Merge pull request #2579 from Autodesk/t_gamaj/MAYA-122706/remove_glo…

…bal_variable_usage

Fix MaterialX compilation on M1 Macs

lib/mayaUsd/render/MaterialXGenOgsXml/GlslFragmentGenerator.cpp

@@ -12,6 +12,8 @@
 #include <MaterialXGenGlsl/GlslShaderGenerator.h>
 #include <MaterialXGenShader/Shader.h>
 
+#include <regex>
+
 MATERIALX_NAMESPACE_BEGIN
 
 namespace Stage {
@@ -25,6 +27,74 @@ const string LIGHT_LOOP_RESULT = "lightLoopResult";
 const string MAYA_ENV_IRRADIANCE_SAMPLE = "diffuseI";
 const string MAYA_ENV_RADIANCE_SAMPLE = "specularI";
 const string MAYA_ENV_ROUGHNESS = "roughness";
+
+// The Apple shader compiler found on M1/M2 machines does not allow using a global variable as a
+// temporary buffer. We will need to handle these inputs differently.
+void fixupVertexDataInstance(ShaderStage& stage)
+{
+    // All the strings start with $. This is an anchor character in regex, so skip it.
+    auto d = [](auto const& s) { return s.substr(1); };
+
+    // Find keywords:                   (as text)
+    //
+    //  vec3 HW::T_POSITION_WORLD       vec3 $normalWorld
+    //
+    // And replace with:
+    //
+    // vec3 unused_T_POSITION_WORLD     vec3 unused_normalWorld
+    //
+
+    static const std::string paramSource = "vec3 [$](" + d(HW::T_POSITION_WORLD) + "|"
+        + d(HW::T_POSITION_OBJECT) + "|" + d(HW::T_NORMAL_WORLD) + "|" + d(HW::T_NORMAL_OBJECT)
+        + "|" + d(HW::T_TANGENT_WORLD) + "|" + d(HW::T_TANGENT_OBJECT) + "|"
+        + d(HW::T_BITANGENT_WORLD) + "|" + d(HW::T_BITANGENT_OBJECT) + ")";
+
+    static const std::regex paramRegex(paramSource.c_str());
+
+    // Find keywords:                                       (as text)
+    //
+    //  HW::T_VERTEX_DATA_INSTANCE.HW::T_POSITION_WORLD     $vd.$normalWorld
+    //
+    // And replace with:
+    //
+    // HW::T_POSITION_WORLD(PIX_IN.HW::T_POSITION_WORLD)    $normalWorld( PIX_IN.$normalWorld )
+    //
+
+    static const std::string vtxSource = "[$]" + d(HW::T_VERTEX_DATA_INSTANCE) + "[.][$]("
+        + d(HW::T_POSITION_WORLD) + "|" + d(HW::T_POSITION_OBJECT) + "|" + d(HW::T_NORMAL_WORLD)
+        + "|" + d(HW::T_NORMAL_OBJECT) + "|" + d(HW::T_TANGENT_WORLD) + "|"
+        + d(HW::T_TANGENT_OBJECT) + "|" + d(HW::T_BITANGENT_WORLD) + "|" + d(HW::T_BITANGENT_OBJECT)
+        + ")";
+
+    static const std::regex vtxRegex(vtxSource.c_str());
+
+    // Find keywords:                   (as text)
+    //
+    //  HW::T_VERTEX_DATA_INSTANCE.     $vd.$inGeomprop_st
+    //
+    // And replace with:
+    //
+    //  (nothing)                       $inGeomprop_st
+    //
+
+    static const std::string vdCleanupSource = "[$]" + d(HW::T_VERTEX_DATA_INSTANCE) + "[.]";
+
+    static const std::regex vdCleanupRegex(vdCleanupSource.c_str());
+
+    std::string code = stage.getSourceCode();
+    code = std::regex_replace(code, paramRegex, "vec3 unused_$1");
+    code = std::regex_replace(code, vtxRegex, "$$$1( PIX_IN.$$$1 )");
+    code = std::regex_replace(code, vdCleanupRegex, "");
+
+#if MX_COMBINED_VERSION >= 13804
+    stage.setSourceCode(code);
+#else
+    // setSourceCode was added in 1.38.4. Use const casting in previous versions to modify the
+    // member variable directly (since getSourceCode returns by reference).
+    std::string& ncCode(const_cast<std::string&>(stage.getSourceCode()));
+    ncCode = code;
+#endif
+}
 } // namespace
 
 const string& HwSpecularEnvironmentSamples::name()
@@ -67,8 +137,6 @@ GlslFragmentGenerator::GlslFragmentGenerator()
     _tokenSubstitutions[HW::T_TANGENT_OBJECT] = "Tm";
     _tokenSubstitutions[HW::T_BITANGENT_WORLD] = "Bw";
     _tokenSubstitutions[HW::T_BITANGENT_OBJECT] = "Bm";
-    _tokenSubstitutions[HW::T_VERTEX_DATA_INSTANCE]
-        = "g_mxVertexData"; // name of a global non-const variable
     if (OgsXmlGenerator::useLightAPI() >= 2) {
         // Use a Maya 2022.1-aware surface node implementation.
         registerImplementation(
@@ -126,34 +194,6 @@ ShaderPtr GlslFragmentGenerator::generate(
     ScopedFloatFormatting floatFormatting(Value::FloatFormatFixed);
 
     const VariableBlock& vertexData = pixelStage.getInputBlock(HW::VERTEX_DATA);
-    if (!vertexData.empty()) {
-        // GLSL shader input blocks are essentially global constants accessible
-        // from any function in the shader, not just the entry point. The
-        // MaterialX GLSL generator makes use of this global access pattern.
-        // We could make it work for VP2 GLSL fragments by referencing the
-        // PIX_IN input block generated by VP2 in the final effect but this
-        // approach has two problems:
-        // 1. VP2 pre-processes some inputs (e.g. Nw) before passing them as
-        // arguments to the fragment's root function. These are the correct
-        // values to use for shading, not the original ones from PIX_IN.
-        // 2. This pattern is not portable to HLSL where shader stage inputs
-        // are passed as arguments to the entry point function and have to be
-        // passed to other functions explicitly.
-        //
-        // Since passing vertex inputs to all functions as arguments would be
-        // too intrusive in GLSL codegen, we instead define a non-const global
-        // struct variable which gets populated from the function arguments in
-        // the fragment's root function and is read from in all other functions
-
-        emitLine("struct", pixelStage, false);
-        emitScopeBegin(pixelStage);
-        emitVariableDeclarations(
-            vertexData, EMPTY_STRING, Syntax::SEMICOLON, context, pixelStage, false);
-        emitScopeEnd(pixelStage, false, false);
-        emitString(" " + HW::T_VERTEX_DATA_INSTANCE, pixelStage);
-        emitLineEnd(pixelStage, true);
-        emitLineBreak(pixelStage);
-    }
 
     // Add global constants and type definitions
     const unsigned int maxLights = std::max(1u, context.getOptions().hwMaxActiveLightSources);
@@ -328,21 +368,6 @@ ShaderPtr GlslFragmentGenerator::generate(
         // to a surface shader, so just output black.
         emitLine("return vec3(0.0)", pixelStage);
     } else {
-        // Copy vertex data values from the root function's arguments to a
-        // global struct variable accessible from all other functions.
-        //
-        for (size_t i = 0; i < vertexData.size(); ++i) {
-            const string& name = vertexData[i]->getVariable();
-
-            emitLineBegin(pixelStage);
-            emitString(HW::T_VERTEX_DATA_INSTANCE, pixelStage);
-            emitString(".", pixelStage);
-            emitString(name, pixelStage);
-            emitString(" = ", pixelStage);
-            emitString(name, pixelStage);
-            emitLineEnd(pixelStage, true);
-        }
-
         if (lighting && OgsXmlGenerator::useLightAPI() < 2) {
             // Store environment samples from light rig:
             emitLine(
@@ -424,6 +449,8 @@ ShaderPtr GlslFragmentGenerator::generate(
     // End function
     emitScopeEnd(pixelStage);
 
+    fixupVertexDataInstance(pixelStage);
+
     // Replace all tokens with real identifier names
     replaceTokens(_tokenSubstitutions, pixelStage);