CanvasKit - Skia + WebAssembly
==============================
Skia now offers a WebAssembly build for easy deployment of our graphics APIs on
the web.
CanvasKit provides a playground for testing new Canvas and SVG platform APIs,
enabling fast-paced development on the web platform.
It can also be used as a deployment mechanism for custom web apps requiring
cutting-edge features, like Skia's [Lottie
animation](https://skia.org/user/modules/skottie) support.
Features
--------
- WebGL context encapsulated as an SkSurface, allowing for direct drawing to
an HTML canvas
- Core set of Skia canvas/paint/path/text APIs available, see bindings
- Draws to a hardware-accelerated backend
- Security tested with Skia's fuzzers
Samples
-------
<style>
#demo canvas {
border: 1px dashed #AAA;
margin: 2px;
}
#patheffect, #ink {
width: 400px;
height: 400px;
}
#sk_legos, #sk_drinks, #sk_party, #sk_onboarding {
width: 300px;
height: 300px;
}
figure {
display: inline-block;
margin: 0;
}
figcaption > a {
margin: 2px 10px;
}
</style>
<div id=demo>
<h3>An Interactive Path</h3>
<figure>
<canvas id=patheffect width=400 height=400></canvas>
<figcaption>
<a href="https://jsfiddle.skia.org/canvaskit/28004d8841e7e497013263598241a3c1edc21dc1cf87a679abba307f39fa5fe6"
target=_blank rel=noopener>
Star JSFiddle</a>
</figcaption>
</figure>
<figure>
<canvas id=ink width=400 height=400></canvas>
<figcaption>
<a href="https://jsfiddle.skia.org/canvaskit/43475699d6d7d3d7dad1004c29f84015752a6a6dee2bb90f2e891b53e31d45cc"
target=_blank rel=noopener>
Ink JSFiddle</a>
</figcaption>
</figure>
<h3>Skottie (click for fiddles)</h3>
<a href="https://jsfiddle.skia.org/canvaskit/092690b273b41076d2f00f0d43d004893d6bb9992c387c0385efa8e6f6bc83d7"
target=_blank rel=noopener>
<canvas id=sk_legos width=300 height=300></canvas>
</a>
<a href="https://jsfiddle.skia.org/canvaskit/e7ac983d9859f89aff1b6d385190919202c2eb53d028a79992892cacceffd209"
target=_blank rel=noopener>
<canvas id=sk_drinks width=500 height=500></canvas>
</a>
<a href="https://jsfiddle.skia.org/canvaskit/0e06547181759731e7369d3e3613222a0826692f48c41b16504ed68d671583e1"
target=_blank rel=noopener>
<canvas id=sk_party width=500 height=500></canvas>
</a>
<a href="https://jsfiddle.skia.org/canvaskit/be3fc1c5c351e7f43cc2840033f80b44feb3475925264808f321bb9e2a21174a"
target=_blank rel=noopener>
<canvas id=sk_onboarding width=500 height=500></canvas>
</a>
</div>
<script type="text/javascript" charset="utf-8">
(function() {
// Tries to load the WASM version if supported, shows error otherwise
let s = document.createElement('script');
var locate_file = '';
if (window.WebAssembly && typeof window.WebAssembly.compile === 'function') {
console.log('WebAssembly is supported!');
locate_file = 'https://unpkg.com/canvaskit-wasm@0.3.0/bin/';
} else {
console.log('WebAssembly is not supported (yet) on this browser.');
document.getElementById('demo').innerHTML = "<div>WASM not supported by your browser. Try a recent version of Chrome, Firefox, Edge, or Safari.</div>";
return;
}
s.src = locate_file + 'canvaskit.js';
s.onload = () => {
var CanvasKit = null;
var legoJSON = null;
var drinksJSON = null;
var confettiJSON = null;
var onboardingJSON = null;
var fullBounds = {fLeft: 0, fTop: 0, fRight: 500, fBottom: 500};
CanvasKitInit({
locateFile: (file) => locate_file + file,
}).then((CK) => {
CanvasKit = CK;
DrawingExample(CanvasKit);
InkExample(CanvasKit);
// Set bounds to fix the 4:3 resolution of the legos
SkottieExample(CanvasKit, 'sk_legos', legoJSON, {fLeft: -50, fTop: 0, fRight: 350, fBottom: 300});
// Re-size to fit
SkottieExample(CanvasKit, 'sk_drinks', drinksJSON, fullBounds);
SkottieExample(CanvasKit, 'sk_party', confettiJSON, fullBounds);
SkottieExample(CanvasKit, 'sk_onboarding', onboardingJSON, fullBounds);
});
fetch('https://storage.googleapis.com/skia-cdn/misc/lego_loader.json').then((resp) => {
resp.text().then((str) => {
legoJSON = str;
SkottieExample(CanvasKit, 'sk_legos', legoJSON, {fLeft: -50, fTop: 0, fRight: 350, fBottom: 300});
});
});
fetch('https://storage.googleapis.com/skia-cdn/misc/drinks.json').then((resp) => {
resp.text().then((str) => {
drinksJSON = str;
SkottieExample(CanvasKit, 'sk_drinks', drinksJSON, fullBounds);
});
});
fetch('https://storage.googleapis.com/skia-cdn/misc/confetti.json').then((resp) => {
resp.text().then((str) => {
confettiJSON = str;
SkottieExample(CanvasKit, 'sk_party', confettiJSON, fullBounds);
});
});
fetch('https://storage.googleapis.com/skia-cdn/misc/onboarding.json').then((resp) => {
resp.text().then((str) => {
onboardingJSON = str;
SkottieExample(CanvasKit, 'sk_onboarding', onboardingJSON, fullBounds);
});
});
function preventScrolling(canvas) {
canvas.addEventListener('touchmove', (e) => {
// Prevents touch events in the canvas from scrolling the canvas.
e.preventDefault();
e.stopPropagation();
});
}
function DrawingExample(CanvasKit) {
const surface = CanvasKit.MakeCanvasSurface('patheffect');
if (!surface) {
console.log('Could not make surface');
}
const context = CanvasKit.currentContext();
const canvas = surface.getCanvas();
const paint = new CanvasKit.SkPaint();
const textPaint = new CanvasKit.SkPaint();
textPaint.setColor(CanvasKit.Color(40, 0, 0, 1.0));
textPaint.setTextSize(30);
textPaint.setAntiAlias(true);
let i = 0;
let X = 200;
let Y = 200;
function drawFrame() {
const path = starPath(CanvasKit, X, Y);
CanvasKit.setCurrentContext(context);
const dpe = CanvasKit.MakeSkDashPathEffect([15, 5, 5, 10], i/5);
i++;
paint.setPathEffect(dpe);
paint.setStyle(CanvasKit.PaintStyle.Stroke);
paint.setStrokeWidth(5.0 + -3 * Math.cos(i/30));
paint.setAntiAlias(true);
paint.setColor(CanvasKit.Color(66, 129, 164, 1.0));
canvas.clear(CanvasKit.Color(255, 255, 255, 1.0));
canvas.drawPath(path, paint);
canvas.drawText('Try Clicking!', 10, 380, textPaint);
canvas.flush();
dpe.delete();
path.delete();
window.requestAnimationFrame(drawFrame);
}
window.requestAnimationFrame(drawFrame);
// Make animation interactive
let interact = (e) => {
if (!e.buttons) {
return;
}
X = e.offsetX;
Y = e.offsetY;
};
document.getElementById('patheffect').addEventListener('pointermove', interact);
document.getElementById('patheffect').addEventListener('pointerdown', interact);
preventScrolling(document.getElementById('patheffect'));
// A client would need to delete this if it didn't go on for ever.
//paint.delete();
}
function InkExample(CanvasKit) {
const surface = CanvasKit.MakeCanvasSurface('ink');
if (!surface) {
console.log('Could not make surface');
}
const context = CanvasKit.currentContext();
const canvas = surface.getCanvas();
let paint = new CanvasKit.SkPaint();
paint.setAntiAlias(true);
paint.setColor(CanvasKit.Color(0, 0, 0, 1.0));
paint.setStyle(CanvasKit.PaintStyle.Stroke);
paint.setStrokeWidth(4.0);
// This effect smooths out the drawn lines a bit.
paint.setPathEffect(CanvasKit.MakeSkCornerPathEffect(50));
// Draw I N K
let path = new CanvasKit.SkPath();
path.moveTo(80, 30);
path.lineTo(80, 80);
path.moveTo(100, 80);
path.lineTo(100, 15);
path.lineTo(130, 95);
path.lineTo(130, 30);
path.moveTo(150, 30);
path.lineTo(150, 80);
path.moveTo(170, 30);
path.lineTo(150, 55);
path.lineTo(170, 80);
let paths = [path];
let paints = [paint];
function drawFrame() {
CanvasKit.setCurrentContext(context);
for (let i = 0; i < paints.length && i < paths.length; i++) {
canvas.drawPath(paths[i], paints[i]);
}
canvas.flush();
window.requestAnimationFrame(drawFrame);
}
let hold = false;
let interact = (e) => {
let type = e.type;
if (type === 'lostpointercapture' || type === 'pointerup' || !e.pressure ) {
hold = false;
return;
}
if (hold) {
path.lineTo(e.offsetX, e.offsetY);
} else {
paint = paint.copy();
paint.setColor(CanvasKit.Color(Math.random() * 255, Math.random() * 255, Math.random() * 255, Math.random() + .2));
paints.push(paint);
path = new CanvasKit.SkPath();
paths.push(path);
path.moveTo(e.offsetX, e.offsetY);
}
hold = true;
};
document.getElementById('ink').addEventListener('pointermove', interact);
document.getElementById('ink').addEventListener('pointerdown', interact);
document.getElementById('ink').addEventListener('lostpointercapture', interact);
document.getElementById('ink').addEventListener('pointerup', interact);
preventScrolling(document.getElementById('ink'));
window.requestAnimationFrame(drawFrame);
}
function starPath(CanvasKit, X=128, Y=128, R=116) {
let p = new CanvasKit.SkPath();
p.moveTo(X + R, Y);
for (let i = 1; i < 8; i++) {
let a = 2.6927937 * i;
p.lineTo(X + R * Math.cos(a), Y + R * Math.sin(a));
}
return p;
}
function SkottieExample(CanvasKit, id, jsonStr, bounds) {
if (!CanvasKit || !jsonStr) {
return;
}
const animation = CanvasKit.MakeAnimation(jsonStr);
const duration = animation.duration() * 1000;
const size = animation.size();
let c = document.getElementById(id);
bounds = bounds || {fLeft: 0, fTop: 0, fRight: size.w, fBottom: size.h};
const surface = CanvasKit.MakeCanvasSurface(id);
if (!surface) {
console.log('Could not make surface');
}
const context = CanvasKit.currentContext();
const canvas = surface.getCanvas();
let firstFrame = new Date().getTime();
function drawFrame() {
let now = new Date().getTime();
let seek = ((now - firstFrame) / duration) % 1.0;
CanvasKit.setCurrentContext(context);
animation.seek(seek);
animation.render(canvas, bounds);
canvas.flush();
window.requestAnimationFrame(drawFrame);
}
window.requestAnimationFrame(drawFrame);
//animation.delete();
}
}
document.head.appendChild(s);
})();
</script>
Lottie files courtesy of the lottiefiles.com community:
[Lego Loader](https://www.lottiefiles.com/410-lego-loader),
[I'm thirsty](https://www.lottiefiles.com/77-im-thirsty),
[Confetti](https://www.lottiefiles.com/1370-confetti),
[Onboarding](https://www.lottiefiles.com/1134-onboarding-1)
Test server
-----------
Test your code on our [CanvasKit Fiddle](https://jsfiddle.skia.org/canvaskit)
Download
--------
Get [CanvasKit on NPM](https://www.npmjs.com/package/canvaskit-wasm)