Improvements to prefiltered environment maps (#1420)

As discussed with @jstone-lucasfilm, MaterialXView's pre-integrated IBL path (i.e. when FIS is turned off) is broken. This PR attempts to fix this issue.

libraries/pbrlib/genglsl/lib/mx_environment_fis.glsl

@@ -1,15 +1,5 @@
 #include "mx_microfacet_specular.glsl"
 
-// https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch20.html
-// Section 20.4 Equation 13
-float mx_latlong_compute_lod(vec3 dir, float pdf, float maxMipLevel, int envSamples)
-{
- const float MIP_LEVEL_OFFSET = 1.5;
- float effectiveMaxMipLevel = maxMipLevel - MIP_LEVEL_OFFSET;
- float distortion = sqrt(1.0 - mx_square(dir.y));
- return max(effectiveMaxMipLevel - 0.5 * log2(float(envSamples) * pdf * distortion), 0.0);
-}
-
 vec3 mx_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, FresnelData fd)
 {
  // Generate tangent frame.

libraries/pbrlib/genglsl/lib/mx_environment_prefilter.glsl

@@ -1,12 +1,5 @@
 #include "mx_microfacet_specular.glsl"
 
-float mx_latlong_compute_lod(float alpha)
-{
- // Select a mip level based on input alpha.
- float lodBias = alpha < 0.25 ? sqrt(alpha) : 0.5*alpha + 0.375;
- return lodBias * float($envRadianceMips);
-}
-
 vec3 mx_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, FresnelData fd)
 {
  N = mx_forward_facing_normal(N, V);
@@ -19,7 +12,7 @@ vec3 mx_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distributio
  float G = mx_ggx_smith_G2(NdotV, NdotV, avgAlpha);
  vec3 FG = fd.refraction ? vec3(1.0) - (F * G) : F * G;
 
- vec3 Li = mx_latlong_map_lookup(L, $envMatrix, mx_latlong_compute_lod(avgAlpha), $envRadiance);
+ vec3 Li = mx_latlong_map_lookup(L, $envMatrix, mx_latlong_alpha_to_lod(avgAlpha), $envRadiance);
  return Li * FG;
 }
 

libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl

@@ -593,3 +593,27 @@ vec3 mx_latlong_map_lookup(vec3 dir, mat4 transform, float lod, sampler2D envSam
  vec2 uv = mx_latlong_projection(envDir);
  return textureLod(envSampler, uv, lod).rgb;
 }
+
+// https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch20.html
+// Section 20.4 Equation 13
+float mx_latlong_compute_lod(vec3 dir, float pdf, float maxMipLevel, int envSamples)
+{
+ const float MIP_LEVEL_OFFSET = 1.5;
+ float effectiveMaxMipLevel = maxMipLevel - MIP_LEVEL_OFFSET;
+ float distortion = sqrt(1.0 - mx_square(dir.y));
+ return max(effectiveMaxMipLevel - 0.5 * log2(float(envSamples) * pdf * distortion), 0.0);
+}
+
+float mx_latlong_alpha_to_lod(float alpha)
+{
+ // Return the mip level associated with the given alpha in a prefiltered environment.
+ float lodBias = (alpha < 0.25) ? sqrt(alpha) : 0.5 * alpha + 0.375;
+ return lodBias * float($envRadianceMips - 1);
+}
+
+float mx_latlong_lod_to_alpha(float lod)
+{
+ // Return the alpha associated with the given mip level in a prefiltered environment.
+ float lodBias = lod / float($envRadianceMips - 1);
+ return (lodBias < 0.5) ? mx_square(lodBias) : 2.0 * (lodBias - 0.375);
+}

libraries/pbrlib/genglsl/lib/mx_prefilter_environment.glsl

@@ -0,0 +1,76 @@
+#include "mx_microfacet_specular.glsl"
+
+// Construct an orthonormal basis from a unit vector.
+// https://graphics.pixar.com/library/OrthonormalB/paper.pdf
+mat3 mx_orthonormal_basis(vec3 N)
+{
+ float sign = (N.z < 0.0) ? -1.0 : 1.0;
+ float a = -1.0 / (sign + N.z);
+ float b = N.x * N.y * a;
+ vec3 X = vec3(1.0 + sign * N.x * N.x * a, sign * b, -sign * N.x);
+ vec3 Y = vec3(b, sign + N.y * N.y * a, -N.y);
+ return mat3(X, Y, N);
+}
+
+// The inverse of mx_latlong_projection.
+vec3 mx_latlong_map_projection_inverse(vec2 uv)
+{
+ float latitude = (uv.y - 0.5) * M_PI;
+ float longitude = (uv.x - 0.5) * M_PI * 2.0;
+
+ float x = -cos(latitude) * sin(longitude);
+ float y = -sin(latitude);
+ float z = cos(latitude) * cos(longitude);
+
+ return vec3(x, y, z);
+}
+
+vec3 mx_prefilter_environment()
+{
+ vec2 uv = gl_FragCoord.xy * pow(2.0, $envPrefilterMip) / vec2(2048.0, 1024.0);
+ float alpha = mx_latlong_lod_to_alpha(float($envPrefilterMip));
+ if ($envPrefilterMip == 0)
+ {
+ return textureLod($envRadiance, uv, 0).rgb;
+ }
+
+ // Compute world normal and transform.
+ vec3 worldN = mx_latlong_map_projection_inverse(uv);
+ mat3 tangentToWorld = mx_orthonormal_basis(worldN);
+
+ // Local normal and view vectors are constant and aligned.
+ vec3 V = vec3(0.0, 0.0, 1.0);
+ float NdotV = 1.0;
+ float G1V = mx_ggx_smith_G1(NdotV, alpha);
+
+ // Integrate the LD term for the given environment and alpha.
+ vec3 radiance = vec3(0.0, 0.0, 0.0);
+ float weight = 0.0;
+ int envRadianceSamples = 1024;
+ for (int i = 0; i < envRadianceSamples; i++)
+ {
+ vec2 Xi = mx_spherical_fibonacci(i, envRadianceSamples);
+
+ // Compute the half vector and incoming light direction.
+ vec3 H = mx_ggx_importance_sample_VNDF(Xi, V, vec2(alpha));
+ vec3 L = -V + 2.0 * H.z * H;
+
+ // Compute dot products for this sample.
+ float NdotL = clamp(L.z, M_FLOAT_EPS, 1.0);
+
+ // Compute the geometric term.
+ float G = mx_ggx_smith_G2(NdotL, NdotV, alpha);
+
+ // Sample the environment light from the given direction.
+ vec3 Lw = tangentToWorld * L;
+ float pdf = mx_ggx_NDF(H, vec2(alpha)) * G1V / (4.0 * NdotV);
+ float lod = mx_latlong_compute_lod(Lw, pdf, float($envRadianceMips - 1), envRadianceSamples);
+ vec3 sampleColor = mx_latlong_map_lookup(Lw, $envMatrix, lod, $envRadiance);
+
+ // Add the radiance contribution of this sample.
+ radiance += G * sampleColor;
+ weight += G;
+ }
+
+ return radiance / weight;
+}

source/JsMaterialX/JsMaterialXGenShader/JsGenOptions.cpp

@@ -42,5 +42,6 @@ EMSCRIPTEN_BINDINGS(GenOptions)
  .property("hwMaxActiveLightSources", &mx::GenOptions::hwMaxActiveLightSources)
  .property("hwNormalizeUdimTexCoords", &mx::GenOptions::hwNormalizeUdimTexCoords)
  .property("hwWriteAlbedoTable", &mx::GenOptions::hwWriteAlbedoTable)
+ .property("hwWriteEnvPrefilter", &mx::GenOptions::hwWriteEnvPrefilter)
  ;
 }

source/MaterialXGenGlsl/GlslShaderGenerator.cpp

@@ -553,7 +553,7 @@ void GlslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& c
  bool lighting = requiresLighting(graph);
 
  // Define directional albedo approach
- if (lighting || context.getOptions().hwWriteAlbedoTable)
+ if (lighting || context.getOptions().hwWriteAlbedoTable || context.getOptions().hwWriteEnvPrefilter)
  {
  emitLine("#define DIRECTIONAL_ALBEDO_METHOD " + std::to_string(int(context.getOptions().hwDirectionalAlbedoMethod)), stage, false);
  emitLineBreak(stage);
@@ -591,6 +591,13 @@ void GlslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& c
  emitLineBreak(stage);
  }
 
+ // Emit environment prefiltering code
+ if (context.getOptions().hwWriteEnvPrefilter)
+ {
+ emitLibraryInclude("pbrlib/genglsl/lib/mx_prefilter_environment.glsl", context, stage);
+ emitLineBreak(stage);
+ }
+
  // Set the include file to use for uv transformations,
  // depending on the vertical flip flag.
  if (context.getOptions().fileTextureVerticalFlip)
@@ -636,6 +643,10 @@ void GlslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& c
  {
  emitLine(outputSocket->getVariable() + " = vec4(mx_generate_dir_albedo_table(), 1.0)", stage);
  }
+ else if (context.getOptions().hwWriteEnvPrefilter)
+ {
+ emitLine(outputSocket->getVariable() + " = vec4(mx_prefilter_environment(), 1.0)", stage);
+ }
  else
  {
  // Add all function calls.

source/MaterialXGenMsl/MslShaderGenerator.cpp

@@ -1059,6 +1059,13 @@ void MslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& co
  emitLineBreak(stage);
  }
 
+ // Emit environment prefiltering code
+ if (context.getOptions().hwWriteEnvPrefilter)
+ {
+ emitLibraryInclude("pbrlib/genglsl/lib/mx_prefilter_environment.glsl", context, stage);
+ emitLineBreak(stage);
+ }
+
  // Set the include file to use for uv transformations,
  // depending on the vertical flip flag.
  if (context.getOptions().fileTextureVerticalFlip)
@@ -1104,6 +1111,10 @@ void MslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& co
  {
  emitLine(outputSocket->getVariable() + " = float4(mx_generate_dir_albedo_table(), 1.0)", stage);
  }
+ else if (context.getOptions().hwWriteEnvPrefilter)
+ {
+ emitLine(outputSocket->getVariable() + " = float4(mx_prefilter_environment(), 1.0)", stage);
+ }
  else
  {
  // Add all function calls.

source/MaterialXGenShader/GenOptions.h

@@ -90,6 +90,7 @@ class MX_GENSHADER_API GenOptions
  hwMaxActiveLightSources(3),
  hwNormalizeUdimTexCoords(false),
  hwWriteAlbedoTable(false),
+ hwWriteEnvPrefilter(false),
  hwImplicitBitangents(true),
  emitColorTransforms(true)
  {
@@ -174,6 +175,10 @@ class MX_GENSHADER_API GenOptions
  /// Defaults to false.
  bool hwWriteAlbedoTable;
 
+ /// Enables the generation of a prefiltered environment map.
+ /// Defaults to false.
+ bool hwWriteEnvPrefilter;
+
  /// Calculate fallback bitangents from existing normals and tangents
  /// inside the bitangent node.
  bool hwImplicitBitangents;

source/MaterialXGenShader/HwShaderGenerator.cpp

@@ -59,6 +59,7 @@ const string T_ENV_RADIANCE = "$envRadiance";
 const string T_ENV_RADIANCE_MIPS = "$envRadianceMips";
 const string T_ENV_RADIANCE_SAMPLES = "$envRadianceSamples";
 const string T_ENV_IRRADIANCE = "$envIrradiance";
+const string T_ENV_PREFILTER_MIP = "$envPrefilterMip";
 const string T_REFRACTION_TWO_SIDED = "$refractionTwoSided";
 const string T_ALBEDO_TABLE = "$albedoTable";
 const string T_ALBEDO_TABLE_SIZE = "$albedoTableSize";
@@ -113,6 +114,7 @@ const string ENV_RADIANCE = "u_envRadiance";
 const string ENV_RADIANCE_MIPS = "u_envRadianceMips";
 const string ENV_RADIANCE_SAMPLES = "u_envRadianceSamples";
 const string ENV_IRRADIANCE = "u_envIrradiance";
+const string ENV_PREFILTER_MIP = "u_envPrefilterMip";
 const string REFRACTION_TWO_SIDED = "u_refractionTwoSided";
 const string ALBEDO_TABLE = "u_albedoTable";
 const string ALBEDO_TABLE_SIZE = "u_albedoTableSize";
@@ -222,6 +224,7 @@ HwShaderGenerator::HwShaderGenerator(SyntaxPtr syntax) :
  _tokenSubstitutions[HW::T_AMB_OCC_GAIN] = HW::AMB_OCC_GAIN;
  _tokenSubstitutions[HW::T_VERTEX_DATA_INSTANCE] = HW::VERTEX_DATA_INSTANCE;
  _tokenSubstitutions[HW::T_LIGHT_DATA_INSTANCE] = HW::LIGHT_DATA_INSTANCE;
+ _tokenSubstitutions[HW::T_ENV_PREFILTER_MIP] = HW::ENV_PREFILTER_MIP;
 
  // Setup closure contexts for defining closure functions
  //
@@ -359,6 +362,16 @@ ShaderPtr HwShaderGenerator::createShader(const string& name, ElementPtr element
  psPrivateUniforms->add(Type::INTEGER, HW::T_ALBEDO_TABLE_SIZE, Value::createValue<int>(64));
  }
 
+ // Add uniforms for environment prefiltering.
+ if (context.getOptions().hwWriteEnvPrefilter)
+ {
+ psPrivateUniforms->add(Type::FILENAME, HW::T_ENV_RADIANCE);
+ psPrivateUniforms->add(Type::INTEGER, HW::T_ENV_PREFILTER_MIP, Value::createValue<int>(1));
+ const Matrix44 yRotationPI = Matrix44::createScale(Vector3(-1, 1, -1));
+ psPrivateUniforms->add(Type::MATRIX44, HW::T_ENV_MATRIX, Value::createValue(yRotationPI));
+ psPrivateUniforms->add(Type::INTEGER, HW::T_ENV_RADIANCE_MIPS, Value::createValue<int>(1));
+ }
+
  // Create uniforms for the published graph interface
  for (ShaderGraphInputSocket* inputSocket : graph->getInputSockets())
  {

source/MaterialXGenShader/HwShaderGenerator.h

@@ -126,6 +126,7 @@ extern MX_GENSHADER_API const string T_ENV_RADIANCE;
 extern MX_GENSHADER_API const string T_ENV_RADIANCE_MIPS;
 extern MX_GENSHADER_API const string T_ENV_RADIANCE_SAMPLES;
 extern MX_GENSHADER_API const string T_ENV_IRRADIANCE;
+extern MX_GENSHADER_API const string T_ENV_PREFILTER_MIP;
 extern MX_GENSHADER_API const string T_REFRACTION_TWO_SIDED;
 extern MX_GENSHADER_API const string T_ALBEDO_TABLE;
 extern MX_GENSHADER_API const string T_ALBEDO_TABLE_SIZE;
@@ -182,6 +183,7 @@ extern MX_GENSHADER_API const string ENV_RADIANCE;
 extern MX_GENSHADER_API const string ENV_RADIANCE_MIPS;
 extern MX_GENSHADER_API const string ENV_RADIANCE_SAMPLES;
 extern MX_GENSHADER_API const string ENV_IRRADIANCE;
+extern MX_GENSHADER_API const string ENV_PREFILTER_MIP;
 extern MX_GENSHADER_API const string REFRACTION_TWO_SIDED;
 extern MX_GENSHADER_API const string ALBEDO_TABLE;
 extern MX_GENSHADER_API const string ALBEDO_TABLE_SIZE;

source/MaterialXRender/ImageHandler.cpp

@@ -165,7 +165,7 @@ void ImageHandler::unbindImages()
  }
 }
 
-bool ImageHandler::createRenderResources(ImagePtr, bool)
+bool ImageHandler::createRenderResources(ImagePtr, bool, bool)
 {
  return false;
 }

source/MaterialXRender/ImageHandler.h

@@ -230,7 +230,7 @@ class MX_RENDER_API ImageHandler
  }
 
  /// Create rendering resources for the given image.
- virtual bool createRenderResources(ImagePtr image, bool generateMipMaps);
+ virtual bool createRenderResources(ImagePtr image, bool generateMipMaps, bool useAsRenderTarget = false);
 
  /// Release rendering resources for the given image, or for all cached images
  /// if no image pointer is specified.

source/MaterialXRender/LightHandler.h

@@ -37,6 +37,7 @@ class MX_RENDER_API LightHandler
  _lightTransform(Matrix44::IDENTITY),
  _directLighting(true),
  _indirectLighting(true),
+ _usePrefilteredMap(false),
  _envSampleCount(DEFAULT_ENV_SAMPLE_COUNT),
  _refractionTwoSided(false)
  {
@@ -101,6 +102,30 @@ class MX_RENDER_API LightHandler
  return _envRadianceMap;
  }
 
+ /// Set the environment radiance map for the prefiltered environment lighting model.
+ void setEnvPrefilteredMap(ImagePtr map)
+ {
+ _envPrefilteredMap = map;
+ }
+
+ /// Return the environment radiance map for the prefiltered environment lighting model.
+ ImagePtr getEnvPrefilteredMap() const
+ {
+ return _envPrefilteredMap;
+ }
+
+ /// Set whether to use the prefiltered environment lighting model.
+ void setUsePrefilteredMap(bool val)
+ {
+ _usePrefilteredMap = val;
+ }
+
+ /// Return whether to use the prefiltered environment lighting model.
+ bool getUsePrefilteredMap()
+ {
+ return _usePrefilteredMap;
+ }
+
  /// Set the environment irradiance map
  void setEnvIrradianceMap(ImagePtr map)
  {
@@ -216,8 +241,10 @@ class MX_RENDER_API LightHandler
  Matrix44 _lightTransform;
  bool _directLighting;
  bool _indirectLighting;
+ bool _usePrefilteredMap;
 
  ImagePtr _envRadianceMap;
+ ImagePtr _envPrefilteredMap;
  ImagePtr _envIrradianceMap;
  int _envSampleCount;
 

source/MaterialXRender/Util.cpp

@@ -76,6 +76,26 @@ ShaderPtr createAlbedoTableShader(GenContext& context,
  return shader;
 }
 
+ShaderPtr createEnvPrefilterShader(GenContext& context,
+ DocumentPtr stdLib,
+ const string& shaderName)
+{
+ // Construct a dummy nodegraph.
+ DocumentPtr doc = createDocument();
+ doc->importLibrary(stdLib);
+ NodeGraphPtr nodeGraph = doc->addNodeGraph();
+ NodePtr constant = nodeGraph->addNode("constant");
+ OutputPtr output = nodeGraph->addOutput();
+ output->setConnectedNode(constant);
+
+ // Generate the shader
+ GenContext tableContext = context;
+ tableContext.getOptions().hwWriteEnvPrefilter = true;
+ ShaderPtr shader = createShader(shaderName, tableContext, output);
+
+ return shader;
+}
+
 ShaderPtr createBlurShader(GenContext& context,
  DocumentPtr stdLib,
  const string& shaderName,

source/MaterialXRender/Util.h

@@ -47,6 +47,11 @@ MX_RENDER_API ShaderPtr createAlbedoTableShader(GenContext& context,
  DocumentPtr stdLib,
  const string& shaderName);
 
+/// Create a shader that generates a prefiltered environment map.
+MX_RENDER_API ShaderPtr createEnvPrefilterShader(GenContext& context,
+ DocumentPtr stdLib,
+ const string& shaderName);
+
 /// Create a blur shader, using the given standard libraries for code generation.
 MX_RENDER_API ShaderPtr createBlurShader(GenContext& context,
  DocumentPtr stdLib,