From: teunis <teunis@computersupportcentre.com>
  To  : ggi-develop@eskimo.com
  Date: Wed, 19 Aug 1998 19:29:23 -0700 (MST)

Re: LibGGI3D RFC

On Wed, 19 Aug 1998, Jon M. Taylor wrote:

> On Thu, 20 Aug 1998, Olivier Galibert wrote:
> 
> > On Wed, Aug 19, 1998 at 05:18:05PM -0700, Jon M. Taylor wrote:
> > > 	The higher layers could clip during tesellation, and as such
> > > they'd be able to take all those coordinates into account.
> > 
> > By "clip" do you mean 2d clipping?  
> 
> 	No.  Yes.  Maybe |->.  It depends on how you clip.  You *could*
> have your 3D clipper turn partially-visible triangles into two triangles
> and do HSR and backface culling, so that when the triangles are sent to
> LibGGI3D for drawing there are no z-overlaps or clipping issues left. 
> 
> > If yes, wouldn't that break gouraud shading?
> 
> 	Not if you do it right.  If the clipper described above were to
> interpolate the vertex normals of the pre-clipped triangle along the two
> clipped sides, it could compute the effective vertex normals of the two
> new triangle vertices which would be created by the clip.  This allows you
> to get the exact same effective shading.

No it doesn't.  Not if you forget the other info present.  A normal won't
interpolate a texture coordinate.  Or a colour coordinate if you do
colour-shading across a texture.  Or other more bizarre data (ie: mixing
coefficient for mixing two textures :)

G'day, eh? :)
	- Teunis