
multiple cylinders-like primitives. The number of cylinders the curve
gets subdivided into can be specified per hair geometry through the
rtcSetTessellationRate(RTCScene scene, unsigned geomID, float rate)
function. By default the tessellation rate for hair curves is 4.
Like for triangle meshes, the user can also specify a geometry mask and additional flags that choose the strategy to handle that mesh in dynamic scenes.
The following example demonstrates how to create some hair geometry:
unsigned geomID = rtcNewBezierHairGeometry2(scene, geomFlags, numCurves, numVertices);
struct Vertex { float x, y, z, r; };
Vertex* vertices = (Vertex*) rtcMapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
// fill vertices here
rtcUnmapBuffer(scene, geomID, RTC_VERTEX_BUFFER);
int* curves = (int*) rtcMapBuffer(scene, geomID, RTC_INDEX_BUFFER);
// fill indices here
rtcUnmapBuffer(scene, geomID, RTC_INDEX_BUFFER);
Also see tutorial [Hair] for an example of how to create and use hair geometry.
The spline curve geometry consists of multiple cubic spline curves with varying radius per control point. As spline basis we currently support Bézier splines and B-splines. The cuve surface is defined as the sweep surface of sweeping a varying radius circle tangential along the Bézier curve. As a limitation, the radius of the curve has to be smaller than the curvature radius of the Bézier curve at each location on the curve. In contrast to hair geometry, the curve geometry is rendered properly even in closeups.
Curve geometries are created using the rtcNewBezierCurveGeometry2 or
rtcNewBSplineCurveGeometry2 function call, and potentially deleted
using the rtcDeleteGeometry function call.
The number of Bézier curves, the number of vertices, and optionally the number of time steps for multi-segment motion blur have to get specified at construction time of the curve geometry.
The curve indices can be set by mapping and writing to the index
buffer (RTC_INDEX_BUFFER) and the control vertices can be set by
mapping and writing into the vertex buffer (RTC_VERTEX_BUFFER). In
case of motion blur, the vertex buffers RTC_VERTEX_BUFFER0+t have to
get filled for each time step.
The index buffer contains an array of 32-bit indices pointing to the
ID of the first of four control vertices, while the vertex buffer
stores all control points in the form of a single precision position
and radius stored in x, y, z, r order in memory. The curve
radii have to be greater or equal zero. All buffers have to get
unmapped before an rtcCommit call to the scene.
Like for triangle meshes, the user can also specify a geometry mask and additional flags that choose the strategy to handle the curves in dynamic scenes.
Also see tutorial [Curves] for an example of how to create and use Bézier curve geometries.
User defined geometries make it possible to extend Embree with arbitrary types of user defined primitives. This is achieved by introducing arrays of user primitives as a special geometry type.
User geometries are created using the rtcNewUserGeometry3 function
call, and potentially deleted using the rtcDeleteGeometry function
call.
When creating a user defined geometry, the user has to set a data pointer, a bounding function closure (function and user pointer) as well as user defined intersect and occluded callback function pointers. The bounding function is used to query the bounds of all timesteps of a user primitive, while the intersect and occluded callback functions are called to intersect the primitive with a ray.
The bounding function to register has the following signature
typedef void (*RTCBoundsFunc3)(void* userPtr, void* geomUserPtr, size_t id, size_t timeStep, RTCBounds& bounds_o);
and can be registered using the rtcSetBoundsFunction3 API function:
rtcSetBoundsFunction3(scene, geomID, userBoundsFunction, userPtr);
When the bounding callback is called, it is passed a user defined
pointer specified at registration time of the bounds function
(userPtr parameter), the per geometry user data pointer
(geomUserPtr parameter), the ID of the primitive to calculate the
bounds for (id parameter), the time step at which to calculate the
bounds (timeStep parameter) and a memory location to write the
calculated bound to (bounds_o parameter).
The signature of supported user defined intersect and occluded function in normal mode is as follows:
typedef void (*RTCIntersectFunc ) ( void* userDataPtr, RTCRay& ray, size_t item);
typedef void (*RTCIntersectFunc4 ) (const void* valid, void* userDataPtr, RTCRay4& ray, size_t item);
typedef void (*RTCIntersectFunc8 ) (const void* valid, void* userDataPtr, RTCRay8& ray, size_t item);
typedef void (*RTCIntersectFunc16) (const void* valid, void* userDataPtr, RTCRay16& ray, size_t item);
The RTCIntersectFunc callback function operates on single rays and
gets passed the user data pointer of the user geometry (userDataPtr
parameter), the ray to intersect (ray parameter), and the ID of the
primitive to intersect (item parameter). The
RTCIntersectFunc4/8/16 callback functions operate on ray packets of
size 4, 8 and 16 and additionally get an integer valid mask as input
(valid parameter). The callback functions should not modify any ray
that is disabled by that valid mask.
In stream mode the following callback function has to get used:
typedef void (*RTCIntersectFuncN ) (const int* valid, void* userDataPtr, const RTCIntersectContext* context, RTCRayN* rays, size_t N, size_t item);
typedef void (*RTCIntersectFunc1Mp)( void* userDataPtr, const RTCIntersectContext* context, RTCRay** rays, size_t M, size_t item);
The RTCIntersectFuncN callback function supports ray packets of
arbitrary size N. The RTCIntersectFunc1Mp callback function get an
array of M pointers to single rays as input.
The user intersect function should return without modifying the ray
structure if the user geometry is missed. Whereas, if an intersection
of the user primitive with the ray segment was found, the intersect
function has to update the hit information of the ray (tfar, u,
v, Ng, geomID, primID components).
The user occluded function should also return without modifying the ray
structure if the user geometry is missed. If the geometry is hit, it
should set the geomID member of the ray to 0.
When performing ray queries using the rtcIntersect and rtcOccluded
function, callbacks of type RTCIntersectFunc are invoked for user
geometries. Consequently, an application only operating on single rays
only has to provide the single ray intersect and occluded
callbacks. Similar when calling the rtcIntersect4/8/16 and
rtcOccluded4/8/16 functions, the RTCIntersectFunc4/8/16 callbacks
of matching packet size and type are called.
If ray stream mode is enabled for the scene only the
RTCIntersectFuncN and RTCIntersectFunc1Mp callback can be used. In
this case specifying an RTCIntersectFuncN callback is mandatory and
the RTCIntersectFunc1Mp callback is optional. Trying to set a
different type of user callback function results in an error.
The following example illustrates creating an array with two user geometries:
int numTimeSteps = 2;
struct UserObject { ... };
void userBoundsFunction(void* userPtr, UserObject* userGeomPtr, size_t i, size_t t, RTCBounds& bounds)
{
bounds = <bounds of userGeomPtr[i] at time t>;
}
void userIntersectFunction(UserObject* userGeomPtr, RTCRay& ray, size_t i)
{
if (<ray misses userGeomPtr[i] at time ray.time>)
return;
<update ray hit information>;
}
void userOccludedFunction(UserObject* userGeomPtr, RTCRay& ray, size_t i)
{
if (<ray misses userGeomPtr[i] at time ray.time>)
return;
geomID = 0;
}
...
UserObject* userGeomPtr = new UserObject[2];
userGeomPtr[0] = ...
userGeomPtr[1] = ...
unsigned geomID = rtcNewUserGeometry3(scene, 2, numTimeSteps);
rtcSetUserData(scene, geomID, userGeomPtr);
rtcSetBoundsFunction3(scene, geomID, userBoundsFunction, userPtr);
rtcSetIntersectFunction(scene, geomID, userIntersectFunction);
rtcSetOccludedFunction(scene, geomID, userOccludedFunction);
See tutorial [User Geometry] for an example of how to use the user defined geometries.
Embree supports instancing of scenes inside another scene by some transformation. As the instanced scene is stored only a single time, even if instanced to multiple locations, this feature can be used to create very large scenes. Only single level instancing is supported by Embree natively, however, multi-level instancing can be implemented through user geometries.
Instances are created using the rtcNewInstance3 (RTCScene target, RTCScene source, size_t numTimeSteps) function call, and
potentially deleted using the rtcDeleteGeometry function call. To
instantiate a scene, one first has to generate the scene B to
instantiate. Now one can add an instance of this scene inside a scene A
the following way:
unsigned instID = rtcNewInstance3(sceneA, sceneB, 1);
rtcSetTransform2(sceneA, instID, RTC_MATRIX_COLUMN_MAJOR, &column_matrix_3x4, 0);
To create some motion blurred instance just pass the number of time steps and specify one matrix for each time step:
unsigned instID = rtcNewInstance3(sceneA, sceneB, 3);
rtcSetTransform2(sceneA, instID, RTC_MATRIX_COLUMN_MAJOR, &column_matrix_t0_3x4, 0);
rtcSetTransform2(sceneA, instID, RTC_MATRIX_COLUMN_MAJOR, &column_matrix_t1_3x4, 1);
rtcSetTransform2(sceneA, instID, RTC_MATRIX_COLUMN_MAJOR, &column_matrix_t2_3x4, 2);
Both scenes have to belong to the same device. One has to call
rtcCommit on scene B before one calls rtcCommit on scene A. When
modifying scene B one has to call rtcUpdate for all instances of
that scene. If a ray hits the instance, then the geomID and primID
members of the ray are set to the geometry ID and primitive ID of the
primitive hit in scene B, and the instID member of the ray is set to
the instance ID returned from the rtcNewInstance3 function.
Some special care has to be taken when using user geometries and
instances in the same scene. Instantiated user geometries should not
set the instID field of the ray as this field is managed by the
instancing already. However, non-instantiated user geometries should
clear the instID field to RTC_INVALID_GEOMETRY_ID, to later
distinguish them from instantiated geometries that have the instID
field set.
The rtcSetTransform2 call can be passed an affine transformation matrix
with different data layouts:
Layout Description
RTC_MATRIX_ROW_MAJOR The 3×4 float matrix is laid out in row major form.
RTC_MATRIX_COLUMN_MAJOR The 3×4 float matrix is laid out in column major form.
RTC_MATRIX_COLUMN_MAJOR_ALIGNED16 The 3×4 float matrix is laid out in column major form, with each column padded by an additional 4th component.
: Matrix layouts for rtcSetTransform2.
Passing homogeneous 4×4 matrices is possible as long as the last row is
(0, 0, 0, 1). If this homogeneous matrix is laid out in row major form,
use the RTC_MATRIX_ROW_MAJOR layout. If this homogeneous matrix is
laid out in column major form, use the
RTC_MATRIX_COLUMN_MAJOR_ALIGNED16 mode. In both cases, Embree will
ignore the last row of the matrix.
The transformation passed to rtcSetTransform2 transforms from the local
space of the instantiated scene to world space.
See tutorial [Instanced Geometry] for an example of how to use instances.
The ray layout to be passed to the ray tracing core is defined in the
embree2/rtcore_ray.h header file. It is up to the user to use the
ray structures defined in that file, or resemble the exact same binary
data layout with their own vector classes. The ray layout might change
with new Embree releases as new features get added, however, will stay
constant as long as the major Embree release number does not
change. The ray contains the following data members:
Member In/Out Description
org in ray origin dir in ray direction (can be unnormalized) tnear in start of ray segment tfar in/out end of ray segment, set to hit distance after intersection time in time used for multi-segment motion blur [0,1] mask in ray mask to mask out geometries Ng out unnormalized geometry normal in object space u out barycentric u-coordinate of hit v out barycentric v-coordinate of hit geomID out geometry ID of hit geometry primID out primitive ID of hit primitive instID out instance ID of hit instance
: Data fields of a ray.
This structure is in struct of array layout (SOA) for API functions accepting ray packets.
To create a single ray you can use the RTCRay ray type defined in
embree2/rtcore_ray.h. To generate a ray packet of size 4, 8, or 16
you can use the RTCRay4, RTCRay8, or RTCRay16
types. Alternatively you can also use the RTCRayNt template to
generate ray packets of an arbitrary compile time known size.
When the ray packet size is not known at compile time (e.g. when
Embree returns a ray packet in the RTCFilterFuncN callback function),
then you can use the helper functions defined in
embree2/rtcore_ray.h to access ray packet components:
float& RTCRayN_org_x(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_org_y(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_org_z(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_dir_x(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_dir_y(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_dir_z(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_tnear(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_tnear(RTCRayN* rays, size_t N, size_t i);
float& RTCRayN_time(RTCRayN* ptr, size_t N, size_t i);
unsigned& RTCRayN_mask(RTCRayN* ptr, size_t N, size_t i);
float& RTCRayN_Ng_x(RTCRayN* ptr, size_t N, size_t i);
float& RTCRayN_Ng_y(RTCRayN* ptr, size_t N, size_t i);
float& RTCRayN_Ng_z(RTCRayN* ptr, size_t N, size_t i);
float& RTCRayN_u (RTCRayN* ptr, size_t N, size_t i);
float& RTCRayN_v (RTCRayN* ptr, size_t N, size_t i);
unsigned& RTCRayN_instID(RTCRayN* ptr, size_t N, size_t i);
unsigned& RTCRayN_geomID(RTCRayN* ptr, size_t N, size_t i);
unsigned& RTCRayN_primID(RTCRayN* ptr, size_t N, size_t i);
These helper functions get a pointer to the ray packet (rays
parameter), the packet size N, and returns a reference to some
component (e.g. x-component of origin) of the the ith ray of the
packet.
Please note that there is some incompatibility in the layout of a
single ray (RTCRay type) and a ray packet of size 1 (RTCRayNt<1>
type) as the org and dir component are aligned to 16 bytes for
single rays (see embree2/rtcore_ray.h). This incompatibility will
get resolved in a future release, but has to be maintained for
compatibility currently. Until then, the ray stream API will always
use the single ray layout RTCRay for rays packets of size N=1, and
the RTCRayNt layout for ray packets of size not equal 1. The helper
functions above to access a ray packet of size N take care of this
incompatibility.
Some callback functions get passed a hit structure with the following data members:
Member In/Out Description
instID in instance ID of hit instance geomID in geometry ID of hit geometry primID in primitive ID of hit primitive u in barycentric u-coordinate of hit v in barycentric v-coordinate of hit t in hit distance Ng in unnormalized geometry normal in object space
: Data fields of a hit.
This structure is in struct of array layout (SOA) for hit packets of
size N. The layout of a hit packet of size N is defined by the
RTCHitNt template in embree2/rtcore_ray.h.
When the hit packet size is not known at compile time (e.g. when
Embree returns a hit packet in the RTCFilterFuncN callback
function), you can use the helper functions defined in
embree2/rtcore_ray.h to access hit packet components:
unsigned& RTCHitN_instID(RTCHitN* hits, size_t N, size_t i);
unsigned& RTCHitN_geomID(RTCHitN* hits, size_t N, size_t i);
unsigned& RTCHitN_primID(RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_u (RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_v (RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_t (RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_Ng_x(RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_Ng_y(RTCHitN* hits, size_t N, size_t i);
float& RTCHitN_Ng_z(RTCHitN* hits, size_t N, size_t i);
These helper functions get a pointer to the hit packet (hits
parameter), the packet size N, and returns a reference to some
component (e.g. u-component) of the the ith hit of the packet.
The API supports finding the closest hit of a ray segment with the
scene (rtcIntersect functions), and determining if any hit between a
ray segment and the scene exists (rtcOccluded functions).
In normal mode the following API functions should be used to trace rays:
void rtcIntersect ( RTCScene scene, RTCRay& ray);
void rtcIntersect4 (const void* valid, RTCScene scene, RTCRay4& ray);
void rtcIntersect8 (const void* valid, RTCScene scene, RTCRay8& ray);
void rtcIntersect16(const void* valid, RTCScene scene, RTCRay16& ray);
void rtcOccluded ( RTCScene scene, RTCRay& ray);
void rtcOccluded4 (const void* valid, RTCScene scene, RTCRay4& ray);
void rtcOccluded8 (const void* valid, RTCScene scene, RTCRay8& ray);
void rtcOccluded16 (const void* valid, RTCScene scene, RTCRay16& ray);
The rtcIntersect and rtcOccluded function operate on single
rays. The rtcIntersect4 and rtcOccluded4 functions operate on ray
packets of size 4. The rtcIntersect8 and rtcOccluded8 functions
operate on ray packets of size 8, and the rtcIntersect16 and
rtcOccluded16 functions operate on ray packets of size 16.
For the ray packet mode with packet size of 4, 8, or 16, the user has
to provide a pointer to 4, 8, or 16 of 32-bit integers that act as a
ray activity mask (valid argument). If one of these integers is set
to 0x00000000 the corresponding ray is considered inactive and if
the integer is set to 0xFFFFFFFF, the ray is considered active. Rays
that are inactive will not update any hit information.
Finding the closest hit distance is done through the rtcIntersect
type functions. These get the activity mask (valid parameter), the
scene (scene parameter), and a ray as input (ray parameter). The
layout of the ray structure is described in Section [Ray Layout]. The
user has to initialize the ray origin (org), ray direction (dir),
and ray segment (tnear, tfar). The ray segment has to be in the
range tnear or tfar are hit or missed. If you want to exclude
intersections at tnear just pass a slighly enlarged tnear and if
you want to include intersections at tfar pass a slighly enlarged
tfar to Embree. The geometry ID (geomID member) has to get
initialized to RTC_INVALID_GEOMETRY_ID (-1). If the scene contains
instances, also the instance ID (instID) has to get initialized to
RTC_INVALID_GEOMETRY_ID (-1). If the scene contains motion blur
geometries, also the ray time (time) has to get initialized to a
value in the range mask) has to get initialized. After tracing
the ray, the hit distance (tfar), geometry normal (Ng)^[Note that
Ng is in object space and needs to be transformed to world space for
instanced scenes.], local hit
coordinates (u, v), geometry ID (geomID), and primitive ID
(primID) are set. If the scene contains instances, also the instance
ID (instID) is set, if an instance is hit. The geometry ID
corresponds to the ID returned at creation time of the hit geometry,
and the primitive ID corresponds to the $n$th primitive of that
geometry, e.g. $n$th triangle. The instance ID corresponds to the ID
returned at creation time of the instance.
Testing if any geometry intersects with the ray segment is done through
the rtcOccluded functions. Initialization has to be done as for
rtcIntersect. If some geometry got found along the ray segment, the
geometry ID (geomID) will get set to 0. Other hit information of the
ray is undefined after calling rtcOccluded.
In normal mode, data alignment requirements for ray query functions operating on single rays is 16 bytes for the ray. Data alignment requirements for query functions operating on AOS packets of 4, 8, or 16 rays, is 16, 32, and 64 bytes respectively, for the valid mask and the ray. To operate on packets of 4 rays, the CPU has to support SSE, to operate on packets of 8 rays, the CPU has to support AVX, and to operate on packets of 16 rays, the CPU has to support AVX-512 instructions. Additionally, the required ISA has to be enabled in Embree at compile time to use the desired packet size.
The following code shows an example of setting up a single ray and traces it through the scene:
RTCRay ray;
ray.org = ray_origin;
ray.dir = ray_direction;
ray.tnear = 0.0f;
ray.tfar = inf;
ray.instID = RTC_INVALID_GEOMETRY_ID;
ray.geomID = RTC_INVALID_GEOMETRY_ID;
ray.primID = RTC_INVALID_GEOMETRY_ID;
ray.mask = 0xFFFFFFFF;
ray.time = 0.0f;
rtcIntersect(scene, ray);
See tutorial [Triangle Geometry] for a complete example of how to trace rays.
For the stream mode new functions got introduced that operate on streams of rays:
void rtcIntersect1M (RTCScene scene, const RTCIntersectContext* context,
RTCRay* rays, size_t M, size_t stride);
void rtcIntersect1Mp (RTCScene scene, const RTCIntersectContext* context,
RTCRay**rays, size_t M);
void rtcIntersectNM (RTCScene scene, const RTCIntersectContext* context,
RTCRayN* rays, size_t N, size_t M, size_t stride);
void rtcIntersectNp (RTCScene scene, const RTCIntersectContext* context,
RTCRayNp& rays, size_t N);
void rtcOccluded1M (RTCScene scene, const RTCIntersectContext* context,
RTCRay* rays, size_t M, size_t stride);
void rtcOccluded1Mp (RTCScene scene, const RTCIntersectContext* context,
RTCRay** rays, size_t M);
void rtcOccludedNM (RTCScene scene, const RTCIntersectContext* context,
RTCRayN* rays, size_t N, size_t M, size_t stride);
void rtcOccludedNp (RTCScene scene, const RTCIntersectContext* context,
RTCRayNp& rays, size_t N, size_t flags);
The rtcIntersectNM and rtcOccludedNM ray stream functions operate
on an array of M ray packets of packet size N. The offset in bytes
between consecutive ray packets can be specified by the stride
parameter. The required data alignment and padding for ray streams is 16
bytes, but for maximum performance, streams should be aligned to the native
SIMD size (e.g. 64 bytes for AVX-512). The packet size N has to be larger than
0 and the stream size M can be an arbitrary positive integer including 0.
Tracing for example a ray stream consisting of four 8-wide SOA ray packets just
requires to set the parameters N to 8, M to 4 and the stride to
sizeof(RTCRay8). A ray in a ray stream is considered inactive during
traversal/intersection if its tnear value is larger than its tfar
value.
The ray streams functions rtcIntersect1M and rtcOccluded1M are
just a shortcut for single ray streams with a packet size of
N=1. rtcIntersect1Mp and rtcOccluded1Mp are similar to
rtcIntersect1M and rtcOccluded1M while taking a stream of pointers
to single rays as input. The rtcIntersectNp and rtcOccludedNp
functions do not require the individual components of the SOA ray
packets to be stored sequentially in memory, but at different addresses
as specified in the RTCRayNp structure.
The intersection context passed to the stream version of the ray query
functions, can specify some intersection flags to optimize traversal
and a userRayExt pointer that can be used to extent the ray with
additional data as described in Section
[Extending the Ray Structure]. The intersection context is propagated
to each stream user callback function invoked.
struct RTCIntersectContext
{
RTCIntersectFlags flags; // intersection flags
void* userRayExt; // can be used to pass extended ray data to callbacks
};
As intersection flag the user can currently specify if Embree should optimize traversal for coherent or incoherent ray distributions.
enum RTCIntersectFlags
{
RTC_INTERSECT_COHERENT = 0, // optimize for coherent rays
RTC_INTERSECT_INCOHERENT = 1 // optimize for incoherent rays
};
The following code shows an example of setting up a stream of single rays and tracing it through the scene:
RTCRay rays[128];
/* first setup all rays */
for (size_t i=0; i<128; i++)
{
rays[i].org = calculate_ray_org(i);
rays[i].dir = calculate_ray_dir(i);
rays[i].tnear = 0.0f;
rays[i].tfar = inf;
rays[i].instID = RTC_INVALID_GEOMETRY_ID;
rays[i].geomID = RTC_INVALID_GEOMETRY_ID;
rays[i].primID = RTC_INVALID_GEOMETRY_ID;
rays[i].mask = 0xFFFFFFFF;
rays[i].time = 0.0f;
}
/* now create a context and trace the ray stream */
RTCIntersectContext context;
context.flags = RTC_INTERSECT_INCOHERENT;
context.userRayExt = nullptr;
rtcIntersectNM(scene, &context, &rays, 1, 128, sizeof(RTCRay));
See tutorial [Stream Viewer] for a complete example of how to trace ray streams.
Smooth interpolation of per-vertex data is supported for triangle
meshes, quad meshs, hair geometry, line segment geometry, and
subdivision geometry using the rtcInterpolate2 API call. This
interpolation function does ignore displacements and always
interpolates the underlying base surface.
void rtcInterpolate2(RTCScene scene,
unsigned geomID, unsigned primID,
float u, float v,
RTCBufferType buffer,
float* P,
float* dPdu, float* dPdv,
float* ddPdudu, float* ddPdvdv, float* ddPdudv,
size_t numFloats);
This call smoothly interpolates the per-vertex data stored in the
specified geometry buffer (buffer parameter) to the u/v location
(u and v parameters) of the primitive (primID parameter) of the
geometry (geomID parameter) of the specified scene (scene
parameter). The interpolation buffer (buffer parameter) has to
contain (at least) numFloats floating point values per vertex to
interpolate. As interpolation buffer one can specify the
RTC_VERTEX_BUFFER0 and RTC_VERTEX_BUFFER1 as well as one of two
special user vertex buffers RTC_USER_VERTEX_BUFFER0 and
RTC_USER_VERTEX_BUFFER1. These user vertex buffers can only get set
using the rtcSetBuffer2 call, they cannot get managed internally by
Embree as they have no default layout. The last element of the buffer
has to be padded to 16 bytes, such that it can be read safely using
SSE instructions.
The rtcInterpolate call stores numFloats interpolated floating
point values to the memory location pointed to by P. One can avoid
storing the interpolated value by setting P to NULL.
The first order derivative of the interpolation by u and v are stored
at the dPdu and dPdv memory locations. One can avoid storing first
order derivatives by setting both dPdu and dPdv to NULL.
The second order derivatives are stored at the ddPdudu, ddPdvdv,
and ddPdudv memory locations. One can avoid storing second order
derivatives by setting these three pointers to NULL.
All output arrays must be padded to 16 bytes. The RTC_INTERPOLATE
algorithm flag of a scene has to be enabled to perform interpolations.
It is explicitly allowed to call this function on disabled geometries. This makes it possible to use a separate subdivision mesh with different vertex creases, edge creases, and boundary handling for interpolation of texture coordinates if that is necessary.
The applied interpolation will do linear interpolation for triangle and quad meshes, linear interpolation for line segments, cubic Bézier interpolation for hair, and apply the full subdivision rules for subdivision geometry.
There is also a second interpolate call rtcInterpolateN2 that can be
used for ray packets.
void rtcInterpolateN2(RTCScene scene, unsigned geomID,
const void* valid, const unsigned* primIDs,
const float* u, const float* v, size_t numUVs,
RTCBufferType buffer,
float* dP,
float* dPdu, float* dPdv,
float* ddPdudu, float* ddPdvdv, float* ddPdudv,
size_t numFloats);
This call is similar to the first version, but gets passed numUVs
many u/v coordinates and a valid mask (valid parameter) that
specifies which of these coordinates are valid. The valid mask points
to numUVs integers and a value of -1 denotes valid and 0 invalid. If
the valid pointer is NULL all elements are considers valid. The
destination arrays are filled in structure of array (SoA) layout. The
value numUVs has to be divisible by 4 and the destination buffer has
to be at least numFloats*numUVs elements large.
See tutorial [Interpolation] for an example of using the
rtcInterpolate2 function.
Embree supports sharing of buffers with the application. Each buffer
that can be mapped for a specific geometry can also be shared with the
application, by passing a pointer, offset, stride, and number of
elements of the application side buffer using the rtcSetBuffer2 API
function.
void rtcSetBuffer2(RTCScene scene, unsigned geomID, RTCBufferType type,
void* ptr, size_t offset, size_t stride, size_t size);
The rtcSetBuffer2 function has to get called before any call to
rtcMapBuffer for that buffer, otherwise the buffer will get allocated
internally and the call to rtcSetBuffer2 will fail. The buffer has to
remain valid as long as the geometry exists, and the user is responsible
to free the buffer when the geometry gets deleted. When a buffer is
shared, it is safe to modify that buffer without mapping and unmapping
it. However, for dynamic scenes one still has to call rtcUpdate for
modified geometries and the buffer data has to stay constant from the
rtcCommit call to after the last ray query invocation.
The offset parameter specifies a byte offset to the start of the
first element, the stride parameter specifies a byte stride between
the different elements of the shared buffer and the size parameter
specified the number of elements stored inside the buffer. This
support for offset and stride allows the application quite some
freedom in the data layout of these buffers, however, some
restrictions apply. Index buffers always store 32-bit indices and
vertex buffers always store single precision floating point data. The
start address ptr+offset and stride always have to be aligned to 4
bytes, otherwise the rtcSetBuffer2 function will fail. The size
parameter can be used to change the size of a buffer, which makes it
possible to change the number of elements inside a mesh (by changing
the size of the RTC_INDEX_BUFFER).
For vertex buffers (RTC_VERTEX_BUFFER and RTC_USER_VERTEX_BUFFER),
the last element must be readable using SSE instructions, thus padding
the last element to 16 bytes size is required for some layouts.
The following is an example of how to create a mesh with shared index and vertex buffers:
unsigned geomID = rtcNewTriangleMesh(scene, geomFlags, numTriangles, numVertices);
rtcSetBuffer2(scene, geomID, RTC_VERTEX_BUFFER, vertexPtr, 0, 3*sizeof(float), numVertices);
rtcSetBuffer2(scene, geomID, RTC_INDEX_BUFFER, indexPtr, 0, 3*sizeof(int), numTriangles);
Sharing buffers can significantly reduce the memory required by the
application, thus we recommend using this feature. When enabling the
RTC_COMPACT scene flag, the spatial index structures of Embree might
also share the vertex buffer, resulting in even higher memory savings.
All geometry types support multi-segment motion blur with equidistant
time steps and arbitrary number of time steps in the range of 2
to 129. Each geometry can have a different number of time steps. Some
motion blur geometry is constructed by passing the number of time
steps to the geometry construction function and setting the
vertex arrays RTC_VERTEX_BUFFER0+t for each time step t:
unsigned geomID = rtcNewTriangleMesh(scene, geomFlags, numTris, numVertices, 3);
rtcSetBuffer2(scene, geomID, RTC_VERTEX_BUFFER0+0, vertex0Ptr, 0, sizeof(Vertex), numVertices);
rtcSetBuffer2(scene, geomID, RTC_VERTEX_BUFFER0+1, vertex1Ptr, 0, sizeof(Vertex), numVertices);
rtcSetBuffer2(scene, geomID, RTC_VERTEX_BUFFER0+2, vertex2Ptr, 0, sizeof(Vertex), numVertices);
rtcSetBuffer2(scene, geomID, RTC_INDEX_BUFFER, indexPtr, 0, sizeof(Triangle), numTris);
If a scene contains geometries with motion blur, the user has to set
the time member of the ray to a value in the range
A user data pointer can be specified and queried per geometry, to efficiently map from the geometry ID returned by ray queries to the application representation for that geometry.
void rtcSetUserData (RTCScene scene, unsigned geomID, void* ptr);
void* rtcGetUserData (RTCScene scene, unsigned geomID);
The user data pointer of some user defined geometry get additionally passed to the intersect and occluded callback functions of that user geometry. Further, the user data pointer is also passed to intersection filter callback functions attached to some geometry.
The rtcGetUserData function is on purpose not thread safe with
respect to other API calls that modify the scene. Consequently, this
function can be used to efficiently query the user data pointer during
rendering (also by multiple threads), but should not get called
while modifying the scene with other threads.
A 32-bit geometry mask can be assigned to triangle meshes and hair
geometries using the rtcSetMask call.
rtcSetMask(scene, geomID, mask);
Only if the bitwise and operation of this mask with the mask stored
inside the ray is not 0, primitives of this geometry are hit by a ray.
This feature can be used to disable selected triangle mesh or hair
geometries for specifically tagged rays, e.g. to disable shadow casting
for some geometry. This API feature is disabled in Embree by default at
compile time, and can be enabled in CMake through the
EMBREE_RAY_MASK parameter.
The API supports per geometry filter callback functions that are invoked
for each intersection found during the rtcIntersect or rtcOccluded
calls. The former ones are called intersection filter functions, the
latter ones occlusion filter functions. The filter functions can be used
to implement various useful features, such as accumulating opacity for
transparent shadows, counting the number of surfaces along a ray,
collecting all hits along a ray, etc. Filter functions can also be used
to selectively reject hits to enable backface culling for some
geometries. If the backfaces should be culled in general for all
geometries then it is faster to enable EMBREE_BACKFACE_CULLING during
compilation of Embree instead of using filter functions.
If the RTC_SCENE_HIGH_QUALITY mode is set, the intersection and
occlusion filter functions may be called multiple times for the same
hit. For some usage scenarios, the application may have to work around
this by collecting already reported hits (geomID/primID pairs) and
ignoring duplicates for some usage scenarios.
In normal mode the filter functions provided by the user need to have the following signature:
void RTCFilterFunc ( void* userDataPtr, RTCRay& ray);
void RTCFilterFunc4 (const void* valid, void* userDataPtr, RTCRay4& ray);
void RTCFilterFunc8 (const void* valid, void* userDataPtr, RTCRay8& ray);
void RTCFilterFunc16(const void* valid, void* userDataPtr, RTCRay16& ray);
The valid pointer points to an integer valid mask (0 means invalid
and -1 means valid). The userDataPtr is a user pointer optionally
set per geometry through the rtcSetUserData function. All hit
information inside the ray is valid. If the hit geometry is instanced,
the instID member of the ray is valid and the ray origin, direction,
and geometry normal visible through the ray are in object space.
The filter function can reject a hit by setting the geomID member of
the ray to RTC_INVALID_GEOMETRY_ID, otherwise the hit is
accepted. The filter function is not allowed to modify the ray input
data (org, dir, time, mask, and tnear members), but can
modify the hit data of the ray (u, v, Ng, tfar, geomID,
primID, and instID members). Updating the tfar distance to a
smaller value is possible without limitation. However, increasing the
tfar distance of the ray to a larger value tfar' , does not
guarantee intersections between tfar and tfar' to be reported
later, as the corresponding subtrees might have gotten culled already.
The intersection and occlusion filter functions for different ray types are set for some geometry of a scene using the following API functions:
void rtcSetIntersectionFilterFunction (RTCScene, unsigned geomID, RTCFilterFunc filter);
void rtcSetIntersectionFilterFunction4 (RTCScene, unsigned geomID, RTCFilterFunc4 filter);
void rtcSetIntersectionFilterFunction8 (RTCScene, unsigned geomID, RTCFilterFunc8 filter);
void rtcSetIntersectionFilterFunction16(RTCScene, unsigned geomID, RTCFilterFunc16 filter);
void rtcSetOcclusionFilterFunction (RTCScene, unsigned geomID, RTCFilterFunc filter);
void rtcSetOcclusionFilterFunction4 (RTCScene, unsigned geomID, RTCFilterFunc4 filter);
void rtcSetOcclusionFilterFunction8 (RTCScene, unsigned geomID, RTCFilterFunc8 filter);
void rtcSetOcclusionFilterFunction16(RTCScene, unsigned geomID, RTCFilterFunc16 filter);
The intersection and occlusion filter functions of type RTCFilterFunc
are only called by the rtcIntersect and rtcOccluded
functions. Similar the filter functions of type FilterFunc4,
FilterFunc8, and FilterFunc16 are called by rtcIntersect4/8/16
and rtcOccluded4/8/16 of matching width.
For ray stream mode a new type of filter function RTCFilterFuncN got
introduced:
void RTCFilterFuncN (int* valid,
void* userDataPtr,
const RTCIntersectContext* context,
RTCRayN* ray,
const RTCHitN* potentialHit,
const size_t N);
The stream intersection and occlusion filter functions of this new type are set for some geometry of a scene using the following API functions:
void rtcSetIntersectionFilterFunctionN (RTCScene, unsigned geomID, RTCFilterFuncN filter);
void rtcSetOcclusionFilterFunctionN (RTCScene, unsigned geomID, RTCFilterFuncN filter);
For the callback RTCFilterFuncN, the valid parameter points to an
integer valid mask (0 means invalid and -1 means valid). The
userDataPtr is a user pointer optionally set per geometry through
the rtcSetUserData function. The context parameter points to the
intersection context passed to the ray query function. The ray
parameter contains the current ray. All hit data inside the ray are
undefined, except the tfar value. The potentialHit parameter
points to the new hit to test and update. The N parameter is the
number of rays and hits found in the ray and potentialHit. If the
hit geometry is instanced, the instID member of the ray is valid and
the ray as well as the potential hit are in object space.
As the ray packet size N can be arbitrary, the ray and hit should
get accessed through the helper functions as describe in Section
[Ray Layout].
The callback function has the task to check for each valid ray whether
it wants to accept or reject the corresponding hit. To reject a hit,
the filter callback function just has to write 0 to the integer
valid mask of the corresponding ray. The filter function is not
allowed to modify the ray input data (org, dir, time, mask,
and tnear members), nor the potential hit, nor inactive components.
An intersection filter callback function can accept a hit by updating
all hit data members of the ray (u, v, Ng, tfar, geomID,
primID, and instID members) and keep the valid mask set to -1.
An occlusion filter callback function can accept a hit by setting the
geomID member of the ray to 0 and keep the valid mask set to -1.
The intersection filter callback of most applications will just copy
the potentialHit into the appropiate fields of the ray, but this is
not a requirement and the hit data of the ray can get modified
arbitrarily. Updating the tfar distance to a smaller value (e.g. the
t distance of the potential hit) is possible without
limitation. However, increasing the tfar distance of the ray to a
larger value tfar' , does not guarantee intersections between tfar
and tfar' to be reported later, as the corresponding subtrees might
have gotten culled already.
The API supports displacement mapping for subdivision meshes. A
displacement function can be set for some subdivision mesh using the
rtcSetDisplacementFunction API call.
void rtcSetDisplacementFunction2(RTCScene, unsigned geomID, RTCDisplacementFunc, RTCBounds*);
A displacement function of NULL will delete an already set
displacement function. The bounds parameter is optional. If NULL is
passed as bounds, then the displacement shader will get evaluated
during the build process to properly bound displaced geometry. If a
pointer to some bounds of the displacement are passed, then the
implementation can choose to use these bounds to bound displaced
geometry. When bounds are specified, then these bounds have to be
conservative and should be tight for best performance.
The displacement function has to have the following type:
typedef void (*RTCDisplacementFunc2)(void* ptr,
unsigned geomID, unsigned primID, unsigned timeStep,
const float* u, const float* v,
const float* nx, const float* ny, const float* nz,
float* px, float* py, float* pz,
size_t N);
The displacement function is called with the user data pointer of the
geometry (ptr), the geometry ID (geomID), and primitive ID
(primID) of a patch to displace. For motion blur the time step
timeStep is also specified, such that the function can be time
varying. For the patch, a number N of points to displace are
specified in a struct of array layout. For each point to displace the
local patch UV coordinates (u and v arrays), the normalized
geometry normal (nx, ny, and nz arrays), as well as world space
position (px, py, and pz arrays) are provided. The task of the
displacement function is to use this information and move the world
space position inside the allowed specified bounds around the point.
All passed arrays are guaranteed to be 64 bytes aligned, and properly padded to make wide vector processing inside the displacement function possible.
The displacement mapping functions might get called during the
rtcCommit call, or lazily during the rtcIntersect or
rtcOccluded calls.
Also see tutorial [Displacement Geometry] for an example of how to use the displacement mapping functions.
If Embree is used in normal mode, the ray passed to the filter callback functions and user geometry callback functions is guaranteed to be the same ray pointer initially provided to the ray query function by the user. For that reason, it is safe to extend the ray by additional data and access this data inside the filter callback functions (e.g. to accumulate opacity) and user geometry callback functions.
If Embree is used in stream mode, the ray passed to the filter
callback and user geometry callback functions is not guaranteed to
be the same ray pointer initially passed to the ray query function, as
the stream implementation may decide to copy rays around, reorder
them, and change the data layout internally when appropiate (e.g. SOA
to AOS conversion).
To identify specific rays in the callback functions, the user has to
pass an ID with each ray and set the userRayExt member of the
intersection context to point to its ray extensions. The ray
extensions can be stored in a seprarate memory location but also just
after the end of each ordinary ray (or ray packet). In the latter
case, you can just point the userRayExt to the input rays.
To encode a ray ID the ray mask field can be used entirely when the ray mask feature is disabled, or unused bits of the ray mask can be used in case the ray mask feature is enabled (e.g. by using the lower 16 bits as ray ID, and the upper 16 bits as ray mask, and setting the lower 16 bits of each geometry mask always to 0).
The intersection context provided to the stream ray query functions is
passed to each stream callback function (e.g. RTCIntersectFuncN,
RTCIntersectFunc1Mp, or RTCFilterFuncN). Thus, in the callback
function, the ray ID can get decoded, and the extended ray data
accessed through the userRayExt pointer stored inside the
intersection context. For SPMD type programs this access requires
gather and scatter operations to access the user ray extensions.
Not that using the ray ID to access the ray extensions is necessary,
as the ray IDs might have changed from the IDs passed to the ray query
function. E.g. if you trace a ray packet with 8 rays 0 to 8, then even
if a callback gets called with a ray packet of 8 rays, they rays might
have gotten reordered. Further, the callback might get called with a
subpacket of a size smaller than 8 (e.g. N=5). However, optimizing
for the common case in which Embree keeps such a packet intact (thus
having a special codepath for N=8 and unchanged IDs) can give higher
performance.
On some implementations, Embree supports using the application threads when building internal data structures, by using the
void rtcCommitThread(RTCScene, unsigned threadIndex, unsigned threadCount);
API call to commit the scene. This function has to get called by all
threads that want to cooperate in the scene commit. Each call is
provided the scene to commit, the index of the calling thread in the
range [0, threadCount-1], and the number of threads that will call
into this commit operation for the scene. All threads will return
again from this function after the scene commit is finished.
Multiple such scene commit operations can also be running at the same
time, e.g. it is possible to commit many small scenes in parallel
using one thread per commit operation. Subsequent commit operations
for the same scene can use different number of threads in the
rtcCommitThread or use the Embree internal threads using the
rtcCommit call.
Note: When using Embree with the Intel® Threading Building Blocks
(which is the default) you should not use the rtcCommitThread
function. Sharing of your threads with TBB is not possible and TBB
will always generate its own set of threads. We recommend to also use
TBB inside your application to share threads with the Embree
library. When using TBB inside your application do never use the
rtcCommitThread function.
Note: When enabling the Embree internal tasking system the
rtcCommitThread feature will work as expected and use the
application threads for hierarchy building.
The special rtcCommitJoin function can be used from multiple threads
to join a scene build operation. All thread have to consistently call
rtcCommitJoin and no other commit variant.
This feature allows a flexible way to lazily create hierarchies during
rendering. A thread reaching a not yet constructed sub-scene of a
two-level scene, can generate the sub-scene geometry and call
rtcCommitJoin on that just generated scene. During construction,
further threads reaching the not-yet-built scene, can join the build
operation by also invoking rtcCommitJoin. A thread that calls
rtcCommitJoin after the build finishes, will directly return from
the rtcCommitJoin call (even for static scenes).
Note: When using Embree with the Intel® Threading Building Blocks,
thread that call rtcCommitJoin will join the build operation, but
other TBB worker threads might also participate in the build. To avoid
thread oversubscription, we recommend using TBB also inside the
application. Further, the join mode only works properly starting with
TBB v4.4 Update 1. For earlier TBB versions threads that call
rtcCommitJoin to join a running build will just wait for the build
to finish.
Note: When using Embree with the internal tasking system,
exclusively threads that call rtcCommitJoin will perform the build
operation, and no additional worker threads are scheduled.
Using the memory monitor callback mechanism, the application can track the memory consumption of an Embree device, and optionally terminate API calls that consume too much memory.
The user provided memory monitor callback function must have the following signature:
bool (*RTCMemoryMonitorFunc2)(void* userPtr, const ssize_t bytes, const bool post);
A single such callback function per device can be registered by calling
rtcDeviceSetMemoryMonitorFunction2(RTCDevice, RTCMemoryMonitorFunc2, void* userPtr);
and deregistered again by calling it with NULL as function
pointer. Once registered the Embree device will invoke the callback
function before or after it allocates or frees important memory
blocks. The userPtr value that is set at registration time is
passed to each invokation of the callback function. The callback
function might get called from multiple threads concurrently.
The application can track the current memory usage of the Embree
device by atomically accumulating the provided bytes input
parameter. This parameter will be >0 for allocations and <0 for
deallocations. The post input parameter is true if the callback
function was invoked after the allocation or deallocation, otherwise
it is false.
Embree will continue its operation normally when returning true from
the callback function. If false is returned, Embree will cancel the
current operation with the RTC_OUT_OF_MEMORY error code. Cancelling
will only happen when the callback was called for allocations (bytes >
0), otherwise the cancel request will be ignored. If a callback that
was invoked before the allocation happens (post == false) cancels
the operation, then the bytes parameter should not get accumulated,
as the allocation will never happen. If a callback that was called
after the allocation happened (post == true) cancels the operation,
then the bytes parameter should get accumulated, as the allocation
properly happened. Issuing multiple cancel requests for the same
operation is allowed.
The progress monitor callback mechanism can be used to report progress of hierarchy build operations and to cancel long lasting build operations.
The user provided progress monitor callback function has to have the following signature:
bool (*RTCProgressMonitorFunc)(void* userPtr, const double n);
A single such callback function can be registered per scene by calling
rtcSetProgressMonitorFunction(RTCScene, RTCProgressMonitorFunc, void* userPtr);
and deregistered again by calling it with NULL for the callback
function. Once registered Embree will invoke the callback function
multiple times during hierarchy build operations of the scene, by
providing the userPtr pointer that was set at registration time, and a
double n in the range
When returning true from the callback function, Embree will continue
the build operation normally. When returning false Embree will
cancel the build operation with the RTC_CANCELLED error code. Issuing
multiple cancel requests for the same build operation is allowed.
Some internal device parameters can be set and queried using the
rtcDeviceSetParameter1i and rtcDeviceGetParameter1i API call. The
parameters from the following table are available to set/query:
Parameter Description Read/Write
RTC_CONFIG_VERSION_MAJOR returns Embree major version Read only
RTC_CONFIG_VERSION_MINOR returns Embree minor version Read only
RTC_CONFIG_VERSION_PATCH returns Embree patch version Read only
RTC_CONFIG_VERSION returns Embree version as integer Read only e.g. Embree v2.8.2 → 20802
RTC_CONFIG_INTERSECT1 checks if rtcIntersect1 is Read only
supported
RTC_CONFIG_INTERSECT4 checks if rtcIntersect4 is Read only
supported
RTC_CONFIG_INTERSECT8 checks if rtcIntersect8 is Read only
supported
RTC_CONFIG_INTERSECT16 checks if rtcIntersect16 is Read only
supported
RTC_CONFIG_INTERSECT_STREAM checks if rtcIntersect1M,
rtcIntersect1Mp, rtcIntersectNM, Read only
and rtcIntersectNp are supported
RTC_CONFIG_TRIANGLE_GEOMETRY checks if triangle geometries are Read only supported
RTC_CONFIG_QUAD_GEOMETRY checks if quad geometries are Read only supported
RTC_CONFIG_LINE_GEOMETRY checks if line geometries are Read only supported
RTC_CONFIG_HAIR_GEOMETRY checks if hair geometries are Read only supported
RTC_CONFIG_SUBDIV_GEOMETRY checks if subdivision meshes are Read only supported
RTC_CONFIG_USER_GEOMETRY checks if user geometries are Read only supported
RTC_CONFIG_RAY_MASK checks if ray masks are supported Read only
RTC_CONFIG_BACKFACE_CULLING checks if backface culling is Read only supported
RTC_CONFIG_INTERSECTION_FILTER checks if intersection filters are Read only enabled
RTC_CONFIG_INTERSECTION_FILTER_RESTORE checks if intersection filters Read only restore previous hit
RTC_CONFIG_IGNORE_INVALID_RAYS checks if invalid rays are ignored Read only
RTC_CONFIG_TASKING_SYSTEM return used tasking system Read only (0 = INTERNAL, 1 = TBB, 2 = PPL)
RTC_SOFTWARE_CACHE_SIZE Configures the software cache size Write only (used to cache subdivision surfaces for instance). The size is specified as an integer number of bytes. The software cache cannot be configured during rendering.
RTC_CONFIG_COMMIT_JOIN Checks if rtcCommit can be used to Read only join build operation (not supported when Embree is compiled with some older TBB versions)
RTC_CONFIG_COMMIT_THREAD Checks if rtcCommitThread is Read only available (not supported when Embree is compiled with some older TBB versions)
: Parameters for rtcDeviceSetParameter and rtcDeviceGetParameter.
For example, to configure the size of the internal software
cache that is used to handle subdivision surfaces use the
RTC_SOFTWARE_CACHE_SIZE parameter to set desired size of the cache
in bytes:
rtcDeviceSetParameter1i(device, RTC_SOFTWARE_CACHE_SIZE, bytes);
The software cache cannot get configured while any Embree API call is executed. Best configure the size of the cache only once at application start.
You can use the TBB API to limit the number of threads used by Embree during hierarchy construction. Therefore just create a global taskscheduler_init object, initialized with the number of threads to use:
#include <tbb/tbb.h>
tbb::task_scheduler_init init(numThreads);
Tasking systems like TBB create worker threads on demand which will
add a runtime overhead for the very first rtcCommit call. In case
you want to benchmark the scene build time, you should start threads
at application startup. You can let Embree start TBB threads by
passing start_threads=1 to the init parameter of rtcNewDevice.
On machines with a high thread count (e.g. dual-socket Xeon or Xeon
Phi machines), affinitizing TBB worker threads increases build and
rendering performance. You can let Embree affinitize TBB worker
threads by passing set_affinity=1 to the init parameter of
rtcNewDevice. By default threads are not affinitized by Embree with
the exception of Xeon Phi Processors where they are affinitized by
default.
All Embree tutorials automatically start and affinitize TBB worker threads
by passing start_threads=1,set_affinity=1 to rtcNewDevice.
Embree supports 2MB huge pages under Windows, Linux, and MacOSX. Under
Linux huge page support is enabled by default and under Windows and
MacOSX disabled by default. Huge page support can get enabled in
Embree by passing hugepages=1 to rtcNewDevice or disabled by
passing hugepages=0 to rtcNewDevice.
We recommend using 2MB huge pages with Embree under Linux as this improves ray tracing performance by about 5 - 10%. Under Windows using huge pages requires the application to run in elavated mode which is a security issue. Under MacOSX huge pages are rarely available as memory tends to get quickly fragmented.
To use huge pages under Windows, the current user must have the "Lock pages in memory" (SeLockMemoryPrivilege) assigned. This can be configured through the "Local Security Policy" application, by adding a user to "Local Policies" -> "User Rights Assignment" -> "Lock pages in memory". You have to log out and in again for this change to take effect.
Further, your application has to be executed as an elevated process
("Run as administrator") and the "SeLockMemoryPrivilege" must
explicitely be enabled by your application. Example code on how to
enable this privilege can be found in the "common/sys/alloc.cpp" file
of Embree. Alternatively, Embree will try to enable this privilege
when passing enable_selockmemoryprivilege=1 to
rtcNewDevice. Further, huge pages have to get enabled in Embree by
passing hugepages=1 to rtcNewDevice.
When the system was running for a while, physical memory gets fragmented, which can slow down the allocation of huge pages significantly.
Linux supports transparent huge pages and explicit huge pages. To enable transparent huge page support under Linux execute the following as root:
echo always > /sys/kernel/mm/transparent_hugepage/enabled
When transparent huge pages are enabled, the kernel tries to merge 4k pages to 2MB pages when possible as a background job. See the following webpage for more information on transparent huge pages under Linux. In this mode each application, including your rendering application building on Embree, will automatically tend to use huge pages.
Using transparent huge pages the transitioning from 4k to 2MB pages
might take some time. For that reason Embree also supports allocating
2MB pages directly when a huge page pool is configured. Such a pool
can get configured by writing some number of huge pages to alloacte to
/proc/sys/vm/nr_overcommit_hugepages as root user. E.g. to configure
2GB of adress space for huge page allocation, execute the following as
root:
echo 1000 > /proc/sys/vm/nr_overcommit_hugepages
See the following webpage for more information on huge pages under Linux.
To use huge pages under MacOSX you have to pass hugepages=1 to
rtcNewDevice to enable that feature in Embree.
When the system was running for a while, physical memory gets quickly fragmented, and causes huge page allocations to fail. For this reason huge pages not very usefull under MacOSX in practise.
The Embree API exposes internal BVH builders to build BVHs with any
desired node and leaf layout. To invoke the BVH builder you have to
create a BVH object using the rtcNewBVH function and deleted again
using the rtcDeleteBVH function.
RTCBVH rtcNewBVH(RTCDevice);
void rtcDeleteBVH(RTCBVH);
This BVH contains some builder state and fast node allocator. Some settings have to be passed to be BVH build function:
enum RTCBuildQuality
{
RTC_BUILD_QUALITY_LOW = 0, // build low quality BVH (good for dynamic scenes)
RTC_BUILD_QUALITY_NORMAL = 1, // build standard quality BVH
RTC_BUILD_QUALITY_HIGH = 2, // build high quality BVH
};
struct RTCBuildSettings
{
unsigned size; // size of this structure in bytes
RTCBuildQuality quality; // quality of BVH build
unsigned maxBranchingFactor; // branching factor of BVH to build
unsigned maxDepth; // maximal depth of BVH to build
unsigned sahBlockSize; // blocksize for SAH heuristic
unsigned minLeafSize; // minimal size of a leaf
unsigned maxLeafSize; // maximal size of a leaf
float travCost; // estimated cost of one traversal step
float intCost; // estimated cost of one primitive intersection
unsigned extraSpace; // for spatial splitting we need extra space at end of primitive array
};
Some default values for the settings can be obtained using the
rtcDefaultBuildSettings function. Using the quality setting, one
can select between a faster low quality build which is good for
dynamic scenes, and a standard quality build for static scenes. One
can also specify the desired maximal branching factor of the BVH
(maxBranchingFactor setting), the maximal depth the BVH should have
(maxDepth setting), some power of 2 block size for the SAH heuristic
(sahBlockSize), the minimal and maximal leaf size (minLeafSize and
maxLeafSize setting), and the estimated cost of one traversal step
and primitve intersection (travCost and intCost setting). To
spatially split primitives in high quality mode, the builder needs
some extra space at the end of the build primitive array. The amount
of extra space can be passed using the extraSpace setting, and
should be about the same size as there are primitives. The size
member has always to be set to the size of the RTCBuildSettings
structure in bytes.
Four callback functions have to get registered which are invoked
during build to create BVH nodes (RTCCreateNodeFunc), set the
pointers to all children (RTCSetNodeChildrenFunc), set the bounding
boxes of all children (RTCSetNodeBoundsFunc), and to create a leaf
node (RTCCreateLeafFunc).
typedef void* (*RTCCreateNodeFunc) (RTCThreadLocalAllocator, size_t numChildren, void* userPtr);
typedef void (*RTCSetNodeChildFunc) (void* nodePtr, void** childPtrs, size_t numChildren,
void* userPtr);
typedef void (*RTCSetNodeBoundsFunc) (void* nodePtr, const RTCBounds**, size_t numChildren,
void* userPtr);
typedef void* (*RTCCreateLeafFunc) (RTCThreadLocalAllocator, const RTCBuildPrimitive* prims,
size_t numPrimitives, void* userPtr);
typedef void (*RTCSplitPrimitiveFunc) (const RTCBuildPrimitive&, unsigned dim, float pos,
RTCBounds& lbounds, RTCBounds& rbounds, void* userPtr);
The RTCCreateNodeFunc and RTCCreateLeafFunc type callbacks are
passed a thread local allocator object that should be used for fast
allocation of nodes using the rtcThreadLocalAlloc function.
void* rtcThreadLocalAlloc(RTCThreadLocalAllocator, size_t bytes, size_t align);
We strongly recommend using this allocation mechanism, as alternative
approaches like standard malloc can be over 10× slower. The
allocator object passed to the create callbacks has to be used only
inside the current thread. Memory allocated using
rtcThreadLocalAlloc is automatically freed when the RTCBVH object
is deleted. If you use your own memory allocation scheme you have to
free the memory yourself after the RTCBVH object got deleted.
The RTCCreateNodeFunc callback additionally gets passed the number
of children for this node in the range from 2 to maxBranchingFactor
(numChildren argument).
The RTCSetNodeChildFunc callback function, gets passed a pointer to
the node as input (nodePtr argument), an array of pointers to the
children (childPtrs argument), and the size of this array
(numChildren argument).
The RTCSetNodeBoundsFunc callback function, get a pointer to the
node as input (nodePtr argument), an array of pointers to the
bounding boxes of the children (bounds argument), and the size of
this array (numChildren argument).
The RTCCreateLeafFunc callback additionally get an array of
primitives as input (primitives argument), and the size of this
array (numPrimitives argument). The callback should read the
geomID and primID members from the passed primitives to construct
the leaf.
The RTCSplitPrimitiveFunc callback is invoked in high quality mode
to split a primitive (prim argument) at some specified position
(pos argument) and dimension (dim argument). The callback should
return bounds of the clipped left and right part of the primitive
(lbounds and rbounds arguments).
There is an optional progress callback function that can be used to get progress on the BVH build.
typedef void (*RTCBuildProgressFunc) (size_t N, void* userPtr);
This progress function is called with a number N of primitives the
build is finished for. Accumulating over all invokations will sum up
to the number of primitives passed to be BVH build function.
All callback functions are typically called from multiple threads, thus their implementation has to be thread safe.
All callback function get a user defined pointer (userPtr argument)
as input which is provided to the rtcBuildBVH call. This pointer can
be used to access the application scene object inside the callback
functions.
The BVH build is invoked using the rtcBuildBVH function:
void* rtcBuildBVH(RTCBVH bvh, // BVH to build
const RTCBuildSettings& settings, // settings for BVH builder
RTCBuildPrimitive* primitives, // list of input primitives
size_t numPrimitives, // number of input primitives
RTCCreateNodeFunc createNode, // creates a node
RTCSetNodeChildrenFunc setNodeChildren, // sets pointer to a child
RTCSetNodeBoundsFunc setNodeBounds, // sets bound of a child
RTCCreateLeafFunc createLeaf, // creates a leaf
RTCSplitPrimitiveFunc splitPrimitive, // splits a primitive into two halves
RTCBuildProgressFunc buildProgress // used to report build progress
void* userPtr); // user pointer passed to callback functions
The function gets passed the BVH objects (bvh argument), the build
settings to use (settings argument), the array of primitives
(primitives argument) and its size (numPrimitives argument), the
previously described callback function pointers, and a user defined
pointer (userPtr argument) that is passed to all callback
functions. The function pointer to the primitive split function
(splitPrimitive argument) may be NULL, however, then no spatial
splitting in high quality mode is possible. The function pointer used
to report the build progress (buildProgress argument) is optional
and may also be NULL. The primitives array can be freed by the
application again after the BVH is built.
For static scenes that do not require a further rtcBuildBVH call one
should use the rtcMakeStatic function after the build which clears
some internal data.
void rtcMakeStaticBVH(RTCBVH);
Embree comes with a set of tutorials aimed at helping users understand
how Embree can be used and extended. All tutorials exist in an ISPC and
C++ version to demonstrate the two versions of the API. Look for files
named tutorialname_device.ispc for the ISPC implementation of the
tutorial, and files named tutorialname_device.cpp for the single ray C++
version of the tutorial. To start the C++ version use the tutorialname
executables, to start the ISPC version use the tutorialname_ispc
executables.
For all tutorials, you can select an initial camera using the -vp
(camera position), -vi (camera look-at point), -vu (camera up
vector), and -fov (vertical field of view) command line parameters:
./triangle_geometry -vp 10 10 10 -vi 0 0 0
You can select the initial windows size using the -size command line
parameter, or start the tutorials in fullscreen using the -fullscreen
parameter:
./triangle_geometry -size 1024 1024
./triangle_geometry -fullscreen
Implementation specific parameters can be passed to the ray tracing core
through the -rtcore command line parameter, e.g.:
./triangle_geometry -rtcore verbose=2,threads=1,accel=bvh4.triangle1
The navigation in the interactive display mode follows the camera orbit
model, where the camera revolves around the current center of interest.
With the left mouse button you can rotate around the center of interest
(the point initially set with -vi). Holding Control pressed while
clicking the left mouse button rotates the camera around its location.
You can also use the arrow keys for navigation.
You can use the following keys:
F1 : Default shading
F2 : Gray EyeLight shading
F3 : Traces occlusion rays only.
F4 : UV Coordinate visualization
F5 : Geometry normal visualization
F6 : Geometry ID visualization
F7 : Geometry ID and Primitive ID visualization
F8 : Simple shading with 16 rays per pixel for benchmarking.
F9 : Switches to render cost visualization. Pressing again reduces brightness.
F10 : Switches to render cost visualization. Pressing again increases brightness.
f : Enters or leaves full screen mode.
c : Prints camera parameters.
ESC : Exits the tutorial.
q : Exits the tutorial.
![][imgTriangleGeometry]
This tutorial demonstrates the creation of a static cube and ground
plane using triangle meshes. It also demonstrates the use of the
rtcIntersect and rtcOccluded functions to render primary visibility
and hard shadows. The cube sides are colored based on the ID of the hit
primitive.
![][imgDynamicScene]
This tutorial demonstrates the creation of a dynamic scene, consisting
of several deformed spheres. Half of the spheres use the
RTC_GEOMETRY_DEFORMABLE flag, which allows Embree to use a refitting
strategy for these spheres, the other half uses the
RTC_GEOMETRY_DYNAMIC flag, causing a rebuild of their spatial data
structure each frame. The spheres are colored based on the ID of the hit
sphere geometry.
![][imgUserGeometry]
This tutorial shows the use of user defined geometry, to re-implement instancing and to add analytic spheres. A two level scene is created, with a triangle mesh as ground plane, and several user geometries, that instance other scenes with a small number of spheres of different kind. The spheres are colored using the instance ID and geometry ID of the hit sphere, to demonstrate how the same geometry, instanced in different ways can be distinguished.
![][imgViewer]
This tutorial demonstrates a simple OBJ viewer that traces primary visibility rays only. A scene consisting of multiple meshes is created, each mesh sharing the index and vertex buffer with the application. Demonstrated is also how to support additional per-vertex data, such as shading normals.
You need to specify an OBJ file at the command line for this tutorial to work:
./viewer -i model.obj
![][imgViewerStream]
This tutorial demonstrates a simple OBJ viewer that demonstrates the use of ray streams. You need to specify an OBJ file at the command line for this tutorial to work:
./viewer_stream -i model.obj
![][imgInstancedGeometry]
This tutorial demonstrates the in-build instancing feature of Embree, by instancing a number of other scenes build from triangulated spheres. The spheres are again colored using the instance ID and geometry ID of the hit sphere, to demonstrate how the same geometry, instanced in different ways can be distinguished.
![][imgIntersectionFilter]
This tutorial demonstrates the use of filter callback functions to efficiently implement transparent objects. The filter function used for primary rays, lets the ray pass through the geometry if it is entirely transparent. Otherwise the shading loop handles the transparency properly, by potentially shooting secondary rays. The filter function used for shadow rays accumulates the transparency of all surfaces along the ray, and terminates traversal if an opaque occluder is hit.
![][imgPathtracer]
This tutorial is a simple path tracer, building on the viewer tutorial.
You need to specify an OBJ file and light source at the command line for this tutorial to work:
./pathtracer -i model.obj -ambientlight 1 1 1
As example models we provide the "Austrian Imperial Crown" model by Martin Lubich and the "Asian Dragon" model from the Stanford 3D Scanning Repository.
To render these models execute the following:
./pathtracer -c crown/crown.ecs
./pathtracer -c asian_dragon/asian_dragon.ecs
![][imgHairGeometry]
This tutorial demonstrates the use of the hair geometry to render a hairball.
![][imgCurveGeometry]
This tutorial demonstrates the use of the Bézier curve geometry.
![][imgSubdivisionGeometry]
This tutorial demonstrates the use of Catmull Clark subdivision
surfaces. Per default the edge tessellation level is set adaptively
based on the distance to the camera origin. Embree currently supports
three different modes for efficiently handling subdivision surfaces in
various rendering scenarios. These three modes can be selected at the
command line, e.g. -lazy builds internal per subdivision patch data
structures on demand, -cache uses a small (per thread) tessellation
cache for caching per patch data, and -pregenerate to generate and
store most per patch data during the initial build process. The
cache mode is most effective for coherent rays while providing a
fixed memory footprint. The pregenerate modes is most effective for
incoherent ray distributions while requiring more memory. The lazy
mode works similar to the pregenerate mode but provides a middle
ground in terms of memory consumption as it only builds and stores
data only when the corresponding patch is accessed during the ray
traversal. The cache mode is currently a bit more efficient at
handling dynamic scenes where only the edge tessellation levels are
changing per frame.
![][imgDisplacementGeometry]
This tutorial demonstrates the use of Catmull Clark subdivision surfaces with procedural displacement mapping using a constant edge tessellation level.
![][imgMotionBlurGeometry]
This tutorial demonstrates rendering of motion blur using the multi segment motion blur feature. Shown is motion blur of a triangle mesh, quad mesh, subdivision surface, line segments, hair geometry, bezier curves, instantiated triangle mesh where the instance moves, instantiated quad mesh where the instance and the quads move, and user geometry.
The number of time steps used can be configured using the --time-steps <int> and --time-steps2 <int> command line parameters, and the
geometry can be rendered at a specific time using the the --time <float> command line parameter.
![][imgInterpolation]
This tutorial demonstrates interpolation of user defined per-vertex data.
This tutorial demonstrates how to use the templated hierarchy builders of Embree to build a bounding volume hierarchy with a user defined memory layout using a high quality SAH builder and very fast morton builder.
This tutorial demonstrates how to access the internal triangle acceleration structure build by Embree. Please be aware that the internal Embree data structures might change between Embree updates.
This tutorial demonstrates how to use the FIND_PACKAGE CMake feature
to use an installed Embree. Under Linux and Mac OS X the tutorial finds
the Embree installation automatically, under Windows the embree_DIR
CMake variable has to be set to the following folder of the Embree
installation: C:\Program Files\Intel\Embree X.Y.Z\lib\cmake\embree-X.Y.Z.
[Embree API]: #embree-api
[Ray Layout]: #ray-layout
[Extending the Ray Structure]: #extending-the-ray-structure
[Embree Example Renderer]: https://embree.github.io/renderer.html
[Triangle Geometry]: #triangle-geometry
[Stream Viewer]: #stream-viewer
[User Geometry]: #user-geometry
[Instanced Geometry]: #instanced-geometry
[Intersection Filter]: #intersection-filter
[Hair]: #hair
[Curves]: #bézier-curves
[Subdivision Geometry]: #subdivision-geometry
[Displacement Geometry]: #displacement-geometry
[BVH Builder]: #bvh-builder
[Interpolation]: #interpolation
[Individual Contributor License Agreement (ICLA)]: https://embree.github.io/data/Embree-ICLA.pdf
[Corporate Contributor License Agreement (CCLA)]: https://embree.github.io/data/Embree-CCLA.pdf
[imgTriangleUV]: https://embree.github.io/images/triangle_uv.png
[imgQuadUV]: https://embree.github.io/images/quad_uv.png
[imgTriangleGeometry]: https://embree.github.io/images/triangle_geometry.jpg
[imgDynamicScene]: https://embree.github.io/images/dynamic_scene.jpg
[imgUserGeometry]: https://embree.github.io/images/user_geometry.jpg
[imgViewer]: https://embree.github.io/images/viewer.jpg
[imgViewerStream]: https://embree.github.io/images/viewer_stream.jpg
[imgInstancedGeometry]: https://embree.github.io/images/instanced_geometry.jpg
[imgIntersectionFilter]: https://embree.github.io/images/intersection_filter.jpg
[imgPathtracer]: https://embree.github.io/images/pathtracer.jpg
[imgHairGeometry]: https://embree.github.io/images/hair_geometry.jpg
[imgCurveGeometry]: https://embree.github.io/images/curve_geometry.jpg
[imgSubdivisionGeometry]: https://embree.github.io/images/subdivision_geometry.jpg
[imgDisplacementGeometry]: https://embree.github.io/images/displacement_geometry.jpg
[imgMotionBlurGeometry]: https://embree.github.io/images/motion_blur_geometry.jpg
[imgInterpolation]: https://embree.github.io/images/interpolation.jpg
