dnass / Svelte Canvas
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svelte-canvas
Reactive canvas rendering with Svelte.
Installation
npm install svelte svelte-canvas
Usage
<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}>
<Layer {render} />
</Canvas>
More examples:
API
Canvas
Canvas is the top-level element. It's a Svelte wrapper around an HTML <canvas> element.
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 |
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 |
Events
All DOM events on the <canvas> element are forwarded to the Canvas component, so handling an event is as simple as <Canvas on:click={handleClick}>.
Layer
Layer is a layer to be rendered onto the canvas. It takes three props: setup, render, and priority. setup and render both require 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 higher priority layers appear on top of the scene.
t
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.