Previously we maintained an `isInteractable` flag, which was derived from these layer flags:
- Locked/unlocked
- Enabled/disabled
- Layer's type visible/hidden
When a layer was not interactable, we blocked all layer actions.
After comparing to the behaviour in Affinity and considering user feedback, I've loosened these restrictions while maintaining safety. First, some definitions.
There two kinds of layer actions - mutating actions and non-mutating actions.
- Mutating actions are drawing on the layer, cropping it, filtering it, converting it, etc. Anything that changes the layer.
- Non-mutating actions are copying the layer, saving the layer to gallery, etc. Anything that _uses_ the layer.
Then, there are two broad canvas states - busy and not busy. "Busy" means the canvas is actively filtering, staging, compositing layers together, etc - something that is "single-threaded" by nature.
And here are the revised restrictions:
- When canvas is busy, you cannot initiate any layer actions.
- When the canvas is not busy, and the layer is locked, you initiate any mutating actions.
- When the canvas is not busy and the layer is not locked, you can initiate any layer action.
Besides safely giving users more freedom, it also fixes an issue where the context menu for a layer was disabled if it was not the selected layer.
Track various canvas states:
- Filtering an entity
- Transforming an entity
- Rasterizing an entity
- Compositing
- Busy (derived from all of the above)
Also track individual entity states:
- Locked
- Disabled
- All of type are hidden
- Has objects
- Interactable (derived from all of the above)
These states then gate various actions. For example:
- Cannot invoke while the canvas is busy.
- Cannot transform, filter, duplicate, or delete when the canvas is busy.
Tool interaction restrictions are not yet implemented.
