1use refineable::Refineable as _;
 2
 3use crate::{
 4    Bounds, Element, ElementId, GlobalElementId, IntoElement, Pixels, Style, StyleRefinement,
 5    Styled, WindowContext,
 6};
 7
 8/// Construct a canvas element with the given paint callback.
 9/// Useful for adding short term custom drawing to a view.
10pub fn canvas<T>(
11    prepaint: impl 'static + FnOnce(Bounds<Pixels>, &mut WindowContext) -> T,
12    paint: impl 'static + FnOnce(Bounds<Pixels>, T, &mut WindowContext),
13) -> Canvas<T> {
14    Canvas {
15        prepaint: Some(Box::new(prepaint)),
16        paint: Some(Box::new(paint)),
17        style: StyleRefinement::default(),
18    }
19}
20
21/// A canvas element, meant for accessing the low level paint API without defining a whole
22/// custom element
23pub struct Canvas<T> {
24    prepaint: Option<Box<dyn FnOnce(Bounds<Pixels>, &mut WindowContext) -> T>>,
25    paint: Option<Box<dyn FnOnce(Bounds<Pixels>, T, &mut WindowContext)>>,
26    style: StyleRefinement,
27}
28
29impl<T: 'static> IntoElement for Canvas<T> {
30    type Element = Self;
31
32    fn into_element(self) -> Self::Element {
33        self
34    }
35}
36
37impl<T: 'static> Element for Canvas<T> {
38    type RequestLayoutState = Style;
39    type PrepaintState = Option<T>;
40
41    fn id(&self) -> Option<ElementId> {
42        None
43    }
44
45    fn request_layout(
46        &mut self,
47        _id: Option<&GlobalElementId>,
48        cx: &mut WindowContext,
49    ) -> (crate::LayoutId, Self::RequestLayoutState) {
50        let mut style = Style::default();
51        style.refine(&self.style);
52        let layout_id = cx.request_layout(style.clone(), []);
53        (layout_id, style)
54    }
55
56    fn prepaint(
57        &mut self,
58        _id: Option<&GlobalElementId>,
59        bounds: Bounds<Pixels>,
60        _request_layout: &mut Style,
61        cx: &mut WindowContext,
62    ) -> Option<T> {
63        Some(self.prepaint.take().unwrap()(bounds, cx))
64    }
65
66    fn paint(
67        &mut self,
68        _id: Option<&GlobalElementId>,
69        bounds: Bounds<Pixels>,
70        style: &mut Style,
71        prepaint: &mut Self::PrepaintState,
72        cx: &mut WindowContext,
73    ) {
74        let prepaint = prepaint.take().unwrap();
75        style.paint(bounds, cx, |cx| {
76            (self.paint.take().unwrap())(bounds, prepaint, cx)
77        });
78    }
79}
80
81impl<T> Styled for Canvas<T> {
82    fn style(&mut self) -> &mut crate::StyleRefinement {
83        &mut self.style
84    }
85}