Re: [Flightgear-devel] New texture draw method

[Curtis L. O. <cu...@fl...>]

John Check writes:
> 
> 
> On Sat, 25 Aug 2001, Alex Perry wrote:
> 
> > > Hmmm, I don't ever recall doing anything like that.  Typcially the
> > > solution is to make sure that shared verticies are *exactly* the same
> > > which can be hard to do in some circumstances.
> >
> > I've seen problems, occasionally along tile boundaries and often along
> > whole-degrees-of latitude or longitude.  I doubt we can do much about that.
> 
> I'd be happy with a pat answer. "Homnna homna homna" doesn't cut it when
> somebody asks. As trivial as it might seem to us, its a big honkin' issue
> in a pink tutu stoking a di'napoli and guzzling cheap gin to somebody off
> the street

The problem is that if two verticies that area supposed to be
coincident go through two *different* transformations they don't
always end up exactly the same place.  It wouldn't be a problem with
infinite precision math, but we are stuck doing this with floats
because that is what opengl uses interenally.  Given the lack of
precision floats, by the time you transform the two points to screen
space, one could get rounded up, the other down and then you could see
a pixel wide gap flicker between the two objects.

Curt.
-- 
Curtis Olson   Human Factors Research Lab       FlightGear Project
Twin Cities    cu...@hf...                cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org