Run results for: OffscreenCanvas vs HTMLCanvasElement drawImage() (w/ Transferables) (version: 1)

1. drawImage on the main thread 2. drawImage on a worker thread (passing messages as Strings) 3. drawImage on a worker thread (passing messages as ArrayBuffer(100)) 4. drawImage on a worker thread (Transferable messages as ArrayBuffer(100))

Run details:

User agent: Mozilla/5.0 (Linux; Android 8.1.0; A502DL) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.136 Mobile Safari/537.36

Browser: Chrome Mobile 74

Operating system: Android 8.1.0

Device Platform: Mobile

Date tested: 5 years ago

Test name	Executions per second
drawImage on the main thread	15247.7 Ops/sec
drawImage on a worker thread (passing messages as Strings)	45978.2 Ops/sec
drawImage on a worker thread (passing messages as ArrayBuffer(100))	40865.5 Ops/sec
drawImage on a worker thread (Transferable messages as ArrayBuffer(100))	5341.2 Ops/sec

Script Preparation code:


var blob = new Blob([
`
  let bitmap = undefined;
  let canvas = undefined;
  let ctx    = undefined;
  let buffer = undefined;

let postAMessage=self.postMessage;

function render()
{
		ctx.clearRect(0,0,640,480);
		ctx.drawImage(bitmap, 0,0);
		requestAnimationFrame(render);
}

self.onmessage = function(ev) {



  if(ev.data.msg === 'bitmap' && canvas != undefined) {
		bitmap = ev.data.imageB;
		console.log("Received an ImageBitmap next!");
		render();
  }

  if(ev.data.msg === 'init' && bitmap != undefined) {
    canvas = ev.data.canvas;
    ctx = canvas.getContext('2d');
	console.log("Received a canvas next!");
	render();

  }

  if(ev.data.msg === 'bitmap' && canvas == undefined) {
	console.log("Received a bitmap first!");
	
		bitmap = ev.data.imageB;
  }

  if(ev.data.msg === 'init' && bitmap == undefined) {
	console.log("Received a canvas first!");
	
    canvas = ev.data.canvas;
    ctx = canvas.getContext('2d');

  }
  if(ev.data.msg === 'buffer') {
	console.log("Clearing buffer " + ev.data.msgIndex + "from pool");
	buffer = ev.data.buffer;
  	self.postMessage({msg:'buffer',buffer: buffer, msgIndex:ev.data.msgIndex}, [buffer]);
  }
}
`]);

var myWorker = new Worker(window.URL.createObjectURL(blob));
var buff = new ArrayBuffer(100);
var buffers = [];

var poolSize = 30;

//create a pool of buffers
for (let i = 0; i < poolSize; i++)
{
buffers.push(new ArrayBuffer(100));
buffers[i].isUsed = false;
}

var img = new Image();

function handleMessageFromWorker(msg) {
    console.log('the thread used buffer: ' + msg.data.msgIndex);
	if (msg.data.msg == "buffer")
    {
      buffers[parseInt(msg.data.msgIndex)] = msg.data.buffer;
      buffers[parseInt(msg.data.msgIndex)].isUsed = false;
    }
}

myWorker.addEventListener('message', handleMessageFromWorker);

img.src = "https://www.google.com/s2/favicons?domain=www.google.com";

img.decode().then(() => {createImageBitmap(img).then(Ibitmap => { myWorker.postMessage({imageB: Ibitmap, msg:'bitmap'}, [Ibitmap]);  })});

var canvas =  document.createElement("canvas");
var c2 =  document.createElement("canvas");
c2.width = 640;
c2.height = 480;
c2 = c2.transferControlToOffscreen();

canvas.width = 640;
canvas.height = 480;
c2.width = 640;
c2.height = 480;

var ctx = canvas.getContext('2d');

myWorker.postMessage({msg: 'init', canvas: c2}, [c2]);

Tests:

drawImage on the main thread
if (img.width > 0){ ctx.drawImage(img, 0, 0); ctx.clearRect(0,0,640,480); }
drawImage on a worker thread (passing messages as Strings)
if (img.width > 0) myWorker.postMessage("255,0,0");
drawImage on a worker thread (passing messages as ArrayBuffer(100))
if (img.width > 0) myWorker.postMessage(buff);
drawImage on a worker thread (Transferable messages as ArrayBuffer(100))
if (img.width > 0) { let buffersFull = true; for (let i = 0; i < buffers.length; i++) { if (!buffers[i].isUsed) {myWorker.postMessage({msg:'buffer', msgIndex:i, buffer:buffers[i]},[buffers[i]]); buffers[i].isUsed = true; buffersFull = false; i = buffers.length;} }if (buffersFull) console.log("All buffers in the pool are full")}