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Java > Open Source Codes > prefuse > util > force > SpringForce


1 package prefuse.util.force;
2
3 /**
4  * Force function that computes the force acting on ForceItems due to a
5  * given Spring.
6  *
7  * @author <a HREF="http://jheer.org">jeffrey heer</a>
8  */
9 public class SpringForce extends AbstractForce {
10
11     private static String JavaDoc[] pnames
12         = new String JavaDoc[] { "SpringCoefficient", "DefaultSpringLength" };
13     
14     public static final float DEFAULT_SPRING_COEFF = 1E-4f;
15     public static final float DEFAULT_MAX_SPRING_COEFF = 1E-3f;
16     public static final float DEFAULT_MIN_SPRING_COEFF = 1E-5f;
17     public static final float DEFAULT_SPRING_LENGTH = 50;
18     public static final float DEFAULT_MIN_SPRING_LENGTH = 0;
19     public static final float DEFAULT_MAX_SPRING_LENGTH = 200;
20     public static final int SPRING_COEFF = 0;
21     public static final int SPRING_LENGTH = 1;
22     
23     /**
24      * Create a new SpringForce.
25      * @param springCoeff the default spring co-efficient to use. This will
26      * be used if the spring's own co-efficient is less than zero.
27      * @param defaultLength the default spring length to use. This will
28      * be used if the spring's own length is less than zero.
29      */
30     public SpringForce(float springCoeff, float defaultLength) {
31         params = new float[] { springCoeff, defaultLength };
32         minValues = new float[]
33             { DEFAULT_MIN_SPRING_COEFF, DEFAULT_MIN_SPRING_LENGTH };
34         maxValues = new float[]
35             { DEFAULT_MAX_SPRING_COEFF, DEFAULT_MAX_SPRING_LENGTH };
36     }
37     
38     /**
39      * Constructs a new SpringForce instance with default parameters.
40      */
41     public SpringForce() {
42         this(DEFAULT_SPRING_COEFF, DEFAULT_SPRING_LENGTH);
43     }
44
45     /**
46      * Returns true.
47      * @see prefuse.util.force.Force#isSpringForce()
48      */
49     public boolean isSpringForce() {
50         return true;
51     }
52     
53     /**
54      * @see prefuse.util.force.AbstractForce#getParameterNames()
55      */
56     protected String JavaDoc[] getParameterNames() {
57         return pnames;
58     }
59     
60     /**
61      * Calculates the force vector acting on the items due to the given spring.
62      * @param s the Spring for which to compute the force
63      * @see prefuse.util.force.Force#getForce(prefuse.util.force.Spring)
64      */
65     public void getForce(Spring s) {
66         ForceItem item1 = s.item1;
67         ForceItem item2 = s.item2;
68         float length = (s.length < 0 ? params[SPRING_LENGTH] : s.length);
69         float x1 = item1.location[0], y1 = item1.location[1];
70         float x2 = item2.location[0], y2 = item2.location[1];
71         float dx = x2-x1, dy = y2-y1;
72         float r = (float)Math.sqrt(dx*dx+dy*dy);
73         if ( r == 0.0 ) {
74             dx = ((float)Math.random()-0.5f) / 50.0f;
75             dy = ((float)Math.random()-0.5f) / 50.0f;
76             r = (float)Math.sqrt(dx*dx+dy*dy);
77         }
78         float d = r-length;
79         float coeff = (s.coeff < 0 ? params[SPRING_COEFF] : s.coeff)*d/r;
80         item1.force[0] += coeff*dx;
81         item1.force[1] += coeff*dy;
82         item2.force[0] += -coeff*dx;
83         item2.force[1] += -coeff*dy;
84     }
85     
86 } // end of class SpringForce
87
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