Rick [Kitty5] wrote:
> Looks so much better with a Texture on the ball - reminds me of the old
> Amiga ball demo

Hi Rick,

Yes, the texturing adds a lot. I surprised myself with how easy the 
orientation macro was to write:

#macro Three_Point_Trans(T1a, T1b, T1c, T2a, T2b, T2c)
   transform {
     #local Y = vnormalize(T1b - T1a);
     #local X = vnormalize(T1c - T1a);
     #local Z = vnormalize(vcross(X, Y));
     #local X = vcross(Z, Y);
     #local T = Shear_Trans(X, Y, Z)
     translate -T1a
     transform { T inverse }
     #local Y = vnormalize(T2b - T2a);
     #local X = vnormalize(T2c - T2a);
     #local Z = vnormalize(vcross(X, Y));
     #local X = vcross(Z, Y);
     Shear_Trans(X, Y, Z)
     translate T2a
   }
#end

The three points a,b,c define a triangle; a is the origin, b-a is the 
primary orientation and abc gives a secondary orientation plane. The two 
orientation axes b-a and c-a do not have to be orthogonal, just 
independant so vcross(b-a,c-a) doesn't return a zero length vector.

So Three_Point_Trans(0,y,x, P0,P1,P2) gives a transform from the origin 
to P0, aligns y with P1-P0 and puts the (x,y) plane in the plane of the 
(P0,P1,P2) triangle.

I never actually had an Amiga; Atari 400, Acorn Electron, BBC B, various 
PC types ... I wrote my first (spheres only) raytracer on my Electron, 
16 colour error-diffusion dithered screen output only :-) The hardware 
and software have improved immeasurably, it's a shame I still can't 
produce anything artistic :-(

Bye for now,
	Mike Andrews.

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