fix for problem with creating weight-paint preview.

In the case where the modifier stack didnt need deform-verts to calculate,
they would not be available for the preview either.

This fixes a bug caused by r57206 which set mirror to preview so the mirrored
weights would be displayed, but it only worked when there was an armature after it, see [#35545].

3 files changed, 24 insertions, 9 deletions

diff --git a/source/blender/blenkernel/BKE_modifier.h b/source/blender/blenkernel/BKE_modifier.h
index e466964c73f..6b9392a4169 100644
--- a/source/blender/blenkernel/BKE_modifier.h
+++ b/source/blender/blenkernel/BKE_modifier.h
@@ -371,11 +371,12 @@ typedef struct CDMaskLink {
  * evaluation, assuming the data indicated by dataMask is required at the
  * end of the stack.
  */
-struct CDMaskLink *modifiers_calcDataMasks(struct Scene *scene, 
+struct CDMaskLink *modifiers_calcDataMasks(struct Scene *scene,
                                            struct Object *ob,
                                            struct ModifierData *md,
                                            CustomDataMask dataMask,
-                                           int required_mode);
+                                           int required_mode,
+                                           ModifierData *previewmd, CustomDataMask previewmask);
 struct ModifierData *modifiers_getLastPreview(struct Scene *scene,
                                               struct ModifierData *md,
                                               int required_mode);
diff --git a/source/blender/blenkernel/intern/DerivedMesh.c b/source/blender/blenkernel/intern/DerivedMesh.c
index fc226288f04..6a21f33ac15 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -1482,7 +1482,7 @@ static void mesh_calc_modifiers(Scene *scene, Object *ob, float (*inputVertexCos
 	ModifierData *firstmd, *md, *previewmd = NULL;
 	CDMaskLink *datamasks, *curr;
 	/* XXX Always copying POLYINDEX, else tessellated data are no more valid! */
-	CustomDataMask mask, nextmask, append_mask = CD_MASK_ORIGINDEX;
+	CustomDataMask mask, nextmask, previewmask = 0, append_mask = CD_MASK_ORIGINDEX;
 	float (*deformedVerts)[3] = NULL;
 	DerivedMesh *dm = NULL, *orcodm, *clothorcodm, *finaldm;
 	int numVerts = me->totvert;
@@ -1532,17 +1532,24 @@ static void mesh_calc_modifiers(Scene *scene, Object *ob, float (*inputVertexCos
 	if (useRenderParams) required_mode = eModifierMode_Render;
 	else required_mode = eModifierMode_Realtime;
 
-	datamasks = modifiers_calcDataMasks(scene, ob, md, dataMask, required_mode);
-	curr = datamasks;
-
 	if (do_mod_wmcol || do_mod_mcol) {
 		/* Find the last active modifier generating a preview, or NULL if none. */
 		/* XXX Currently, DPaint modifier just ignores this.
 		 *     Needs a stupid hack...
 		 *     The whole "modifier preview" thing has to be (re?)designed, anyway! */
 		previewmd = modifiers_getLastPreview(scene, md, required_mode);
+
+		/* even if the modifier doesn't need the data, to make a preview it may */
+		if (previewmd) {
+			if (do_mod_wmcol) {
+				previewmask = CD_MASK_MDEFORMVERT;
+			}
+		}
 	}
 
+	datamasks = modifiers_calcDataMasks(scene, ob, md, dataMask, required_mode, previewmd, previewmask);
+	curr = datamasks;
+
 	if (deform_r) *deform_r = NULL;
 	*final_r = NULL;
 
@@ -2028,7 +2035,7 @@ static void editbmesh_calc_modifiers(Scene *scene, Object *ob, BMEditMesh *em, D
 	dm = NULL;
 	md = modifiers_getVirtualModifierList(ob);
 
-	datamasks = modifiers_calcDataMasks(scene, ob, md, dataMask, required_mode);
+	datamasks = modifiers_calcDataMasks(scene, ob, md, dataMask, required_mode, NULL, 0);
 
 	curr = datamasks;
 	for (i = 0; md; i++, md = md->next, curr = curr->next) {
diff --git a/source/blender/blenkernel/intern/modifier.c b/source/blender/blenkernel/intern/modifier.c
index 1ebe99eb660..c17830639e4 100644
--- a/source/blender/blenkernel/intern/modifier.c
+++ b/source/blender/blenkernel/intern/modifier.c
@@ -363,7 +363,9 @@ bool modifier_isEnabled(struct Scene *scene, ModifierData *md, int required_mode
 	return 1;
 }
 
-CDMaskLink *modifiers_calcDataMasks(struct Scene *scene, Object *ob, ModifierData *md, CustomDataMask dataMask, int required_mode)
+CDMaskLink *modifiers_calcDataMasks(struct Scene *scene, Object *ob, ModifierData *md,
+                                    CustomDataMask dataMask, int required_mode,
+                                    ModifierData *previewmd, CustomDataMask previewmask)
 {
 	CDMaskLink *dataMasks = NULL;
 	CDMaskLink *curr, *prev;
@@ -374,10 +376,15 @@ CDMaskLink *modifiers_calcDataMasks(struct Scene *scene, Object *ob, ModifierDat
 
 		curr = MEM_callocN(sizeof(CDMaskLink), "CDMaskLink");
 		
-		if (modifier_isEnabled(scene, md, required_mode))
+		if (modifier_isEnabled(scene, md, required_mode)) {
 			if (mti->requiredDataMask)
 				curr->mask = mti->requiredDataMask(ob, md);
 
+			if (previewmd == md) {
+				curr->mask |= previewmask;
+			}
+		}
+
 		/* prepend new datamask */
 		curr->next = dataMasks;
 		dataMasks = curr;