Animated object visibilty 1 frame off when turning on motion blur #49163

New Issue

Gottfried Hofmann · 2016-08-25T16:10:12+02:00

Gottfried Hofmann commented

2016-08-25 16:10:12 +02:00

System Information
Win7 x64 Geforce 980ti

Blender Version
Broken: blender-2.77.0-git.bfc5a94-windows64 buildbot
Worked: 2.77a official

Short description of error
Moving objects with animated render visibility show up one frame late when motion blur is turned on, thus the viewport and render show different results.
In 2.77a it still worked as expected.

Exact steps for others to reproduce the error
Open attached .blend -> render: 20160825.bug.visibility.simple.blend

**System Information** Win7 x64 Geforce 980ti **Blender Version** Broken: blender-2.77.0-git.bfc5a94-windows64 buildbot Worked: 2.77a official **Short description of error** Moving objects with animated render visibility show up one frame late when motion blur is turned on, thus the viewport and render show different results. In 2.77a it still worked as expected. **Exact steps for others to reproduce the error** Open attached .blend -> render: [20160825.bug.visibility.simple.blend](https://archive.blender.org/developer/F343275/20160825.bug.visibility.simple.blend)

Gottfried Hofmann commented

2016-08-25 16:10:12 +02:00

Changed status to: 'Open'

Gottfried Hofmann commented

2016-08-25 16:10:12 +02:00

Added subscriber: @GottfriedHofmann

Bastien Montagne commented

2016-08-26 10:56:44 +02:00

Added subscribers: @angavrilov, @Sergey, @mont29

Alexander Gavrilov was assigned by Bastien Montagne

2016-08-26 10:56:44 +02:00

Bastien Montagne commented

2016-08-26 10:56:44 +02:00

@angavrilov think you did some changes in this area in past months, mind having a look? Thanks.

Alexander Gavrilov commented

2016-08-26 11:05:43 +02:00

This is sort of by design: 1f19fba566

The reason is that Cycles cannot correctly render motion blur for objects that appear or disappear during the shutter window, so you can either hide them completely, or have rendering artifacts (specifically, object rendered as if it was perfectly stationary for half a frame). I'd argue that artifacts are worse, especially in case of a cloud of rapidly moving particles.

This is sort of by design: 1f19fba566 The reason is that Cycles cannot correctly render motion blur for objects that appear or disappear during the shutter window, so you can either hide them completely, or have rendering artifacts (specifically, object rendered as if it was perfectly stationary for half a frame). I'd argue that artifacts are worse, especially in case of a cloud of rapidly moving particles.

Alexander Gavrilov commented

2016-08-26 11:21:37 +02:00

This is an example of those artifacts. They are very noticeable among other normally rendered particles, and even in the best case can only be removed by manual touch up of the image.

This is an example of those artifacts. They are very noticeable among other normally rendered particles, and even in the best case can only be removed by manual touch up of the image. ![test-particle-mblur6.png](https://archive.blender.org/developer/F343810/test-particle-mblur6.png)

Gottfried Hofmann commented

2016-08-26 11:37:29 +02:00

I see the problem. But in case of normal objects this behaviour introduces a lot of new problems.

My current scene has many objects switched for others.
Here is the problem: If I animate the visibility so that one object appears when another one disappears, I get a frame without any object in it. So with the new behaviour I would need to make the new object appear one frame before the old one disappears if I want motion blur. But then I get the following problems:

a) I have to keyframe viewport visibilty differently because otherwise the objects would overlap in viewport
b) If I decide to render without motion blur, I have to change the visibility keyframe for all objects, that is overkill
c) playblasts have the overlay issue as well, so I would need to change keyframes for playblasts as well

All in all I got lots and lots of work to do and need lot of muscle memory and the benefit is almost invisible in my case :(

My proposed solution: Keep the old visibilityl behaviour for regular objects and the new one exclusively for particles.

I see the problem. But in case of normal objects this behaviour introduces a lot of new problems. My current scene has many objects switched for others. Here is the problem: If I animate the visibility so that one object appears when another one disappears, I get a frame without any object in it. So with the new behaviour I would need to make the new object appear one frame before the old one disappears if I want motion blur. But then I get the following problems: a) I have to keyframe viewport visibilty differently because otherwise the objects would overlap in viewport b) If I decide to render without motion blur, I have to change the visibility keyframe for all objects, that is overkill c) playblasts have the overlay issue as well, so I would need to change keyframes for playblasts as well All in all I got lots and lots of work to do and need lot of muscle memory and the benefit is almost invisible in my case :( My proposed solution: Keep the old visibilityl behaviour for regular objects and the new one exclusively for particles.

Alexander Gavrilov commented

2016-08-26 11:41:46 +02:00

Added subscriber: @brecht

Alexander Gavrilov commented

2016-08-26 11:41:46 +02:00

That's how my original patch worked, but @brecht decided to apply it to everything.

Alexander Gavrilov removed their assignment 2016-08-26 12:28:07 +02:00

Brecht Van Lommel was assigned by Alexander Gavrilov

2016-08-26 12:28:07 +02:00

Alexander Gavrilov commented

2016-08-26 12:28:07 +02:00

This close to the release the safest approach may be to revert the modified version that applies to all objects, and apply my original that only works on particles. Changing the current code to only work on particles may be tricky, because it uses invalid transforms to store the state instead of separate bool flags that can just be safely ignored for non-particles.

blender-admin commented

2016-08-28 21:20:06 +02:00

This issue was referenced by blender/cycles@f7b6d417bb

This issue was referenced by blender/cycles@f7b6d417bb0f0d8836fb7f4895aecb5bef279968

blender-admin commented

2016-08-28 21:20:06 +02:00

This issue was referenced by 8a02c5fc62

This issue was referenced by 8a02c5fc62ca4d4aaddf787a21cbf3d2cbe3d8a5

Brecht Van Lommel commented

2016-08-28 22:23:41 +02:00

I restricted it to particles again, but kept most of the current code because I want it to work in a more appropriate way for Cycles standalone. In that context is_particle does not clarify what it does exactly, and having to specify and sync separate valid_motion_pre and valid_motion_post is not ideal.

I restricted it to particles again, but kept most of the current code because I want it to work in a more appropriate way for Cycles standalone. In that context `is_particle` does not clarify what it does exactly, and having to specify and sync separate `valid_motion_pre` and `valid_motion_post` is not ideal.

Brecht Van Lommel commented

2016-08-28 22:24:07 +02:00

Changed status from 'Open' to: 'Resolved'

Brecht Van Lommel closed this issue

2016-08-28 22:24:07 +02:00

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Animated object visibilty 1 frame off when turning on motion blur #49163