src/edu/mit/ezyang/gravity/j3d/ArrowGroup.java

   1 /*
   2  * To change this template, choose Tools | Templates
   3  * and open the template in the editor.
   4  */
   5 package edu.mit.ezyang.gravity.j3d;
   6
   7 import com.sun.j3d.utils.geometry.Cylinder;
   8 import javax.media.j3d.BranchGroup;
   9 import javax.media.j3d.Transform3D;
  10 import javax.media.j3d.TransformGroup;
  11 import javax.vecmath.Matrix3f;
  12 import javax.vecmath.Vector3f;
  13
  14 /**
  15  *
  16  * @author Edward Z. Yang <ezyang@mit.edu>
  17  */
  18 public class ArrowGroup extends BranchGroup {
  19     public ArrowGroup(Vector3f velocity) {
  20         Cylinder stem = new Cylinder(0.02f, velocity.length());
  21         stem.getAppearance().getMaterial().setEmissiveColor(0.3f, 0.3f, 0.8f);
  22
  23         setCapability(BranchGroup.ALLOW_DETACH);
  24         TransformGroup arrowTransformGroup = new TransformGroup();
  25         Transform3D arrowTransform3D = new Transform3D();
  26
  27         Vector3f translation = new Vector3f();
  28         translation.scale(1f/2f, velocity);
  29
  30         Vector3f vec_y = (Vector3f) velocity.clone();
  31         vec_y.normalize();
  32
  33         Vector3f vec_x; // reference vector, will correct later
  34         if (vec_y.x == 0 && vec_y.z == 0) {
  35             vec_x = new Vector3f(-vec_y.y, 0f, 0f); // could be optimized
  36         } else {
  37             vec_x = new Vector3f(0f, 1f, 0f);
  38         }
  39
  40         Vector3f vec_z = new Vector3f();
  41         vec_z.cross(vec_x, vec_y);
  42         vec_z.normalize();
  43
  44         vec_x.cross(vec_z, vec_y);
  45         vec_x.normalize();
  46         vec_x.negate();
  47
  48         Matrix3f rotation = new Matrix3f(
  49             vec_x.x, vec_x.y, vec_x.z,
  50             vec_y.x, vec_y.y, vec_y.z,
  51             vec_z.x, vec_z.y, vec_z.z
  52         );
  53         rotation.invert();
  54
  55         arrowTransform3D.set(rotation, translation, 1f);
  56
  57         arrowTransformGroup.setTransform(arrowTransform3D);
  58         arrowTransformGroup.addChild(stem);
  59         addChild(arrowTransformGroup);
  60     }
  61 }