it seems that the report() function of Operator type lets all other routines finish before it actually reports. this makes it useless in many instances: for example, when reporting progress on baking (I have abandoned the idea of a progress bar and merely want to show a message: 'baking ith map out of n maps'). However, this message would always come at the end. Are there ways to supress this behavior and output a message instantaneously? In Excel VBA, there's DoEvents() built-in function. It lets all processes freeze until the ongoing processes finish


probably, such thing as reporting to user interface must be the easiest thing to do in any API but... this is life. anyways, here's what I have found for myself.

Idea in short: so, when blender script runs, Blender does not redraw screen any longer. So I start drawing text into a particular window with blf. Because Blender is not redrawn while the script runs, you actually don't see it. So I force redrawing. And then you can see the text. Don't know how robust that solution is but anyways.

This is the function which starts drawing:

def UI_report_start(message, space_type):

        draws specified message, in the specified space_type. space_type is a value in:

        ['Image Editor',
        'Node Editor',
        'UV Editor', 
        '3D View']

        returns the draw handler and the space type
 for later deletion

    # the drawer function
        import blf

    def draw_message(self, context):
        blf.position(0, 15, 30, 0)
        blf.size(0, 20, 72)
        blf.draw(0, message)

    if space_type == 'Image Editor':
        handler = bpy.types.SpaceImageEditor.draw_handler_add(draw_message, (None, None), 'WINDOW', 'POST_PIXEL')
        return handler, space_type
    elif space_type == 'Node Editor':
        handler = bpy.types.SpaceNodeEditor.draw_handler_add(draw_message, (None, None), 'WINDOW', 'POST_PIXEL')
        return handler, space_type
    elif space_type == '3D View':
        handler = bpy.types.SpaceView3D.draw_handler_add(draw_message, (None, None), 'WINDOW', 'POST_PIXEL')
        return handler, space_type
    elif space_type == 'UV Editor':
        handler = bpy.types.SpaceUVEditor.draw_handler_add(draw_message, (None, None), 'WINDOW', 'POST_PIXEL')
        return handler, space_type
        raise Exception('UI_report_start', 'Incorrect Window type specified')

this is the function that stops drawing:

def UI_report_stop(reporter, space_type):
        stops drawing the report
        the drawing handler and the space type must be input

    if space_type == 'Image Editor':
        bpy.types.SpaceImageEditor.draw_handler_remove(reporter, 'WINDOW')
    elif space_type == 'Node Editor':
        bpy.types.SpaceNodeEditor.draw_handler_remove(reporter, 'WINDOW')
    elif space_type == '3D View':
        bpy.types.SpaceView3D.draw_handler_remove(reporter, 'WINDOW')
    elif space_type == 'UV Editor':
        bpy.types.SpaceUVEditor.draw_handler_remove(reporter, 'WINDOW')
        raise Exception('UI_report_stop', 'Incorrect Window type specified')

this is a hypothetical function taking much time to complete and reporting is embedded into it:

def execute(self, context):
        handler, space = UI_report_start("does it have to be THAT difficult?!?!#$", '3D View') # <--- this starts drawing blf but you don't see it yet!
        bpy.ops.wm.redraw_timer(type='DRAW_WIN_SWAP', iterations=1) # <--- this is redrawing the screen and you see the message!
        # from now on redrawing stops but the message is still 'frozen' in place and you can see it!
        for i in range(0, len(bpy.data.images['heavy'].pixels)):
            bpy.data.images['heavy'].pixels[i] = random()
        UI_report_stop(handler, space) # <-- this removes the message!    
        return {'FINISHED'}

as you can see, it does not draw the progress bar, only a message but I can live with it.

You can also update the screen more frequently but redrawing and drawing blf takes resources, so do it only once in a while

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