On Friday 11 February 2011 12:30:33 Soeren Sandmann wrote: > If I had a time machine, I would go back and make - among others - > these two changes to Render:
[...] > (2) The RGB channels of Alpha-only images would be considered to be > the same as the alpha channel, and not 0 as they are now. For > example, a 0xb9 pixel in an a8 image would be considered > equivalent to 0xb9b9b9b9 and not to 0xb9000000. That is, they > would be considered a translucent white rather than a translucent > black. > > These two changes together would have the effect that (a) the equation > would be much easier to understand visually (composite src and dst, > then clip to the mask and write back), and (b) component alpha would > become completely regular with no need for the "component_alpha" bit > in pictures. Regarding the (b) part, probably as a side effect of current implementation, right now it is possible to do some operations with images having non-premultiplied alpha: src_img = pixman_image_create_bits ( PIXMAN_x8b8g8r8, width, height, src, stride); msk_img = pixman_image_create_bits ( PIXMAN_a8b8g8r8, width, height, src, stride); dst_img = pixman_image_create_bits ( PIXMAN_a8r8g8b8, width, height, dst, stride); pixman_image_composite (PIXMAN_OP_SRC, src_img, msk_img, dst_img, 0, 0, 0, 0, 0, 0, width, height); We only need to wrap the same a8r8g8b8 buffer into x8r8g8b8 and a8r8g8b8 pixman image, and use the latter as a mask for pixman_image_composite() calls. Any operations which don't need mask themselves can use this trick. By also specifying negative stride, this is useful for example when dealing with the data returned by glReadPixels(). So I find it convenient that we are also allowed to work with masks which are basically interpreted as having a8x24 format. -- Best regards, Siarhei Siamashka _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman