From b79d44bf0374fc6414b33507862c9d38927e2d0d Mon Sep 17 00:00:00 2001
From: Paul Molodowitch <pmolodowitch@nvidia.com>
Date: Mon, 29 Jul 2024 23:03:30 -0700
Subject: [PATCH] [hdEmbree] add pxrPbrt/pbrUtils.h

A few small utility functions from pbrt-v4
---
 LICENSE.txt                                   | 17 ++++++
 .../plugin/hdEmbree/pxrPbrt/pbrtUtils.h       | 52 +++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 pxr/imaging/plugin/hdEmbree/pxrPbrt/pbrtUtils.h

diff --git a/LICENSE.txt b/LICENSE.txt
index d3bb1fa530..06a5b356ee 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -508,6 +508,23 @@ Redistributions in binary form must reproduce the above copyright notice, this l
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+============================================================
+pbrt (sampling functions in hdEmbree/pxrPbrt/pbrUtils.h)
+============================================================
+
+Copyright(c) 1998-2020 Matt Pharr, Wenzel Jakob, and Greg Humphreys.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
 
 ============================================================
 Draco
diff --git a/pxr/imaging/plugin/hdEmbree/pxrPbrt/pbrtUtils.h b/pxr/imaging/plugin/hdEmbree/pxrPbrt/pbrtUtils.h
new file mode 100644
index 0000000000..b7fcf4741d
--- /dev/null
+++ b/pxr/imaging/plugin/hdEmbree/pxrPbrt/pbrtUtils.h
@@ -0,0 +1,52 @@
+// pbrt is Copyright(c) 1998-2020 Matt Pharr, Wenzel Jakob, and Greg Humphreys.
+// The pbrt source code is licensed under the Apache License, Version 2.0.
+// SPDX: Apache-2.0
+
+#ifndef PXR_IMAGING_PLUGIN_HD_EMBREE_PBRT_UTILS_H
+#define PXR_IMAGING_PLUGIN_HD_EMBREE_PBRT_UTILS_H
+
+#include "pxr/pxr.h"
+
+#include "pxr/base/arch/math.h"
+#include "pxr/base/gf/vec2f.h"
+#include "pxr/base/gf/vec3f.h"
+
+PXR_NAMESPACE_OPEN_SCOPE
+
+namespace pxr_pbrt {
+
+template <typename T>
+constexpr T pi = static_cast<T>(M_PI);
+
+// Ported from PBRT
+inline GfVec3f
+SphericalDirection(float sinTheta, float cosTheta, float phi)
+{
+    return GfVec3f(GfClamp(sinTheta, -1.0f, 1.0f) * GfCos(phi),
+                   GfClamp(sinTheta, -1.0f, 1.0f) * GfSin(phi),
+                   GfClamp(cosTheta, -1.0f, 1.0f));
+}
+
+// Ported from PBRT
+inline GfVec3f
+SampleUniformCone(GfVec2f const& u, float angle)
+{
+    float cosAngle = GfCos(angle);
+    float cosTheta = (1.0f - u[0]) + u[0] * cosAngle;
+    float sinTheta = GfSqrt(GfMax(0.0f, 1.0f - cosTheta*cosTheta));
+    float phi = u[1] * 2.0f * pi<float>;
+    return SphericalDirection(sinTheta, cosTheta, phi);
+}
+
+// Ported from PBRT
+inline float
+InvUniformConePDF(float angle)
+{
+    return 2.0f * pi<float> * (1.0f - GfCos(angle));
+}
+
+} // namespace pxr_pbrt
+
+PXR_NAMESPACE_CLOSE_SCOPE
+
+#endif // PXR_IMAGING_PLUGIN_HD_EMBREE_PBRT_UTILS_H
\ No newline at end of file