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 * Copyright (c) 2013, Daniel Murphy
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package org.jbox2d.collision;

import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;

/**
 * A manifold for two touching convex shapes. Box2D supports multiple types of contact:
 * 
 * clip point versus plane with radius
 * point versus point with radius (circles)
 * 
 * The local point usage depends on the manifold type:
 * 
 * e_circles: the local center of circleA
 * e_faceA: the center of faceA
 * e_faceB: the center of faceB
 * 
 * Similarly the local normal usage:
 * 
 * e_circles: not used
 * e_faceA: the normal on polygonA
 * e_faceB: the normal on polygonB
 * 
 * We store contacts in this way so that position correction can account for movement, which is
 * critical for continuous physics. All contact scenarios must be expressed in one of these types.
 * This structure is stored across time steps, so we keep it small.
 */
public class Manifold {

  public static enum ManifoldType {
    CIRCLES, FACE_A, FACE_B
  }

  /** The points of contact. */
  public final ManifoldPoint[] points;

  /** not use for Type::e_points */
  public final Vec2 localNormal;

  /** usage depends on manifold type */
  public final Vec2 localPoint;

  public ManifoldType type;

  /** The number of manifold points. */
  public int pointCount;

  /**
   * creates a manifold with 0 points, with it's points array full of instantiated ManifoldPoints.
   */
  public Manifold() {
    points = new ManifoldPoint[Settings.maxManifoldPoints];
    for (int i = 0; i < Settings.maxManifoldPoints; i++) {
      points[i] = new ManifoldPoint();
    }
    localNormal = new Vec2();
    localPoint = new Vec2();
    pointCount = 0;
  }

  /**
   * Creates this manifold as a copy of the other
   * 
   * @param other
   */
  public Manifold(Manifold other) {
    points = new ManifoldPoint[Settings.maxManifoldPoints];
    localNormal = other.localNormal.clone();
    localPoint = other.localPoint.clone();
    pointCount = other.pointCount;
    type = other.type;
    // djm: this is correct now
    for (int i = 0; i < Settings.maxManifoldPoints; i++) {
      points[i] = new ManifoldPoint(other.points[i]);
    }
  }

  /**
   * copies this manifold from the given one
   * 
   * @param cp manifold to copy from
   */
  public void set(Manifold cp) {
    for (int i = 0; i < cp.pointCount; i++) {
      points[i].set(cp.points[i]);
    }

    type = cp.type;
    localNormal.set(cp.localNormal);
    localPoint.set(cp.localPoint);
    pointCount = cp.pointCount;
  }
}