Motion Blur in EEVEE is not blending steps properly for camera motion in newer versions
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Description

System Information
Operating system: Microsoft Windows 10 Pro
Graphics card: Nvidia GeForce GTX 1050
Processor: Intel(R) Core(TM) i5-2500 CPU @ 3.30GHz, 3301 Mhz, 4 Core(s), 4 Logical Processor(s)

Blender Version
Broken: blender-2.92.0-e4728d0a167c-windows64
Worked: New in 2.90, didn't work in older builds of 2.90

Short description of error
When there is very high camera motion blur in EEVEE, a step value greater than 1 introduces noticeable steps which don't get properly blended. There is some post-process blur but not enough to fill the gaps. Changing Max Blur or Background Separation doesn't help.

This bug was previously reported. I thought that the bug got fixed, but in reality time step blur was temporarily not working, making it look like the blending issue was not present. In the newest versions, the bug is now present again.

Exact steps for others to reproduce the error
Start with default blend file
Go to frame 1 and rotate the camera so the default cube is at the left of the screen
Add a keyframe (of rotation)
Go to frame 5 and rotate the camera so the default cube is at the right of the screen
Add another rotation keyframe
Turn on motion blur with steps set to 4
Render a still image at frame 3
Notice stepping artifacts not being blended properly by the post-process motion blur.

Revisions and Commits

rB Blender
	rBaae60f0fecf7 Fix T81752 EEVEE: Camera Motion Blur is not blending steps properly

Related Objects
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		Status	Subtype	Assigned	Task
		Resolved		Germano Cavalcante (mano-wii)	T79595 New Motion Blur in EEVEE is not blending steps properly for camera motion
		Resolved		Clément Foucault (fclem)	T81752 Motion Blur in EEVEE is not blending steps properly for camera motion in newer versions

Event Timeline

artworker created this task.Oct 16 2020, 2:41 AM

I tested it on different versions of 2.90 and got the same result.
What was the subversion of 2.90 that really worked? (you can share the System Info in Help -> Save System Info)

Here the file I used:

eevee_mblur_steps.blend752 KBDownload

But compared to the images in the manual, 4 steps apparently should have a smoother transition.
So I'm not sure if the transition with 4 steps shown in the image is really expected. (@Clément Foucault (fclem)?)

It never actually worked. There was just a version where I couldn't use multiple time steps due to a different bug (https://developer.blender.org/T79646). At first I didn't realize there was a bug, and no time steps meant no blending issues (since there were no steps to blend between) so I thought it was gone. The bug later got fixed (not this blending bug but the time step one) and the blending issues came back. The hash mentioned in the post is rBa93be410c974. So, even in that version the bug was not fixed. As far as I know, it has been there ever since the new motion blur was added. I hope I am clear.

Additional info: this bug only affects camera motion, if I do the exact same thing but changing location of the cube rather than camera position, it blends fine.

Clément Foucault (fclem) changed the task status from Needs Information from User to Confirmed.Oct 17 2020, 8:33 PM

Clément Foucault (fclem) claimed this task.

Clément Foucault (fclem) edited projects, added BF Blender (2.91), EEVEE & Viewport; removed BF Blender.

artworker updated the task description. (Show Details)Oct 24 2020, 3:54 AM

artworker added a parent task: T79595: New Motion Blur in EEVEE is not blending steps properly for camera motion.Oct 25 2020, 1:39 PM

Clément Foucault (fclem) closed this task as Resolved by committing rBaae60f0fecf7: Fix T81752 EEVEE: Camera Motion Blur is not blending steps properly.Nov 5 2020, 6:00 PM

Clément Foucault (fclem) added a commit: rBaae60f0fecf7: Fix T81752 EEVEE: Camera Motion Blur is not blending steps properly.