[FEATURE] StackView shouldn't layout and draw hidden layers about cursive

[gyscos]

Hi, and thanks for the report!

Unfortunately it's not trivial to know a layer is hidden. Layers can be transparent and only draw on part of their allocated rectangle, which makes it harder to know when we can guarantee a layer is not visible.

Note that if you have a bunch of fullscreen layers, you might not actually need them all in the same stackview. For example ScreensView is meant to show one (fullscreen) view at a time (and that fullscreen view can be a StackView). One is already embedded in the Cursive root: you can call Cursive::add_screen to create new, separate screens, and then decide which one to show. This will properly skip layout and draw calls for non-active screens.

[smallB007]

Probably very naive, but would adding flag is_hidden solve that issue?

[gyscos]

You can already wrap some view in a HideableView and toggle that on/off. You could absolutely do this for any full-screen layer you add.

But if you add a non-transparent full-screen layer to the StackView on top of other stuff, chances are a new screen is what you need.

[smallB007]

I am not sure, but "I think" that hideable view blocks input to views "under" it? I remember I wasn't happy the hideableview's concepts were implemented. In my own code base I simply added flag is_hidden to a view and if view is hidden stack "skips it" completely. Simple but works.

[gyscos]

The post is about having a front full-screen layer, and other layers behind it. All layers behind the front one will never be seen, and drawing them is wasted.

Having a front "invisible" layer that does not grab input is a separate issue like #558.

[smallB007]

"The post is about having a front full-screen layer" - I don't think so. The OP complains about stackview calling draw/layout on all layers without checking if Layer/View is is visible or not. Anyway...
As a side note, I think it would be worth mentioning Cursive::add_screen in some tutorial (if it is mentioned in any I've missed it). My point is that in the tutorials this is not the suggested way to have full screen app. Instead add_fullscreen_layer (I believe) is suggested.