Fix T52149: LoopTriArray computation was not correctly protected against concurrency.

Note: this commit seems to work as expected (also with transform
snapping etc.). However, it is rather unsafe - not enough for 2.79 at
least, unless we get much more testing on it. It also depends on three
previous ones.

Note that using a global lock here is far from ideal, we should rather
have a lock per DM, but that will do for now, whole DM thing is doomed
to oblivion anyway in 2.8.

Also, we may need a `DM_DIRTY_LOOPTRIS` dirty flag at some point. Looks
like we can survive without it for now though... Probably because cached
looptris are never copied accross DM's?

1 files changed, 2 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/subsurf_ccg.c b/source/blender/blenkernel/intern/subsurf_ccg.c
index 47dea5ea282..ff0682258c6 100644
--- a/source/blender/blenkernel/intern/subsurf_ccg.c
+++ b/source/blender/blenkernel/intern/subsurf_ccg.c
@@ -4474,10 +4474,10 @@ static void ccgDM_recalcTessellation(DerivedMesh *UNUSED(dm))
 	/* Nothing to do: CCG handles creating its own tessfaces */
 }
 
+/* WARNING! *MUST* be called in an 'loops_cache_rwlock' protected thread context! */
 static void ccgDM_recalcLoopTri(DerivedMesh *dm)
 {
-	BLI_rw_mutex_lock(&loops_cache_rwlock, THREAD_LOCK_WRITE);
-	MLoopTri *mlooptri;
+	MLoopTri *mlooptri = dm->looptris.array;
 	const int tottri = dm->numPolyData * 2;
 	int i, poly_index;
 
@@ -4502,7 +4502,6 @@ static void ccgDM_recalcLoopTri(DerivedMesh *dm)
 		lt->tri[2] = (poly_index * 4) + 2;
 		lt->poly = poly_index;
 	}
-	BLI_rw_mutex_unlock(&loops_cache_rwlock);
 }
 
 static void ccgDM_calcNormals(DerivedMesh *dm)