Fix T78431: Update mesh_cd_layers_type_ to support 8 bytes.

Sculpt vertex colors changed the `DRW_MeshCDMask` from 4 bytes to 8 bytes, but
the functions assumed it still was 4 bytes. This patch updates the functions and
adds a compile time check.

Reviewed By: Clément Foucault

Differential Revision: https://developer.blender.org/D8215

2 files changed, 11 insertions, 4 deletions

diff --git a/source/blender/draw/intern/draw_cache_extract.h b/source/blender/draw/intern/draw_cache_extract.h
index 302f9a0d3a8..f05e8e2f9d6 100644
--- a/source/blender/draw/intern/draw_cache_extract.h
+++ b/source/blender/draw/intern/draw_cache_extract.h
@@ -60,6 +60,10 @@ typedef struct DRW_MeshCDMask {
    *  modifiers could remove it. (see T68857) */
   uint32_t edit_uv : 1;
 } DRW_MeshCDMask;
+/* Keep `DRW_MeshCDMask` struct within an `uint64_t`.
+ * bit-wise and atomic operations are used to compare and update the struct.
+ * See `mesh_cd_layers_type_*` functions. */
+BLI_STATIC_ASSERT(sizeof(DRW_MeshCDMask) <= sizeof(uint64_t), "DRW_MeshCDMask exceeds 64 bits")
 
 typedef enum eMRIterType {
   MR_ITER_LOOPTRI = 1 << 0,
diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index a22e0014bf5..40de0794b9e 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -74,22 +74,25 @@ static void mesh_batch_cache_clear(Mesh *me);
 /* Return true is all layers in _b_ are inside _a_. */
 BLI_INLINE bool mesh_cd_layers_type_overlap(DRW_MeshCDMask a, DRW_MeshCDMask b)
 {
-  return (*((uint32_t *)&a) & *((uint32_t *)&b)) == *((uint32_t *)&b);
+  return (*((uint64_t *)&a) & *((uint64_t *)&b)) == *((uint64_t *)&b);
 }
 
 BLI_INLINE bool mesh_cd_layers_type_equal(DRW_MeshCDMask a, DRW_MeshCDMask b)
 {
-  return *((uint32_t *)&a) == *((uint32_t *)&b);
+  return *((uint64_t *)&a) == *((uint64_t *)&b);
 }
 
 BLI_INLINE void mesh_cd_layers_type_merge(DRW_MeshCDMask *a, DRW_MeshCDMask b)
 {
-  atomic_fetch_and_or_uint32((uint32_t *)a, *(uint32_t *)&b);
+  uint32_t *a_p = (uint32_t *)a;
+  uint32_t *b_p = (uint32_t *)&b;
+  atomic_fetch_and_or_uint32(a_p, *b_p);
+  atomic_fetch_and_or_uint32(a_p + 1, *(b_p + 1));
 }
 
 BLI_INLINE void mesh_cd_layers_type_clear(DRW_MeshCDMask *a)
 {
-  *((uint32_t *)a) = 0;
+  *((uint64_t *)a) = 0;
 }
 
 static void mesh_cd_calc_edit_uv_layer(const Mesh *UNUSED(me), DRW_MeshCDMask *cd_used)