add GenOptions option to control the optimization

Author: ld-kerley

source/MaterialXGenShader/GenOptions.h

@@ -94,7 +94,8 @@ class MX_GENSHADER_API GenOptions
         hwNormalizeUdimTexCoords(false),
         hwWriteAlbedoTable(false),
         hwWriteEnvPrefilter(false),
-        hwImplicitBitangents(true)
+        hwImplicitBitangents(true),
+        optReplaceBsdfMixWithLinearCombination(false)
     {
     }
     virtual ~GenOptions() { }
@@ -197,6 +198,10 @@ class MX_GENSHADER_API GenOptions
     /// Calculate fallback bitangents from existing normals and tangents
     /// inside the bitangent node.
     bool hwImplicitBitangents;
+
+    /// Analyse the graph of ShaderNodes and replace any ND_mix_bsdf nodes
+    /// with a linear combination of their weighted inputs
+    bool optReplaceBsdfMixWithLinearCombination;
 };
 
 MATERIALX_NAMESPACE_END

source/MaterialXGenShader/ShaderGraph.cpp

@@ -971,12 +971,15 @@ void ShaderGraph::optimize(GenContext& context)
     }
 
     // we take a copy of the node list because we might modify it during the optimization
-    const vector<ShaderNode*> nodeList = getNodes();
-    for (ShaderNode* node : nodeList)
+    if (context.getOptions().optReplaceBsdfMixWithLinearCombination)
     {
-        if (node->hasClassification(ShaderNode::Classification::MIX_BSDF))
+        const vector<ShaderNode*> nodeList = getNodes();
+        for (ShaderNode* node : nodeList)
         {
-            optimizeMixBsdf(node, context);
+            if (node->hasClassification(ShaderNode::Classification::MIX_BSDF))
+            {
+                optimizeMixBsdf(node, context);
+            }
         }
     }
 }

source/MaterialXGraphEditor/RenderView.cpp

@@ -162,6 +162,7 @@ RenderView::RenderView(mx::DocumentPtr doc,
     // Make sure all uniforms are added so value updates can
     // find the corresponding uniform.
     _genContext.getOptions().shaderInterfaceType = mx::SHADER_INTERFACE_COMPLETE;
+    _genContext.getOptions().optReplaceBsdfMixWithLinearCombination = true;
 
     setDocument(doc);
     _stdLib = stdLib;

source/MaterialXView/Viewer.cpp

@@ -255,6 +255,7 @@ Viewer::Viewer(const std::string& materialFilename,
     _genContext.getOptions().fileTextureVerticalFlip = true;
     _genContext.getOptions().hwShadowMap = true;
     _genContext.getOptions().hwImplicitBitangents = false;
+    _genContext.getOptions().optReplaceBsdfMixWithLinearCombination = true;
 
 #ifdef MATERIALXVIEW_METAL_BACKEND
     _renderPipeline = MetalRenderPipeline::create(this);
@@ -267,6 +268,7 @@ Viewer::Viewer(const std::string& materialFilename,
     _genContextEssl.getOptions().targetColorSpaceOverride = "lin_rec709";
     _genContextEssl.getOptions().fileTextureVerticalFlip = false;
     _genContextEssl.getOptions().hwMaxActiveLightSources = 1;
+    _genContextEssl.getOptions().optReplaceBsdfMixWithLinearCombination = true;
 #endif
 #if MATERIALX_BUILD_GEN_OSL
     // Set OSL generator options.