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      2  * Copyright (c) 2013, Daniel Murphy
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     24 package org.jbox2d.collision;
     25 
     26 import org.jbox2d.common.Settings;
     27 import org.jbox2d.common.Vec2;
     28 
     29 /**
     30  * A manifold for two touching convex shapes. Box2D supports multiple types of contact:
     31  * <ul>
     32  * <li>clip point versus plane with radius</li>
     33  * <li>point versus point with radius (circles)</li>
     34  * </ul>
     35  * The local point usage depends on the manifold type:
     36  * <ul>
     37  * <li>e_circles: the local center of circleA</li>
     38  * <li>e_faceA: the center of faceA</li>
     39  * <li>e_faceB: the center of faceB</li>
     40  * </ul>
     41  * Similarly the local normal usage:
     42  * <ul>
     43  * <li>e_circles: not used</li>
     44  * <li>e_faceA: the normal on polygonA</li>
     45  * <li>e_faceB: the normal on polygonB</li>
     46  * </ul>
     47  * We store contacts in this way so that position correction can account for movement, which is
     48  * critical for continuous physics. All contact scenarios must be expressed in one of these types.
     49  * This structure is stored across time steps, so we keep it small.
     50  */
     51 public class Manifold {
     52 
     53   public static enum ManifoldType {
     54     CIRCLES, FACE_A, FACE_B
     55   }
     56 
     57   /** The points of contact. */
     58   public final ManifoldPoint[] points;
     59 
     60   /** not use for Type::e_points */
     61   public final Vec2 localNormal;
     62 
     63   /** usage depends on manifold type */
     64   public final Vec2 localPoint;
     65 
     66   public ManifoldType type;
     67 
     68   /** The number of manifold points. */
     69   public int pointCount;
     70 
     71   /**
     72    * creates a manifold with 0 points, with it's points array full of instantiated ManifoldPoints.
     73    */
     74   public Manifold() {
     75     points = new ManifoldPoint[Settings.maxManifoldPoints];
     76     for (int i = 0; i < Settings.maxManifoldPoints; i++) {
     77       points[i] = new ManifoldPoint();
     78     }
     79     localNormal = new Vec2();
     80     localPoint = new Vec2();
     81     pointCount = 0;
     82   }
     83 
     84   /**
     85    * Creates this manifold as a copy of the other
     86    *
     87    * @param other
     88    */
     89   public Manifold(Manifold other) {
     90     points = new ManifoldPoint[Settings.maxManifoldPoints];
     91     localNormal = other.localNormal.clone();
     92     localPoint = other.localPoint.clone();
     93     pointCount = other.pointCount;
     94     type = other.type;
     95     // djm: this is correct now
     96     for (int i = 0; i < Settings.maxManifoldPoints; i++) {
     97       points[i] = new ManifoldPoint(other.points[i]);
     98     }
     99   }
    100 
    101   /**
    102    * copies this manifold from the given one
    103    *
    104    * @param cp manifold to copy from
    105    */
    106   public void set(Manifold cp) {
    107     for (int i = 0; i < cp.pointCount; i++) {
    108       points[i].set(cp.points[i]);
    109     }
    110 
    111     type = cp.type;
    112     localNormal.set(cp.localNormal);
    113     localPoint.set(cp.localPoint);
    114     pointCount = cp.pointCount;
    115   }
    116 }
    117