[cairo] Concerns about using filters for downscaling

[Krzysztof Kosiński]

2014-03-22 4:26 GMT+01:00 Owen Taylor <otaylor at redhat.com>:
> On Sat, 2014-03-22 at 03:24 +0100, Krzysztof Kosiński wrote:
>> This would make Cairo 1.14 completely unusable for Inkscape, so we
>> would have to postpone the long overdue 0.91 release for another year
>> or more, and probably stop using Cairo.
>
> I don't quite understand this - presumably 0.91 will be the same in this
> regard as previous versions of Inkscape. Is there some work-around in
> older Inkscape that you are trying to remove?

The previous version of Inkscape (0.48) used a completely different
renderer, not based on Cairo at all, which has been removed. Moving to
Cairo fixed around 50 long-standing rendering bugs, so going back is
not really an option.

>> The downscaling method used in
>> 1.12 is simply incorrect and due to severe visual artifacts makes it
>> impossible to use Inkscape to edit drawings that contain large
>> bitmaps, e.g. photos. It's no use being fast if the result is wrong.
>
> Hmm, can you use BEST? That seems to be the right constant to use if you
> quality is the absolute requirement and performance is secondary.

Lanczos3 is far too slow for interactive rendering.

As a compromise, I propose the following mapping:

BEST = Lanczos3 / Lanczos3
GOOD = linear / box
BILINEAR = linear / box
DEFAULT = linear / impulse
FAST = nearest / impulse

Regards, Krzysztof