生成wasm
V编译器支持wasm后端，将V源代码编译生成wasm代码。
安装依赖
当第一次运行 v -b wasm xxx.v时，编译器会提示，缺少外部依赖库binaryen，需要先执行脚本下载对应平台的预编译版本。安装脚本会下载并解压到path_to_v/thirdparty/binaryen目录中。
path_to_v/cmd/tools/install_binaryen.vsh也可以直接下载binaryen源代码，自行编译，编译步骤如下：
git clone https://github.com/WebAssembly/binaryen.git
git submodule init
git submodule update
cmake . && make #需要提前安装好cmake
make install编译目标系统
v -b wasm -os wasi #编译为符合wasi标准的代码，不特别指定-os选项值，默认是wasi
v -b wasm -os browser #编译为浏览器环境的代码示例代码：
mandelbrot.v
fn JS.canvas_x() int
fn JS.canvas_y() int
fn JS.setpixel(x int, y int, c f64)
// `main` must be public!
pub fn main() {
max_x := JS.canvas_x()
max_y := JS.canvas_y()
println('starting main.main!')
mut y := 0
for y < max_y {
y += 1
mut x := 0
for x < max_x {
x += 1
e := (f64(y) / 50) - 1.5
f := (f64(x) / 50) - 1.0
mut a := 0.0
mut b := 0.0
mut i := 0.0
mut j := 0.0
mut c := 0.0
for i * i + j * j < 4 && c < 255 {
i = a * a - b * b + e
j = 2 * a * b + f
a = i
b = j
c += 1
}
JS.setpixel(x, y, c)
}
}
panic('reached the end!')
}mandelbrot.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>V Mandelbrot WebAssembly Example</title>
</head>
<body>
<canvas id="canvas" width="200" height="200" style="width:100%;height:100%;image-rendering: crisp-edges;"></canvas>
<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var memory;
function get_string(ptr, len) {
const buf = new Uint8Array(memory.buffer, ptr, len);
const str = new TextDecoder("utf8").decode(buf);
return str
}
const env = {
canvas_x: () => canvas.width,
canvas_y: () => canvas.height,
setpixel: (x, y, c) => {
ctx.fillStyle = "rgba(1,1,1,"+(c/255)+")";
ctx.fillRect(x, y, 1, 1);
},
__writeln: (ptr, len) => {
console.log(get_string(ptr, len))
},
__panic_abort: (ptr, len) => {
throw get_string(ptr, len);
}
}
WebAssembly.instantiateStreaming(fetch("mandelbrot.wasm"), {env: env}).then((res) => {
memory = res.instance.exports['memory'];
console.time('main.main')
res.instance.exports['main.main']()
console.timeEnd('main.main')
});
</script>
</body>
</html>编译生成wasm文件：
v -b wasm -os browser mandelbrot.v就可以打开mandelbrot.html运行wasm文件。
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