slint/internal/compiler/passes/z_order.rs

// Copyright © SixtyFPS GmbH <info@slint.dev>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0

/*! re-order the children by their z-order
*/

use std::rc::Rc;

use crate::diagnostics::BuildDiagnostics;
use crate::expression_tree::{Expression, Unit};
use crate::langtype::ElementType;
use crate::object_tree::{Component, ElementRc};

pub fn reorder_by_z_order(root_component: &Rc<Component>, diag: &mut BuildDiagnostics) {
    crate::object_tree::recurse_elem_including_sub_components(
        root_component,
        &(),
        &mut |elem: &ElementRc, _| {
            reorder_children_by_zorder(elem, diag);
        },
    )
}

fn reorder_children_by_zorder(
    elem: &Rc<std::cell::RefCell<crate::object_tree::Element>>,
    diag: &mut BuildDiagnostics,
) {
    // maps indexes to their z order
    let mut children_z_order = vec![];
    for (idx, child_elm) in elem.borrow().children.iter().enumerate() {
        let z = child_elm
            .borrow_mut()
            .bindings
            .remove("z")
            .and_then(|e| eval_const_expr(&e.borrow().expression, "z", &*e.borrow(), diag));
        let z =
            z.or_else(|| {
                child_elm.borrow().repeated.as_ref()?;
                if let ElementType::Component(c) = &child_elm.borrow().base_type {
                    c.root_element.borrow_mut().bindings.remove("z").and_then(|e| {
                        eval_const_expr(&e.borrow().expression, "z", &*e.borrow(), diag)
                    })
                } else {
                    None
                }
            });

        if let Some(z) = z {
            if children_z_order.is_empty() {
                for i in 0..idx {
                    children_z_order.push((i, 0.));
                }
            }
            children_z_order.push((idx, z));
        } else if !children_z_order.is_empty() {
            children_z_order.push((idx, 0.));
        }
    }

    if !children_z_order.is_empty() {
        children_z_order.sort_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap());

        let new_children = children_z_order
            .into_iter()
            .map(|(idx, _)| elem.borrow().children[idx].clone())
            .collect();
        elem.borrow_mut().children = new_children;
    }
}

fn eval_const_expr(
    expression: &Expression,
    name: &str,
    span: &dyn crate::diagnostics::Spanned,
    diag: &mut BuildDiagnostics,
) -> Option<f64> {
    match expression {
        Expression::NumberLiteral(v, Unit::None) => Some(*v),
        Expression::Cast { from, .. } => eval_const_expr(from, name, span, diag),
        Expression::UnaryOp { sub, op: '-' } => eval_const_expr(sub, name, span, diag).map(|v| -v),
        Expression::UnaryOp { sub, op: '+' } => eval_const_expr(sub, name, span, diag),
        _ => {
            diag.push_error(format!("'{}' must be an number literal", name), span);
            None
        }
    }
}