From: Jon M. Taylor <taylorj@ecs.csus.edu>
  To  : ggi-develop@eskimo.com
  Date: Mon, 8 Nov 1999 19:35:02 -0800 (PST)

Re: roblems over matrox fb

On Mon, 8 Nov 1999, Andreas Beck wrote:

> > > So we either document that giving negative values to any drawing function is
> > > undefined or we make sure every function obeys them as appropriate.
> > Bad wording on my side, that is what I mean.
> 
> O.K. - which of both do we choose, then.
> 
> IMHO a good compromise regarding minimum work at maximum functionality would 
> be:
> 
> LibGGI does support clipping on all of its primitives. It is permissible to
> give negative values to LibGGI and they will be clipped correctly.
> Please note, that some accelerators will not support efficient means for
> clipping lines that have negative endpoints. Thus it is possible, that
> applications making use of negative endpoints will suffer a performance
> penalty on some targets. So if you are concerned with speed, negative
> coordinates should be avoided.

	OTOH, use of negative coordinates is quite legal with some
hardware which supports memory tiling, and there are circumstances under
which it is actually faster to specify a negative offset instead of
recalculating a positive offset from the previous tile.

Jon

---
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