[hdEmbree] add distant light support

pxr/imaging/plugin/hdEmbree/CMakeLists.txt

@@ -49,6 +49,9 @@ pxr_plugin(hdEmbree
         debugCodes
         implicitSurfaceSceneIndexPlugin
 
+    PRIVATE_HEADERS
+        pxrPbrt/pbrtUtils.h
+
     RESOURCE_FILES
         plugInfo.json
 

pxr/imaging/plugin/hdEmbree/light.cpp

@@ -97,6 +97,8 @@ HdEmbree_Light::HdEmbree_Light(SdfPath const& id, TfToken const& lightType)
         _lightData.lightVariant = HdEmbree_Cylinder();
     } else if (lightType == HdSprimTypeTokens->diskLight) {
         _lightData.lightVariant = HdEmbree_Disk();
+    } else if (lightType == HdSprimTypeTokens->distantLight) {
+        _lightData.lightVariant = HdEmbree_Distant();
     } else if (lightType == HdSprimTypeTokens->domeLight) {
         _lightData.lightVariant = HdEmbree_Dome();
     } else if (lightType == HdSprimTypeTokens->rectLight) {
@@ -180,6 +182,12 @@ HdEmbree_Light::Sync(HdSceneDelegate *sceneDelegate,
                 sceneDelegate->GetLightParamValue(id, HdLightTokens->radius)
                     .GetWithDefault(0.5f),
             };
+        } else if constexpr (std::is_same_v<T, HdEmbree_Distant>) {
+            typedLight = HdEmbree_Distant{
+                float(GfDegreesToRadians(
+                    sceneDelegate->GetLightParamValue(id, HdLightTokens->angle)
+                        .GetWithDefault(0.53f) / 2.0f)),
+            };
         } else if constexpr (std::is_same_v<T, HdEmbree_Dome>) {
             typedLight = HdEmbree_Dome{};
             _SyncLightTexture(id, _lightData, sceneDelegate);

pxr/imaging/plugin/hdEmbree/light.h

@@ -35,6 +35,11 @@ struct HdEmbree_Disk
     float radius;
 };
 
+struct HdEmbree_Distant
+{
+    float halfAngleRadians;
+};
+
 // Needed for HdEmbree_LightVariant
 struct HdEmbree_Dome
 {};
@@ -54,6 +59,7 @@ using HdEmbree_LightVariant = std::variant<
     HdEmbree_UnknownLight,
     HdEmbree_Cylinder,
     HdEmbree_Disk,
+    HdEmbree_Distant,
     HdEmbree_Dome,
     HdEmbree_Rect,
     HdEmbree_Sphere>;

pxr/imaging/plugin/hdEmbree/renderDelegate.cpp

@@ -38,6 +38,7 @@ const TfTokenVector HdEmbreeRenderDelegate::SUPPORTED_SPRIM_TYPES =
     HdPrimTypeTokens->extComputation,
     HdPrimTypeTokens->cylinderLight,
     HdPrimTypeTokens->diskLight,
+    HdPrimTypeTokens->distantLight,
     HdPrimTypeTokens->domeLight,
     HdPrimTypeTokens->rectLight,
     HdPrimTypeTokens->sphereLight,
@@ -338,6 +339,7 @@ HdEmbreeRenderDelegate::CreateSprim(TfToken const& typeId,
     } else if (typeId == HdPrimTypeTokens->extComputation) {
         return new HdExtComputation(sprimId);
     } else if (typeId == HdPrimTypeTokens->light ||
+               typeId == HdPrimTypeTokens->distantLight ||
                typeId == HdPrimTypeTokens->diskLight ||
                typeId == HdPrimTypeTokens->domeLight ||
                typeId == HdPrimTypeTokens->rectLight ||
@@ -361,6 +363,7 @@ HdEmbreeRenderDelegate::CreateFallbackSprim(TfToken const& typeId)
     } else if (typeId == HdPrimTypeTokens->extComputation) {
         return new HdExtComputation(SdfPath::EmptyPath());
     } else if (typeId == HdPrimTypeTokens->light ||
+               typeId == HdPrimTypeTokens->distantLight ||
                typeId == HdPrimTypeTokens->diskLight ||
                typeId == HdPrimTypeTokens->domeLight ||
                typeId == HdPrimTypeTokens->rectLight ||

pxr/imaging/plugin/hdEmbree/renderer.cpp

@@ -9,6 +9,7 @@
 #include "pxr/imaging/plugin/hdEmbree/config.h"
 #include "pxr/imaging/plugin/hdEmbree/light.h"
 #include "pxr/imaging/plugin/hdEmbree/mesh.h"
+#include "pxr/imaging/plugin/hdEmbree/pxrPbrt/pbrtUtils.h"
 #include "pxr/imaging/plugin/hdEmbree/renderBuffer.h"
 
 #include "pxr/imaging/hd/perfLog.h"
@@ -449,6 +450,51 @@ _EvalLightBasic(HdEmbree_LightData const& light)
     return Le;
 }
 
+_LightSample
+_EvalDistantLight(HdEmbree_LightData const& light, GfVec3f const& position,
+                    float u1, float u2)
+{
+    auto const& distant = std::get<HdEmbree_Distant>(light.lightVariant);
+
+    GfVec3f Le = _EvalLightBasic(light);
+
+    if (distant.halfAngleRadians > 0.0f)
+    {
+        if (light.normalize)
+        {
+            float sinTheta = sinf(distant.halfAngleRadians);
+            Le /= _Sqr(sinTheta) * _pi<float>;
+        }
+
+        // There's an implicit double-negation of the wI direction here
+        GfVec3f localDir = pxr_pbrt::SampleUniformCone(GfVec2f(u1, u2),
+                                              distant.halfAngleRadians);
+        GfVec3f wI = light.xformLightToWorld.TransformDir(localDir);
+        wI.Normalize();
+
+        return _LightSample {
+            Le,
+            wI,
+            std::numeric_limits<float>::max(),
+            pxr_pbrt::InvUniformConePDF(distant.halfAngleRadians)
+        };
+    }
+    else
+    {
+        // delta case, infinite pdf
+        GfVec3f wI = light.xformLightToWorld.TransformDir(
+            GfVec3f(0.0f, 0.0f, 1.0f));
+        wI.Normalize();
+
+        return _LightSample {
+            Le,
+            wI,
+            std::numeric_limits<float>::max(),
+            1.0f,
+        };
+    }
+}
+
 _LightSample
 _EvalAreaLight(HdEmbree_LightData const& light, _ShapeSample const& ss,
                GfVec3f const& position)
@@ -615,6 +661,10 @@ class _LightSampler {
         return _EvalDomeLight(_lightData, _normal, _u1, _u2);
     }
 
+    _LightSample operator()(HdEmbree_Distant const& distant) {
+        return _EvalDistantLight(_lightData, _hitPosition, _u1, _u2);
+    }
+
 private:
     _LightSampler(HdEmbree_LightData const& lightData,
                  GfVec3f const& hitPosition,