Struct CanvasWidget 

pub struct CanvasWidget { /* private fields */ }

Declarative custom painting over the [PaintScene] trait object — a chart, a node-and-edge graph, a game board — without hand-rolling a View/ Widget pair. canvas takes a paint closure that runs in local space (the widget’s own top-left is always (0, 0), and painting past its own size is clipped, never a bug to chase) — flat-re-exported from frust-widgets so app code never names that crate directly. See CanvasView’s own doc for the full builder contract (.size/.expand sizing, .on_hit-gated .on_tap/.on_pointer, and .repaint_key for paint-only dirtying driven by data outside the ordinary View diff).

use frust::authoring::{PaintCtx, PaintScene};
use frust::{Component, View, canvas};
use kurbo::{Point, Size};
use peniko::Color;

#[derive(Default)]
struct Clock;

impl Component for Clock {
    type State = u32;

    fn init(&self) -> Self::State {
        0
    }

    fn build(&self, state: &mut Self::State) -> impl View<Self::State> {
        Self::face(*state)
    }
}

impl Clock {
    fn face(ticks: u32) -> impl View<u32> {
        canvas(move |scene: &mut dyn PaintScene, size: Size, _ctx: &PaintCtx| {
            scene.fill_rect(Point::ZERO, size, Color::from_rgb8(0x10, 0x10, 0x10));
        })
        .expand()
        .repaint_key(ticks)
    }
}

frust::app!(Clock);

The retained widget for a CanvasView. See the module docs.

Trait Implementations

impl Widget for CanvasWidget

fn layout(&mut self, _ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

Choose a size within bc and return it. Under a render root the call may be skipped (see ChildPod::layout_child), so the result must depend only on bc, the context’s globals and state changed through a pod-dirtying channel: a LAYOUT rebuild, request_layout, an unpaced frame request, or a handled / redraw-requesting event.

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

Emit draw commands into scene. Paint may advance animation state; it must then call PaintCtx::request_frame until the animation rests.

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

Handle an input event and report whether it was consumed; defaults to EventResult::Ignored. Containers forward via ChildPod::event_child.

fn semantics(&self, _ctx: &mut SemanticsCtx)

Contribute accessibility node(s) after layout; defaults to none. A container forwards via ChildPod::semantics_child.

fn type_name(&self) -> &'static str

This widget’s concrete type name, for diagnostics only (docs/LIMITATIONS.md focus-wrapper-erasure-swap-blind); override only in a transparent wrapper.

fn visit_children(&self, _visitor: &mut dyn FnMut(&ChildPod))

Visit this widget’s owned ChildPods in paint order, for read-only tooling; defaults to none and must not mutate pass state.

fn is_focusable(&self) -> bool

Whether keyboard traversal (Tab / Shift+Tab at the root) may stop on this widget’s pod.

fn visit_focus_children(&self, visitor: &mut dyn FnMut(&ChildPod))

Visit the children traversal may enter, in focus order; defaults to Widget::visit_children. A container showing only some children narrows it.

fn as_sliver(&mut self) -> Option<&mut (dyn SliverWidget + 'static)>

This widget as a sliver (crate::sliver), if it speaks that protocol. Defaults to None; transparent wrappers forward it.