[Blender 2.91] blf module bug

blf_bug.py

bl_info = {
    "name": "Modal Operator Demo 1",
    "author": "nutti",
    "version": (1, 0, 0),
    "blender": (2, 91, 0),
    "location": "3D View > Sidebar > Modal Ops",
    "category": "System",
}


import bpy
import blf


REGION_TYPE = 'UI'


def draw_callback_fn(context):
    font_id = 0
    font_size = 30
    dpi = context.preferences.system.dpi

    blf.size(font_id, font_size, dpi)
    blf.position(font_id, 200, 200, 0)
    blf.draw(font_id, "Text")


class DEMO_OT_ModalOps(bpy.types.Operator):
    bl_idname = "wm.demo_modal_ops"
    bl_label = "Modal Ops"
    bl_description = "Modal Ops Desc"
    bl_options = {'REGISTER'}

    draw_handler = None
    timer = None

    def finalize(self, context):
        cls = self.__class__

        bpy.types.SpaceView3D.draw_handler_remove(cls.draw_handler, REGION_TYPE)
        context.window_manager.event_timer_remove(cls.timer)
        cls.timer = None
        cls.draw_handler = None

    def modal(self, context, event):
        cls = self.__class__

        if cls.draw_handler is None:
            return {'FINISHED'}
        
        context.area.tag_redraw()

        return {'PASS_THROUGH'}

    def invoke(self, context, event):
        cls = self.__class__

        if cls.draw_handler:
            self.finalize(context)
            context.area.tag_redraw()
            return {'FINISHED'}
        else:
            context.window_manager.modal_handler_add(self)
            cls.draw_handler = bpy.types.SpaceView3D.draw_handler_add(
                draw_callback_fn, (context, ), REGION_TYPE, 'POST_PIXEL')
            cls.timer = context.window_manager.event_timer_add(0.1, window=context.window)
            context.area.tag_redraw()
            return {'RUNNING_MODAL'}


class DEMO_PT_ModalOps(bpy.types.Panel):
    bl_idname = "DEMO_PT_ModalOps"
    bl_label = "Modal Ops"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = "Modal Ops"

    def draw(self, context):
        layout = self.layout

        layout.operator(DEMO_OT_ModalOps.bl_idname)


classes = [
    DEMO_OT_ModalOps,
    DEMO_PT_ModalOps,
]


def register():
    for cls_ in classes:
        bpy.utils.register_class(cls_)


def unregister():
    for cls_ in reversed(classes):
        bpy.utils.unregister_class(cls_)


if __name__ == "__main__":
    register()