Geometry Objects - Interactive Web-Based Virtual Reality with Java 3D - page 49

Figure 23. Code segment and result of DoubleHelix.java

1. int n = 360; // number of vertices used

2. double a = 0.5; // radius of helix

3. double i; int j; // counting variables

4.
5. int[] strip = new int[2 + n/2];
6. strip[0] = n; //for one of the helix

7. strip[1] = n; //for the other helix

8. for ( int k=2; k<(2+n/2); k++ ) strip[k] = 2; //for the lines connecting the two helix

9.
10. //there are n vertices on each helix, and n/2 lines connecting each
11. //helix, thus there are in total n+n+n vertices to be set.
12. LineStripArray lsa = new LineStripArray( (2*n + n ), GeometryArray.COORDINATES, strip );
13.
14. //for the first helix; i is in degrees. To do 720 degrees of revolution
15. for ( i=0,j=0; j<n; i=i+(720/n), j++ )
16. lsa.setCoordinate( j, new Point3d((double)a*Math.cos(i*Math.PI/180),

17. (double)(-1.25 + (i*Math.PI/180)/5.0 ), (double)a*Math.sin(i*Math.PI/180)));

18.
19. //for the second helix
20. for ( i=0, j=0; j<n; i=i+(720/n), j++ )
21. lsa.setCoordinate( j+n, new Point3d( (double)-a*Math.cos(i*Math.PI/180),
22. (double)(-1.25 + (i*Math.PI/180)/5.0 ), (double)-a*Math.sin(i*Math.PI/180) ) );

23.
24. //for the lines connecting the helix together
25. for ( i=0, j=0; j<n && i<720; i=i+(10*720/n) )
26. {
27. lsa.setCoordinate( j+(2*n), new Point3d((double)a*Math.cos(i*Math.PI/180),
28. (double)(-1.25 + (i*Math.PI/180)/5.0 ), (double)a*Math.sin(i*Math.PI/180) ) );

29. j++;
30. lsa.setCoordinate( j+(2*n), new Point3d((double)-a*Math.cos(i*Math.PI/180),
31. (double)(-1.25 + (i*Math.PI/180)/5.0 ), (double)-a*Math.sin(i*Math.PI/180) ) );

32. j++;
33. }
34.