Add new pixman_filter_create_separable_convolution() API

This new API is a helper function to create filter parameters suitable
for use with PIXMAN_FILTER_SEPARABLE_CONVOLUTION.

For each dimension, given a scale factor, reconstruction and sample
filter kernels, and a subsampling resolution, this function will
compute a convolution of the two kernels scaled appropriately, then
sample that convolution and return the resulting vectors in a form
suitable for being used as parameters to
PIXMAN_FILTER_SEPARABLE_CONVOLUTION.

The filter kernels offered are the following:

  - IMPULSE:            Dirac delta function, ie., point sampling
  - BOX:                Box filter
  - LINEAR:             Linear filter, aka. "Tent" filter
  - CUBIC:              Cubic filter, currently Mitchell-Netravali
  - GAUSSIAN:           Gaussian function, sigma=1, support=3*sigma
  - LANCZOS2:           Two-lobed Lanczos filter
  - LANCZOS3:           Three-lobed Lanczos filter
  - LANCZOS3_STRETCHED: Three-lobed Lanczos filter, stretched by 4/3.0.
                        This is the "Nice" filter from Dirty Pixels by
                        Jim Blinn.

The intended way to use this function is to extract scaling factors
from the transformation and then pass those to this function to get a
filter suitable for compositing with that transformation. The filter
kernels can be chosen according to quality and performance tradeoffs.

To get equivalent quality to GdkPixbuf for downscalings, use BOX for
both reconstruction and sampling. For upscalings, use LINEAR for
reconstruction and IMPULSE for sampling (though note that for
upscaling in both X and Y directions, simply using
PIXMAN_FILTER_BILINEAR will likely be a better choice).

1 files changed, 2 insertions, 2 deletions

diff --git a/pixman/pixman-bits-image.c b/pixman/pixman-bits-image.c
index 97db108..e76b78c 100644
--- a/pixman/pixman-bits-image.c
+++ b/pixman/pixman-bits-image.c
@@ -427,7 +427,7 @@ bits_image_fetch_pixel_convolution (bits_image_t   *image,
 }
 
 static uint32_t
-bits_image_fetch_pixel_convolution_separable (bits_image_t *image,
+bits_image_fetch_pixel_separable_convolution (bits_image_t *image,
                                               pixman_fixed_t x,
                                               pixman_fixed_t y,
                                               get_pixel_t    get_pixel)
@@ -548,7 +548,7 @@ bits_image_fetch_pixel_filtered (bits_image_t *image,
 	break;
 
     case PIXMAN_FILTER_SEPARABLE_CONVOLUTION:
-        return bits_image_fetch_pixel_convolution_separable (image, x, y, get_pixel);
+        return bits_image_fetch_pixel_separable_convolution (image, x, y, get_pixel);
         break;
 
     default: