[Pixman] [cairo] Pixman coordinates

Soeren Sandmann sandmann at daimi.au.dk
Tue Jul 6 08:48:03 PDT 2010

M Joonas Pihlaja <jpihlaja at cc.helsinki.fi> writes:

> > I heard there were plans to switch Pixman to 24.8 coordinate format.
> I don't recall this plan exactly, but it's plausible Soren had a 24.8 
> pixman branch at some point, but I don't see it at a glance of his 
> branches.  He's got a branch for everything else under the sun.  
> Cairo itself switched from 16.16 to 24.8 around 2006-2007 IIRC.  In 
> any case, perhaps internally pixman may switch, but the core X 
> protocol's 16.16 coordinate format won't change, so unless the pixman 
> API changes too (and it might, as an API shake up has been on the 
> table) you probably won't see the 32k limit lifted.

As far as pixman is concerned, I consider the remaining 16 bit
limitations bugs that should be fixed. Here are some that remains:

- Transformations are stored in 16.16 fixed point internally.

- Gradients have some coordinate system issues. 

- Trapezoids use 16.16 coordinates. I'd probably take a patch to make
  them use 24.8 internally (and add a corresponding 24.8 API), but a
  better solution would be to add a polygon image type.

I think these things can be fixed without breaking the pixman API, but
as you say, changing the API at some point is not off the table.


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