[cairo] Pixels Are Not Little Squares

[Lawrence D'Oliveiro]

On Mon, 25 Apr 2016 00:19:54 -0700, Krzysztof Kosiński wrote:

> 2016-04-24 19:40 GMT-07:00 Lawrence D'Oliveiro
> <ldo at geek-central.gen.nz>:
>> On Sun, 24 Apr 2016 18:07:01 -0700, Krzysztof Kosiński wrote:
>>  
>>> As far as I know, Cairo does use an approximation of the box filter
>>> when sampling polygons, or at least does so by default.  
>>
>> The available antialias settings for drawing shapes and text are
>> documented here
>> <http://cairographics.org/manual/cairo-cairo-t.html#cairo-antialias-t>.
> 
> What I am talking about is the sampling filter, not the reconstruction
> filter.

That is the sampling filter. Shapes and text with perfectly-sharp edges
have spatial frequencies that extend beyond the Nyquist limit, which is
what causes aliasing. To prevent this, you have to filter the excess
frequencies (softening the edges). That is what anti-aliasing does.