Orchid XP v2 <voi### [at] devnull> wrote:
> (Actually, the code that generates the 4 points guarantees them to form 
> a rectangle. To be specific, A and B are identical except for the Z 
> coordinate, as are C and D...)

  I don't think that's a guarantee of rectangularity nor even
parallelogramity.

-- 
                                                          - Warp

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Tor Olav Kristensen <tor### [at] toberemovedgmailcom> wrote:
> > Assuming that all 4 points are actually co-plannar, what would the *the 
> > simplest* way to fit a box{} object into the middle of the thing?

> Use Matrix_Trans() or Shear_Trans()

  That will only work if the points form a perfect parallelogram.

-- 
                                                          - Warp

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Warp wrote:
> Tor Olav Kristensen <tor### [at] toberemovedgmailcom> wrote:
>>> Assuming that all 4 points are actually co-plannar, what would the *the 
>>> simplest* way to fit a box{} object into the middle of the thing?
> 
>> Use Matrix_Trans() or Shear_Trans()
> 
>   That will only work if the points form a perfect parallelogram.

Yes, that's true.

(But I assumed that he wanted to use his macro for his wireframe 
letters. See his latest post in povray.binaries.images)

-- 
Tor Olav
http://subcube.com

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>>(Actually, the code that generates the 4 points guarantees them to form 
>>a rectangle. To be specific, A and B are identical except for the Z 
>>coordinate, as are C and D...)
> 
> 
>   I don't think that's a guarantee of rectangularity nor even
> parallelogramity.

Why not?

Oh, did I not mention that A and C have *the same* Z coordinate? (As do 
B and D...)

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> Use Matrix_Trans() or Shear_Trans()
> (These are macros in transforms.inc)

Thanks for the tip! :-D

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This seems to work...

#macro DrawPoly(Points, Radius)
   #local A = Points[0];
   #local B = Points[1];
   #local C = Points[2];

   #local AB = B - A;
   #local AC = C - A;
   #local Norm = vnormalize(vcross(AB, AC));

   #local V1 = Norm;
   #local V2 = vnormalize(AB);
   #local V3 = vcross(V1, V2);

   prism
   {
     linear_sweep
     linear_spline
     -Radius, +Radius, dimension_size(Points, 1),

     #local lp = 0;
     #while (lp < dimension_size(Points, 1))
       <vdot(V3, Points[lp]), vdot(V2, Points[lp])>

       #local lp = lp + 1;
     #end

     translate +y*vdot(A, Norm)
     Reorient_Trans(y, Norm)
   }
#end

In case it way be of use to anybod else...

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Orchid XP v2 wrote:
> This seems to work...
>
> In case it way be of use to anybod else...

Could you provide an example of use? I can't get it to work in the test 
scene below. Granted, it doesn't use a parallelogram, but it looks like it 
is meant to handle other coplanar points too. Besides, doesn't work with a 
parallelogram either. If you really need it for parallelograms only, then I 
can think of a simpler solution that uses a box instead of a prism.

#include "transforms.inc"

#macro Rectangle(A, B, C, D, r)
   sphere {A, r}
   sphere {B, r}
   sphere {C, r}
   sphere {D, r}
   cylinder {A, B, r}
   cylinder {B, C, r}
   cylinder {C, D, r}
   cylinder {D, A, r}
#end

#macro DrawPoly(Points, Radius)
   #local A = Points[0];
   #local B = Points[1];
   #local C = Points[2];

   #local AB = B - A;
   #local AC = C - A;
   #local Norm = vnormalize(vcross(AB, AC));

   #local V1 = Norm;
   #local V2 = vnormalize(AB);
   #local V3 = vcross(V1, V2);

   prism
   {
     linear_sweep
     linear_spline
     -Radius, +Radius, dimension_size(Points, 1),

     #local lp = 0;
     #while (lp < dimension_size(Points, 1))
       <vdot(V3, Points[lp]), vdot(V2, Points[lp])>

       #local lp = lp + 1;
     #end

     translate +y*vdot(A, Norm)
     Reorient_Trans(y, Norm)
   }
#end

#declare Points = array[4] {<-1,-1,0>, <1,-2,1>, <1,2,1>, <-1,2,0>}

camera {location -6*z}
light_source {<-1,2,-3>*1000, color rgb 1}

union {
   Rectangle(Points[0],Points[1],Points[2],Points[3], 0.3)
   DrawPoly(Points, 0.3)
   pigment {rgb 1}
}


Rune
-- 
http://runevision.com

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>>This seems to work...
>>
>>In case it way be of use to anybod else...
> 
> 
> Could you provide an example of use? I can't get it to work in the test 
> scene below. Granted, it doesn't use a parallelogram, but it looks like it 
> is meant to handle other coplanar points too. Besides, doesn't work with a 
> parallelogram either. If you really need it for parallelograms only, then I 
> can think of a simpler solution that uses a box instead of a prism.

It *is* supposed to work for any polygone. Apparently it doesn't...

Please rip out the line at the end of DrawPoly() that says

   Reorient_Trans(y, Norm)

and replace it with

   Shear_Trans(V3, V1, V2)

Let me know if that fixes the problem...

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Orchid XP v2 wrote:
> It *is* supposed to work for any polygone. Apparently it doesn't...
>
> Please rip out the line at the end of DrawPoly() that says
>
>   Reorient_Trans(y, Norm)
>
> and replace it with
>
>   Shear_Trans(V3, V1, V2)
>
> Let me know if that fixes the problem...

It seems to fix it. :)

Rune
-- 
http://runevision.com

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>>Let me know if that fixes the problem...
> 
> 
> It seems to fix it. :)

Introduces an extra rotation that just happens not to be necessary in 
the special case I had when I designed the thing. ;-)

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