Sketches

A sketch is a struct that owns its own animation state plus a draw() method called every frame. Implement the Sketch trait on your struct, then mount it into a Div tree with sketch(key, impl).

The Sketch trait

#![allow(unused)]
fn main() {
use blinc_canvas_kit::prelude::*;
use blinc_core::layer::Color;

struct Bouncer {
    x: f32,
    vx: f32,
}

impl Sketch for Bouncer {
    fn draw(&mut self, ctx: &mut SketchContext<'_>, _t: f32, dt: f32) {
        self.x += self.vx * dt;
        if self.x < 0.0 || self.x + 40.0 > ctx.width {
            self.vx = -self.vx;
        }

        let mut p = ctx.painter();
        p.fill(Color::WHITE).no_stroke();
        p.rect(self.x, 100.0, 40.0, 40.0);
    }
}
}

The trait has two methods:

Sketches must be Send + 'static — their state lives behind an Arc<Mutex<...>> in Blinc’s persistent state bag.

Mounting: sketch()

#![allow(unused)]
fn main() {
fn build_ui() -> impl ElementBuilder {
    div()
        .w(600)
        .h(400)
        .child(sketch("bouncer", Bouncer { x: 0.0, vx: 200.0 }))
}
}

The key identifies the sketch for state persistence. Every sketch("bouncer", ...) with the same key reuses the same persisted state across rebuilds — hot reload, layout changes, route transitions all preserve counters, particle systems, and elapsed time. Pick unique keys per instance.

Wrap the returned Div in a sized container (.w(...), .h(...), .aspect_ratio(...), or a flex parent) to control bounds. The sketch fills its parent.

SketchContext

The per-frame context exposes the canvas size, a frame counter, and three drawing entry points:

#![allow(unused)]
fn main() {
pub struct SketchContext<'a> {
    pub width: f32,        // Canvas width in layout units
    pub height: f32,       // Canvas height in layout units
    pub frame_count: u64,  // Frames drawn since setup()
    // ...
}
}

painter() and draw_context() each mutably borrow the underlying DrawContext — drop one before calling the other.

Painter2D

The painter holds a current fill, stroke, and transform stack so you don’t repeat those arguments on every primitive call.

Fill & stroke state

#![allow(unused)]
fn main() {
let mut p = ctx.painter();

p.fill(Color::RED).no_stroke();     // Red fill, no outline
p.rect(10.0, 10.0, 100.0, 50.0);

p.stroke(Color::BLACK, 2.0);         // Add a 2px black stroke
p.circle(200.0, 200.0, 40.0);

p.no_fill().stroke(Color::BLUE, 1.0);
p.line(0.0, 0.0, 300.0, 300.0);
}

Transform stack

push() / pop() bracket grouped transforms. A single pop() undoes every transform pushed since its matching push():

#![allow(unused)]
fn main() {
p.push();
p.translate(100.0, 100.0);
p.rotate(std::f32::consts::FRAC_PI_4);
p.scale(2.0, 2.0);
p.rect(-10.0, -10.0, 20.0, 20.0);   // All three transforms active
p.pop();                              // All three transforms undone
}

Calling translate / rotate / scale without a surrounding push() still pushes onto the underlying stack, but pop() can’t undo them. Always use the bracketed pattern for scoped transforms.

When Painter2D’s operations aren’t enough — gradients, glass, clips, 3D, images, text — drop the painter and reach for ctx.draw_context() directly. See Canvas Drawing for the full DrawContext surface.