From efe71ffd1e4294337282fbc4270c69c71081d09e Mon Sep 17 00:00:00 2001
From: Paul Molodowitch <pmolodowitch@nvidia.com>
Date: Mon, 29 Jul 2024 23:27:05 -0700
Subject: [PATCH] [hdEmbree] add lighting support for IES files

---
 pxr/imaging/plugin/hdEmbree/light.cpp    | 36 ++++++++++++++++++++++++
 pxr/imaging/plugin/hdEmbree/light.h      | 10 +++++++
 pxr/imaging/plugin/hdEmbree/renderer.cpp | 24 ++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/pxr/imaging/plugin/hdEmbree/light.cpp b/pxr/imaging/plugin/hdEmbree/light.cpp
index 2388d346fe..6885d20965 100644
--- a/pxr/imaging/plugin/hdEmbree/light.cpp
+++ b/pxr/imaging/plugin/hdEmbree/light.cpp
@@ -233,6 +233,42 @@ HdEmbree_Light::Sync(HdSceneDelegate *sceneDelegate,
         _lightData.shaping.coneSoftness = value.UncheckedGet<float>();
     }
 
+    if (const auto value = sceneDelegate->GetLightParamValue(
+            id, HdLightTokens->shapingIesFile);
+        value.IsHolding<SdfAssetPath>()) {
+        SdfAssetPath iesAssetPath = value.UncheckedGet<SdfAssetPath>();
+        std::string iesPath = iesAssetPath.GetResolvedPath();
+        if (iesPath.empty()) {
+            iesPath = iesAssetPath.GetAssetPath();
+        }
+
+        if (!iesPath.empty()) {
+            std::ifstream in(iesPath);
+            if (!in.is_open()) {
+                TF_WARN("could not open ies file %s", iesPath.c_str());
+            } else {
+                std::stringstream buffer;
+                buffer << in.rdbuf();
+
+                if (!_lightData.shaping.ies.iesFile.load(buffer.str())) {
+                    TF_WARN("could not load ies file %s", iesPath.c_str());
+                }
+            }
+        }
+    }
+
+    if (const auto value = sceneDelegate->GetLightParamValue(
+            id, HdLightTokens->shapingIesNormalize);
+        value.IsHolding<bool>()) {
+        _lightData.shaping.ies.normalize = value.UncheckedGet<bool>();
+    }
+
+    if (const auto value = sceneDelegate->GetLightParamValue(
+            id, HdLightTokens->shapingIesAngleScale);
+        value.IsHolding<float>()) {
+        _lightData.shaping.ies.angleScale = value.UncheckedGet<float>();
+    }
+
     _PopulateRtcLight(device, scene);
 
     HdEmbreeRenderer *renderer = embreeRenderParam->GetRenderer();
diff --git a/pxr/imaging/plugin/hdEmbree/light.h b/pxr/imaging/plugin/hdEmbree/light.h
index 3f756ebedf..1020de3cea 100644
--- a/pxr/imaging/plugin/hdEmbree/light.h
+++ b/pxr/imaging/plugin/hdEmbree/light.h
@@ -7,6 +7,8 @@
 #ifndef PXR_IMAGING_PLUGIN_HD_EMBREE_LIGHT_H
 #define PXR_IMAGING_PLUGIN_HD_EMBREE_LIGHT_H
 
+#include "pxr/imaging/plugin/hdEmbree/pxrIES/pxrIES.h"
+
 #include "pxr/base/gf/vec3f.h"
 #include "pxr/base/gf/matrix3f.h"
 #include "pxr/base/gf/matrix4f.h"
@@ -71,12 +73,20 @@ struct HdEmbree_LightTexture
     int height = 0;
 };
 
+struct HdEmbree_IES
+{
+    PxrIESFile iesFile;
+    bool normalize = false;
+    float angleScale = 0.0f;
+};
+
 struct HdEmbree_Shaping
 {
     GfVec3f focusTint;
     float focus = 0.0f;
     float coneAngle = 180.0f;
     float coneSoftness = 0.0f;
+    HdEmbree_IES ies;
 };
 
 struct HdEmbree_LightData
diff --git a/pxr/imaging/plugin/hdEmbree/renderer.cpp b/pxr/imaging/plugin/hdEmbree/renderer.cpp
index 28587f0d4c..72b29656d3 100644
--- a/pxr/imaging/plugin/hdEmbree/renderer.cpp
+++ b/pxr/imaging/plugin/hdEmbree/renderer.cpp
@@ -389,6 +389,27 @@ _IntersectAreaLight(HdEmbree_LightData const& light, RTCRayHit const& rayHit)
     };
 }
 
+float
+_EvalIES(HdEmbree_LightData const& light, GfVec3f const& wI)
+{
+    HdEmbree_IES const& ies = light.shaping.ies;
+
+    if (!ies.iesFile.valid()) {
+        // Either none specified or there was an error loading. In either case,
+        // just ignore
+        return 1.0f;
+    }
+
+    // emission direction in light space
+    GfVec3f wE = light.xformWorldToLight.TransformDir(wI).GetNormalized();
+
+    float theta = _Theta(wE);
+    float phi = _Phi(wE);
+    float norm = ies.normalize ? ies.iesFile.power() : 1.0f;
+
+    return ies.iesFile.eval(theta, phi, ies.angleScale) / norm;
+}
+
 GfVec3f
 _EvalLightBasic(HdEmbree_LightData const& light)
 {
@@ -495,6 +516,9 @@ _EvalAreaLight(HdEmbree_LightData const& light, _ShapeSample const& ss,
     const float thetaOffZ = acosf(cosThetaOffZ);
     Le *= 1.0f - _Smoothstep(thetaOffZ, GfRange1f(thetaSoft, thetaCone));
 
+    // Apply IES
+    Le *= _EvalIES(light, wI);
+
     return _LightSample {
         Le,
         wI,