Bug in addon to Change header color dynamically

Question

Bug in addon to change header color dynamically

I made an add-on that changes the theme color of the header if the automatic keyframe feature is enabled.

The color change function works fine.

However, the following bug occurs in the object gizmo transform gizmo.

• Mouse hovers no longer highlight
• Drag operation is delayed a little
  
  Why do bugs occur in Gizmo by changing the theme color? I have no idea.

python

import bpy

bl_info = {
    "name" : "header_color_change",
    "author" : "Bookyakuno",
    "version" : (1, 0, 0),
    "blender" : (2, 80, 0),
    "location" : "hoge",
    "description" : "hoge",
    "category" : "UI"
}


def TEST_HT_header_color_change(self, context):
    layout = self.layout
    layout.label(text="")


    if bpy.context.scene.tool_settings.use_keyframe_insert_auto == True:
        bpy.context.preferences.themes[0].topbar.space.header = (0.4, 0.000000, 0.000000, 1.000000)

    else:
        bpy.context.preferences.themes[0].topbar.space.header = (0.137255, 0.137255, 0.137255, 1.000000)

    return {'FINISHED'}


def register():
    bpy.types.TOPBAR_HT_upper_bar.append(TEST_HT_header_color_change)

def unregister():
    bpy.types.TOPBAR_HT_upper_bar.remove(TEST_HT_header_color_change)

if __name__ == "__main__":
    register()

'''

Answer 1

I think that the issue comes from changing preference data during a UI draw, that is, you are accessing data that should not be altered while drawing the UI.

An alternative approach that seems to work is using handlers to alter the theme settings. In 2.80 the scene_update_* handlers have been renamed to depsgraph_update_*.

def TEST_prefset(scene):
    prefs = bpy.context.preferences

    if scene.tool_settings.use_keyframe_insert_auto == True:
        prefs.themes[0].topbar.space.header = (0.4, 0.000000, 0.000000, 1.000000)

    else:
        prefs.themes[0].topbar.space.header = (0.137255, 0.137255, 0.137255, 1.000000)


def register():
    bpy.app.handlers.depsgraph_update_post.append(TEST_prefset)

def unregister():
    bpy.app.handlers.depsgraph_update_post.remove(TEST_prefset)

Answer 2

In a draw callback

As an alternative to using onload and update handlers, could make it a draw callback on the 3d view space.

The added bonus here is can write some text to screen, in addition to or instead of colouring header.

EDIT minor adjustment to keep themes bg color. Only tested running from console.

import blf
import bpy
bl_info = {
    "name": "New Object",
    "author": "Your Name Here",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "View3D > Add > Mesh > New Object",
    "description": "Adds a new Mesh Object",
    "warning": "",
    "wiki_url": "",
    "category": "Add Mesh",
}
highlight_color = (0.4, 0, 0, 1)
class DrawingClass:
    def init(self, prop):
        print("INT DC")
        from bpy import context
        self.prop = prop
        self.col = context.preferences.themes[0].topbar.space.header[:] 
        self.handle = bpy.types.SpaceView3D.draw_handler_add(
            self.draw_text_callback, (), 'WINDOW', 'POST_PIXEL')
def draw_text_callback(self):
    from bpy import context
    font_id = 0  # XXX, need to find out how best to get this.
    if not hasattr(context, "scene"):
        return None
    scene = context.scene
    if scene.tool_settings.use_keyframe_insert_auto:
        context.preferences.themes[0].topbar.space.header = highlight_color
        # draw some text
        blf.position(font_id, 15, 50, 0)
        blf.size(font_id, 20, 72)
        blf.draw(font_id, "%s %s" % (context.scene.name, self.prop))

    else:
        context.preferences.themes[0].topbar.space.header = self.col

def remove_handle(self):
    from bpy import context
    context.preferences.themes[0].topbar.space.header = self.col
    bpy.types.SpaceView3D.draw_handler_remove(self.handle, 'WINDOW')



dc = None
def register():
    global dc
    dc = DrawingClass("Draw This On Screen")
def unregister():
    global dc
    if dc:
        dc.remove_handle()
        dc = None
if name == "main":
    register()