Fix VP2 rendering of UsdPreviewSurface with opacityThreshold

lib/mayaUsd/render/vp2ShaderFragments/UsdPreviewSurfaceLightAPI2.xml

@@ -49,6 +49,7 @@ limitations under the License.
         <float name="roughness" ref="usdPreviewSurfaceLightingAPI2.specularRoughness"/>
         <float3 name="specularColor" ref="usdPreviewSurfaceLightingAPI2.specularColor"/>
         <float name="opacity" ref="opacityToTransparency.opacity"/>
+        <float name="opacityThreshold" ref="usdPreviewSurfaceLightingAPI2.opacityThreshold"/>
         <bool name="useSpecularWorkflow" ref="usdPreviewSurfaceLightingAPI2.useSpecularWorkflow"/>
 
         <!-- Maya Parameters for Lighting -->
@@ -86,6 +87,7 @@ limitations under the License.
         <float3 name="specularColor" value="0.0,0.0,0.0"/>
         <!-- The shader computes transparency from its "opacity" attribute. -->
         <float name="opacity" value="1.0"/>
+        <float name="opacityThreshold" value="0.0"/>
         <bool name="useSpecularWorkflow" value="false"/>
 
         <!-- Default values for Maya-provided parameters. -->

lib/mayaUsd/render/vp2ShaderFragments/UsdPreviewSurfaceLightAPI3.xml

@@ -49,6 +49,7 @@ limitations under the License.
         <float name="roughness" ref="usdPreviewSurfaceLightingAPI3.specularRoughness"/>
         <float3 name="specularColor" ref="usdPreviewSurfaceLightingAPI3.specularColor"/>
         <float name="opacity" ref="opacityToTransparency.opacity"/>
+        <float name="opacityThreshold" ref="usdPreviewSurfaceLightingAPI3.opacityThreshold"/>
         <bool name="useSpecularWorkflow" ref="usdPreviewSurfaceLightingAPI3.useSpecularWorkflow"/>
 
         <!-- Maya Parameters for Lighting -->
@@ -86,6 +87,7 @@ limitations under the License.
         <float3 name="specularColor" value="0.0,0.0,0.0"/>
         <!-- The shader computes transparency from its "opacity" attribute. -->
         <float name="opacity" value="1.0"/>
+        <float name="opacityThreshold" value="0.0"/>
         <bool name="useSpecularWorkflow" value="false"/>
 
         <!-- Default values for Maya-provided parameters. -->

lib/mayaUsd/render/vp2ShaderFragments/usdPreviewSurfaceLightingAPI2.xml

@@ -379,15 +379,24 @@ surfaceShader(vec3 Peye, vec3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
+    result.outGlowColor = vec3(0.0);
 
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        } 
+        result.outTransparency = vec3(0.0);
+        result.outMatteOpacity = vec3(1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = vec3(opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -406,12 +415,6 @@ surfaceShader(vec3 Peye, vec3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = vec3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = vec3(opacity);
-
     return result;
 }
 
@@ -733,15 +736,24 @@ surfaceShader(vec3 Peye, vec3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
+    result.outGlowColor = vec3(0.0);
 
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        }
+        result.outTransparency = vec3(0.0);
+        result.outMatteOpacity = vec3(1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = vec3(opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -760,12 +772,6 @@ surfaceShader(vec3 Peye, vec3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = vec3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = vec3(opacity);
-
     return result;
 }
 
@@ -1087,15 +1093,24 @@ surfaceShader(float3 Peye, float3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
+    result.outGlowColor = float3(0.0, 0.0, 0.0);
 
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        }
+        result.outTransparency = float3(0.0, 0.0, 0.0);
+        result.outMatteOpacity = float3(1.0, 1.0, 1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = float3(opacity, opacity, opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -1114,12 +1129,6 @@ surfaceShader(float3 Peye, float3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = float3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = float3(opacity, opacity, opacity);
-
     return result;
 }
 

lib/mayaUsd/render/vp2ShaderFragments/usdPreviewSurfaceLightingAPI3.xml

@@ -379,15 +379,24 @@ surfaceShader(vec3 Peye, vec3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
+    result.outGlowColor = vec3(0.0);
 
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        }
+        result.outTransparency = vec3(0.0);
+        result.outMatteOpacity = vec3(1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = vec3(opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -406,12 +415,6 @@ surfaceShader(vec3 Peye, vec3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = vec3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = vec3(opacity);
-
     return result;
 }
 
@@ -733,15 +736,24 @@ surfaceShader(vec3 Peye, vec3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
-
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    result.outGlowColor = vec3(0.0);
+
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        }
+        result.outTransparency = vec3(0.0);
+        result.outMatteOpacity = vec3(1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = vec3(opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -760,12 +772,6 @@ surfaceShader(vec3 Peye, vec3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = vec3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = vec3(opacity);
-
     return result;
 }
 
@@ -1087,15 +1093,24 @@ surfaceShader(float3 Peye, float3 Neye,
     float specularAmount
 )
 {
-    float opacity = 1.0 - transparency.r;
-    if (opacity < opacityThreshold) {
-        discard;
-    } 
-
     mayaSurfaceShaderOutput result;
-
-    // Pre-multiply diffuse color by opacity if not done so already
-    diffuseColor *= opacity;
+    result.outGlowColor = float3(0.0, 0.0, 0.0);
+
+    // Transparency and cutout.
+    float opacity = 1.0 - transparency.r;
+    if (opacityThreshold > 0.0) {
+        if (opacity < opacityThreshold) {
+            discard;
+        }
+        result.outTransparency = float3(0.0, 0.0, 0.0);
+        result.outMatteOpacity = float3(1.0, 1.0, 1.0);
+    } else {
+        result.outTransparency = transparency;
+        result.outMatteOpacity = float3(opacity, opacity, opacity);
+
+        // Pre-multiply diffuse color by opacity if not done so already
+        diffuseColor *= opacity;
+    }
 
     // Evaluate all lights.
     result.outColor = evaluateLights(
@@ -1114,12 +1129,6 @@ surfaceShader(float3 Peye, float3 Neye,
         Peye,
         Neye);
 
-    // Transparency
-    result.outTransparency = transparency;
-
-    result.outGlowColor = float3(0.0, 0.0, 0.0);
-    result.outMatteOpacity = float3(opacity, opacity, opacity);
-
     return result;
 }
 

lib/usd/pxrUsdPreviewSurface/usdPreviewSurface.cpp

@@ -444,8 +444,8 @@ MStatus PxrMayaUsdPreviewSurface::compute(const MPlug& plug, MDataBlock& dataBlo
         CHECK_MSTATUS(status);
         const float opacityThreshold = opacityThresholdData.asFloat();
 
-        if (opacity < opacityThreshold) {
-            opacity = 0.0f;
+        if (opacityThreshold > 0.0f) {
+            opacity = (opacity < opacityThreshold) ? 0.0f : 1.0f;
         }
 
         const float        transparency = 1.0f - opacity;

test/lib/mayaUsd/render/vp2RenderDelegate/testVP2RenderDelegateUSDPreviewSurface.py

@@ -271,5 +271,42 @@ def testDoubleSided(self):
         mayaUtils.setBasicCamera(3)
         self.assertSnapshotClose('doubleSided_disabled_back.png')
 
+    def testOpacityThreshold(self):
+        '''
+        Test UsdPreviewSurface transparency cut-out. The surface fragments should be
+        should be fully transparent or fully opaque when opacityThreshold is positive.
+        '''
+        cmds.file(new=True, force=True)
+        mayaUtils.loadPlugin('mayaUsdPlugin')
+
+        # Import the USD file.
+        testFile = testUtils.getTestScene('UsdPreviewSurface', 'TestOpacityThreshold.usda')
+        mayaUtils.createProxyFromFile(testFile)
+
+        # Frame the scene for the snapshot.
+        cmds.xform("persp", t= (0, 1, 2.25))
+        cmds.xform("persp", ro=[-25, 0, 0], ws=True)
+
+        # Create a light to cast a shadow.
+        white_light = cmds.directionalLight(rgb=(1, 1, 1))
+        white_transform = cmds.listRelatives(white_light, parent=True)[0]
+        cmds.xform(white_transform, ro=(-35, -35, 0), ws=True)
+
+        # Turn on texturing, lighting, shadows.
+        cmds.modelEditor(
+            mayaUtils.activeModelPanel(),
+            edit=True,
+            displayTextures=True,
+            displayLights='all',
+            shadows=True,
+            lights=False
+        )
+
+        # This option is needed for VP2 to discard shadow map samples.
+        cmds.setAttr('hardwareRenderingGlobals.transparentShadow', True)
+
+        # Snapshot and assert similarity.
+        self.assertSnapshotClose('opacityThreshold.png')
+
 if __name__ == '__main__':
     fixturesUtils.runTests(globals())