Cycles: motion blur only applies on Left view #93995

New Issue

System Information
Operating system: Win 10
Graphics card: RTX 2060 NVIDIA

Blender Version
Broken: 3.0, 2.93
Caused by 97f1e4782a

Short description of error
When rendering a stereoscopic animation with the motion blur option activated, motion blur only applies on Left view and not to both views. There is no motion blur on the right view.

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

Add objects to the scene
Setup a camera animation
Turn on stereoscopy
Turn on motion blur option
Render

Test File:
STEREOSCOPY MOTION BLUR BUG.blend

**System Information** Operating system: Win 10 Graphics card: RTX 2060 NVIDIA **Blender Version** Broken: 3.0, 2.93 Caused by 97f1e4782a **Short description of error** When rendering a stereoscopic animation with the motion blur option activated, motion blur only applies on Left view and not to both views. There is no motion blur on the right view. **Exact steps for others to reproduce the error** Based on the default startup or an attached .blend file (as simple as possible). Add objects to the scene Setup a camera animation Turn on stereoscopy Turn on motion blur option Render Test File: [STEREOSCOPY MOTION BLUR BUG.blend](https://archive.blender.org/developer/F12734634/STEREOSCOPY_MOTION_BLUR_BUG.blend)

Added subscriber: @Bil55

#95758 was marked as duplicate of this issue

Added subscriber: @PratikPB2123

Changed status from 'Needs Triage' to: 'Confirmed'

Hi, thanks for the report. Looks like a regression (Works fine here on 2.92, 2.93.0LTS)

Added subscriber: @michael64

Yes, this is a regression. The last version that produced properly motion blurred images for the left and right view was 2.93.1.
The fix for #89884 had the side effect of breaking motion blur for the right image.
Blender 2.93.2 was the first version in which motion blur with stereoscopy stopped working.

Keeping the mentioned fix while not setting has_updates_ to false (intern/cycles/blender/sync.cpp) for motion blur scenes
keeps the Carros.blend example from flickering in the cycles render preview
while enabling the motion blur for the right image of this scene.

  if (scene->need_motion() != Scene::MOTION_BLUR) {
    has_updates_ = false;
  }

Likewise

  if (scene->need_motion() == Scene::MOTION_NONE) {
    has_updates_ = false;
  }

should also work to handle the cases of both tickets but I am unsure
if has_updates_ should be set to false for the MOTION_PASS case.
Could this cause the the cycles render preview to flicker? I don't know.

Yes, this is a regression. The last version that produced properly motion blurred images for the left and right view was 2.93.1. The fix for #89884 had the side effect of breaking motion blur for the right image. Blender 2.93.2 was the first version in which motion blur with stereoscopy stopped working. Keeping the mentioned fix while not setting has_updates_ to false (intern/cycles/blender/sync.cpp) for motion blur scenes keeps the Carros.blend example from flickering in the cycles render preview while enabling the motion blur for the right image of this scene. ``` if (scene->need_motion() != Scene::MOTION_BLUR) { has_updates_ = false; } ``` Likewise ``` if (scene->need_motion() == Scene::MOTION_NONE) { has_updates_ = false; } ``` should also work to handle the cases of both tickets but I am unsure if has_updates_ should be set to false for the MOTION_PASS case. Could this cause the the cycles render preview to flicker? I don't know.

The fix for #89884 had the side effect of breaking motion blur for the right image.

Hi @michael64 , I don't think this has been introduced with the fix of #89884.
Its actually broken between 9dabb342ba - a1556fa05c

(Unsure about the commit which caused this issue)

> The fix for #89884 had the side effect of breaking motion blur for the right image. Hi @michael64 , I don't think this has been introduced with the fix of `#89884`. Its actually broken between 9dabb342ba - a1556fa05c (Unsure about the commit which caused this issue)

I was git bisecting between v2.93.1 and v2.93.2 to find the first commit that introduced the motion blur error into the blender-v2.93-release branch which is fdb811f030.
That code of fdb811f030 seems to be an identical backport of 97f1e4782a which might be what you were looking for on the master branch.

Checking out 97f1e4782a, compiling and running it with this scene results in missing motion blur for the right view. Loading the Carros.blend scene from #89884 and switching to render preview with Cycles works fine.

Now checking out the direct ancestor of 97f1e4782a which is 1c1fa15ce1, compiling and running it
results in the opposite. This ancestor had correct motion blur for the right view but switching
to render preview with Cycles now results in Cycles continously rerendering the first sample.

Is 97f1e4782a what you were looking for? My two fix suggestions are of course still the same for the same code on the master branch.

I was git bisecting between v2.93.1 and v2.93.2 to find the first commit that introduced the motion blur error into the blender-v2.93-release branch which is fdb811f030. That code of fdb811f030 seems to be an identical backport of 97f1e4782a which might be what you were looking for on the master branch. Checking out 97f1e4782a, compiling and running it with this scene results in missing motion blur for the right view. Loading the Carros.blend scene from #89884 and switching to render preview with Cycles works fine. Now checking out the direct ancestor of 97f1e4782a which is 1c1fa15ce1, compiling and running it results in the opposite. This ancestor had correct motion blur for the right view but switching to render preview with Cycles now results in Cycles continously rerendering the first sample. Is 97f1e4782a what you were looking for? My two fix suggestions are of course still the same for the same code on the master branch.

Added subscriber: @Sergey

Is 97f1e4782a what you were looking for?

Hi Michael. Thanks for bisecting.
cc @Sergey

My two fix suggestions are of course still the same for the same code on the master branch.

Please submit a diff so that developer can review your fix: https://developer.blender.org/differential/diff/create/

(Also see Contributing code wiki to understand the process.)

> Is `97f1e4782a` what you were looking for? Hi Michael. Thanks for bisecting. cc @Sergey > My two fix suggestions are of course still the same for the same code on the master branch. Please submit a diff so that developer can review your fix: https://developer.blender.org/differential/diff/create/ (Also see [Contributing code ](https://wiki.blender.org/wiki/Process/Contributing_Code) wiki to understand the process.)

The proposed diff is D13567.

The proposed diff is [D13567](https://archive.blender.org/developer/D13567).

This issue was referenced by 1c04d22ebf

This issue was referenced by 1c04d22ebf803d19bd9174a3a57249513fbe7093

This issue was referenced by b32f5a922f

This issue was referenced by b32f5a922f05989ff129c3d266ebbed14b751e2a

Changed status from 'Confirmed' to: 'Resolved'

Added subscribers: @dscherr, @Alaska

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Cycles: motion blur only applies on Left view #93995