Canvas Pixel Manipulation

JavaScript performance comparison

Revision 78 of this test case created

Info

Tests two different methods of manipulating pixels using the canvas.

NOTE: Now takes endianness into account.

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);
   
    // 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;
    }
};

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

Preparation code output

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Testing in unknown unknown
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;

    var value = x * y & 0xff;

    data[index] = value; // red
    data[++index] = value; // green
    data[++index] = value; // blue
    data[++index] = 255; // alpha
  }
}
pending…
32-bit Pixel Manipulation
if (isLittleEndian) {
  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 | value << 16 | value << 8 | value;
    }
  }
} else {
  for (y = 0; y < canvasHeight; ++y) {
    for (x = 0; x < canvasWidth; ++x) {
      value = x * y & 0xff;

      data32[y * canvasWidth + x] = value << 24 | value << 16 | value << 8 | 255;
    }
  }
}

imageData.data.set(buf8);
pending…
32-bit Pixel Manipulation with conditional inside loop
for (var y = 0; y < canvasHeight; ++y) {
  for (var x = 0; x < canvasWidth; ++x) {
    var value = x * y & 0xff;

    if (isLittleEndian) {
      data32[y * canvasWidth + x] = 255 << 24 | value << 16 | value << 8 | value;
    } else {
      data32[y * canvasWidth + x] = value << 24 | value << 16 | value << 8 | 255;
    }
  }
}
pending…

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