Clarify GLSL data generation shaders

- Use the word "generate" consistently in GLSL data generation files and functions, e.g. mx_generate_albedo_table.glsl, mx_generate_prefilter_env.glsl.
- Improve documentation for GLSL data generation functions.
- Replace constant texture dimensions with the textureSize call.

libraries/pbrlib/genglsl/lib/mx_prefilter_environment.glsl → libraries/pbrlib/genglsl/lib/mx_generate_prefilter_env.glsl

@@ -25,22 +25,17 @@ vec3 mx_latlong_map_projection_inverse(vec2 uv)
     return vec3(x, y, z);
 }
 
-vec3 mx_prefilter_environment()
+vec3 mx_generate_prefilter_env()
 {
-    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;
-    }
+    // The tangent view vector is aligned with the normal.
+    vec3 V = vec3(0.0, 0.0, 1.0);
+    float NdotV = 1.0;
 
-    // Compute world normal and transform.
+    // Compute derived properties.
+    vec2 uv = gl_FragCoord.xy * pow(2.0, $envPrefilterMip) / vec2(textureSize($envRadiance, 0));
     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 alpha = mx_latlong_lod_to_alpha(float($envPrefilterMip));
     float G1V = mx_ggx_smith_G1(NdotV, alpha);
 
     // Integrate the LD term for the given environment and alpha.

libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl

@@ -594,6 +594,7 @@ vec3 mx_latlong_map_lookup(vec3 dir, mat4 transform, float lod, sampler2D envSam
     return textureLod(envSampler, uv, lod).rgb;
 }
 
+// Return the mip level with the appropriate coverage for a filtered importance sample.
 // 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)
@@ -604,16 +605,16 @@ float mx_latlong_compute_lod(vec3 dir, float pdf, float maxMipLevel, int envSamp
     return max(effectiveMaxMipLevel - 0.5 * log2(float(envSamples) * pdf * distortion), 0.0);
 }
 
+// Return the mip level associated with the given alpha in a prefiltered environment.
 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);
 }
 
+// Return the alpha associated with the given mip level in a prefiltered environment.
 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);
 }

source/MaterialXGenGlsl/GlslShaderGenerator.cpp

@@ -587,14 +587,14 @@ void GlslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& c
     // Emit directional albedo table code.
     if (context.getOptions().hwWriteAlbedoTable)
     {
-        emitLibraryInclude("pbrlib/genglsl/lib/mx_table.glsl", context, stage);
+        emitLibraryInclude("pbrlib/genglsl/lib/mx_generate_albedo_table.glsl", context, stage);
         emitLineBreak(stage);
     }
 
     // Emit environment prefiltering code
     if (context.getOptions().hwWriteEnvPrefilter)
     {
-        emitLibraryInclude("pbrlib/genglsl/lib/mx_prefilter_environment.glsl", context, stage);
+        emitLibraryInclude("pbrlib/genglsl/lib/mx_generate_prefilter_env.glsl", context, stage);
         emitLineBreak(stage);
     }
 
@@ -645,7 +645,7 @@ void GlslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& c
     }
     else if (context.getOptions().hwWriteEnvPrefilter)
     {
-        emitLine(outputSocket->getVariable() + " = vec4(mx_prefilter_environment(), 1.0)", stage);
+        emitLine(outputSocket->getVariable() + " = vec4(mx_generate_prefilter_env(), 1.0)", stage);
     }
     else
     {

source/MaterialXGenMsl/MslShaderGenerator.cpp

@@ -1055,14 +1055,14 @@ void MslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& co
         // Emit directional albedo table code.
         if (context.getOptions().hwWriteAlbedoTable)
         {
-            emitLibraryInclude("pbrlib/genglsl/lib/mx_table.glsl", context, stage);
+            emitLibraryInclude("pbrlib/genglsl/lib/mx_generate_albedo_table.glsl", context, stage);
             emitLineBreak(stage);
         }
 
         // Emit environment prefiltering code
         if (context.getOptions().hwWriteEnvPrefilter)
         {
-            emitLibraryInclude("pbrlib/genglsl/lib/mx_prefilter_environment.glsl", context, stage);
+            emitLibraryInclude("pbrlib/genglsl/lib/mx_generate_prefilter_env.glsl", context, stage);
             emitLineBreak(stage);
         }
 
@@ -1113,7 +1113,7 @@ void MslShaderGenerator::emitPixelStage(const ShaderGraph& graph, GenContext& co
         }
         else if (context.getOptions().hwWriteEnvPrefilter)
         {
-            emitLine(outputSocket->getVariable() + " = float4(mx_prefilter_environment(), 1.0)", stage);
+            emitLine(outputSocket->getVariable() + " = float4(mx_generate_prefilter_env(), 1.0)", stage);
         }
         else
         {