Anim: Make NLA Tweak Mode not affect library linking #120573

New Issue

Sybren A. Stüvel · 2024-04-12T15:11:38+02:00

Sybren A. Stüvel commented

2024-04-12 15:11:38 +02:00

Entering NLA Tweak Mode swaps around some pointers: datablock.animation_data.action will point to the tweaked action (instead of to whatever action was originally assigned). Exiting tweak mode restores the original value of that pointer.

The result of this is that, when saving the blend file in tweak mode, linking the animated data-block into another file will behave incorrectly.

Forward Compatibility

For forward compatibility, care has to be taken that opening new files with an older Blender still works. We may need to add a few more pointers to the AnimData struct to make this work.

Suggested Approach

When saving the blend file to disk (but not to the in-memory undo buffer):

Detect that NLA tweak mode is enabled. Then write the animdata as if it is not (taking care of both the flags and the pointers).
When writing the scene, always clear the 'NLA tweak mode enabled' flag. Yes, this is stored on the scene too, for some reason.
Somehow store that tweak mode was enabled, and on which animated data-block. That way this change is transparent to the user, as when opening the file it is in the same state as when they saved it.

Chosen Approach

Instead of changing the writing, we chose to change the reading. This ensures forward compatibility (on disk, nothing changed) and avoids any unforseen side-effects.

When linking an animated ID, its NLA tweak mode is always disabled. This fixes the "ghost NLA tweak mode" that cannot be disabled (because linked data cannot be edited).
After applying library overrides, the pointers & flags that make up NLA Tweak Mode are made consistent. This ensures that tweak mode is either on, or off, but not in some in-between state.

Entering NLA Tweak Mode swaps around some pointers: `datablock.animation_data.action` will point to the tweaked action (instead of to whatever action was originally assigned). Exiting tweak mode restores the original value of that pointer. The result of this is that, when saving the blend file in tweak mode, linking the animated data-block into another file will behave incorrectly. ### Forward Compatibility For [forward compatibility](https://developer.blender.org/docs/handbook/guidelines/compatibility_handling_for_blend_files/#forward-compatibility), care has to be taken that opening new files with an older Blender still works. We may need to add a few more pointers to the `AnimData` struct to make this work. ### Suggested Approach When saving the blend file to disk (but not to the in-memory undo buffer): - Detect that NLA tweak mode is enabled. Then write the animdata as if it is not (taking care of both the flags and the pointers). - When writing the scene, always clear the 'NLA tweak mode enabled' flag. Yes, this is stored on the scene too, for some reason. - Somehow store that tweak mode was enabled, and on which animated data-block. That way this change is transparent to the user, as when opening the file it is in the same state as when they saved it. ### Chosen Approach Instead of changing the _writing_, we chose to change the _reading_. This ensures forward compatibility (on disk, nothing changed) and avoids any unforseen side-effects. - When linking an animated ID, its NLA tweak mode is always disabled. This fixes the "ghost NLA tweak mode" that cannot be disabled (because linked data cannot be edited). - After applying library overrides, the pointers & flags that make up NLA Tweak Mode are made consistent. This ensures that tweak mode is either on, or off, but not in some in-between state.

Sybren A. Stüvel added the

labels 2024-04-12 15:11:38 +02:00

Simon Thommes referenced this issue

2024-04-12 15:20:03 +02:00

Broken animation when saving file with NLA tweak mode entered #120574

Sybren A. Stüvel referenced this issue

2024-04-19 17:20:02 +02:00

Fix #120574: Broken animation when saving file with NLA tweak mode entered #120830