Fix recent regressions

devices/rtx/device/frame/Frame.cu

@@ -192,11 +192,10 @@ __global__ void compositeBackground(vec4 *__restrict__ accumColor,
 
   vec3 rgb = vec3(rendered);
   float alpha = rendered.a;
-  accumulateValue(rgb, vec3(bg) * bg.a, alpha);
-  accumulateValue(alpha, bg.a, alpha);
 
-  if (!renderer.premultipliedAlpha && alpha > 0.0f)
-    rgb *= 1.0f / alpha;
+  const bool premultiplyBg = renderer.premultiplyBackground;
+  accumulateValue(rgb, premultiplyBg ? vec3(bg) * bg.a : vec3(bg), alpha);
+  accumulateValue(alpha, bg.a, alpha);
 
   vec4 rgba = vec4(rgb, alpha);
   if (format == FrameFormat::SRGB) {

devices/rtx/device/gpu/gpu_objects.h

@@ -732,7 +732,7 @@ struct RendererGPUData
   float inverseVolumeSamplingRate;
   float occlusionDistance;
   bool cullTriangleBF;
-  bool premultipliedAlpha;
+  bool premultiplyBackground;
   bool fireflyFilter; // enable internal tonemapping during sample accumulation
   glm::vec4 cutPlane; // cutting plane (nx,ny,nz,d); disabled when all zero (GPU
                       // default)

devices/rtx/device/gpu/gpu_util.h

@@ -247,11 +247,15 @@ VISRTX_DEVICE vec3 sampleUnitSphere(RandState &rs, const vec3 &normal)
       * vec3(sint * cosf(phi), sint * sinf(phi), -cost);
 }
 
-#define ulpEpsilon 0x1.fp-21
-
-VISRTX_DEVICE float epsilonFrom(const vec3 &P)
+VISRTX_DEVICE float epsilonFrom(const vec3 &P, const vec3 &dir, float t)
 {
-  return glm::compMax(abs(P)) * ulpEpsilon;
+  constexpr float hitEpsilonScale = 0x1.fp-21f;
+  constexpr float minHitEpsilon = 1e-8f;
+
+  const float pMag = glm::compMax(glm::abs(P));
+  const float dMag = glm::compMax(glm::abs(dir)) * t;
+
+  return fmaxf(glm::max(pMag, dMag) * hitEpsilonScale, minHitEpsilon);
 }
 
 // Hanika's shadow-terminator fix (Ray Tracing Gems II, ch. 4): lifts a
@@ -293,8 +297,8 @@ VISRTX_DEVICE vec3 shadingHitpoint(const SurfaceHit &hit)
   if (tri.vertexNormalsFV == nullptr && tri.vertexNormals == nullptr)
     return hit.hitpoint;
 
-  const uvec3 idx = tri.indices ? tri.indices[hit.primID]
-                                : uvec3(0, 1, 2) + hit.primID * 3;
+  const uvec3 idx =
+      tri.indices ? tri.indices[hit.primID] : uvec3(0, 1, 2) + hit.primID * 3;
   const vec3 v0 = tri.vertices[idx.x];
   const vec3 v1 = tri.vertices[idx.y];
   const vec3 v2 = tri.vertices[idx.z];

devices/rtx/device/gpu/populateHit.h

@@ -401,7 +401,7 @@ VISRTX_DEVICE void populateSurfaceHit(SurfaceHit &hit)
   hit.primID = ray::primID();
   hit.objID = sd.id;
   hit.instID = isd.id;
-  hit.epsilon = epsilonFrom(hit.hitpoint);
+  hit.epsilon = epsilonFrom(ray::hitpoint(), ray::direction(), ray::t());
   ray::computeTangentSpace(gd, ray::primID(), hit);
 
   const auto &handle = optixGetTransformListHandle(0);

devices/rtx/device/gpu/sampleLight.h

@@ -189,8 +189,8 @@ VISRTX_DEVICE LightSample sampleRectLight(
   // Front only: use cosTheta as-is (positive for front face)
 
   if (cosTheta > 0.0f) {
-    // Lambertian emission: radiance scaled by cosine factor
-    ls.radiance = ld.color * ld.rect.intensity * cosTheta;
+    // Lambertian radiance. cosTheta is handled through pdf below.
+    ls.radiance = ld.color * ld.rect.intensity;
 
     // Convert area PDF to solid angle PDF for proper Monte Carlo integration
     // Area PDF = 1 / area, Solid angle PDF = area_pdf * distance² / |cos θ|
@@ -257,8 +257,8 @@ VISRTX_DEVICE LightSample sampleRingLight(
 
   if (spot > 0.0f) {
     if (cosTheta > 0.0f) {
-      // Apply both spot attenuation and Lambert's cosine law
-      ls.radiance = ld.color * ld.ring.intensity * spot * cosTheta;
+      // Lambertian radiance. cosTheta is handled through pdf below.
+      ls.radiance = ld.color * ld.ring.intensity * spot;
 
       // Convert area PDF to solid angle PDF for proper Monte Carlo integration
       // Ring area = π(R² - r²), so area PDF = 1 / ring_area

devices/rtx/device/renderer/Renderer.cpp

@@ -170,8 +170,7 @@ void Renderer::commitParameters()
   m_cullTriangleBF = getParam<bool>("cullTriangleBackfaces", false);
   m_volumeSamplingRate =
       std::clamp(getParam<float>("volumeSamplingRate", 0.125f), 1e-3f, 10.f);
-  m_premultipliedAlpha = getParam<bool>(
-      "premultipliedAlpha", getParam<bool>("premultiplyBackground", false));
+  m_premultiplyBackground = getParam<bool>("premultiplyBackground", false);
   m_cutPlane = getParam<vec4>("cutPlane", vec4(0.f));
   if (m_checkerboard)
     m_spp = 1;
@@ -212,7 +211,7 @@ void Renderer::populateFrameData(FrameGPUData &fd) const
   fd.renderer.fireflyFilter = m_fireflyFilter;
   fd.renderer.inverseVolumeSamplingRate = 1.f / m_volumeSamplingRate;
   fd.renderer.numIterations = std::max(m_spp, 1);
-  fd.renderer.premultipliedAlpha = m_premultipliedAlpha;
+  fd.renderer.premultiplyBackground = m_premultiplyBackground;
   fd.renderer.cutPlane = m_cutPlane;
 }
 

devices/rtx/device/renderer/Renderer.h

@@ -94,7 +94,7 @@ struct Renderer : public Object
       true}; // enable internal tonemapping during sample accumulation
   int m_sampleLimit{0};
   bool m_cullTriangleBF{false};
-  bool m_premultipliedAlpha{false};
+  bool m_premultiplyBackground{false};
   float m_volumeSamplingRate{1.f};
   vec4 m_cutPlane{0.f};
 

devices/rtx/device/visrtx_renderer_fast.json

@@ -1,18 +1,20 @@
 {
-  "info" : {
-    "name" : "VISRTX_RENDERER_FAST",
-    "type" : "extension",
-    "dependencies" : ["anari_core_1_0"],
-    "implements" : [
+  "info": {
+    "name": "VISRTX_RENDERER_FAST",
+    "type": "extension",
+    "dependencies": [
+      "anari_core_1_0"
+    ],
+    "implements": [
       "khr_renderer_background_color",
       "khr_renderer_background_image",
       "khr_renderer_ambient_light"
     ]
   },
-  "objects" : [
+  "objects": [
     {
-      "type" : "ANARI_RENDERER",
-      "name" : "fast",
+      "type": "ANARI_RENDERER",
+      "name": "fast",
       "parameters": [
         {
           "name": "sampleLimit",
@@ -66,13 +68,13 @@
           "description": "suppress fireflies via reversible tonemapping before accumulation"
         },
         {
-          "name": "premultipliedAlpha",
+          "name": "premultiplyBackground",
           "types": [
             "ANARI_BOOL"
           ],
           "tags": [],
           "default": false,
-          "description": "pre-multiply RGB by alpha in the composited output pixel"
+          "description": "pre-multiply alpha channel with background color"
         },
         {
           "name": "cullTriangleBackfaces",
@@ -161,4 +163,4 @@
       ]
     }
   ]
-}
+}

devices/rtx/device/visrtx_renderer_interactive.json

@@ -1,18 +1,20 @@
 {
-  "info" : {
-    "name" : "VISRTX_RENDERER_INTERACTIVE",
-    "type" : "extension",
-    "dependencies" : ["anari_core_1_0"],
-    "implements" : [
+  "info": {
+    "name": "VISRTX_RENDERER_INTERACTIVE",
+    "type": "extension",
+    "dependencies": [
+      "anari_core_1_0"
+    ],
+    "implements": [
       "khr_renderer_background_color",
       "khr_renderer_background_image",
       "khr_renderer_ambient_light"
     ]
   },
-  "objects" : [
+  "objects": [
     {
-      "type" : "ANARI_RENDERER",
-      "name" : "interactive",
+      "type": "ANARI_RENDERER",
+      "name": "interactive",
       "parameters": [
         {
           "name": "sampleLimit",
@@ -57,13 +59,13 @@
           "description": "suppress fireflies via reversible tonemapping before accumulation"
         },
         {
-          "name": "premultipliedAlpha",
+          "name": "premultiplyBackground",
           "types": [
             "ANARI_BOOL"
           ],
           "tags": [],
           "default": false,
-          "description": "pre-multiply RGB by alpha in the composited output pixel"
+          "description": "pre-multiply alpha channel with background color"
         },
         {
           "name": "cullTriangleBackfaces",
@@ -163,4 +165,4 @@
       ]
     }
   ]
-}
+}

devices/rtx/device/visrtx_renderer_quality.json

@@ -1,18 +1,20 @@
 {
-  "info" : {
-    "name" : "VISRTX_RENDERER_QUALITY",
-    "type" : "extension",
-    "dependencies" : ["anari_core_1_0"],
-    "implements" : [
+  "info": {
+    "name": "VISRTX_RENDERER_QUALITY",
+    "type": "extension",
+    "dependencies": [
+      "anari_core_1_0"
+    ],
+    "implements": [
       "khr_renderer_background_color",
       "khr_renderer_background_image",
       "khr_renderer_ambient_light"
     ]
   },
-  "objects" : [
+  "objects": [
     {
-      "type" : "ANARI_RENDERER",
-      "name" : "quality",
+      "type": "ANARI_RENDERER",
+      "name": "quality",
       "parameters": [
         {
           "name": "sampleLimit",
@@ -57,13 +59,13 @@
           "description": "suppress fireflies via reversible tonemapping before accumulation"
         },
         {
-          "name": "premultipliedAlpha",
+          "name": "premultiplyBackground",
           "types": [
             "ANARI_BOOL"
           ],
           "tags": [],
           "default": false,
-          "description": "pre-multiply RGB by alpha in the composited output pixel"
+          "description": "pre-multiply alpha channel with background color"
         },
         {
           "name": "cullTriangleBackfaces",
@@ -120,4 +122,4 @@
       ]
     }
   ]
-}
+}