revert use of "opacity" property to "transparency" to support pxrUsdP…

…reviewSurface

This returns the fragment graph property to the way it was before it was moved
out of the pxrUsdPreviewSurface shading node.

lib/mayaUsd/render/vp2ShaderFragments/UsdPreviewSurface.xml

@@ -37,7 +37,6 @@ limitations under the License.
         <fragment_ref name="lightingContributions" ref="lightingContributions"/>
         <fragment_ref name="scaledDiffusePassThrough" ref="scaledDiffusePassThrough"/>
         <fragment_ref name="scaledSpecularPassThrough" ref="scaledSpecularPassThrough"/>
-        <fragment_ref name="opacityToTransparency" ref="opacityToTransparency"/>
         <fragment_ref name="maya16LightAccum" ref="maya16LightAccum"/>
         <fragment_ref name="usdPreviewSurfaceCombiner" ref="usdPreviewSurfaceCombiner"/>
 
@@ -74,7 +73,6 @@ limitations under the License.
         <connect from="maya16LightAccum.scaledSpecular" to="usdPreviewSurfaceCombiner.specularIrradianceIn" name="specularIrradianceIn"/>
         <connect from="diffuseColorPassThrough.mayafloat3PassThrough" to="usdPreviewSurfaceCombiner.diffuseColor" name="diffuseColor"/>
         <connect from="specularColorPassThrough.mayafloat3PassThrough" to="usdPreviewSurfaceCombiner.specularColor" name="specularColor"/>
-        <connect from="opacityToTransparency.transparency" to="usdPreviewSurfaceCombiner.transparency" name="transparency"/>
         <connect from="usdPreviewSurfaceCombiner.usdPreviewSurfaceCombiner" to="mayaComputeSurfaceFinal.input" name="input"/>
         <connect from="maya_FogDepthSurface.maya_FogDepthSurface" to="mayaComputeSurfaceFinal.maya_FogDepthSurface" name="maya_FogDepthSurface"/>
         <connect from="mayaComputeSurfaceFinal.mayaComputeSurfaceFinal" to="mayaSurfaceShaderOutput.mayaSurfaceShaderOutput" name="mayaSurfaceShaderOutput"/>
@@ -90,7 +88,7 @@ limitations under the License.
         <float name="occlusion" ref="usdPreviewSurfaceLighting.occlusion"/>
         <float name="roughness" ref="usdPreviewSurfaceLighting.specularRoughness"/>
         <float3 name="specularColor" ref="specularColorPassThrough.input"/>
-        <float name="opacity" ref="opacityToTransparency.opacity"/>
+        <float3 name="transparency" ref="usdPreviewSurfaceCombiner.transparency"/>
         <bool name="useSpecularWorkflow" ref="usdPreviewSurfaceLighting.useSpecularWorkflow"/>
 
         <!-- Maya Parameters for Lighting -->
@@ -128,7 +126,7 @@ limitations under the License.
         <float name="roughness" value="0.5"/>
         <float3 name="specularColor" value="0.0,0.0,0.0"/>
         <!-- The shader computes transparency from its "opacity" attribute. -->
-        <float name="opacity" value="1.0"/>
+        <float3 name="transparency" value="0.0,0.0,0.0"/>
         <bool name="useSpecularWorkflow" value="false"/>
 
         <!-- Default values for Maya-provided parameters. -->