Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1070 with Max-Q Design/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.35
CPU: Intel i7-8750H @ 2.20 GHz
RAM: 16 GB
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-07-05 16:36, hash: rB699193713fc0
Worked: version: 2.79 (sub 0), branch: master, commit date: 2018-03-22 14:10, hash: f4dc9f9d68b
Short description of error
Motion Blur of fast rotating objects "randomly" glitches.
Basically I was rendering some car animation in 2.80 and I noticed that in some frames the wheel motion blur was glitching as if there was a sudden change in the wheel rotation speed.
Exact steps for others to reproduce the error
Open the .blend file in Blender 2.80 and render the animation.
If opened and rendered in Blender 2.79 the animation gives the expected result.
A comparison between the renders in 2.79 and 2.80. The wheel is rotating at a constant speed on the x-axis, no easing. No other variables are animated. Of course I'm expecting the usual temporal aliasing/wagon wheel artifact, but those jumps in 2.8 just look wrong.
Comparison between same "glitched" frame [Frame006] rendered in 2.79 and 2.80.
If relevant, in the given example the rotation on the x-axis for the wheel is:
|Frame number||X Rotation||Glitching?|
A test render from my project, here the (invisible) car is moving and the camera is parented to the car rig. The wheels are animated via a rig using bones.
I've been doing some testing, but no matter what I try I always get the same result. Of course, depending on the speed of the wheel, the frames in which it happens vary.
I tried playing with Position Center/Start/End on Frame, shutter, rendering with CPU and GPU, using quaternions and eulers. I really can't understand, I think it's a Cycles related problem.
It almost looks like there's a limit when calculating angles differences between frames for motion blur, or some kind of clamping/wrapping/overflow/(?)
I also tried older 2.8 builds (oldest build I've been testing with: 2.80 (sub 41), branch: blender2.7, commit date: 2019-01-21 00:28, hash: dd3f5186260e) but the bug is already there.
Same thing on other Windows 10 machines.
I think that it's a bug and not a desired behaviour.