Re: Getting Gouraud Color
Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Wed, 22 Jan 1997 17:50:13 +0000
On Jan 22, 10:48am, Steve Baker wrote:
> Subject: Re: Getting Gouraud Color
> On Jan 21, 5:58pm, SCOTT OFRIEL wrote:
>
> > Is it possible to get the RGB color value from any place between the two
end
> > points of a Gouraud shaded line? The line is a pfGeoSet.
>
> Angus Dorbie <dorbie++at++bitch.reading.sgi.com> replied:
>
> > This is a linear interpolation in screen space.
> >
> > Problems will arise if you want to calculate this for projected
> > screen space and the line is in perspective because the colour
> > interpolation is not perspective correct. This gets real fun
> > when you clip the line because the colour gets shaded from the
> > interpolated clipped line end colour.
>
> In fact, it's even worse than that - the colour of some point
> on a gouraud shaded line/polygon can be different on different
> channels.
Yep, you can experience some shading discontinuities across
channels but this is really the result of the same effect.
But the worseness is even more worser than the worsening you
mention :-). If you have lighting calculations they
move around as a result of the clipping and can produce obvious
anomalies, especially if you have specular materials.
Cheers,
Angus.
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on Mon Aug 10 1998 - 17:54:26 PDT