Mesh: Add validation of CD_MDISPS tangent vector data

This commit adds support for validating and correcting Multires tangent
data stored in CD_MDISPS when called via `BKE_mesh_validate` when
importing or on demand when users call `mesh.validate()` via the Python
API.

Any non-finite values are set to 0. While this will result in likely odd
looking data on a multires mesh, it will prevent further propagation of
bad float data and will allow users to restore their mesh to a workable
state in the case of data corruption.

Ref: #149205

Pull Request: https://projects.blender.org/blender/blender/pulls/149320

source/blender/blenkernel/intern/mesh_validate.cc

@@ -762,6 +762,49 @@ static bool validate_generic_attributes(const Mesh &mesh, const bool verbose, Me
   return all_attributes_valid;
 }
 
+static bool validate_mdisps(const Mesh &mesh, const bool verbose, Mesh *mesh_mut)
+{
+  const MDisps *mdisps = static_cast<const MDisps *>(
+      CustomData_get_layer(&mesh.corner_data, CD_MDISPS));
+  if (!mdisps) {
+    return true;
+  }
+
+  IndexMaskMemory memory;
+  const IndexMask invalid = IndexMask::from_predicate(
+      IndexRange(mesh.corners_num), GrainSize(4096), memory, [&](const int i) {
+        const Span<float> disps = Span(reinterpret_cast<const float3 *>(mdisps[i].disps),
+                                       mdisps[i].totdisp)
+                                      .cast<float>();
+        return std::any_of(
+            disps.begin(), disps.end(), [&](const float &v) { return !std::isfinite(v); });
+      });
+
+  if (invalid.is_empty()) {
+    return true;
+  }
+
+  if (verbose) {
+    print_error_with_indices(invalid, "Multires displacement has invalid values");
+  }
+
+  if (mesh_mut) {
+    if (MDisps *mdisp_mut = static_cast<MDisps *>(
+            CustomData_get_layer_for_write(&mesh_mut->corner_data, CD_MDISPS, mesh.corners_num)))
+    {
+      invalid.foreach_index(GrainSize(512), [&](const int i) {
+        MutableSpan<float> disps = MutableSpan(reinterpret_cast<float3 *>(mdisp_mut[i].disps),
+                                               mdisp_mut[i].totdisp)
+                                       .cast<float>();
+        for (float &disp_component : disps) {
+          disp_component = std::isfinite(disp_component) ? disp_component : 0.0f;
+        }
+      });
+    }
+  }
+  return false;
+}
+
 static bool mesh_validate_impl(const Mesh &mesh, const bool verbose, Mesh *mesh_mut)
 {
   IndexMaskMemory memory;
@@ -825,6 +868,7 @@ static bool mesh_validate_impl(const Mesh &mesh, const bool verbose, Mesh *mesh_
   valid &= validate_material_indices(mesh, true, verbose, mesh_mut);
   valid &= validate_selection_history(mesh, verbose, mesh_mut);
   valid &= validate_generic_attributes(mesh, verbose, mesh_mut);
+  valid &= validate_mdisps(mesh, verbose, mesh_mut);
 
   if (valid) {
     return true;

tests/files/sculpting/invalid_mdisp_cube.blend

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b399e423de04c458891984f225f22c5d9e6ae4fb74ed5f36a1379246747163eb
+size 72185

tests/python/CMakeLists.txt

@@ -417,6 +417,8 @@ if(TEST_SRC_DIR_EXISTS)
   add_blender_test_allow_error(
     mesh_validate
     --python ${TEST_PYTHON_DIR}/mesh_validate.py
+    --
+    --testdir "${TEST_SRC_DIR}"
   )
 
   add_blender_test(

tests/python/mesh_validate.py

@@ -6,6 +6,11 @@
 import unittest
 import bpy
 import sys
+import pathlib
+
+"""
+blender -b --factory-startup --python tests/python/mesh_validate.py -- --testdir tests/files/
+"""
 
 
 class TestMeshValidate(unittest.TestCase):
@@ -108,6 +113,34 @@ class TestMeshValidate(unittest.TestCase):
         self.assertFalse(mesh.validate(verbose=True))
 
 
+args = None
+
+
+class TestMeshValidateExistingFile(unittest.TestCase):
+    def setUp(self):
+        bpy.ops.wm.open_mainfile(filepath=str(args.testdir / "sculpting/invalid_mdisp_cube.blend"), load_ui=False)
+
+    def test_mesh_with_bad_multires_displacements(self):
+        mesh = bpy.context.active_object.data
+        self.assertTrue(mesh.validate(verbose=True))
+        self.assertFalse(mesh.validate(verbose=True))
+
+
+def main():
+    global args
+    import argparse
+
+    argv = [sys.argv[0]]
+    if '--' in sys.argv:
+        argv += sys.argv[sys.argv.index('--') + 1:]
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--testdir', required=True, type=pathlib.Path)
+
+    args, remaining = parser.parse_known_args(argv)
+
+    unittest.main(argv=remaining)
+
+
 if __name__ == '__main__':
-    sys.argv = [__file__] + (sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else [])
-    unittest.main()
+    main()