Fix Chiang hair model for Metal Shading language (AcademySoftwareFoun…

…dation#2057) The current approach for converting GLSL code to MSL doesn't work for the recent Chiang hair PR AcademySoftwareFoundation#1968.
autodesk-forks · Oct 10, 2024 · 0f2438e · 0f2438e
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Showing 2 changed files with 34 additions and 3 deletions.
diff --git a/libraries/pbrlib/genglsl/mx_hair_bsdf.glsl b/libraries/pbrlib/genglsl/mx_hair_bsdf.glsl
@@ -240,12 +240,21 @@ vec3 mx_chiang_hair_bsdf(
     float alpha = cuticle_angle * M_PI - (M_PI / 2.0);  // remap [0, 1] to [-PI/2, PI/2]
     mx_hair_alpha_angles(alpha, sinThetaI, cosThetaI, angles);
 
-    vec3 tint[4] = vec3[](tint_R, tint_TT, tint_TRT, tint_TRT);
+    vec3 tint[4];
+    tint[0] = tint_R;
+    tint[1] = tint_TT;
+    tint[2] = tint_TRT;
+    tint[3] = tint_TRT;
 
     roughness_R = clamp(roughness_R, 0.001, 1.0);
     roughness_TT = clamp(roughness_TT, 0.001, 1.0);
     roughness_TRT = clamp(roughness_TRT, 0.001, 1.0);
-    vec2 vs[4] = vec2[](roughness_R, roughness_TT, roughness_TRT, roughness_TRT);
+
+    vec2 vs[4];
+    vs[0] = roughness_R;
+    vs[1] = roughness_TT;
+    vs[2] = roughness_TRT;
+    vs[3] = roughness_TRT;
 
     // R, TT, TRT, TRRT+
     vec3 F = vec3(0.0);

diff --git a/source/MaterialXGenMsl/MslShaderGenerator.cpp b/source/MaterialXGenMsl/MslShaderGenerator.cpp
@@ -237,7 +237,29 @@ void MslShaderGenerator::MetalizeGeneratedShader(ShaderStage& shaderStage) const
                     }
                     size_t typename_end = pos;
                     std::string typeName = sourceCode.substr(typename_beg, typename_end - typename_beg);
-                    sourceCode.replace(beg, typename_end - beg, "thread " + typeName + "&");
+
+                    while (std::isspace(sourceCode[pos]))
+                    {
+                        ++pos;
+                    }
+                    size_t varname_beg = pos;
+                    while (!std::isspace(sourceCode[pos]) && sourceCode[pos] != '\n' && sourceCode[pos] != ',' && sourceCode[pos] != ')' )
+                    {
+                        ++pos;
+                    }
+                    size_t varname_end = pos;
+                    std::string varName = sourceCode.substr(varname_beg, varname_end - varname_beg);
+
+                    if (varName.find('[') != std::string::npos)
+                    {
+                        // if the variable is an array then we don't need to declare it as a reference,
+                        // we will effectively just be passing the pointer to the array
+                        sourceCode.replace(beg, typename_end - beg, "thread " + typeName);
+                    }
+                    else
+                    {
+                        sourceCode.replace(beg, typename_end - beg, "thread " + typeName + "&");
+                    }
                 }
                 pos = sourceCode.find(keyword, pos);
             }