discourse/public/javascripts/media-optimization-worker.js

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function resizeWithAspect(
input_width,
input_height,
target_width,
target_height
) {
if (!target_width && !target_height) {
throw Error("Need to specify at least width or height when resizing");
}
if (target_width && target_height) {
return { width: target_width, height: target_height };
}
if (!target_width) {
return {
width: Math.round((input_width / input_height) * target_height),
height: target_height,
};
}
return {
width: target_width,
height: Math.round((input_height / input_width) * target_width),
};
}
function logIfDebug(...messages) {
if (DedicatedWorkerGlobalScope.debugMode) {
// eslint-disable-next-line no-console
console.log(...messages);
}
}
async function optimize(imageData, fileName, width, height, settings) {
const mozJpegDefaultOptions = {
quality: settings.encode_quality,
baseline: false,
arithmetic: false,
progressive: true,
optimize_coding: true,
smoothing: 0,
color_space: 3 /*YCbCr*/,
quant_table: 3,
trellis_multipass: false,
trellis_opt_zero: false,
trellis_opt_table: false,
trellis_loops: 1,
auto_subsample: true,
chroma_subsample: 2,
separate_chroma_quality: false,
chroma_quality: 75,
};
const initialSize = imageData.byteLength;
logIfDebug(`Worker received imageData: ${initialSize}`);
let maybeResized;
// resize
if (width > settings.resize_threshold) {
try {
const target_dimensions = resizeWithAspect(
width,
height,
settings.resize_target
);
const resizeResult = self.codecs.resize(
new Uint8ClampedArray(imageData),
width, //in
height, //in
target_dimensions.width, //out
target_dimensions.height, //out
3, // 3 is lanczos
settings.resize_pre_multiply,
settings.resize_linear_rgb
);
if (resizeResult[3] !== 255) {
throw "Image corrupted during resize. Falling back to the original for encode";
}
maybeResized = new ImageData(
resizeResult,
target_dimensions.width,
target_dimensions.height
).data;
width = target_dimensions.width;
height = target_dimensions.height;
logIfDebug(`Worker post resizing file: ${maybeResized.byteLength}`);
} catch (error) {
console.error(`Resize failed: ${error}`);
maybeResized = imageData;
}
} else {
logIfDebug(`Skipped resize: ${width} < ${settings.resize_threshold}`);
maybeResized = imageData;
}
// mozJPEG re-encode
const result = self.codecs.mozjpeg_enc.encode(
maybeResized,
width,
height,
mozJpegDefaultOptions
);
const finalSize = result.byteLength;
logIfDebug(`Worker post reencode file: ${finalSize}`);
logIfDebug(`Reduction: ${(initialSize / finalSize).toFixed(1)}x speedup`);
if (finalSize < 20000) {
throw "Final size suspiciously small, discarding optimizations";
}
let transferrable = Uint8Array.from(result).buffer; // decoded was allocated inside WASM so it **cannot** be transferred to another context, need to copy by value
return transferrable;
}
onmessage = async function (e) {
switch (e.data.type) {
case "compress":
try {
DedicatedWorkerGlobalScope.debugMode = e.data.settings.debug_mode;
let optimized = await optimize(
e.data.file,
e.data.fileName,
e.data.width,
e.data.height,
e.data.settings
);
postMessage(
{
type: "file",
file: optimized,
fileName: e.data.fileName,
fileId: e.data.fileId,
},
[optimized]
);
} catch (error) {
console.error(error);
postMessage({
type: "error",
file: e.data.file,
fileName: e.data.fileName,
fileId: e.data.fileId,
});
}
break;
case "install":
try {
await loadLibs(e.data.settings);
postMessage({ type: "installed" });
} catch (error) {
postMessage({ type: "installFailed", errorMessage: error.message });
}
break;
default:
logIfDebug(`Sorry, we are out of ${e}.`);
}
};
async function loadLibs(settings) {
if (self.codecs) return;
importScripts(settings.mozjpeg_script);
importScripts(settings.resize_script);
let encoderModuleOverrides = {
locateFile: function (path, prefix) {
// if it's a mem init file, use a custom dir
if (path.endsWith(".wasm")) return settings.mozjpeg_wasm;
// otherwise, use the default, the prefix (JS file's dir) + the path
return prefix + path;
},
onRuntimeInitialized: function () {
return this;
},
};
const mozjpeg_enc_module = await mozjpeg_enc(encoderModuleOverrides);
const { resize } = wasm_bindgen;
await wasm_bindgen(settings.resize_wasm);
self.codecs = { mozjpeg_enc: mozjpeg_enc_module, resize: resize };
}