Merge pull request #3264 from erikaharrison-adsk/adsk/bugfix/mtlx_met…

…al_shadow

Autodesk: Bugfix for MaterialX shadows in Metal

(Internal change: 2341291)

pxr/imaging/hdSt/materialXShaderGen.cpp

@@ -660,8 +660,10 @@ HdStMaterialXShaderGen<Base>::emitLine(
     // When emitting the Light loop code for the Surface node, the variable
     // 'occlusion' represents shadow occlusion. We don't use MaterialX's
     // shadow implementation (hwShadowMap is false). Instead, use our own 
-    // per-light occlusion value calculated in mxInit() and stored in lightData
-    if (_emittingSurfaceNode && str == "vec3 L = lightShader.direction") {
+    // per-light occlusion value calculated in mxInit() and stored in lightData.
+    // Note: Metal uses float3, Glsl uses vec3, in the line we're looking for.
+    if (_emittingSurfaceNode && (str == "vec3 L = lightShader.direction" ||
+                                 str == "float3 L = lightShader.direction" )) {
         emitLine(
             "occlusion = u_lightData[activeLightIndex].shadowOcclusion", stage);
     }