GPv3: improve/optimize caches handling in edit mode undo. #118318

New Issue

Bastien Montagne · 2024-02-15T11:56:34+01:00

Bastien Montagne commented

2024-02-15 11:56:34 +01:00

In merged !117072 PR, an initial Undo support has been added to GreasePencil Edit mode.

However, its handling of caches is currently sub-optimal, since it essentially re-create all drawings' caches every time an undo step is loaded. Two main ideas were discussed so far to improve this situation.

Only invalidate the cache when needed.

It should be possible to detect when the current drawing and the one being restored from the undo step are 'identical enough', and then avoid clearing the current cache.

A very basic WIP implementation of such solution can be found in PR !118317.

Also store the caches in Undo steps.

This would store caches in undo steps, using the SharedCache system.

To avoid storing tens of caches that would only be kept for undo step data (once the current data has been modified and related caches has been updated), this requires a mechanism to free and invalidate such caches once only undo steps are using them.

Exact design for this is not clear yet, some ideas:

Having a new 'weak reference' type of cache, which does not prevent freeing data once only weak users are referencing it, together with a mechanism to invalidate these weak pointers. User (e.g. undo step read code) would then be responsible to ensure that such weak shared cache are still valid before using them.
Making undo system responsible to check for these shared caches, and free them when undo steps are the only remaining users.

In merged !117072 PR, an initial Undo support has been added to GreasePencil Edit mode. However, its handling of caches is currently sub-optimal, since it essentially re-create all drawings' caches every time an undo step is loaded. Two main ideas were discussed so far to improve this situation. ### Only invalidate the cache when needed. It should be possible to detect when the current drawing and the one being restored from the undo step are 'identical enough', and then avoid clearing the current cache. A very basic WIP implementation of such solution can be found in PR !118317. ### Also store the caches in Undo steps. This would store caches in undo steps, using the SharedCache system. To avoid storing tens of caches that would only be kept for undo step data (once the current data has been modified and related caches has been updated), this requires a mechanism to free and invalidate such caches once only undo steps are using them. Exact design for this is not clear yet, some ideas: * Having a new 'weak reference' type of cache, which does not prevent freeing data once only weak users are referencing it, together with a mechanism to invalidate these weak pointers. User (e.g. undo step read code) would then be responsible to ensure that such weak shared cache are still valid before using them. * Making undo system responsible to check for these shared caches, and free them when undo steps are the only remaining users.

Bastien Montagne added the

labels 2024-02-15 11:56:35 +01:00

Bastien Montagne added this to the Grease Pencil project 2024-02-15 11:56:37 +01:00

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