From: Marcus Sundberg <mackan@stacken.kth.se>
  To  : ggi-develop@eskimo.com
  Date: 06 Nov 1999 19:44:37 +0100

Re: roblems over matrox fb

Andreas Beck <becka@rz.uni-duesseldorf.de> writes:

> > Sample:
> > ggiDrawLine(-10, 20, 90, 120);
> > ggiDrawBox(-10, 20, 100, 100);
> > 
> > line left top end is pointed somewhere
> > Box disappeared from the screen
> > 
> > I have no problem with X target. I never tested vesafb.
> 
> Hmmm - might be a problem with HW-Accel. Marcus - are these HW-acceled in
> the matrox driver ?

Yes.

> If so and the problem is reproducible, could you fix 
> that behaviour ? It is important, that HW-acceled functions behave exactly
> as defined by LibGGI standards.

This is not defined anywhere, and I strongly believe this behaviour
should be documented, not "fixed".

The problem here is simple - the coordinate system in LibGGI ranges
from (0,0) to (oo,oo). Negative starting coordinates happens to work
when you use software clipping, but with hardware clipping and drawing
the results are undefined.

The reason this behaviour should not be changed is that for lines it
isn't as simple as truncating negative values to zero. I do not
intend to put a full software line-drawer into the matrox sublib
for the sole purpose of supporting broken applications.

//Marcus
-- 
-------------------------------+------------------------------------
        Marcus Sundberg        | http://www.stacken.kth.se/~mackan
 Royal Institute of Technology |       Phone: +46 707 295404
       Stockholm, Sweden       |   E-Mail: mackan@stacken.kth.se