From: Bill Spitzak <spit...@gmail.com> v9: Described arguments and more filter combinations, fixed some errors.
v11: Further correction, in particular replaced "scale" with "size" Signed-off-by: Bill Spitzak <spit...@gmail.com> Acked-by: Oded Gabbay <oded.gab...@redhat.com> --- pixman/pixman-filter.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c index f582187..2bf289a 100644 --- a/pixman/pixman-filter.c +++ b/pixman/pixman-filter.c @@ -350,6 +350,57 @@ filter_width (pixman_kernel_t reconstruct, pixman_kernel_t sample, double size) /* Create the parameter list for a SEPARABLE_CONVOLUTION filter * with the given kernels and size parameters + * + * Returns pointer to the block of numbers + * + * n_values: pointer to integer to store size of the block + * + * size_x/y: amount to stretch the sample filter. The best value to + * use is the derivative of the sample location. This value is + * approximately 1/scale when scaling an image. If size < 1.0 then you + * will get square pixels as an image is enlarged, using 1.0 instead + * will get the more customary "blurry" enlargement. + * + * reconstruct_x/y: filter that is not resized. + * + * sample_x/y: filter that is resized. Result is convolved with reconstruct filter. + * + * subsample_bits_x/y: If positive there are 2^n subpixel positions computed for + * the filter. If negative then -n (rounded up to the next power of 2) positions + * are calculated when size==1, but fewer are computed for larger sizes and + * more for smaller sizes. + * + * Some interesting reconstruct.sample combinations: + * + * IMPULSE.x - Uses the sample function only. This is what many other pieces of + * software do. Does not work for size < 1.0, so you must pass + * max(size, 1.0). Or use x.IMPULSE for size < 1.0. + * + * x.IMPULSE - Same as IMPULSE.x at size==1, size is ignored. + * + * LINEAR.IMPULSE - Same as the bilinear filter. At size==1 this is the exact + * same shape as BOX.BOX and IMPULSE.LINEAR, making it possible + * to do seamless transitions between these filters at size==1. + * + * BOX.BOX - Produces a trapazoid-shape. Narrowest possible filter with antialiasing. + * Matches a *lot* of other software, some call it "box", others call it + * "linear". + * + * BOX.x - For size < 1.0 this produces square pixels. For size > 1.0 this + * approaches IMPULSE.x as size gets larger. + * + * BOX.LINEAR - At size==1 this is what some software calls a Quadratic filter + * + * IMPULSE.LINEAR - Some software calls this "linear" or "triangle". Not a good filter. + * + * LINEAR.LINEAR - At size==1 this is what some software calls "cubic interpolation". + * + * IMPULSE.LANCZOS2 - Close to what a lot of other software calls "cubic interpolation" + * + * IMPULSE.CUBIC - A third thing often called "cubic interpolation", sometimes called + * "Mitchell" in other software. + * + * IMPULSE.GAUSSIAN - Best removal of aliasing but usually considered too blurry */ PIXMAN_EXPORT pixman_fixed_t * pixman_filter_create_separable_convolution (int *n_values, -- 1.9.1 _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/pixman
