Next event estimation (#71)

* test next event estimation

* start implementing shadow catcher

* add shadow catcher support (kindof)

* big cleanup

* more tweaks

* revert scene changes

* set strataCount back to default

Author: Lucas Crane

scenes/renderer-test/main.js

@@ -197,6 +197,8 @@ function init() {
     const geo = new THREE.PlaneBufferGeometry(1000, 1000);
     const mat = new THREE.MeshStandardMaterial();
     mat.shadowCatcher = true;
+    mat.roughness = 0.5;
+    mat.metalness = 0.0;
     const mesh = new THREE.Mesh(geo, mat);
     mesh.rotateX(Math.PI / 2);
     model.add(mesh);

scenes/sample-models/main.js

@@ -105,7 +105,7 @@ function createGroundMesh() {
   const geo = new THREE.PlaneBufferGeometry(100, 100);
   const mat = new THREE.MeshStandardMaterial();
   mat.color.set(0xffffff);
-  mat.roughness = 1.0;
+  mat.roughness = 0.5;
   mat.metalness = 0.0;
   mat.shadowCatcher = true;
   const mesh = new THREE.Mesh(geo, mat);

src/renderer/RayTracePass.js

@@ -21,8 +21,8 @@ export function makeRayTracePass(gl, {
   const samplingDimensions = [];
 
   for (let i = 1; i <= bounces; i++) {
-    // specular or diffuse reflection, light importance sampling, material sampling, next path direction
-    samplingDimensions.push(2, 2, 2, 2);
+    // specular or diffuse reflection, light importance sampling, next path direction
+    samplingDimensions.push(2, 2, 2);
     if (i >= 2) {
       // russian roulette sampling
       // this step is skipped on the first bounce

src/renderer/RenderingPipeline.js

@@ -30,6 +30,8 @@ export function makeRenderingPipeline({
   // higher number results in faster convergence over time, but with lower quality initial samples
   const strataCount = 6;
 
+  const desiredTimeForPreview = 14;
+
   const decomposedScene = decomposeScene(scene);
 
   const mergedMesh = mergeMeshesToGeometry(decomposedScene.meshes);
@@ -159,7 +161,6 @@ export function makeRenderingPipeline({
   }
 
   function setPreviewBufferDimensions() {
-    const desiredTimeForPreview = 10;
     const numPixelsForPreview = desiredTimeForPreview / tileRender.getTimePerPixel();
 
     const aspectRatio = screenWidth / screenHeight;

src/renderer/glsl/chunks/random.glsl

@@ -33,4 +33,20 @@ float randomSample() {
 vec2 randomSampleVec2() {
   return vec2(randomSample(), randomSample());
 }
+
+struct MaterialSamples {
+  vec2 s1;
+  vec2 s2;
+  vec2 s3;
+};
+
+MaterialSamples getRandomMaterialSamples() {
+  MaterialSamples samples;
+
+  samples.s1 = randomSampleVec2();
+  samples.s2 = randomSampleVec2();
+  samples.s3 = randomSampleVec2();
+
+  return samples;
+}
 `;

src/renderer/glsl/chunks/rayTraceCore.glsl

@@ -4,8 +4,6 @@ export default `
   #define THICK_GLASS 2
   #define SHADOW_CATCHER 3
 
-  #define SAMPLES_PER_MATERIAL 8
-
   const float IOR = 1.5;
   const float INV_IOR = 1.0 / IOR;
 
@@ -71,11 +69,11 @@ export default `
   struct Path {
     Ray ray;
     vec3 li;
-    vec3 albedo;
     float alpha;
     vec3 beta;
     bool specularBounce;
     bool abort;
+    float misWeight;
   };
 
   uniform Camera camera;

src/renderer/glsl/chunks/sampleGlassSpecular.glsl

@@ -3,17 +3,20 @@ export default `
 #ifdef USE_GLASS
 
 void sampleGlassSpecular(SurfaceInteraction si, int bounce, inout Path path) {
+  bool lastBounce = bounce == BOUNCES;
   vec3 viewDir = -path.ray.d;
   float cosTheta = dot(si.normal, viewDir);
 
+  MaterialSamples samples = getRandomMaterialSamples();
+
+  float reflectionOrRefraction = samples.s1.x;
+
   float F = si.materialType == THIN_GLASS ?
     fresnelSchlick(abs(cosTheta), R0) : // thin glass
     fresnelSchlickTIR(cosTheta, R0, IOR); // thick glass
 
   vec3 lightDir;
 
-  float reflectionOrRefraction = randomSample();
-
   if (reflectionOrRefraction < F) {
     lightDir = reflect(-viewDir, si.normal);
   } else {
@@ -23,13 +26,13 @@ void sampleGlassSpecular(SurfaceInteraction si, int bounce, inout Path path) {
     path.beta *= si.color;
   }
 
+  path.misWeight = 1.0;
+
   initRay(path.ray, si.position + EPS * lightDir, lightDir);
 
-  // advance sample index by unused stratified samples
-  const int usedSamples = 1;
-  sampleIndex += SAMPLES_PER_MATERIAL - usedSamples;
+  path.li += lastBounce ? path.beta * sampleBackgroundFromDirection(lightDir) : vec3(0.0);
 
-  path.li += bounce == BOUNCES ? path.beta * sampleBackgroundFromDirection(lightDir) : vec3(0.0);
+  path.specularBounce = true;
 }
 
 #endif

src/renderer/glsl/chunks/sampleMaterial.glsl

@@ -3,123 +3,106 @@
 
 export default `
 
-vec3 importanceSampleLight(SurfaceInteraction si, vec3 viewDir, bool lastBounce, vec2 random) {
-  vec3 li;
+void sampleMaterial(SurfaceInteraction si, int bounce, inout Path path) {
+  bool lastBounce = bounce == BOUNCES;
+  mat3 basis = orthonormalBasis(si.normal);
+  vec3 viewDir = -path.ray.d;
 
-  float lightPdf;
-  vec2 uv;
-  vec3 lightDir = sampleEnvmap(random, uv, lightPdf);
+  MaterialSamples samples = getRandomMaterialSamples();
 
-  float cosThetaL = dot(si.normal, lightDir);
+  vec2 diffuseOrSpecular = samples.s1;
+  vec2 lightDirSample = samples.s2;
+  vec2 bounceDirSample = samples.s3;
 
-  float orientation = dot(si.faceNormal, viewDir) * cosThetaL;
-  if (orientation < 0.0) {
-    return li;
-  }
+  // Step 1: Add direct illumination of the light source (the hdr map)
+  // On every bounce but the last, importance sample the light source
+  // On the last bounce, multiple importance sample the brdf AND the light source, determined by random var
 
-  float diffuseWeight = 1.0;
-  Ray ray;
-  initRay(ray, si.position + EPS * lightDir, lightDir);
-  if (intersectSceneShadow(ray)) {
-    if (lastBounce) {
-      diffuseWeight = 0.0;
-    } else {
-      return li;
-    }
+  vec3 lightDir;
+  vec2 uv;
+  float lightPdf;
+  bool brdfSample = false;
+
+  if (lastBounce && diffuseOrSpecular.x < 0.5) {
+    // reuse this sample by multiplying by 2 to bring sample from [0, 0.5), to [0, 1)
+    lightDir = 2.0 * diffuseOrSpecular.x < mix(0.5, 0.0, si.metalness) ?
+      lightDirDiffuse(si.faceNormal, viewDir, basis, lightDirSample) :
+      lightDirSpecular(si.faceNormal, viewDir, basis, si.roughness, lightDirSample);
+
+    uv = cartesianToEquirect(lightDir);
+    lightPdf = envmapPdf(uv);
+    brdfSample = true;
+  } else {
+    lightDir = sampleEnvmap(lightDirSample, uv, lightPdf);
   }
 
-  vec3 irr = textureLinear(envmap, uv).xyz;
-
-  float scatteringPdf;
-  vec3 brdf = materialBrdf(si, viewDir, lightDir, cosThetaL, diffuseWeight, scatteringPdf);
-
-  float weight = powerHeuristic(lightPdf, scatteringPdf);
-
-  li = brdf * irr * abs(cosThetaL) * weight / lightPdf;
-
-  return li;
-}
-
-vec3 importanceSampleMaterial(SurfaceInteraction si, vec3 viewDir, bool lastBounce, vec3 lightDir) {
-  vec3 li;
-
   float cosThetaL = dot(si.normal, lightDir);
 
+  float occluded = 1.0;
+
   float orientation = dot(si.faceNormal, viewDir) * cosThetaL;
   if (orientation < 0.0) {
-    return li;
+    // light dir points towards surface. invalid dir.
+    occluded = 0.0;
   }
 
   float diffuseWeight = 1.0;
-  Ray ray;
-  initRay(ray, si.position + EPS * lightDir, lightDir);
-  if (intersectSceneShadow(ray)) {
+
+  initRay(path.ray, si.position + EPS * lightDir, lightDir);
+  if (intersectSceneShadow(path.ray)) {
     if (lastBounce) {
       diffuseWeight = 0.0;
     } else {
-      return li;
+      occluded = 0.0;
     }
   }
 
-  vec2 uv = cartesianToEquirect(lightDir);
-
-  float lightPdf = envmapPdf(uv);
-
   vec3 irr = textureLinear(envmap, uv).rgb;
 
   float scatteringPdf;
   vec3 brdf = materialBrdf(si, viewDir, lightDir, cosThetaL, diffuseWeight, scatteringPdf);
 
-  float weight = powerHeuristic(scatteringPdf, lightPdf);
-
-  li += brdf * irr * abs(cosThetaL) * weight / scatteringPdf;
-
-  return li;
-}
+  float weight;
+  if (lastBounce) {
+    weight = brdfSample ?
+      2.0 * powerHeuristic(scatteringPdf, lightPdf) / scatteringPdf :
+      2.0 * powerHeuristic(lightPdf, scatteringPdf) / lightPdf;
+  } else {
+    weight = powerHeuristic(lightPdf, scatteringPdf) / lightPdf;
+  }
 
-void sampleMaterial(SurfaceInteraction si, int bounce, inout Path path) {
-  mat3 basis = orthonormalBasis(si.normal);
-  vec3 viewDir = -path.ray.d;
+  path.li += path.beta * occluded * brdf * irr * abs(cosThetaL) * weight;;
 
-  vec2 diffuseOrSpecular = randomSampleVec2();
+  // Step 2: Setup ray direction for next bounce by importance sampling the BRDF
 
-  vec3 lightDir = diffuseOrSpecular.x < mix(0.5, 0.0, si.metalness) ?
-    lightDirDiffuse(si.faceNormal, viewDir, basis, randomSampleVec2()) :
-    lightDirSpecular(si.faceNormal, viewDir, basis, si.roughness, randomSampleVec2());
+  if (lastBounce) {
+    return;
+  }
 
-  bool lastBounce = bounce == BOUNCES;
+  lightDir = diffuseOrSpecular.y < mix(0.5, 0.0, si.metalness) ?
+    lightDirDiffuse(si.faceNormal, viewDir, basis, bounceDirSample) :
+    lightDirSpecular(si.faceNormal, viewDir, basis, si.roughness, bounceDirSample);
 
-  // Add path contribution
-  path.li += path.beta * (
-      importanceSampleLight(si, viewDir, lastBounce, randomSampleVec2()) +
-      importanceSampleMaterial(si, viewDir, lastBounce, lightDir)
-    );
+  cosThetaL = dot(si.normal, lightDir);
 
-  // Get new path direction
+  orientation = dot(si.faceNormal, viewDir) * cosThetaL;
+  path.abort = orientation < 0.0;
 
-  if (lastBounce) {
+  if (path.abort) {
     return;
   }
 
-  lightDir = diffuseOrSpecular.y < mix(0.5, 0.0, si.metalness) ?
-    lightDirDiffuse(si.faceNormal, viewDir, basis, randomSampleVec2()) :
-    lightDirSpecular(si.faceNormal, viewDir, basis, si.roughness, randomSampleVec2());
+  brdf = materialBrdf(si, viewDir, lightDir, cosThetaL, 1.0, scatteringPdf);
 
-  float cosThetaL = dot(si.normal, lightDir);
+  uv = cartesianToEquirect(lightDir);
+  lightPdf = envmapPdf(uv);
 
-  float scatteringPdf;
-  vec3 brdf = materialBrdf(si, viewDir, lightDir, cosThetaL, 1.0, scatteringPdf);
+  path.misWeight = powerHeuristic(scatteringPdf, lightPdf);
 
   path.beta *= abs(cosThetaL) * brdf / scatteringPdf;
 
-  initRay(path.ray, si.position + EPS * lightDir, lightDir);
-
-  // If new ray direction is pointing into the surface,
-  // the light path is physically impossible and we terminate the path.
-  float orientation = dot(si.faceNormal, viewDir) * cosThetaL;
-  path.abort = orientation < 0.0;
-
   path.specularBounce = false;
-}
 
+  initRay(path.ray, si.position + EPS * lightDir, lightDir);
+}
 `;