[Pixman] [PATCH 3/3] BILINEAR->NEAREST filter optimization for simple rotation and translation

[Andrea Canciani]

On Mon, May 23, 2011 at 8:43 AM, Andrea Canciani <ranma42 at gmail.com> wrote:
> On Sun, May 22, 2011 at 11:15 PM, Siarhei Siamashka
> <siarhei.siamashka at gmail.com> wrote:
>> From: Siarhei Siamashka <siarhei.siamashka at nokia.com>
>>
>> Simple rotation and translation are the additional cases when BILINEAR
>> filter can be safely reduced to NEAREST.
>
> I believe that this reduction is valid for any matrix which describes
> a unit transform followed
> by an integer translation (i.e. rotation(90 degrees), scale(-1,1),
> translate(1,0) composed
> in any possible way).
>
> This happens whenever the translational component of the matrix is
> integral, the projective
> component is identity (already tested by AFFINE_TRANSFORM) and the
> upper-left 2x2
> matrix multiplied by its transpose results in the 2x2 identity.

Uh, we already have an implementation of this (which is what cairo
uses to optimize filters to nearest):
http://cgit.freedesktop.org/cairo/tree/src/cairo-matrix.c#n728
(lines 728-762)

>
> Andrea
>
>> ---
>>  pixman/pixman-image.c |   37 +++++++++++++++++++++++++++++++++++++
>>  1 files changed, 37 insertions(+), 0 deletions(-)
>>
>> diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
>> index 4784c22..583e7a7 100644
>> --- a/pixman/pixman-image.c
>> +++ b/pixman/pixman-image.c
>> @@ -256,6 +256,43 @@ compute_image_info (pixman_image_t *image)
>>        {
>>            flags |= FAST_PATH_NEAREST_FILTER;
>>        }
>> +       else if (
>> +                /* affine and integer translation components in matrix ... */
>> +                ((flags & FAST_PATH_AFFINE_TRANSFORM) &&
>> +                 !pixman_fixed_frac (image->common.transform->matrix[0][2] |
>> +                                     image->common.transform->matrix[1][2])) &&
>> +                (
>> +                 /* ... combined with a simple rotation */
>> +                 (flags & (FAST_PATH_ROTATE_90_TRANSFORM |
>> +                           FAST_PATH_ROTATE_180_TRANSFORM |
>> +                           FAST_PATH_ROTATE_270_TRANSFORM)) ||
>> +                 /* ... or combined with a simple non-rotated translation */
>> +                 (image->common.transform->matrix[0][0] == pixman_fixed_1 &&
>> +                  image->common.transform->matrix[1][1] == pixman_fixed_1 &&
>> +                  image->common.transform->matrix[0][1] == 0 &&
>> +                  image->common.transform->matrix[1][0] == 0)
>> +                )
>> +               )
>> +       {
>> +           /* FIXME: there are some affine-test failures, showing that
>> +            * handling of BILINEAR and NEAREST filter is not quite
>> +            * equivalent when getting close to 32K for the translation
>> +            * components of the matrix. That's likely some bug, but for
>> +            * now just skip BILINEAR->NEAREST optimization in this case.
>> +            */
>> +           pixman_fixed_t magic_limit = pixman_int_to_fixed (30000);
>> +           if (image->common.transform->matrix[0][2] > magic_limit  ||
>> +               image->common.transform->matrix[1][2] > magic_limit  ||
>> +               image->common.transform->matrix[0][2] < -magic_limit ||
>> +               image->common.transform->matrix[1][2] < -magic_limit)
>> +           {
>> +               flags |= FAST_PATH_BILINEAR_FILTER;
>> +           }
>> +           else
>> +           {
>> +               flags |= FAST_PATH_NEAREST_FILTER;
>> +           }
>> +       }
>>        else
>>        {
>>            flags |= FAST_PATH_BILINEAR_FILTER;
>> --
>> 1.7.3.4
>>
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>