Canvas Pixel Manipulation

JavaScript performance comparison

Revision 102 of this test case created by

Preparation code

<canvas id="canvas" height="256" width="256"></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 Uint8ClampedArray(buf);
  var data32 = new Uint32Array(buf);
  var view = new DataView(buf);
  
  // Determine whether Uint32 is little- or big-endian.
  data32[1] = 0x0a0b0c0d;
  
  var isLittleEndian = true;
  if (buf[4] === 0x0a && buf[5] === 0x0b && buf[6] === 0x0c &&
    buf[7] === 0x0d) {
    isLittleEndian = false;
  }
  
  
  
  function getPixel(data, x, y) {
    var val = data[y * canvasWidth + x];
    return [(val) & 0xFF, (val >> 8) & 0xFF, (val >> 16) & 0xFF, (val >> 24) & 0xFF];
  }
  
  function setPixel(data, x, y, r, g, b, a) {
    if (isLittleEndian) {
      data[y * canvasWidth + x] =
        (a << 24) | // alpha
      (b << 16) | // blue
      (g << 8) | // green
      r; // red
    } else {
      data[y * canvasWidth + x] =
        (r << 24) | // red
      (g << 16) | // green
      (b << 8) | // blue
      a; // alpha
  
    }
  }
  
  for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
      var index = (y * canvasWidth + x) * 4;
  
      var value = x * y & 0xff;
  
      data[index] = value; // red
      data[++index] = value; // green
      data[++index] = value; // blue
      data[++index] = 255; // alpha
    }
  }

};

Benchmark.prototype.teardown = function() {
  ctx.putImageData(imageData, 0, 0);

};
</script>

Preparation code output

<canvas id="canvas" height="256" width="256"></canvas>

Test runner

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Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
8-bit Pixel Manipulation
for (var y = 0; y < canvasHeight; ++y) {
  for (var x = 0; x < canvasWidth; ++x) {
    var index = (y * canvasWidth + x) * 4;

    data[index] = data[index] / 2; // red
    data[++index] = data[index] / 2; // green
    data[++index] = data[index] / 2; // blue
    data[++index] = 255; // alpha
  }
}
pending…
32-bit Pixel Manipulation
  for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
      var val = data32[y * canvasWidth + x];
      var r = (val) & 0xFF;
      var g = (val >> 8) & 0xFF;
      var b = (val >> 16) & 0xFF;
      var a = (val >> 24) & 0xFF;

      data32[y * canvasWidth + x] =
        (255 << 24) | // alpha
      ((value / 2) << 16) | // blue
      ((value / 2) << 8) | // green
      (value / 2); // red
    }
  }

  imageData.data.set(buf8);
pending…
32-bit Pixel Manipulation with get & setPixel call
  for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
      var index = (y * canvasWidth + x) * 4;

      setPixel(data, x, y, data[index] / 2, data[index + 1] / 2, data[index + 2] / 3, 255);
    }
  }

  imageData.data.set(buf8);
pending…

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