MetalANGLE - OpenGL ES to Apple Metal API Translation Layer

This is a fork of Google's ANGLE project. It adds Metal API backend support. Apple announced OpenGL (ES) deprecation in 2018. So the purpose of MetalANGLE is to allow OpenGL ES applications to continue operate on Apple platforms by translating OpenGL ES draw calls to Metal draw calls under the hood. It also supports OpenGL ES & Metal's interop.

30 Jun 2021 Update: Most of this repo's OpenGL ES 3.0 implementing code in Metal has been merged into official ANGLE repo. Initially, this was the only place where Metal backend's developments took place. It is not true anymore as Apple are also making modifications and are in a progress of merging their changes into official ANGLE. See current Differences between MetalANGLE and official ANGLE.

Preliminary Metal based WebGL benchmarks (based on gles3-dev branch code):

• Metal (54 fps) vs native OpenGL (46 fps) drawing 20k fish:
• This benchmark runs https://webglsamples.org/aquarium/aquarium.html on Chromium browser using AMD Radeon Pro 560 GPU.

Current Metal backend implementation status

• MetalANGLE has been migrated into official ANGLE repo. See current Differences between MetalANGLE and official ANGLE.
• OpenGL ES 2.0 functionalities are 100% completed.
• OpenGL ES 3.0 status:
  • Occlusion queries.
  • MSAA.
  • Multiple render targets (Not all GL formats are supported on old iOS GPUs due to pixel storage's limits. See #issue 64).
  • 3D, array, shadow textures.
  • Texture swizzles (supported on iOS 13.0+, macOS 10.15+ only).
  • Uniform buffers.
  • Fence sync (supported on iOS 12.0+, macOS 10.14+ only).
  • Pixel buffer objects.
  • Primitive Restart. Metal's primitive restart doesn't work reliably.
  • Flat shading with last provoking vertex. Metal's default is first provoking vertex.
  • Transform feedbacks.
• OpenGL ES 1.0 is not recommended to be used. Its implementation is not actively maintained by original ANGLE project and currently buggy/not fully compliant.
• All basic samples are working.
• Almost all of ANGLE end2end tests have been passed. See List of failed tests.
• 98% of OpenGL ES 2.0 conformance tests passed. 90%+ of OpenGL ES 3.0 conformance tests passed. See Khronos VK-GL-CTS.
• These extensions have been implemented:
  • EXT_instanced_arrays/ANGLE_instanced_arrays: Instanced draw calls for GLES 2.0.
  • OES_depth_texture.
  • EXT_draw_buffers: Multiple render targets for GLES 2.0.
  • ANGLE_framebuffer_blit.
  • APPLE_clip_distance: Custom clip planes.
• MGLKit utilities classes have been added. Providing kind of similar functionalies to Apples's GLKit.
• Urho3D engine's demos have been tested using MetalANGLE without issues. See Urho3D's MetalANGLE integration testing branch.
• Irrlicht Engine's integration with MetalANGLE sample: https://github.com/kakashidinho/irrlicht.
• Interop with Metal is supported, see Qt example: https://github.com/kakashidinho/qml-metalangle.
• No GL_TRIANGLE_FAN & GL_LINE_LOOP support in draw calls yet.
• Metal doesn't allow buffer offset not being multiple of 4 bytes or multiple of attribute's size. Hence, draw calls that use unsupported offsets, strides, and vertex formats will force MetalANGLE to do conversions on the fly.
• MSAA is not supported yet.
• Old OpenGL ES 2.0 only implementation can be found on gles2 branch
• Platforms supports:
  • MetalANGLE only supports MacOS 10.13+ for Mac.
  • For iOS, the min supported version is iOS 9.0. However, Metal acceleration is only available for iOS 11.0+, any version prior to that will fall back to use native Apple OpenGL ES implementation instead of Metal. Furthermore, most of the sample apps are compiled for iOS 11.0+. So if you want to test the sample apps on 10.0 devices and below, it won't run, except a few ones (e.g. MGLKitSampleApp_ios9.0).
  • iPhone 5 and below are not supported.
  • MacCatalyst 13.0+ is supported.

TODO lists

• Make sure it passes all ANGLE's tests.
• Support GL_TRIANGLE_FAN & GL_LINE_LOOP by generating index buffer on the fly using Metal compute shader.
• Use compute shader to convert unsupported offsets, strides & vertex formats.
• Support MSAA.
• Fully support OpenGL ES 3.0.

How to build Metal ANGLE for MacOS & iOS

View the Metal backend's Dev setup instructions.

Currently, for convenience, MetalANGLE can also be built using an Xcode project provided in ios/xcode & mac/xcode folder. The Xcode project also builds MGLKit utilities wrapper library which provides MGLContext, MGLLayer, MGLKView, MGLKViewController, similar to Apple's provided GLKit classes such as CAEAGLContext, CAEAGLLayer, GLKView, GLKViewController. Please open MGLKitSamples.xcodeproj for example iOS app using this MGLKit library. This documents contains some guides to port GLKit apps to use MGLKit.

Nevertheless, you still need to setup the required environment and dependencies properly as mentioned in Metal backend's Dev setup instructions first.

Differences between MetalANGLE and Google's ANGLE

• Before June 2021, most of the Metal back-end code are shared between MetalANGLE and ANGLE.
• From Aug-Sep 2021 onward, there would be some changes from Apple directly to ANGLE repo. Those changes might not be included in MetalANGLE because of some development conflicts. Most of the Apple's changes benefit the Webkit's WebGL standards and might not have optimal performance for normal uses. These changes from Apple include:
  • Rewriting the index buffer on the fly to support last provoking vertex of flat shading. While this helps conforming to OpenGL ES's flat shading's specifications, it makes draw calls using flat shading become slower. In majority of use cases, user wouldn't care whether flat shading uses last or first provoking vertex.
• MetalANGLE includes iOS supports and high level API such as MGLKit that mimics Apple's deprecated EAGL & GLKit API. These features are unlikely to be merged into ANGLE since ANGLE project doesn't have any plan to support iOS in near future.

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Google's ANGLE - Almost Native Graphics Layer Engine

The goal of ANGLE is to allow users of multiple operating systems to seamlessly run WebGL and other OpenGL ES content by translating OpenGL ES API calls to one of the hardware-supported APIs available for that platform. ANGLE currently provides translation from OpenGL ES 2.0 and 3.0 to desktop OpenGL, OpenGL ES, Direct3D 9, and Direct3D 11. Support for translation from OpenGL ES to Vulkan is underway, and future plans include compute shader support (ES 3.1) and MacOS support.

Level of OpenGL ES support via backing renderers

	Direct3D 9	Direct3D 11	Desktop GL	GL ES	Vulkan	Metal
OpenGL ES 2.0	complete	complete	complete	complete	complete	complete
OpenGL ES 3.0		complete	complete	complete	in progress	90% complete
OpenGL ES 3.1		in progress	complete	complete	in progress
OpenGL ES 3.2			planned	planned	planned

Platform support via backing renderers

	Direct3D 9	Direct3D 11	Desktop GL	GL ES	Vulkan	Metal
Windows	complete	complete	complete	complete	complete
Linux			complete		complete
Mac OS X			complete			complete
iOS						complete
Chrome OS				complete	planned
Android				complete	complete
Fuchsia					in progress

ANGLE v1.0.772 was certified compliant by passing the ES 2.0.3 conformance tests in October 2011. ANGLE also provides an implementation of the EGL 1.4 specification.

ANGLE is used as the default WebGL backend for both Google Chrome and Mozilla Firefox on Windows platforms. Chrome uses ANGLE for all graphics rendering on Windows, including the accelerated Canvas2D implementation and the Native Client sandbox environment.

Portions of the ANGLE shader compiler are used as a shader validator and translator by WebGL implementations across multiple platforms. It is used on Mac OS X, Linux, and in mobile variants of the browsers. Having one shader validator helps to ensure that a consistent set of GLSL ES shaders are accepted across browsers and platforms. The shader translator can be used to translate shaders to other shading languages, and to optionally apply shader modifications to work around bugs or quirks in the native graphics drivers. The translator targets Desktop GLSL, Direct3D HLSL, and even ESSL for native GLES2 platforms.

Sources

ANGLE repository is hosted by Chromium project and can be browsed online or cloned with

git clone https://chromium.googlesource.com/angle/angle

Building

View the Dev setup instructions.

Contributing

• Join our Google group to keep up to date.

• Join us on IRC in the #ANGLEproject channel on FreeNode.

• Join us on Slack in the #angle channel.

• File bugs in the issue tracker (preferably with an isolated test-case).

• Choose an ANGLE branch to track in your own project.

• Read ANGLE development documentation.

• Look at pending and merged changes.

• Become a code contributor.

• Use ANGLE's coding standard.

• Learn how to build ANGLE for Chromium development.

• Get help on debugging ANGLE.

• Go through ANGLE's orientation and sift through starter projects.

• Read about WebGL on the Khronos WebGL Wiki.

• Learn about implementation details in the OpenGL Insights chapter on ANGLE and this ANGLE presentation.

• Learn about the past, present, and future of the ANGLE implementation in this presentation.

• Watch a short presentation on the Vulkan back-end.

• Track the dEQP test conformance

• Read design docs on the Vulkan back-end

• If you use ANGLE in your own project, we'd love to hear about it!