Painting: Canvas switcher for painting brushes/tools.

This patch adds color attributes to TexPaintSlot. This allows an easier selection
when painting color attributes.

Previously when selecting a paint tool the user had to start a stroke, before the
UI reflected the correct TexPaintSlot. Now when switching the slot the active
tool is checked and immediate the UI is drawn correctly.

In the future the canvas selector will also be used to select an image or image texture node
to paint on. Basic implementation has already been done inside this patch.

A limitation of this patch is that is isn't possible anymore to rename images directly from
the selection panel. This is currently allowed in master. But as CustomDataLayers
aren't ID fields and not owned by the material supporting this wouldn't be easy.

{F12953989}

In the future we should update the create slot operator to also include color attributes.
Sources could also be extended to use other areas of the object that use image textures
(particles, geom nodes, etc... ).

Reviewed By: brecht

Maniphest Tasks: T96709

Differential Revision: https://developer.blender.org/D14455

release/scripts/startup/bl_ui/properties_data_mesh.py

@@ -565,7 +565,7 @@ class DATA_PT_mesh_attributes(MeshButtonsPanel, Panel):
         layout.label(text="Name collisions: " + ", ".join(set(colliding_names)), icon='ERROR')
 
 
-class MESH_UL_color_attributes(UIList):
+class ColorAttributesListBase():
     display_domain_names = {
         'POINT': "Vertex",
         'EDGE': "Edge",
@@ -588,6 +588,8 @@ class MESH_UL_color_attributes(UIList):
 
         return ret, idxs
 
+
+class MESH_UL_color_attributes(UIList, ColorAttributesListBase):
     def draw_item(self, _context, layout, data, attribute, _icon, _active_data, _active_propname, _index):
         data_type = attribute.bl_rna.properties['data_type'].enum_items[attribute.data_type]
 
@@ -613,6 +615,12 @@ class MESH_UL_color_attributes(UIList):
         sub.label(text="%s ▶ %s" % (domain_name, data_type.name))
 
 
+class MESH_UL_color_attributes_selector(UIList, ColorAttributesListBase):
+    def draw_item(self, _context, layout, data, attribute, _icon, _active_data, _active_propname, _index):
+        layout.emboss = 'NONE'
+        layout.prop(attribute, "name", text="", icon='COLOR')
+
+
 class DATA_PT_vertex_colors(DATA_PT_mesh_attributes, Panel):
     bl_label = "Color Attributes"
     bl_options = {'DEFAULT_CLOSED'}
@@ -663,6 +671,7 @@ classes = (
     DATA_PT_customdata,
     DATA_PT_custom_props_mesh,
     MESH_UL_color_attributes,
+    MESH_UL_color_attributes_selector,
 )
 
 if __name__ == "__main__":  # only for live edit.