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Compositing Nodes from 2.79 break when file opened in 2.78
Closed, InvalidPublic

Description

System Information
Windows 10, nVidia GTX970

Blender Version
Broken: 2.79
Worked: (optional)

Short description of error
When file is saved in 2.79 and opened in 2.78, compositing tree is broken in some nodes. For example in 2.79, Render Layer outputs are Depth and Speed, while in previous versions is Z and Vector. When that file is opened in 2.78, anything connected to those outputs is disconnected. Hue Saturation Value node, when opened in 2.78 becomes red and titled "Undefined"

Exact steps for others to reproduce the error
Open Blender default scene in 2.79. Enable vector pass in render layers/passes. In compositing nodes, add vector blur node, and connect Depth output to Z input and Speed output to Vector input. Add a Hue, Saturation Value node after it, and connect it to Composite. Save the scene. There are probably other nodes that don't work.

Open the scene in 2.78. You'll find that Vector Blur node has been disconnected from Render Layer in it's Z and Vector inputs, and Hue Saturation Value is now red and "Undefined"

This file can be used as a test file to quickly see what's happening:

Event Timeline

Brecht Van Lommel (brecht) changed the task status from Unknown Status to Unknown Status.Sep 8 2017, 10:19 PM
Brecht Van Lommel (brecht) claimed this task.

Thanks for the report, but we can't consider this a bug. In general opening a .blend file in an older version of Blender will lead to loss of data, since the old version does not support all the same features as the new version. We can only preserve compatibility when opening old files in a new Blender version.

Render layers in 2.79 had some changes to let external render engines create their own passes, and the HSV node was changed to make Hue/Saturation/Value linkable.

Thomas Beck (plasmasolutions) raised the priority of this task from 90 to Unbreak Now!.Sep 8 2017, 10:23 PM

I can confirm this, tested it with 2.78a and it shows exactly the behavior @Relja Trajković (Relja) is describing.

Setting it to "Unbreak now" as this should not be out in the wild with the release of 2.79 imho.
@Lukas Stockner (lukasstockner97) could it be that this is happening due to layer refactorings when you were implementing denoising (just guessing) ?

Ah damn, @Brecht Van Lommel (brecht) was faster - ok if that's intended then we should definitely add that to the release logs!

Brecht Van Lommel (brecht) lowered the priority of this task from Unbreak Now! to Normal.EditedSep 8 2017, 10:41 PM

This is something that happens with every release, and with every commit that adds or changes a property even. I'm not sure it's something we should mention specifically in the 2.79 release notes. Some types of data loss are worse than others, but in general editing .blend files with an older Blender version is just not recommended. The same is true in similar 3D applications.

Ok, thanks. Had to report it. :)