Proprosed break in libGL / DRI driver ABI

[Brian Paul]

Julien Lafon wrote:
> On Apr 5, 2005 10:11 PM, Brian Paul <brian.paul at tungstengraphics.com> wrote:
> 
>>Roland Mainz wrote:
>>
>>>Ian Romanick wrote:
>>>When I look at xc/extras/Mesa/src/mesa/main/config.h I see more items on
>>>my wishlist: Would it be possible to increase |MAX_WIDTH| and
>>>|MAX_HEIGHT| (and the matching texture limits of the software
>>>rasterizer) to 8192 to support larger displays (DMX, Xinerama and Xprint
>>>come in mind) ?
>>
>>If you increase MAX_WIDTH/HEIGHT too far, you'll start to see
>>interpolation errors in triangle rasterization (the software
>>routines).  The full explanation is long, but basically there needs to
>>be enough fractional bits in the GLfixed datatype to accomodate
>>interpolation across the full viewport width/height.
> 
> Will increasing MAX_WIDTH/HEIGHT affect applications which run in
> small windows or only those which use resolutions exceeding the 4Kx4K
> limit?

Increasing MAX_WIDTH/HEIGHT will result in more memory usage 
regardless of window size.

As is, you can't exceed 4K x 4K resolution without increasing 
MAX_WIDTH/HEIGHT.  Your glViewport call will be clamped to those 
limits if you specify larger.


>>In fact, I'm not sure that we've already gone too far by setting
>>MAX_WIDTH/HEIGHT to 4096 while the GLfixed type only has 11 fractional
>>bits.  I haven't heard any reports of bad triangles so far though.
> 
> Do you know any specific application which may expose bad rendering
> when the size gets to large?

No (there's far too many OpenGL apps out there for me to say).


>>But there probably aren't too many people generating 4Kx4K images.
> 
> We've been running tests with the glutdemo applications and Xprint at
> higher resolutions (6Kx8K window size) and did not notice any bad
> rendering using the software rasterizer.

How large are your triangles?

The interpolation error will accumulate and be most noticable with 
very large triangles.

-Brian