Add weight preview to WeightVG modifiers, and first, simple/basic refactor of how modifiers can generate preview.

User side:
* Preview for DynamicPaint should keep the same behavior (for now). Weight preview should be somawhat quicker, though.
* Preview for WeightVG modifiers is only active in WeightPaint mode, and if the affected vgroup is the active one.
* Last active preview modifier in stack wins!

Note: that modifier preview topic is yet to be further refined, quite raw/incomplete for now.

Dev side:
* In draw code, renamed DRAW_DYNAMIC_PAINT_PREVIEW flag to DRAW_MODIFIERS_PREVIEW
* Removed use of MOD_DPAINT_PREVIEW_READY in DynamicPaint code (seems unecessary, and if it was, should be of more general scope).
* Added eModifierTypeFlag_UsesPreview to ModifierTypeFlag, for modifiers that can generate some preview data.
* Added three new modifier funcs, to handle preview modifiers in draw code / mod stack.
* For weights preview: added the generic DM_update_weight_mcol func, which can update WEIGHT_MCOL layer with either a given array of weights (currently used by DynamicPaint only), or from current active vgroup(s).

So now, draw code is fully generic (i.e. no more modifier-type checking in it). Mod stack code is generic to some extent, but will need more work.

1 files changed, 9 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_DerivedMesh.h b/source/blender/blenkernel/BKE_DerivedMesh.h
index 0c47c833cb3..a887412bbf4 100644
--- a/source/blender/blenkernel/BKE_DerivedMesh.h
+++ b/source/blender/blenkernel/BKE_DerivedMesh.h
@@ -538,6 +538,15 @@ int sculpt_get_deform_matrices(struct Scene *scene, struct Object *ob,
 								float (**deformmats)[3][3], float (**deformcos)[3]);
 
 void weight_to_rgb(float r_rgb[3], const float weight);
+/* Update the weight MCOL preview layer.
+ * If weights are NULL, use object's active vgroup(s).
+ * Else, weights must be an array of weight float values.
+ *     If indices is NULL, it must be of numVerts length.
+ *     Else, it must be of num length, as indices, which contains vertices' idx to apply weights to.
+ *         (other vertices are assumed zero weight).
+ */
+void DM_update_weight_mcol(struct Object *ob, struct DerivedMesh *dm, int const draw_flag,
+                           float *weights, int num, const int *indices);
 
 /* convert layers requested by a GLSL material to actually available layers in
  * the DerivedMesh, with both a pointer for arrays and an offset for editmesh */