Fix [#30234] Various problems with CD layers and tesselation, related to modifiers stack.

Should also fix [#30266], [#29451], and partly [#30316].

Here are the changes made by this commit:
* It adds a "dirty" flag to DerivedMesh struct (for now, only DM_DIRTY_TESS_CDLAYERS, but more might be added as needed).
* It adds a new func, DM_update_tessface_data, which assumes tessfaces themselves are valid, but updates tessellated customdata from their poly/loop counter parts.
* At end of modstack, when valid tessellated faces are present in finaldm , but the cdlayers dirty flag is set, call that function (instead of recomputing the whole tessellation).
* Edits to the codes concerned (UVProject, DynamicPaint, and Subsurf modifiers).
* Also add to subsurf dm generation code the creation of a CD_POLYINDEX layer (mandatory for DM_update_tessface_data to work well, and imho all tessellated dm should have one).

Note: some pieces of old code are just #if 0’ed, will clean them later.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_DerivedMesh.h b/source/blender/blenkernel/BKE_DerivedMesh.h
index 493a5ec285f..aefa94d07de 100644
--- a/source/blender/blenkernel/BKE_DerivedMesh.h
+++ b/source/blender/blenkernel/BKE_DerivedMesh.h
@@ -147,6 +147,11 @@ typedef enum DMDrawFlag {
 	DM_DRAW_ALWAYS_SMOOTH = 2
 } DMDrawFlag;
 
+typedef enum DMDirtyFlag {
+	/* dm has valid tessellated faces, but tessellated CDDATA need to be updated. */
+	DM_DIRTY_TESS_CDLAYERS = 1 << 0,
+} DMDirtyFlag;
+
 typedef struct DerivedMesh DerivedMesh;
 struct DerivedMesh {
 	/* Private DerivedMesh data, only for internal DerivedMesh use */
@@ -158,6 +163,7 @@ struct DerivedMesh {
 	struct GPUDrawObject *drawObject;
 	DerivedMeshType type;
 	float auto_bump_scale;
+	DMDirtyFlag dirty;
 
 	/* calculate vert and face normals */
 	void (*calcNormals)(DerivedMesh *dm);
@@ -540,6 +546,8 @@ void DM_DupPolys(DerivedMesh *source, DerivedMesh *target);
 
 void DM_ensure_tessface(DerivedMesh *dm);
 
+void DM_update_tessface_data(DerivedMesh *dm);
+
 /* interpolates vertex data from the vertices indexed by src_indices in the
  * source mesh using the given weights and stores the result in the vertex
  * indexed by dest_index in the dest mesh