Fix T59848: precisely represent the dependencies of Armature modifier.

When the modifier uses vertex groups, the set of the bones it actually
needs is precisely defined by the set of the group names. If envelopes
are enabled, this refinement is not available, because any bone can
potentially be used.

This can be used in the dependency graph construction to allow objects
deformed by a part of the armature to be used in constraints on other
bones, e.g. for placing cartoon-style face elements on top of the body
mesh via Shrinkwrap constraints.

Since the list of vertex group names is now used as an input by
the dependency graph, adding/removing/renaming groups should now
be triggering a graph rebuild.

Differential Revision: https://developer.blender.org/D4715

1 files changed, 22 insertions, 1 deletions

diff --git a/source/blender/modifiers/intern/MOD_armature.c b/source/blender/modifiers/intern/MOD_armature.c
index 6a01b01c0d9..31a1f5207c6 100644
--- a/source/blender/modifiers/intern/MOD_armature.c
+++ b/source/blender/modifiers/intern/MOD_armature.c
@@ -24,11 +24,13 @@
 #include <string.h>
 
 #include "BLI_utildefines.h"
+#include "BLI_listbase.h"
 
 #include "DNA_armature_types.h"
 #include "DNA_object_types.h"
 #include "DNA_mesh_types.h"
 
+#include "BKE_action.h"
 #include "BKE_editmesh.h"
 #include "BKE_lattice.h"
 #include "BKE_library.h"
@@ -91,7 +93,26 @@ static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphConte
 {
   ArmatureModifierData *amd = (ArmatureModifierData *)md;
   if (amd->object != NULL) {
-    DEG_add_object_relation(ctx->node, amd->object, DEG_OB_COMP_EVAL_POSE, "Armature Modifier");
+    /* If not using envelopes, create relations to individual bones for more rigging flexibility. */
+    if ((amd->deformflag & ARM_DEF_ENVELOPE) == 0 && (amd->object->pose != NULL) &&
+        ELEM(ctx->object->type, OB_MESH, OB_LATTICE, OB_GPENCIL)) {
+      /* If neither vertex groups nor envelopes are used, the modifier has no bone dependencies. */
+      if ((amd->deformflag & ARM_DEF_VGROUP) != 0) {
+        /* Enumerate groups that match existing bones. */
+        LISTBASE_FOREACH (bDeformGroup *, dg, &ctx->object->defbase) {
+          if (BKE_pose_channel_find_name(amd->object->pose, dg->name) != NULL) {
+            /* Can't check BONE_NO_DEFORM because it can be animated. */
+            DEG_add_bone_relation(
+                ctx->node, amd->object, dg->name, DEG_OB_COMP_BONE, "Armature Modifier");
+          }
+        }
+      }
+    }
+    /* Otherwise require the whole pose to be complete. */
+    else {
+      DEG_add_object_relation(ctx->node, amd->object, DEG_OB_COMP_EVAL_POSE, "Armature Modifier");
+    }
+
     DEG_add_object_relation(ctx->node, amd->object, DEG_OB_COMP_TRANSFORM, "Armature Modifier");
   }
   DEG_add_modifier_to_transform_relation(ctx->node, "Armature Modifier");