[Bf-python] Non-blocking OpenGL animation rendering.

[Adhi Hargo]

Hi, everyone.

I'm currently writing a custom preview render operator, internally
calling bpy.ops.render.opengl(). The problem is, opengl() runs
blocking (made the UI unresponsive) if called from another operator,
though it isn't if called directly from GUI. I see that executing it
runs the underlying C function, screen_render_exec, which is blocking.

Is there any way to get non-blocking OpenGL render from Python code? I
haven't found any addon/sample that does this. Tried using
context.window_manager.invoke* functions, or running it in a separate
thread, but they crash Blender. If all else fails, I may have to spawn
new Blender process to do the job.

Thank you in advance.

--
- Adhi Hargo