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lvglwasm.js
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lvglwasm.js
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// Render LVGL in WebAssembly, compiled with Zig Compiler. Based on...
// https://github.com/daneelsan/minimal-zig-wasm-canvas/blob/master/script.js
// https://github.com/daneelsan/zig-wasm-logger/blob/master/script.js
// Log WebAssembly Messages from Zig to JavaScript Console
// https://github.com/daneelsan/zig-wasm-logger/blob/master/script.js
const text_decoder = new TextDecoder();
let console_log_buffer = "";
// WebAssembly Helper Functions
const wasm = {
// WebAssembly Instance
instance: undefined,
// Init the WebAssembly Instance
init: function (obj) {
this.instance = obj.instance;
},
// Fetch the Zig String from a WebAssembly Pointer
getString: function (ptr, len) {
const memory = this.instance.exports.memory;
return text_decoder.decode(
new Uint8Array(memory.buffer, ptr, len)
);
},
};
// Export JavaScript Functions to Zig
const importObject = {
// JavaScript Functions exported to Zig
env: {
// Render the LVGL Canvas from Zig to HTML
// https://github.com/daneelsan/minimal-zig-wasm-canvas/blob/master/script.js
render: function() { // TODO: Add width and height
// Get the WebAssembly Pointer to the LVGL Canvas Buffer
console.log("render: start");
const bufferOffset = wasm.instance.exports.getCanvasBuffer();
console.log({ bufferOffset });
// Load the WebAssembly Pointer into a JavaScript Image Data
const memory = wasm.instance.exports.memory;
const ptr = bufferOffset;
const len = (canvas.width * canvas.height) * 4;
const imageDataArray = new Uint8Array(memory.buffer, ptr, len)
imageData.data.set(imageDataArray);
// Render the Image Data to the HTML Canvas
context.clearRect(0, 0, canvas.width, canvas.height);
context.putImageData(imageData, 0, 0);
console.log("render: end");
},
// Write to JavaScript Console from Zig
// https://github.com/daneelsan/zig-wasm-logger/blob/master/script.js
jsConsoleLogWrite: function(ptr, len) {
console_log_buffer += wasm.getString(ptr, len);
},
// Flush JavaScript Console from Zig
// https://github.com/daneelsan/zig-wasm-logger/blob/master/script.js
jsConsoleLogFlush: function() {
console.log(console_log_buffer);
console_log_buffer = "";
},
}
};
// Get the HTML Canvas Context and Image Data
const canvas = window.document.getElementById("lvgl_canvas");
const context = canvas.getContext("2d");
const imageData = context.createImageData(canvas.width, canvas.height);
context.clearRect(0, 0, canvas.width, canvas.height);
// Main Function
function main() {
console.log("main: start");
// Render Loop
const loop = function() {
console.log("loop: start");
// Render the LVGL Widgets in Zig
wasm.instance.exports.lv_demo_widgets();
// loop to next frame. Disabled for now because it slows down the browser.
// TODO: window.requestAnimationFrame(loop);
console.log("loop: end");
};
loop();
console.log("main: end");
};
// Load the WebAssembly Module and start the Main Function
async function bootstrap() {
// Load the WebAssembly Module
// https://developer.mozilla.org/en-US/docs/WebAssembly/JavaScript_interface/instantiateStreaming
const result = await WebAssembly.instantiateStreaming(
fetch("lvglwasm.wasm"),
importObject
);
// Store references to WebAssembly Functions and Memory exported by Zig
wasm.init(result);
// Start the Main Function
main();
}
// Start the loading of WebAssembly Module
bootstrap();