subroutines perpec and lookat
Thant Tessman
thant at horus.sgi.com
Sat Jul 29 08:44:06 AEST 1989
In article <39135 at sgi.SGI.COM>, tarolli at dragon.wpd.sgi.com (Gary Tarolli) writes:
> In article <38766 at sgi.SGI.COM>, thant at horus.sgi.com (Thant Tessman) writes:
> > In article <8907250331.AA20644 at prism.gatech.edu>, ccsupos%prism at GATECH.EDU ("SCHREIBER, O. A.") writes:
> >
> >
> > This is probably due you assuming that z is up (a perfectly reasonable
> > assumption, one would think) but that the 'lookat' for historical reasons
> > thinks that y is up, not z.
> >
> >
>
> I think it is perfectly reasonable for y to be the up axis. Its not a
> historical reason, its a logical one. If z was up, then zbuffers would
> be called ybuffers wouldn't they? Zbuffers are called zbuffers because
> the z axis runs along the line of sight! This implies x and y are
> therefore up/down and right/left.
> --
> Gary Tarolli
>
>
These are exactly the historical reasons I was refering to. It's logical
to computer scientists who started out having to address pixels on a
screen using x and y. (Zbuffers are called zbuffers because X and Y were
taken already.) Unfortunately for computer scientists, the
rest of the world thinks z is up. If we were building these things just
for computer scientists it would have also had a left handed coordinate
system (gods be praised it doesn't).
Seriously, the hotline has spent a man-century or two trying to explain
why the 'twist' never seems to do what people thought it did.
thant at sgi.com
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