From 4c8c043e6f15d452aedc68b3ba122230b802de95 Mon Sep 17 00:00:00 2001
From: Paul Molodowitch <pmolodowitch@nvidia.com>
Date: Tue, 30 Jul 2024 00:27:19 -0700
Subject: [PATCH] [hdEmbree] add light texture support

---
 pxr/imaging/plugin/hdEmbree/light.cpp    | 56 ++++++++++++++++++++++++
 pxr/imaging/plugin/hdEmbree/light.h      |  8 ++++
 pxr/imaging/plugin/hdEmbree/renderer.cpp | 19 ++++++++
 3 files changed, 83 insertions(+)

diff --git a/pxr/imaging/plugin/hdEmbree/light.cpp b/pxr/imaging/plugin/hdEmbree/light.cpp
index 082e4605d2..f8ffb4c4b8 100644
--- a/pxr/imaging/plugin/hdEmbree/light.cpp
+++ b/pxr/imaging/plugin/hdEmbree/light.cpp
@@ -21,6 +21,61 @@
 #include <sstream>
 #include <vector>
 
+namespace {
+
+PXR_NAMESPACE_USING_DIRECTIVE
+
+HdEmbree_LightTexture
+_LoadLightTexture(std::string const& path)
+{
+    if (path.empty()) {
+        return HdEmbree_LightTexture();
+    }
+
+    HioImageSharedPtr img = HioImage::OpenForReading(path);
+    if (!img) {
+        return HdEmbree_LightTexture();
+    }
+
+    int width = img->GetWidth();
+    int height = img->GetHeight();
+
+    std::vector<GfVec3f> pixels(width * height * 3.0f);
+
+    HioImage::StorageSpec storage;
+    storage.width = width;
+    storage.height = height;
+    storage.depth = 1;
+    storage.format = HioFormatFloat32Vec3;
+    storage.data = &pixels.front();
+
+    if (img->Read(storage)) {
+        return {std::move(pixels), width, height};
+    }
+    TF_WARN("Could not read image %s", path.c_str());
+    return { std::vector<GfVec3f>(), 0, 0 };
+}
+
+
+void
+_SyncLightTexture(const SdfPath& id, HdEmbree_LightData& light, HdSceneDelegate *sceneDelegate)
+{
+    std::string path;
+    if (VtValue textureValue = sceneDelegate->GetLightParamValue(
+            id, HdLightTokens->textureFile);
+        textureValue.IsHolding<SdfAssetPath>()) {
+        SdfAssetPath texturePath =
+            textureValue.UncheckedGet<SdfAssetPath>();
+        path = texturePath.GetResolvedPath();
+        if (path.empty()) {
+            path = texturePath.GetAssetPath();
+        }
+    }
+    light.texture = _LoadLightTexture(path);
+}
+
+
+} // anonymous namespace
 PXR_NAMESPACE_OPEN_SCOPE
 
 HdEmbree_Light::HdEmbree_Light(SdfPath const& id, TfToken const& lightType)
@@ -112,6 +167,7 @@ HdEmbree_Light::Sync(HdSceneDelegate *sceneDelegate,
                 sceneDelegate->GetLightParamValue(id, HdLightTokens->height)
                     .Get<float>(),
             };
+            _SyncLightTexture(id, _lightData, sceneDelegate);
         } else if constexpr (std::is_same_v<T, HdEmbree_Sphere>) {
             typedLight = HdEmbree_Sphere{
                 sceneDelegate->GetLightParamValue(id, HdLightTokens->radius)
diff --git a/pxr/imaging/plugin/hdEmbree/light.h b/pxr/imaging/plugin/hdEmbree/light.h
index 906ba185bc..9b54575bc3 100644
--- a/pxr/imaging/plugin/hdEmbree/light.h
+++ b/pxr/imaging/plugin/hdEmbree/light.h
@@ -53,6 +53,13 @@ using HdEmbree_LightVariant = std::variant<
     HdEmbree_Rect,
     HdEmbree_Sphere>;
 
+struct HdEmbree_LightTexture
+{
+    std::vector<GfVec3f> pixels;
+    int width = 0;
+    int height = 0;
+};
+
 struct HdEmbree_Shaping
 {
     GfVec3f focusTint;
@@ -67,6 +74,7 @@ struct HdEmbree_LightData
     GfMatrix3f normalXformLightToWorld;
     GfMatrix4f xformWorldToLight;
     GfVec3f color;
+    HdEmbree_LightTexture texture;
     float intensity = 1.0f;
     float exposure = 0.0f;
     float colorTemperature = 6500.0f;
diff --git a/pxr/imaging/plugin/hdEmbree/renderer.cpp b/pxr/imaging/plugin/hdEmbree/renderer.cpp
index 92e5f89cb2..9863ec0a44 100644
--- a/pxr/imaging/plugin/hdEmbree/renderer.cpp
+++ b/pxr/imaging/plugin/hdEmbree/renderer.cpp
@@ -216,6 +216,19 @@ struct _LightSample {
     float invPdfW;
 };
 
+GfVec3f
+_SampleLightTexture(HdEmbree_LightTexture const& texture, float s, float t)
+{
+    if (texture.pixels.empty()) {
+        return GfVec3f(0.0f);
+    }
+
+    int x = float(texture.width) * s;
+    int y = float(texture.height) * t;
+
+    return texture.pixels.at(y*texture.width + x);
+}
+
 _ShapeSample
 _SampleRect(GfMatrix4f const& xf, GfMatrix3f const& normalXform, float width,
             float height, float u1, float u2)
@@ -363,6 +376,12 @@ _EvalAreaLight(HdEmbree_LightData const& light, _ShapeSample const& ss,
         _EvalLightBasic(light)
         : GfVec3f(0.0f);
 
+    // Multiply by the texture, if there is one
+    if (!light.texture.pixels.empty()) {
+        Le = GfCompMult(Le, _SampleLightTexture(light.texture, ss.uv[0],
+                                                1.0f - ss.uv[1]));
+    }
+
     // If normalize is enabled, we need to divide the luminance by the surface
     // area of the light, which for an area light is equivalent to multiplying
     // by the area pdf, which is itself the reciprocal of the surface area