Remco de Korte <rem### [at] xs4allnl> wrote:.
> I don't know exactly what caused your problem but the code above has some
typos.
>
> Here is what I made of it:
>
> #declare sides=5;
>
> prism {
>   linear_sweep
>   linear_spline
>   -0.5,
>    0.5,
>   sides+1,
>
> #local rotation_no = 0;
> #while (rotation_no<sides)
> #local angle_of_rotation = 360/sides;
> // #local temp_vec=vrotate(<0,1,0>,<0,1,angle_of_rotation*rotation_no>);
> #local temp_vec=vrotate(<0,1,0>,<0,0,angle_of_rotation*rotation_no>);
> // #local vec=<temp_vec.y,temp_vec.z>;
> #local vec=<temp_vec.x,temp_vec.y>;
> #if (rotation_no=0)
>   #declare vec0=vec;
> #end
> vec,
> #local rotation_no = rotation_no+1;
> #end
> vec0
> pigment{rgb 1}
> rotate x*90
> }
>
> When I tried this it worked fine.

In the first line you've commented out above, the rotation of +y by 1 degree
about the y axis actually has no effect (although your second version is
more correct).  The real change is in the code in which you extract the 2D
vector from the rotated 3D vector: in the commented-out line, the temp_vec.z
component will always be 0 which obviously won't give the desired result!

At any rate, as I posted in my other reply it is not necessary to convert
the 3D to 2D vectors as you have done, as long as the vectors lie correctly
in the X-Z plane.  Also, for better coding you should remove the calculation
of the rotation angle outside the while loop; otherwise, you're simply
recalculating the same value over and over again!  Finally, for the closing
of the prism/polygon, all you really need is the unrotated radius vector at
the beginning and end.  Using this you can avoid any rounding errors and
unnecessary calculations, eg:

#macro regular_prism (Sides, Height1, Height2)
  #local RotAngle = 360/Sides;
  prism {linear_sweep linear_spline
    Height1, Height2, Sides+1, x,
    #local Count = 1; #while (Count < Sides)
      vrotate (x, y*RotAngle*Count),
    #local Count = Count + 1; #end
    x}
#end

From here you could adjust the basic code to create star-shaped prisms, or
use curved splines to create petal shapes, etc.

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