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Cycles not rendering shadows on GPU when MotionBlur enabled
Open, Waiting for Developer to ReproducePublic

Description

System Information
Operating system: Windows 10 Pro 1903 (18362.356)
Graphics card: Radeon 5700XT

Blender Version
Broken: 2.81 (sub 11), branch: master, commit date: 2019-09-15 10:29, hash: 87c017985719, type: Release

Short description of error
Shadows not rendered when Motion blur enabled (cycles)

Exact steps for others to reproduce the error
As far as I can tell, this only happens on GPU rendered tiles. When rendering with CPU+GPU OpenCL scene, the tiles rendered by a CPU have shadows, tiles rendered by the GPU have not.

As you can see on the picture, there are no shadows. By rendering it again I watched which tiles are rendered by what device and I found out it is only GPU. Tiles render in same order every time, so the same spot on a image had no shadows rendered.

Image (I highlighted missing shadows):

Source of light: Sun and one other light

Details

Type
Bug

Event Timeline

Philipp Oeser (lichtwerk) lowered the priority of this task from Needs Triage by Developer to Needs Information from User.Sep 16 2019, 2:04 PM

Just to be sure we are all on the same page [this might depend on certain settings]:

  • could you share your .blend file where this happens?

Yes sure, frames 320-400

Bastien Montagne (mont29) raised the priority of this task from Needs Information from User to Waiting for Developer to Reproduce.Tue, Oct 1, 9:29 PM

I am afraid I cannot reproduce this...

The only frame that seems off is frame 400 [it is one frame before the camera makes a drastic "cut"] where motion blur goes bunkers [but that happens on both CPU & GPU for me -- and is more or less expected, since the camera makes a jump (would advise to use two cameras here and work with camera markers here...)]

I will try to dig deeper and produce simplistic deterministic case. I had problems with Motion blur on other PC also, where it just straight crashed when GPU tried to render the frame (https://developer.blender.org/T69908), same version of 2.81.