Add Selector layer

[PoignardAzur]

No description provided.

[xStrom]

Overall this looks like a great step towards having a decent selector menu.

There are a bunch of potential race conditions. I don't think they need to be necessarily solved in this PR, but they should at least be documented.

[PoignardAzur]

I've added more comments and TODOs.

Overall, I think all three potential races conditions can be fixed by using a future change which I'm calling "associated layers", which will basically means that widgets store a list of layers they created, and Masonry keeps that list up to date.

[xStrom]

Some churn to deal with but we're getting close to landing this!

[xStrom]

Suggested change

	use accesskit::{Node, Role};
	use masonry_core::core::NoAction;
	use tracing::{Span, trace_span};
	use vello::Scene;
	use crate::core::MeasureCtx;
	use crate::core::{
	AccessCtx, AccessEvent, ChildrenIds, EventCtx, LayoutCtx, PaintCtx, PointerEvent,
	PropertiesMut, PropertiesRef, RegisterCtx, TextEvent, Update, UpdateCtx, Widget, WidgetId,
	WidgetMut, WidgetPod,
	};
	use crate::kurbo::{Axis, Size};
	use crate::layout::{LayoutSize, LenReq, SizeDef};
	use crate::properties::{BorderWidth, BoxShadow, Padding};
	use crate::widgets::Label;
	use accesskit::{Node, Role};
	use tracing::{Span, trace_span};
	use vello::Scene;
	use crate::core::MeasureCtx;
	use crate::core::{
	AccessCtx, AccessEvent, ChildrenIds, EventCtx, LayoutCtx, NoAction, PaintCtx, PointerEvent,
	PropertiesMut, PropertiesRef, RegisterCtx, TextEvent, Update, UpdateCtx, Widget, WidgetId,
	WidgetMut, WidgetPod,
	};
	use crate::kurbo::{Axis, Size};
	use crate::layout::{LayoutSize, LenReq, SizeDef};
	use crate::widgets::Label;

[xStrom]

measure can now be a lot simpler.

Suggested change

	fn measure(
	&mut self,
	ctx: &mut MeasureCtx<'_>,
	props: &PropertiesRef<'_>,
	axis: Axis,
	len_req: LenReq,
	cross_length: Option<f64>,
	) -> f64 {
	// TODO: Remove HACK: Until scale factor rework happens, just pretend it's always 1.0.
	// https://github.com/linebender/xilem/issues/1264
	let scale = 1.0;
	let border = props.get::<BorderWidth>();
	let padding = props.get::<Padding>();
	let border_length = border.length(axis).dp(scale);
	let padding_length = padding.length(axis).dp(scale);
	let cross = axis.cross();
	let cross_space = cross_length.map(|cross_length| {
	let cross_border_length = border.length(cross).dp(scale);
	let cross_padding_length = padding.length(cross).dp(scale);
	(cross_length - cross_border_length - cross_padding_length).max(0.)
	});
	let auto_length = len_req.reduce(border_length + padding_length).into();
	let context_size = LayoutSize::maybe(cross, cross_space);
	let child_length = ctx.compute_length(
	&mut self.child,
	auto_length,
	context_size,
	axis,
	cross_space,
	);
	child_length + border_length + padding_length
	}
	fn measure(
	&mut self,
	ctx: &mut MeasureCtx<'_>,
	_props: &PropertiesRef<'_>,
	axis: Axis,
	len_req: LenReq,
	cross_length: Option<f64>,
	) -> f64 {
	let auto_length = len_req.into();
	let context_size = LayoutSize::maybe(axis.cross(), cross_length);
	ctx.compute_length(
	&mut self.child,
	auto_length,
	context_size,
	axis,
	cross_length,
	)
	}

[xStrom]

layout can be simplified as well.

Suggested change

	fn layout(&mut self, ctx: &mut LayoutCtx<'_>, props: &PropertiesRef<'_>, size: Size) {
	// TODO: Remove HACK: Until scale factor rework happens, just pretend it's always 1.0.
	// https://github.com/linebender/xilem/issues/1264
	let scale = 1.0;
	let border = props.get::<BorderWidth>();
	let padding = props.get::<Padding>();
	let shadow = props.get::<BoxShadow>();
	let space = border.size_down(size, scale);
	let space = padding.size_down(space, scale);
	let child_size = ctx.compute_size(&mut self.child, SizeDef::fit(space), space.into());
	ctx.run_layout(&mut self.child, child_size);
	let child_origin = ((size - child_size).to_vec2() * 0.5).to_point();
	ctx.place_child(&mut self.child, child_origin);
	let baseline = ctx.child_baseline_offset(&self.child);
	let baseline = border.baseline_up(baseline, scale);
	let baseline = padding.baseline_up(baseline, scale);
	ctx.set_baseline_offset(baseline);
	if shadow.is_visible() {
	ctx.set_paint_insets(shadow.get_insets());
	}
	}
	fn layout(&mut self, ctx: &mut LayoutCtx<'_>, _props: &PropertiesRef<'_>, size: Size) {
	let child_size = ctx.compute_size(&mut self.child, SizeDef::fit(size), size.into());
	ctx.run_layout(&mut self.child, child_size);
	let child_origin = ((size - child_size).to_vec2() * 0.5).to_point();
	ctx.place_child(&mut self.child, child_origin);
	let child_baseline = ctx.child_baseline_offset(&self.child);
	let child_bottom = child_origin.y + child_size.height;
	let bottom_gap = size.height - child_bottom;
	ctx.set_baseline_offset(child_baseline + bottom_gap);
	}