Is this an impossible shape in 3-D? I can't work out if it is or isn't. I'm thinking of using this in Chapter 33 (or is it 34)... as an example of how OpenGL can be used in 2-d drawings to achieve effects otherwise not possible.




Here's the code. You'll need OpenGL running though. You might want to fiddle around with k_rectangles to get the thing running reasonably well. Watch out for the Moray patterns though! 

b e n 

import javax.media.opengl.* ;
import processing.opengl.*;

//
//  Inf 1.
//
//  Draw a twistig ring shape.
//

final int    k_rectangles = 300 ;
final int    k_width = 50 ;
final int    k_height = 50 ;
final color  k_background_colour = color( 100, 200, 128, 255 ) ;
final color  k_edge_colour = color( 200, 200, 200, 255 ) ;
final color  k_fill_colour = color( 255, 255, 255, 255 ) ;

void setup()
{
  // size( 640, 480, JAVA2D ) ; // , P3D ) ;
  size( 640, 480, OPENGL ) ;

  smooth() ;
}

void draw()
{
  //
  // Clear the background and set up a drawing style for the rectangles.
  //
  background( k_background_colour ) ;

  stroke( k_edge_colour ) ;
  fill( k_fill_colour ) ;
  rectMode( RADIUS ) ;

  //
  // Draw a circle using  a sequence of rectangles painted on top of each other.
  //
  for ( int i = 0 ; i < k_rectangles ; ++i )
  {

    pushMatrix() ;

    //
    // Fudge the depth of the rectangles so that the last few rectangles are painted
    // underneath the starting rectangles.
    //
    float dz = i > k_rectangles / 4 ? -0.1 : 0.0 ;

    PGraphicsOpenGL pgl = (PGraphicsOpenGL) g ;
    GL gl = pgl.beginGL() ;  

    if ( i < k_rectangles / 5 )
      gl.glEnable( gl.GL_DEPTH_TEST ) ;
    else
      if ( i < k_rectangles / 2 )
        gl.glDisable( gl.GL_DEPTH_TEST ) ;
      else
        gl.glEnable( gl.GL_DEPTH_TEST ) ;

    pgl.endGL() ;


    //
    // Draw the rectangle.
    // The Processing variable frameCount is used to animate the rotation of the rectangles.
    //
    translate( width/2 + 150 * sin( PI * 2.0 * i / k_rectangles ), height/2 + 150 * cos( PI * 2.0 * i / k_rectangles ), dz ) ;
    rotate( frameCount * 0.01 ) ;

    rect( 0, 0, k_width, k_height ) ;

    popMatrix() ;

  }
}