Add a tool - Vertex groups merger (#113)

This inconvenience was a thing from Reloaded times. Different costumes for the same character could have some variety, for example, Jill Battlesuit has 2 breast bones, while Jill BSAA only 1, so to port the same mesh for different costumes you need to merge two vertex groups into one.
Unfortunately the Blender way to do it with modifiers is cumbersome. 
It was tolerable for RE5 but porting RE5 characters to other games became a challenge because of how over-complicated the RE5 skeleton is in comparison with later games.

This new tool quickly merges 2 vertex groups into one.

albam/blender_ui/tools.py

@@ -37,6 +37,8 @@ class ToolsSettings(bpy.types.PropertyGroup):
         default="Body"
     )
     bone_names_preset: bone_names_enum
+    vg_a: bpy.props.StringProperty()
+    vg_b: bpy.props.StringProperty()
 
 
 @blender_registry.register_blender_type
@@ -76,6 +78,38 @@ def draw(self, context):
             text="",)
 
 
+@blender_registry.register_blender_type
+class ALBAM_PT_VGMerger(bpy.types.Panel):
+    '''UI Tool subpanel in Mesh Object Data'''
+    bl_label = "Vertex Groups Merger"
+    bl_idname = "ALBAM_PT_VGMerger"
+    bl_parent_id = "ALBAM_PT_ToolsPanel"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "UI"
+    bl_options = {"DEFAULT_CLOSED"}
+
+    def draw(self, context):
+        layout = self.layout
+
+        scn = context.scene.albam.tools_settings
+        row = layout.row()
+        row.prop_search(scn, "vg_a", context.active_object, "vertex_groups", text="Group A")
+        row = layout.row()
+        row.prop_search(scn, "vg_b", context.active_object, "vertex_groups", text="Group B")
+        row = layout.row()
+        row.operator("albam.vg_merge")
+
+    @classmethod
+    def poll(cls, context):
+        selection = bpy.context.selected_objects
+        selected_meshes = [obj for obj in selection if obj.type == 'MESH']
+        if selection:
+            if selected_meshes:
+                return True
+        else:
+            return False
+
+
 @blender_registry.register_blender_type
 class ALBAM_OT_SplitUVSeams(bpy.types.Operator):
     '''
@@ -90,7 +124,7 @@ class ALBAM_OT_SplitUVSeams(bpy.types.Operator):
     transfer_normals: bpy.props.BoolProperty(default=False)
 
     @classmethod
-    def poll(self, context):  # pragma: no cover
+    def poll(self, context):
         if not bpy.context.selected_objects:
             return False
         return True
@@ -188,6 +222,36 @@ def execute(self, context):
         return {'FINISHED'}
 
 
+@blender_registry.register_blender_type
+class MergeVertexGroups(bpy.types.Operator):
+    '''
+    Merges weights from groups A and B to group A
+    The B group will be removed
+    '''
+    bl_idname = "albam.vg_merge"
+    bl_label = "Merge vertex groups"
+    bl_options = {'UNDO'}
+
+    @classmethod
+    def poll(self, context):
+        ob = bpy.context.active_object
+        scn = bpy.context.scene.albam.tools_settings
+        if scn.vg_a == "" or scn.vg_b == "":
+            return False
+        elif scn.vg_a == scn.vg_b:
+            return False
+        elif not (scn.vg_a in ob.vertex_groups and scn.vg_b in ob.vertex_groups):
+            return False
+        else:
+            return True
+
+    def execute(self, context):
+        scn = bpy.context.scene.albam.tools_settings
+        merge_vgroups(scn.vg_a, scn.vg_b)
+        scn.vg_b = ""
+        return {'FINISHED'}
+
+
 @blender_registry.register_blender_type
 class ALBAM_OT_AutoRenameBones(bpy.types.Operator):
     '''Rename bones in the characters armature'''
@@ -313,3 +377,30 @@ def rename_bones(armature_ob, names_preset):
         bone_name = names_preset.get(int(reference_bone_id), None)
         if bone_name:
             bone.name = bone_name
+
+
+def merge_vgroups(vg_a, vg_b):
+    # based on https://blender.stackexchange.com/a/42779
+
+    # Get both groups and add them into third
+    ob = bpy.context.active_object
+    if (vg_a in ob.vertex_groups and vg_b in ob.vertex_groups):
+
+        vg_merged = ob.vertex_groups.new(name=vg_a + "+" + vg_b)
+
+        for id, vert in enumerate(ob.data.vertices):
+            available_groups = [v_group_elem.group for v_group_elem in vert.groups]
+            A = B = 0
+            if ob.vertex_groups[vg_a].index in available_groups:
+                A = ob.vertex_groups[vg_a].weight(id)
+            if ob.vertex_groups[vg_b].index in available_groups:
+                B = ob.vertex_groups[vg_b].weight(id)
+
+            # only add to vertex group is weight is > 0
+            sum = A + B
+            if sum > 0:
+                vg_merged.add([id], sum, 'REPLACE')
+        # remove two vertex groups and rename the third as Group A
+        ob.vertex_groups.remove(ob.vertex_groups[vg_a])
+        ob.vertex_groups.remove(ob.vertex_groups[vg_b])
+        vg_merged.name = vg_a