Bugfix [#31994] Blend from Shape "Add" mode incorrectly added the full mesh

shape instead of just the difference/deltas applied by the source shape

Apparently this was a regression from that crept in during the BMesh merge. I've
just restored the pre-BMesh method, adapted for the BMesh style.

Also, removed a somewhat superfluous (?) copy at the end of each step (from co
back to sco). It didn't seem to be serving any purpose (i.e. we're not trying to
modify the source shape at all).

1 files changed, 21 insertions, 8 deletions

diff --git a/source/blender/editors/mesh/editmesh_tools.c b/source/blender/editors/mesh/editmesh_tools.c
index 072c66c60d8..0de4c148d95 100644
--- a/source/blender/editors/mesh/editmesh_tools.c
+++ b/source/blender/editors/mesh/editmesh_tools.c
@@ -31,6 +31,7 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "DNA_key_types.h"
 #include "DNA_material_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_modifier_types.h"
@@ -2231,6 +2232,8 @@ static int edbm_blend_from_shape_exec(bContext *C, wmOperator *op)
 {
 	Object *obedit = CTX_data_edit_object(C);
 	Mesh *me = obedit->data;
+	Key *key = me->key;
+	KeyBlock *kb = NULL;
 	BMEditMesh *em = me->edit_btmesh;
 	BMVert *eve;
 	BMIter iter;
@@ -2244,24 +2247,34 @@ static int edbm_blend_from_shape_exec(bContext *C, wmOperator *op)
 	totshape = CustomData_number_of_layers(&em->bm->vdata, CD_SHAPEKEY);
 	if (totshape == 0 || shape < 0 || shape >= totshape)
 		return OPERATOR_CANCELLED;
-
+	
+	/* get shape key - needed for finding reference shape (for add mode only) */
+	if (key) {
+		kb = BLI_findlink(&key->block, shape);
+	}
+	
+	/* perform blending on selected vertices*/
 	BM_ITER_MESH (eve, &iter, em->bm, BM_VERTS_OF_MESH) {
 		if (!BM_elem_flag_test(eve, BM_ELEM_SELECT) || BM_elem_flag_test(eve, BM_ELEM_HIDDEN))
 			continue;
-
+		
+		/* get coordinates of shapekey we're blending from */
 		sco = CustomData_bmesh_get_n(&em->bm->vdata, eve->head.data, CD_SHAPEKEY, shape);
 		copy_v3_v3(co, sco);
-
-
+		
 		if (add) {
-			mul_v3_fl(co, blend);
-			add_v3_v3v3(eve->co, eve->co, co);
+			/* in add mode, we add relative shape key offset */
+			if (kb) {
+				float *rco = CustomData_bmesh_get_n(&em->bm->vdata, eve->head.data, CD_SHAPEKEY, kb->relative);
+				sub_v3_v3v3(co, co, rco);
+			}
+			
+			madd_v3_v3fl(eve->co, co, blend);
 		}
 		else {
+			/* in blend mode, we interpolate to the shape key */
 			interp_v3_v3v3(eve->co, eve->co, co, blend);
 		}
-		
-		copy_v3_v3(sco, co);
 	}
 
 	EDBM_update_generic(C, em, TRUE);