Reactive canvas rendering with Svelte.
npm install svelte svelte-canvas
<script>
import { Canvas, Layer, t } from "svelte-canvas";
$: render = ({ context, width, height }) => {
context.fillStyle = `hsl(${$t / 40}, 100%, 50%)`;
context.beginPath();
context.arc(($t / 4) % width, ($t / 4) % height, 100, 0, Math.PI * 2);
context.fill();
};
</script>
<Canvas width={640} height={640} autoclear>
<Layer {render} />
</Canvas>
Canvas is the top-level element. It's a Svelte wrapper around an HTML <canvas> element. It takes these parameters:
| parameter | default | description |
|---|---|---|
width |
640 | Canvas width |
height |
640 | Canvas height |
pixelRatio |
window.devicePixelRatio |
Canvas pixel ratio |
style |
null |
A CSS style string which will be applied to the canvas element |
autoclear |
true |
If true, will use context.clearRect to clear the canvas at the start of each render cycle |
And exposes these methods:
| method | description |
|---|---|
getCanvas |
Returns a reference to the canvas DOM element |
getContext |
Returns the canvas's 2D rendering context |
redraw |
Forces a re-render of the canvas |
Layer is a layer to be rendered onto the canvas. It takes three props. setup and render both take functions with one argument that receives an object with the properties context, width, and height. context is the 2D rendering context of the parent canvas. width and height are the canvas's dimensions.
setup is optional and is called once at initialization. render is called every time the canvas redraws.
Declaring your render function reactively lets svelte-canvas re-render anytime the values that the function depends on change.
The third prop, priority, takes a positive integer which determines the layer's render priority. Layers with a priority will be rendered after other layers, in ascending order of priority, so that they appear on top of the scene.
t is a readable store that provides the time in milliseconds since initialization. Subscribing to t within your render function lets you easily create animations.