Scripting: Allow specifying layer types for which a Tool should be enabled

[eishiya]

Scripted Tools can be set to enabled or disabled, but in most cases, this just needs to react to the currently selected layer(s) without much complex logic. We have Tool.updateEnabledState() in which to make these decisions, but it would be great to offload this work to Tiled and just specify what kinds of layers the tool should be enabled or disabled on. Tiled already handles similar logic with Tool.usesSelectedTiles, which prevents the tool from changing when the user picks a tile in a tileset.

In #3246, it was suggested to have boolean properies like allowForObjectLayers, allowForTileLayers. I think it might be better to specify a single property like activateOn: ObjectGroup | ImageLayer | GroupLayer, so that its absence can less ambiguously mean "active for all layers".

It would be cool to have an additional property that decides whether to activate the tool when any of the selected layers are valid vs requiring all selected layers to be valid. Or I guess there can be one default behaviour, and if someone wants it different, they can override it in their script using the usual (tedious) method.

If Tileset tools are ever added, this could be expanded with Tileset as an additional acceptable item.

[bjorn]

It would be cool to have an additional property that decides whether to activate the tool when any of the selected layers are valid vs requiring all selected layers to be valid.

Hmm, for most existing tools, they actually base their enabled state only on the "current layer", not the "selected layers". I think it would make sense to do the same for this setting, or if we choose a different behavior for this setting, to do the same for the existing tools (but I'm currently not sure if that's beneficial or which problems that might introduce).

[eishiya]

I agree that it should be consistent for scripted and built-in tools. Currently, most of Tiled's tools only work on either one layer (often, but not always, the current layer) or on any relevant layer, so making them activate based on selected layers wouldn't make sense. I'd like to say I'd love to see some of those tools modified to make sense for working on multiple selected layers, but that just doesn't have very clear logic as to how it should work. For example, it'd be great to Select Same Tile from several layers, but which tile is chosen when you click?

So, in the interest of consistency, until/unless more of Tiled's built-in tools can benefit from being selected based on selected layers rather than current layer, I'm fine with it being based on the current layer.

That said, I think the behaviour of setting the current layer could be improved. It's currently very easy to end up in a situation where you have only Tile Layers selected but can only choose Object tools because the current layer is an Object Layer or vice versa, if you deselect layers by modifier+clicking on them. Whenever possible, I think the current layer should be one of the selected layers.

[bjorn]

It's currently very easy to end up in a situation where you have only Tile Layers selected but can only choose Object tools because the current layer is an Object Layer or vice versa, if you deselect layers by modifier+clicking on them. Whenever possible, I think the current layer should be one of the selected layers.

Yeah, actually it tries to do that, so possibly the deselection case is a bit of a bug. The question is how to address it. I guess we could try switching the current layer to the next selected layer, when available.

Thanks for your feedback!