[cairo] Pixman coordinates

[M Joonas Pihlaja]

Hi Krzysztof,

On Wed, 30 Jun 2010, [UTF-8] Krzysztof Kosi?ski wrote:

> A secondary problem is that it's not possible to create image 
> surfaces larger than 32767px in any dimension.

I would be extremely hesitant to increase this due to arithmetic 
precision issues within both cairo and pixman.  In my experience, if 
you've got images this large then you're better off treating cairo as 
a limited precision output device (because it is, even if those limits 
are undocumented!) and taking control of your precision requirements 
by doing tiled rendering.

> 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.

Chers,

Joonas