1use refineable::Refineable as _;
 2
 3use crate::{Bounds, Element, ElementContext, IntoElement, Pixels, Style, StyleRefinement, Styled};
 4
 5/// Construct a canvas element with the given paint callback.
 6/// Useful for adding short term custom drawing to a view.
 7pub fn canvas<T>(
 8    after_layout: impl 'static + FnOnce(Bounds<Pixels>, &mut ElementContext) -> T,
 9    paint: impl 'static + FnOnce(Bounds<Pixels>, T, &mut ElementContext),
10) -> Canvas<T> {
11    Canvas {
12        after_layout: Some(Box::new(after_layout)),
13        paint: Some(Box::new(paint)),
14        style: StyleRefinement::default(),
15    }
16}
17
18/// A canvas element, meant for accessing the low level paint API without defining a whole
19/// custom element
20pub struct Canvas<T> {
21    after_layout: Option<Box<dyn FnOnce(Bounds<Pixels>, &mut ElementContext) -> T>>,
22    paint: Option<Box<dyn FnOnce(Bounds<Pixels>, T, &mut ElementContext)>>,
23    style: StyleRefinement,
24}
25
26impl<T: 'static> IntoElement for Canvas<T> {
27    type Element = Self;
28
29    fn into_element(self) -> Self::Element {
30        self
31    }
32}
33
34impl<T: 'static> Element for Canvas<T> {
35    type BeforeLayout = Style;
36    type AfterLayout = Option<T>;
37
38    fn before_layout(&mut self, cx: &mut ElementContext) -> (crate::LayoutId, Self::BeforeLayout) {
39        let mut style = Style::default();
40        style.refine(&self.style);
41        let layout_id = cx.request_layout(&style, []);
42        (layout_id, style)
43    }
44
45    fn after_layout(
46        &mut self,
47        bounds: Bounds<Pixels>,
48        _before_layout: &mut Style,
49        cx: &mut ElementContext,
50    ) -> Option<T> {
51        Some(self.after_layout.take().unwrap()(bounds, cx))
52    }
53
54    fn paint(
55        &mut self,
56        bounds: Bounds<Pixels>,
57        style: &mut Style,
58        after_layout: &mut Self::AfterLayout,
59        cx: &mut ElementContext,
60    ) {
61        let after_layout = after_layout.take().unwrap();
62        style.paint(bounds, cx, |cx| {
63            (self.paint.take().unwrap())(bounds, after_layout, cx)
64        });
65    }
66}
67
68impl<T> Styled for Canvas<T> {
69    fn style(&mut self) -> &mut crate::StyleRefinement {
70        &mut self.style
71    }
72}