W dniu 11 sierpnia 2010 03:18 użytkownik Soeren Sandmann <[email protected]> napisał: >> 2. Shouldn't we use nearest-neighbor sampling to obtain subpixels? > > That's determined by what filter is being used in the call > bits_fetch_pixel_filtered(). So if you call > > pixman_image_set_filter() > > with FILTER_NEAREST, then the subpixel will be obtained through > nearest-neighbor sampling. If you set it to LINEAR, then it will use > bilinear interpolation.
My point is that maybe the filter should affect the way the pixels are combined, not how the subpixel values are computed. If there are many subpixels averaged together, it doesn't make a lot of sense to use an expensive method of computing them - the cheapest one (nearest-neighbor) might be sufficient. > - As you mention in a comment, it would be faster to compute fractions > and then repeatedly add them. If this creates precision problems, > maybe we need to look into using floating point. What is the policy on floating point use in Pixman right now? It seems to use fixed point almost everywhere, even though this causes rendering artifacts, for example this one: https://bugs.freedesktop.org/show_bug.cgi?id=29470 Maybe floating point / fixed point use should be determined at build time, so architectures with fast FPUs can get high precision while integer-only architectures can trade precision for performance? Regards, Krzysztof _______________________________________________ Pixman mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/pixman
