Complete fix for [#33002] Wrong vertex color.

Appart from the color glitch, there was several problems with vpaint:
* "fast_update" mode was never on, because of wrong testing code;
* drawing refresh during stroke in "fast_update" (i.e. no dm rebuild) mode was broken in VBO mode, because updated (tess data) mcol wasn't moved to colors GPUBuffer.

Solved the later point by adding a new DM_DIRTY_MCOL_UPDATE_DRAW flag to DerivedMesh dirty var, which is set each time vpaint stroke directly update me->mcol, and forces GPU_color_setup() to refresh the gpu's colors buffer.

Also got rid of the uggly GPU_color3_upload(), which basically did the same thing, but with an additional intermediate buffer !

1 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_DerivedMesh.h b/source/blender/blenkernel/BKE_DerivedMesh.h
index fa9223ba6e2..738d9101e8e 100644
--- a/source/blender/blenkernel/BKE_DerivedMesh.h
+++ b/source/blender/blenkernel/BKE_DerivedMesh.h
@@ -148,6 +148,11 @@ typedef enum DMDrawFlag {
 typedef enum DMDirtyFlag {
 	/* dm has valid tessellated faces, but tessellated CDDATA need to be updated. */
 	DM_DIRTY_TESS_CDLAYERS = 1 << 0,
+	/* One of the MCOL layers have been updated, force updating of GPUDrawObject's colors buffer.
+	 * This is necessary with modern, VBO draw code, as e.g. in vpaint mode me->mcol may be updated
+	 * 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;
 
 typedef struct DerivedMesh DerivedMesh;