Fix T80967: Alembic, crash when the imported sim from Houdini starts

Compare mesh loop count with number of loop normals before reading the
loop normals.

Houdini doesn't always write the correct loop normals to Alembic. When a
mesh is animated and then replaced by a fluid simulation, Houdini will
still write the original mesh's loop normals, but the mesh
verts/loops/polys are from the simulation. In such cases the normals
cannot be mapped to the mesh, so it's better to ignore them.

1 files changed, 10 insertions, 1 deletions

diff --git a/source/blender/io/alembic/intern/abc_reader_mesh.cc b/source/blender/io/alembic/intern/abc_reader_mesh.cc
index 5a42be2bb02..ead908e87c2 100644
--- a/source/blender/io/alembic/intern/abc_reader_mesh.cc
+++ b/source/blender/io/alembic/intern/abc_reader_mesh.cc
@@ -271,10 +271,19 @@ static void process_loop_normals(CDStreamConfig &config, const N3fArraySamplePtr
     return;
   }
 
+  Mesh *mesh = config.mesh;
+  if (loop_count != mesh->totloop) {
+    /* This happens in certain Houdini exports. When a mesh is animated and then replaced by a
+     * fluid simulation, Houdini will still write the original mesh's loop normals, but the mesh
+     * verts/loops/polys are from the simulation. In such cases the normals cannot be mapped to the
+     * mesh, so it's better to ignore them. */
+    process_no_normals(config);
+    return;
+  }
+
   float(*lnors)[3] = static_cast<float(*)[3]>(
       MEM_malloc_arrayN(loop_count, sizeof(float[3]), "ABC::FaceNormals"));
 
-  Mesh *mesh = config.mesh;
   MPoly *mpoly = mesh->mpoly;
   const N3fArraySample &loop_normals = *loop_normals_ptr;
   int abc_index = 0;