On 11/13/10 12:20 PM, Evgeny Burzak wrote:
But , the test results looks similar for all vendors! On average the difference in processing speed is about 2-3 times (five times in Firefox 4).
> This is due to the fact that loops take less time (width x
height * 4 vs. width x height) and arrays with less elements take less memory. Though I realize that main idea for data structure was simplicity, but in this case it seems simplicity is evil, not good.
At least Gecko and Webkit implement canvas imagedata as something more like a WebGL typed array, not a JS array. So in particular, the memory usage is the same or better as for your "compact" array version (in the case of Gecko actually 2x better, since your "compact" array uses 8 bytes per color, while the native imagedata uses 4 bytes per color). Yes that gives a significant speedup due to less memory traffic and better cache locality.
But this is only a problem for emulating canvas, no? And only in UAs that don't support typed arrays, say. That all seems like a transitory problem.
For what it's worth, I just tried modifying your testcase to include a test of Uint8ClampedArray, which is what Gecko uses for canvas imagedata under the hood; the test looks just like your "canvas data" test except for the different array type in the new() call. That test ends up about 20% faster than your "packed" test...
-Boris
