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index.html
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index.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Zig WASM Canvas demo</title>
<style>
html,
body {
margin: 0;
padding: 0;
background-color: grey;
}
canvas {
width: 400px;
background-color: white;
}
</style>
<script type="module">
import indexWasmUrl from "./index.wasm?url"
const canvas = document.body.querySelector("canvas")
const ctx = canvas.getContext("2d")
const module = await WebAssembly.compileStreaming(fetch(indexWasmUrl))
const decodeString = (pointer, length) => {
const slice = new Uint8Array(
memory.buffer,
pointer,
length
)
return new TextDecoder().decode(slice)
}
const encodeString = (string) => {
const buffer = new TextEncoder().encode(string)
const pointer = allocUint8(buffer.length + 1)
const slice = new Uint8Array(
memory.buffer,
pointer,
buffer.length + 1
)
slice.set(buffer)
slice[buffer.length] = 0
return pointer
}
const {
exports: { memory, _draw, allocUint8, free },
} = await WebAssembly.instantiate(module, {
app: {
_allocPromptName(pointer, length) {
const message = decodeString(pointer, length)
const name = window.prompt(message) ?? "Human"
return encodeString(name)
},
},
env: {
_throwError(pointer, length) {
const message = decodeString(pointer, length)
throw new Error(message)
},
_consoleLog(pointer, length) {
const message = decodeString(pointer, length)
console.log(message)
},
},
ctx: {
save: ctx.save.bind(ctx),
restore: ctx.restore.bind(ctx),
translate(x, y) {
ctx.translate(x, y)
},
scale(x, y) {
ctx.scale(x, y)
},
rotate(angle) {
ctx.rotate(angle)
},
beginPath() {
ctx.beginPath()
},
moveTo(x, y) {
ctx.moveTo(x, y)
},
lineTo(x, y) {
ctx.lineTo(x, y)
},
_font(pointer, length) {
ctx.font = decodeString(pointer, length)
},
_fillStyle(pointer, length) {
ctx.fillStyle = decodeString(pointer, length)
},
_fillText(pointer, length, x, y) {
const text = decodeString(pointer, length)
ctx.fillText(text, x, y)
},
fill() {
ctx.fill()
},
lineWidth(width) {
ctx.lineWidth = width
},
_lineCap(pointer, length) {
ctx.lineCap = decodeString(pointer, length)
},
_strokeStyle(pointer, length) {
ctx.strokeStyle = decodeString(pointer, length)
},
_strokeText(pointer, length, x, y) {
const text = decodeString(pointer, length)
ctx.strokeText(text, x, y)
},
stroke() {
ctx.stroke()
},
},
})
_draw();
</script>
</head>
<body>
<canvas width="800" height="800">Canvas required. Please use Chrome, Firefox, or Safari</canvas>
</body>
</html>