The canvas react components pass canvas entity identifiers around, then redux selectors are used to access that entity. This is good for perf - entity states may rapidly change. Passing only the identifiers allows components and other logic to have more granular state updates.
Unfortunately, this design opens the possibility for for an entity identifier to point to an entity that does not exist.
To get around this, I had created a redux selector `selectEntityOrThrow` for canvas entities. As the name implies, it throws if the entity is not found.
While it prevents components/hooks from needing to deal with missing entities, it results in mysterious errors if an entity is missing. Without sourcemaps, it's very difficult to determine what component or hook couldn't find the entity.
Refactoring the app to not depend on this behaviour is tricky. We could pass the entity state around directly as a prop or via context, but as mentioned, this could cause performance issues with rapidly changing entities.
As a workaround, I've made two changes:
- `<CanvasEntityStateGate/>` is a component that takes an entity identifier, returning its children if the entity state exists, or null if not. This component is wraps every usage of `selectEntityOrThrow`. Theoretically, this should prevent the entity not found errors.
- Add a `caller: string` arg to `selectEntityOrThrow`. This string is now added to the error message when the assertion fails, so we can more easily track the source of the errors.
In the future we can work out a way to not use this throwing selector and retain perf. The app has changed quite a bit since that selector was created - so we may not have to worry about perf at all.
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.
- Add lock toggle
- Tweak lock and enabled styles
- Update entity list action bar w/ delete & delete all
- Move add layer menu to action bar
- Adjust opacity slider style
Previously, canvas actions specific to an entity type only needed the id of that entity type. This allowed you to pass in the id of an entity of the wrong type.
All actions for a specific entity now take a full entity identifier, and the entity identifier type can be narrowed.
`selectEntity` and `selectEntityOrThrow` now need a full entity identifier, and narrow their return values to a specific entity type _if_ the entity identifier is narrowed.
The types for canvas entities are updated with optional type parameters for this purpose.
All reducers, actions and components have been updated.
- create a context for entity identifiers, massively simplifying UI for each entity int he list
- consolidate common redux actions
- remove now-unused code
