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Fix for webgl-based canvas sources rendering flipped in 0.40.0 + non-animated optimization #5303

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merged 4 commits into from
Sep 18, 2017
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Fix for webgl-based canvas sources rendering flipped in 0.40.0 + non-animated optimization #5303

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04e9a15
Flip webgl-based canvas pixels before copying them to intermediary bu…
Sep 14, 2017
f53eaad
Use subarray instead of slice for more performant Uint8Array copying
Sep 15, 2017
0be38ed
Don't reread canvas if not animated or resized
Sep 15, 2017
e7a4f1c
Eliminate temporary array for flipping webgl canvases
Sep 18, 2017
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6 changes: 5 additions & 1 deletion src/source/canvas_source.js
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Original file line number Diff line number Diff line change
Expand Up @@ -127,7 +127,11 @@ class CanvasSource extends ImageSource {
gl.readPixels(0, 0, this.width, this.height, gl.RGBA, gl.UNSIGNED_BYTE, data);
if (!this.secondaryContext) this.secondaryContext = window.document.createElement('canvas').getContext('2d');
const imageData = this.secondaryContext.createImageData(this.width, this.height);
imageData.data.set(data);
const flipped = new Uint8Array(this.width * this.height * 4);
for (let i = this.height - 1, j = 0; i >= 0; i--, j++) {
flipped.set(data.slice(i * this.width * 4, (i + 1) * this.width * 4), j * this.width * 4);
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I'd suggest avoiding many slice operations since they create a new array every time. 4 lines setting each of the 4 values of the array will be faster.

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The array looks like its an entire row, not just four values. It might make sense to try data.subarray(begin, end) which is like .slice() except it provides a view into the existing array without copying it.

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Oh, you're right. In that case a secondary inner loop might get also work well.

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Oh cool, did not know about subarray — thanks @ansis @mourner. (I tried the secondary loop in this test as well for good measure: )
image

}
imageData.data.set(flipped);
return imageData;
}
}
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