[Pixman] [PATCH 2/2] More general BILINEAR=>NEAREST reduction

[Søren Sandmann]

> +            *
>> +            * and the destination coordinates are (n + 0.5, m + 0.5).
>> Then
>> +            * the transformed x coordinate is:
>> +            *
>> +            *     tx = t00 * (n + 0.5) + t01 * (m + 0.5) + t02
>> +            *        = t00 * n + t01 * m + t02 + (t00 + t01) * 0.5
>>
>
> I would use u,v rather than tx,ty for the source coordinates. More complex
> analysis of transforms gets very hard to read unless the variables are kept
> to one letter.
>

We use tx in one other place in pixman, so I kept it that way.

+               /* 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_NEAREST_FILTER;
>> +               }
>>
>
> Can this be tested to see if the bug still exists?
>
> The comment should be reworded to point out that the bug is in the
> BILINEAR code, not the NEAREST code, but this patch is needed to not have
> the NEAREST case "fix" the ones that are broken and thus make the fast path
> output different.
>

Sure, this can be done. And in fact, it appears this bug doesn't exist
anymore. However, I think such a change belongs in a different patch set.

I have addressed your other comments in the new series that I just sent out.


Søren
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