Custom OpenGL renderer UI lock

Archive Python API
1

I am implementing an OpenGL based rendering engine and came up with a little inconvenience, that the blender UI gets frozen when rendering. As a side effect, this does not allow me to show actual progress of the rendering. So I wonder if this is a bug or an expected behavior as maybe OpenGL interfere with blender’s UI rendering somehow?
Just to demonstrate here’s a little script that you can run.

import bpy
import time

class CustomRenderEngine(bpy.types.RenderEngine):
    bl_idname = 'CustomRenderEngine'
    bl_label = 'Progress Bar Bug'
    bl_use_gpu_context = True

    def render(self, scene):
        for i in range(100):
            time.sleep(0.025)
            self.update_progress(float(i) / 100.)

bpy.utils.register_class(CustomRenderEngine)

And if you set bl_use_gpu_context = False you will see the render progress bar when invoking render with F12 for example. If you leave bl_use_gpu_context = True the UI freezes during render.

A small update. In case bl_use_gpu_context = True the UI freezes after any input from the user, e.g. rotating the camera

2

Most of the UI in blender is drawn by python which can’t run while your render method which is also python is running.

3

Does it mean that there’s no intended way of doing it? As I don’t really want hacky workarounds, it would mean that I should abandon the idea of having progress bar for my renderer.

4

I was thinking about doing same thing for my batch render addon for work and as far as I can tell, you should be able to show render progress by creating new thread and render new window independently from main process while it frozen. I haven’t had time to check it for my own, but maybe it’ll help you. Also, there’re a few gotchas with creating new thread (you need to join it with main thread, I think I’ve read it in docs).
For now I just open up a console and just print progress there