This commit frees list ui items from their dependencies to Panel, and hence from all the limitations this implied (mostly, the "only one list per panel" one).

It introduces a new (py-extendable and registrable) RNA type, UIList (roughly similar to Panel one), which currently contains only "standard" list's scroll pos and size (but may be expended to include e.g. some filtering data, etc.). This now makes lists completely independent from Panels!

This UIList has a draw_item callback which allows to customize items' drawing from python, that all addons can now use. Incidentally, this also greatly simplifies the C code of this widget, as we do not code any "special case" here anymore!

To make all this work, other changes were also necessary:

* Now all buttons (uiBut struct) have a 'custom_data' void pointer, used currently to store the uiList struct associated with a given uiLayoutListBox.

* DynamicPaintSurface now exposes a new bool, use_color_preview (readonly), saying whether that surface has some 3D view preview data or not.

* UILayout class has now four new (static) functions, to get the actual icon of any RNA object (important e.g. with materials or textures), and to get an enum item's UI name, description and icon.

* UILayout's label() func now takes an optional 'icon_value' integer parameter, which if not zero will override the 'icon' one (mandatory to use "custom" icons as generated for material/texture/... previews).
  Note: not sure whether we should add that one to all UILayout's prop funcs?

Note: will update addons using template list asap.

release/scripts/startup/bl_ui/properties_data_mesh.py

@@ -18,7 +18,7 @@
 
 # <pep8 compliant>
 import bpy
-from bpy.types import Menu, Panel
+from bpy.types import Menu, Panel, UIList
 from rna_prop_ui import PropertyPanel
 
 
@@ -54,6 +54,57 @@ class MESH_MT_shape_key_specials(Menu):
         layout.operator("object.shape_key_add", icon='ZOOMIN', text="New Shape From Mix").from_mix = True
 
 
+class MESH_UL_vgroups(UIList):
+    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
+        if not isinstance(item, bpy.types.VertexGroup):
+            return
+        vgroup = item
+        if self.layout_type in {'DEFAULT', 'COMPACT'}:
+            layout.label(vgroup.name, icon_value=icon)
+            icon = 'LOCKED' if vgroup.lock_weight else 'UNLOCKED'
+            layout.prop(vgroup, "lock_weight", text="", icon=icon, emboss=False)
+        elif self.layout_type in {'GRID'}:
+            layout.alignment = 'CENTER'
+            layout.label("", icon_value=icon)
+
+
+class MESH_UL_shape_keys(UIList):
+    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
+        if not isinstance(item, bpy.types.ShapeKey):
+            return
+        obj = active_data
+        key = data
+        key_block = item
+        if self.layout_type in {'DEFAULT', 'COMPACT'}:
+            split = layout.split(0.66, False)
+            split.label(item.name, icon_value=icon)
+            row = split.row(True)
+            if key_block.mute or (obj.mode == 'EDIT' and not (obj.use_shape_key_edit_mode and obj.type == 'MESH')):
+                row.active = False
+            if not item.relative_key or index > 0:
+                row.prop(key_block, "value", text="", emboss=False)
+            else:
+                row.label("")
+            row.prop(key_block, "mute", text="", emboss=False)
+        elif self.layout_type in {'GRID'}:
+            layout.alignment = 'CENTER'
+            layout.label("", icon_value=icon)
+
+
+class MESH_UL_uvmaps_vcols(UIList):
+    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
+        if not isinstance(item, (bpy.types.MeshTexturePolyLayer, bpy.types.MeshLoopColorLayer)):
+            print(item.__class__)
+            return
+        if self.layout_type in {'DEFAULT', 'COMPACT'}:
+            layout.label(item.name, icon_value=icon)
+            icon = 'RESTRICT_RENDER_OFF' if item.active_render else 'RESTRICT_RENDER_ON'
+            layout.prop(item, "active_render", text="", icon=icon, emboss=False)
+        elif self.layout_type in {'GRID'}:
+            layout.alignment = 'CENTER'
+            layout.label("", icon_value=icon)
+
+
 class MeshButtonsPanel():
     bl_space_type = 'PROPERTIES'
     bl_region_type = 'WINDOW'
@@ -144,7 +195,8 @@ class DATA_PT_vertex_groups(MeshButtonsPanel, Panel):
             rows = 5
 
         row = layout.row()
-        row.template_list(ob, "vertex_groups", ob.vertex_groups, "active_index", rows=rows)
+        row.template_list("MESH_UL_vgroups", "", ob, "vertex_groups", ob.vertex_groups, "active_index", rows=rows)
+
 
         col = row.column(align=True)
         col.operator("object.vertex_group_add", icon='ZOOMIN', text="")
@@ -202,7 +254,7 @@ class DATA_PT_shape_keys(MeshButtonsPanel, Panel):
         rows = 2
         if kb:
             rows = 5
-        row.template_list(key, "key_blocks", ob, "active_shape_key_index", rows=rows)
+        row.template_list("MESH_UL_shape_keys", "", key, "key_blocks", ob, "active_shape_key_index", rows=rows)
 
         col = row.column()
 
@@ -282,7 +334,7 @@ class DATA_PT_uv_texture(MeshButtonsPanel, Panel):
         row = layout.row()
         col = row.column()
 
-        col.template_list(me, "uv_textures", me.uv_textures, "active_index", rows=2)
+        col.template_list("MESH_UL_uvmaps_vcols", "", me, "uv_textures", me.uv_textures, "active_index", rows=2)
 
         col = row.column(align=True)
         col.operator("mesh.uv_texture_add", icon='ZOOMIN', text="")
@@ -305,7 +357,7 @@ class DATA_PT_vertex_colors(MeshButtonsPanel, Panel):
         row = layout.row()
         col = row.column()
 
-        col.template_list(me, "vertex_colors", me.vertex_colors, "active_index", rows=2)
+        col.template_list("MESH_UL_uvmaps_vcols", "", me, "vertex_colors", me.vertex_colors, "active_index", rows=2)
 
         col = row.column(align=True)
         col.operator("mesh.vertex_color_add", icon='ZOOMIN', text="")