Subdiv: Enable topology cache in edit mode

The general idea of this change is to have a runtime data pointer
in the ModifierData, so it can be preserved through copy-on-write
updates by the dependency graph.

This is where subdivision surface modifier can store its topology
cache, so it is not getting trashed on every copy-on-write which
is happening when moving a vertex.

Similar mechanism should be used by multiresolution, dynamic paint
and some other modifiers which cache evaluated data.

This fixes T61746.

Thing to keep in mind, that there are more reports about slow
subdivision surface in the tracker, but that boils down to the
fact that those have a lot of extraordinary vertices, and hence
a lot slower to evaluated topology.
Other thing is, this speeds up oeprations which doesn't change
topology (i.e. moving vertices).

Reviewers: brecht

Reviewed By: brecht

Maniphest Tasks: T61746

Differential Revision: https://developer.blender.org/D4541

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/modifiers/intern/MOD_triangulate.c b/source/blender/modifiers/intern/MOD_triangulate.c
index 802bde21b5c..e39698e142e 100644
--- a/source/blender/modifiers/intern/MOD_triangulate.c
+++ b/source/blender/modifiers/intern/MOD_triangulate.c
@@ -148,4 +148,5 @@ ModifierTypeInfo modifierType_Triangulate = {
 	/* dependsOnNormals */	NULL,
 	/* foreachObjectLink */ NULL,
 	/* foreachIDLink */     NULL,
+	/* freeRuntimeData */   NULL,
 };