Fix display color not matching the source Lambert materials

lib/mayaUsd/render/vp2RenderDelegate/mesh.cpp

@@ -373,6 +373,10 @@ void _getColorData(
 
         infoMap[HdTokens->displayColor] = std::make_unique<PrimvarInfo>(
             PrimvarSource(VtValue(colorArray), interpolation, PrimvarSource::CPUCompute), nullptr);
+    } else {
+        for (size_t i = 0; i < colorArray.size(); ++i) {
+            colorArray[i] = MayaUsd::utils::ConvertLinearToMaya(colorArray[i]);
+        }
     }
 }
 
@@ -1933,9 +1937,12 @@ void HdVP2Mesh::_UpdateDrawItem(
             if ((colorInterp == HdInterpolationConstant || colorInterp == HdInterpolationInstance)
                 && (alphaInterp == HdInterpolationConstant
                     || alphaInterp == HdInterpolationInstance)) {
-                const GfVec3f& clr3f = MayaUsd::utils::ConvertLinearToMaya(colorArray[0]);
+                const GfVec3f& clr3f = colorArray[0];
                 const MColor   color(clr3f[0], clr3f[1], clr3f[2], alphaArray[0]);
                 shader = _delegate->GetFallbackShader(color);
+                if (shader) {
+                    shader->setParameter("diffuse", 1.0f);
+                }
                 // The color of the fallback shader is ignored when the interpolation is
                 // instance
             } else {

lib/mayaUsd/render/vp2RenderDelegate/render_delegate.cpp

@@ -73,6 +73,7 @@ inline const TfTokenVector& _SupportedBprimTypes()
 
 const MString _diffuseColorParameterName = "diffuseColor"; //!< Shader parameter name
 const MString _solidColorParameterName = "solidColor";     //!< Shader parameter name
+const MString _diffuseParameterName = "diffuse";           //!< Shader parameter name
 const MString _pointSizeParameterName = "pointSize";       //!< Shader parameter name
 const MString _curveBasisParameterName = "curveBasis";     //!< Shader parameter name
 const MString _structOutputName = "outSurfaceFinal"; //!< Output struct name of the fallback shader
@@ -181,6 +182,9 @@ class MShaderCache final
         TF_VERIFY(_3dDefaultMaterialShader);
 
         _3dCPVSolidShader = shaderMgr->getStockShader(MHWRender::MShaderManager::k3dCPVSolidShader);
+        if (TF_VERIFY(_3dCPVSolidShader)) {
+            _3dCPVSolidShader->setParameter(_diffuseParameterName, 1.0f);
+        }
 
         TF_VERIFY(_3dCPVSolidShader);
 
@@ -204,6 +208,7 @@ class MShaderCache final
                 if (it != _curveBasisParameterValueMapping.end()) {
                     shader->setParameter(_curveBasisParameterName, it->second);
                 }
+                shader->setParameter(_diffuseParameterName, 1.0f);
             }
 
             _fallbackCPVShaders[i] = shader;

test/lib/mayaUsd/render/vp2RenderDelegate/CMakeLists.txt

@@ -2,6 +2,7 @@
 set(TEST_SCRIPT_FILES "")
 
 list(APPEND TEST_SCRIPT_FILES
+    testVP2RenderDelegateDisplayColors.py
 	testVP2RenderDelegateGeomSubset.py
     testVP2RenderDelegatePointInstanceOrientation.py
 )

test/lib/mayaUsd/render/vp2RenderDelegate/testVP2RenderDelegateDisplayColors.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env mayapy
+#
+# Copyright 2022 Autodesk
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import fixturesUtils
+import imageUtils
+import mayaUtils
+import usdUtils
+import testUtils
+
+from mayaUsd import lib as mayaUsdLib
+from mayaUsd import ufe as mayaUsdUfe
+
+from maya import cmds
+
+import ufe
+
+import os
+
+
+class testVP2RenderDelegateDisplayColors(imageUtils.ImageDiffingTestCase):
+    """
+    Tests imaging using the Viewport 2.0 render delegate when using per-instance
+    inherited data on instances.
+    """
+
+    @classmethod
+    def setUpClass(cls):
+        # The test USD data is authored Z-up, so make sure Maya is configured
+        # that way too.
+        cmds.upAxis(axis='z')
+
+        inputPath = fixturesUtils.setUpClass(__file__,
+            initializeStandalone=False, loadPlugin=False)
+
+        cls._baselineDir = os.path.join(inputPath,
+            'VP2RenderDelegateDisplayColorsTest', 'baseline')
+
+        cls._testDir = os.path.abspath('.')
+
+    def assertSnapshotClose(self, imageName):
+        baselineImage = os.path.join(self._baselineDir, imageName)
+        snapshotImage = os.path.join(self._testDir, imageName)
+        imageUtils.snapshot(snapshotImage, width=960, height=540)
+        return self.assertImagesClose(baselineImage, snapshotImage)
+
+    def _StartTest(self, testName):
+        cmds.file(force=True, new=True)
+        mayaUtils.loadPlugin("mayaUsdPlugin")
+
+        self._testName = testName
+        testFile = testUtils.getTestScene("displayColors", self._testName + ".ma")
+
+        cmds.file(testFile, o=True)
+
+        exportedFile = os.path.join(self._testDir, "ColorTest.usda")
+        cmds.mayaUSDExport(mergeTransformAndShape=True,
+            file=exportedFile,
+            shadingMode='none',
+            exportDisplayColor=True)
+
+        shapeNode = mayaUtils.createProxyFromFile(exportedFile)[0]
+        cmds.move(0, 0, -1, shapeNode)
+
+        globalSelection = ufe.GlobalSelection.get()
+        globalSelection.clear()
+        self.assertSnapshotClose('%s_unselected.png' % self._testName)
+
+    def testPerInstanceInheritedData(self):
+        self._StartTest('ColorTest')
+
+
+
+if __name__ == '__main__':
+    fixturesUtils.runTests(globals())