Canvas Pixel Manipulation

JavaScript performance comparison

Revision 85 of this test case created

Info

Tests manipulating pixels in canvas with and without y*canvasWidth

Preparation code

<canvas id="canvas" height="448" width="768">
</canvas>
<script>
Benchmark.prototype.setup = function() {
    var canvas = document.getElementById('canvas');
    var canvasWidth = canvas.width;
    var canvasHeight = canvas.height;
    var ctx = canvas.getContext('2d');
    var imageData = ctx.getImageData(0, 0, canvasWidth, canvasHeight);
   
    var data = imageData.data;
   
    var buf = new ArrayBuffer(imageData.data.length);
    var buf8 = new Uint8Array(buf);
    var data32 = new Uint32Array(buf);
};

Benchmark.prototype.teardown = function() {
    ctx.putImageData(imageData, 0, 0);
};
</script>

Preparation code output

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Testing in unknown unknown
Test Ops/sec
32-bit Pixel Manipulation
for (var y = 0; y < canvasHeight; ++y) {
  for (var x = 0; x < canvasWidth; ++x) {
    var value = x * y & 0xff;

    data32[y * canvasWidth + x] = (255 << 24) | // alpha
    (value << 16) | // blue
    (value << 8) | // green
    value; // red
  }
}

imageData.data.set(buf8);
ctx.putImageData(imageData, 0, 0);
pending…
32-bit Pixel Manipulation w/index lookup
var index = 0;
for (var y = 0; y < canvasHeight; ++y) {
  for (var x = 0; x < canvasWidth; ++x) {
    var value = x * y & 0xff;

    data32[index++] = (255 << 24) | // alpha
    (value << 16) | // blue
    (y << 8) | // green
    x; // red
  }
}

imageData.data.set(buf8);
ctx.putImageData(imageData, 0, 0);
pending…
var ch = canvasHeight;
var cw = canvasWidth;
var index = 0;
for (var y = 1; y < ch; ++y) {
  for (var x = 1; x < cw; ++x) {
    var value = x * y & 0xff;

    data32[index++] = (255 << 24) | // alpha
    (value << 16) | // blue
    (value << 8) | // green
    value; // red
  }
}

imageData.data.set(buf8);
ctx.putImageData(imageData, 0, 0);
pending…

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