patina/src/layout/arr/container.rs

use super::ArrangementCalculator;
use crate::{
    layout::{LayoutNodeAccess, SizePolicy2D},
    math::PixelBox,
};

#[derive(Clone, Debug)]
pub struct ContainerArrangement;

impl ArrangementCalculator for ContainerArrangement {
    fn arrange_step(&self, node: LayoutNodeAccess) -> SizePolicy2D {
        let Some(child) = node.child(0) else {
            return SizePolicy2D::new(node.width_policy(), node.height_policy())
                + node.margin_as_policy();
        };
        SizePolicy2D::new(
            node.width_policy.max_preserve_slack(child.width_policy()),
            node.height_policy.max_preserve_slack(child.height_policy()),
        ) + node.margin_as_policy()
    }

    fn layout_step(&self, node: LayoutNodeAccess, inside: PixelBox) {
        let inside = super::do_align(&node, inside);

        node.with_state(|ns| {
            if Some(inside) != ns.area {
                ns.area = Some(inside);
                ns.needs_render = true;
            }
        });

        let Some(child) = node.child(0) else {
            return;
        };

        child
            .child_arrangement
            .layout_step(child, inside.inner_box(node.margin()));
    }
}