modifier stack: lazy initialize normals

many modifiers were calculating normals, when those normals were ignored by the next modifier.
now flag normals as dirty and recalculate for modifiers that set use `dependsOnNormals()` callback.

Quick test on mesh with 12 modifiers (mostly build type), calculated normals 6 times, now it only runs once - so this will give some speedup too.

1 files changed, 5 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_DerivedMesh.h b/source/blender/blenkernel/BKE_DerivedMesh.h
index f0df766ffde..668eac5e8bc 100644
--- a/source/blender/blenkernel/BKE_DerivedMesh.h
+++ b/source/blender/blenkernel/BKE_DerivedMesh.h
@@ -160,7 +160,10 @@ typedef enum DMDirtyFlag {
 	 * without actually rebuilding dm (hence by defautl keeping same GPUDrawObject, and same colors
 	 * buffer, which prevents update during a stroke!). */
 	DM_DIRTY_MCOL_UPDATE_DRAW = 1 << 1,
-} DMDirtyFlag;
+
+	/* check this with modifier dependsOnNormals callback to see if normals need recalculation */
+	DM_DIRTY_NORMALS = 1 << 2,
+}  DMDirtyFlag;
 
 typedef struct DerivedMesh DerivedMesh;
 struct DerivedMesh {
@@ -560,6 +563,7 @@ void DM_free_poly_data(struct DerivedMesh *dm, int index, int count);
 /*sets up mpolys for a DM based on face iterators in source*/
 void DM_DupPolys(DerivedMesh *source, DerivedMesh *target);
 
+void DM_ensure_normals(DerivedMesh *dm);
 void DM_ensure_tessface(DerivedMesh *dm);
 
 void DM_update_tessface_data(DerivedMesh *dm);