Operating system: Arch Linux
Graphics card: GTX 970
Broken: 2.80 (master, c68c81a870baa438a45e870aee677178632cce18)
Short description of error
The function RenderEngine.update_result()method no longer seems to work, as intermediate results are not shown in the render view. Only the final rendered image is shown after end_result() is called.
It worked until recently (sorry, don't have a specific working hash).
Exact steps for others to reproduce the error
See test case based on the example from https://docs.blender.org/api/blender2.8/bpy.types.RenderEngine.html, which adds 4 "samples" in different colors and calls update_result() for each of them. The status information is updated, but the render view stays empty. Only after end_result() is called is the final result shown in the render view.
blender -P blender_render_engine.2.8.py -E CUSTOM <F12>