Check skin cluster weights

lib/mayaUsd/fileio/utils/jointWriteUtils.cpp

@@ -237,6 +237,27 @@ int UsdMayaJointUtil::getCompressedSkinWeights(
     unsigned int numInfluences;
     skinCluster.getWeights(outputDagPath, components.object(), weights, numInfluences);
 
+    if (numInfluences <= 0) {
+        MString msg("No influences found for skinCluster ");
+        msg += skinCluster.name();
+        MGlobal::displayError(msg);
+        throw std::runtime_error(msg.asChar());
+    }
+
+    if (weights.length() < numVertices * numInfluences) {
+        MString msg("The number of vertices on the exported mesh ");
+        msg += outputDagPath.partialPathName();
+        msg += "(";
+        msg += numVertices;
+
+        msg += ") do not match the number of vertices where the skinCluster was applied (";
+        msg += weights.length() / numInfluences;
+        msg += "). Remove any nodes that change mesh topology after the skinCluster.";
+
+        MGlobal::displayError(msg);
+        throw std::runtime_error(msg.asChar());
+    }
+
     // Determine how many influence/weight "slots" we actually need per point.
     // For example, if there are the joints /a, /a/b, and /a/c, but each point
     // only has non-zero weighting for a single joint, then we only need one
@@ -463,4 +484,4 @@ MObject UsdMayaJointUtil::writeSkinningData(
     return inMeshObj;
 }
 
-PXR_NAMESPACE_CLOSE_SCOPE
+PXR_NAMESPACE_CLOSE_SCOPE

test/lib/usd/translators/CMakeLists.txt

@@ -39,6 +39,7 @@ set(TEST_SCRIPT_FILES
     testUsdExportSelection.py
     testUsdExportSelectionHierarchy.py
     testUsdExportSkeleton.py
+    testUsdExportSkin.py
     testUsdExportStripNamespaces.py
     testUsdExportStroke.py
     testUsdExportUserTaggedAttributes.py

test/lib/usd/translators/testUsdExportSkin.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env mayapy
+#
+# Copyright 2023 Apple Inc. All rights reserved.
+#
+# 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 os
+import unittest
+
+from maya import cmds
+from maya import standalone
+from maya.api import OpenMaya as OM
+
+from pxr import Gf, Sdf, Tf, Usd, UsdGeom, UsdSkel, UsdUtils, Vt
+
+import fixturesUtils
+
+
+def build_scene():
+    """Set up simple skinCluster, add a polyReduce after"""
+    cmds.file(f=1, new=1)
+    root = cmds.joint()
+    cmds.joint()
+    sphere = cmds.polySphere()
+    cmds.select(root, add=1)
+    group = cmds.group()
+
+    cmds.skinCluster(root, sphere[0])
+    cmds.select(sphere[0])
+
+    cmds.polyReduce(p=50)
+    return group
+
+class TestUsdExportSkin(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        inputPath = fixturesUtils.setUpClass(__file__)
+        # cls.outFile = os.path.join
+
+    @classmethod
+    def tearDownClass(cls):
+        standalone.uninitialize()
+
+    def test_exportSkinDifferingTopology(self):
+        """Raise a runtime error if the topology has changed downstream from the skinCluster"""
+        grp = build_scene()
+        self.assertRaises(RuntimeError, cmds.mayaUSDExport, file="Does_not_export.usdc", skn="auto", skl="auto")
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)