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, 4 insertions, 0 deletions

diff --git a/source/blender/modifiers/intern/MOD_uvproject.c b/source/blender/modifiers/intern/MOD_uvproject.c
index cd4858fcb4d..b9a4821bb7a 100644
--- a/source/blender/modifiers/intern/MOD_uvproject.c
+++ b/source/blender/modifiers/intern/MOD_uvproject.c
@@ -378,6 +378,10 @@ static DerivedMesh *uvprojectModifier_do(UVProjectModifierData *umd,
 			}
 		}
 	}
+
+	/* Mark tessellated CD layers as dirty. */
+	dm->dirty |= DM_DIRTY_TESS_CDLAYERS;
+
 	return dm;
 }