[cairo] Concerns about using filters for downscaling

[Krzysztof Kosiński]

2014-03-24 22:04 GMT+01:00 Owen Taylor <otaylor at redhat.com>:
> On Sun, 2014-03-23 at 02:30 +0100, Søren Sandmann wrote:
>> Owen Taylor <otaylor at redhat.com> writes:
>>
>> > (Søren pointed out on IRC that the pixman implemention of convolution
>> > is not SIMD optimized, so their would be future opportunity to improve
>> > what we can do within the constraints of 5-10x slower.)
>
> I took a stab at implementing a pretty straightforward port of the
> pixman-fast-path.c code to SSE2 - attached. I was able to get roughly
> a 2x speedup:
>
>>    scale    NEAREST BILINEAR   GOOD    BEST
>>    ----     ------  --------  -----   ------
>>      1.1      656     2860    15163   149147
>>      1.5      350     1574     7918   108820
>>      1.9      220      965     7176    89324
>>      2.0       51      873     6397    95665
>>      2.5       34      114     4331    71975
>>      3.0       25      392     4074    67211
>>      3.5       66      290     3101    60168
>>      4.0       15      223     3135    59207
>>      4.5       12       37     2524    58586
>>      5.0       34      143     2643    56798
>
>     scale    NEAREST BILINEAR   GOOD    BEST     MIPMAP
>     -----    ------- --------   ----    ----     ------
>       1.1      478     3073    10267    74341     3022
>       1.5      264     1662     5549    53639     1680
>       1.9      171     1053     3467    50495     1058
>       2.0       60      943     3080    46139      151
>       2.5       40      115     2709    40281      729
>       3.0       29      431     1907    37104      556
>       3.5       55      324     1878    35542      439
>       4.0       19      244     1515    34569      173
>       4.5       16       39     1451    33327      364
>       5.0       30      157     1219    33239      330
>
> I've added another column which is an implementation (in my test
> program) of the technique of creating a temporary power-of-two scaled
> down image and bilinear-filtering from that. As you can see, even
> tossing away the mipmaps, the performance is much better than with
> convolution - even though either way we have to touch all the pixels in
> the source image, it's much easier to write fast, cache friendly
> average-of-four-pixels code, then convolution code.

FWIW, the optimal method for Inkscape would be trilinear interpolation
from a mipmap or a ripmap. This would give the best interactive
transformation performance while maintaining good quality.

Regards, Krzysztof