org.jbox2d.collision.WorldManifold Maven / Gradle / Ivy

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 * Copyright (c) 2013, Daniel Murphy
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
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package org.jbox2d.collision;

import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Rot;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Transform;
import org.jbox2d.common.Vec2;

/**
 * This is used to compute the current state of a contact manifold.
 * 
 * @author daniel
 */
public class WorldManifold {
  /**
   * World vector pointing from A to B
   */
  public final Vec2 normal;

  /**
   * World contact point (point of intersection)
   */
  public final Vec2[] points;

  /**
   * A negative value indicates overlap, in meters.
   */
  public final float[] separations;

  public WorldManifold() {
    normal = new Vec2();
    points = new Vec2[Settings.maxManifoldPoints];
    separations = new float[Settings.maxManifoldPoints];
    for (int i = 0; i < Settings.maxManifoldPoints; i++) {
      points[i] = new Vec2();
    }
  }

  private final Vec2 pool3 = new Vec2();
  private final Vec2 pool4 = new Vec2();

  public final void initialize(final Manifold manifold, final Transform xfA, float radiusA,
      final Transform xfB, float radiusB) {
    if (manifold.pointCount == 0) {
      return;
    }

    switch (manifold.type) {
      case CIRCLES: {
        final Vec2 pointA = pool3;
        final Vec2 pointB = pool4;

        normal.x = 1;
        normal.y = 0;
        Vec2 v = manifold.localPoint;
        // Transform.mulToOutUnsafe(xfA, manifold.localPoint, pointA);
        // Transform.mulToOutUnsafe(xfB, manifold.points[0].localPoint, pointB);
        pointA.x = (xfA.q.c * v.x - xfA.q.s * v.y) + xfA.p.x;
        pointA.y = (xfA.q.s * v.x + xfA.q.c * v.y) + xfA.p.y;
        Vec2 mp0p = manifold.points[0].localPoint;
        pointB.x = (xfB.q.c * mp0p.x - xfB.q.s * mp0p.y) + xfB.p.x;
        pointB.y = (xfB.q.s * mp0p.x + xfB.q.c * mp0p.y) + xfB.p.y;

        if (MathUtils.distanceSquared(pointA, pointB) > Settings.EPSILON * Settings.EPSILON) {
          normal.x = pointB.x - pointA.x;
          normal.y = pointB.y - pointA.y;
          normal.normalize();
        }

        final float cAx = normal.x * radiusA + pointA.x;
        final float cAy = normal.y * radiusA + pointA.y;

        final float cBx = -normal.x * radiusB + pointB.x;
        final float cBy = -normal.y * radiusB + pointB.y;

        points[0].x = (cAx + cBx) * .5f;
        points[0].y = (cAy + cBy) * .5f;
        separations[0] = (cBx - cAx) * normal.x + (cBy - cAy) * normal.y;
      }
        break;
      case FACE_A: {
        final Vec2 planePoint = pool3;

        Rot.mulToOutUnsafe(xfA.q, manifold.localNormal, normal);
        Transform.mulToOut(xfA, manifold.localPoint, planePoint);

        final Vec2 clipPoint = pool4;

        for (int i = 0; i < manifold.pointCount; i++) {
          // b2Vec2 clipPoint = b2Mul(xfB, manifold->points[i].localPoint);
          // b2Vec2 cA = clipPoint + (radiusA - b2Dot(clipPoint - planePoint,
          // normal)) * normal;
          // b2Vec2 cB = clipPoint - radiusB * normal;
          // points[i] = 0.5f * (cA + cB);
          Transform.mulToOut(xfB, manifold.points[i].localPoint, clipPoint);
          // use cA as temporary for now
          // cA.set(clipPoint).subLocal(planePoint);
          // float scalar = radiusA - Vec2.dot(cA, normal);
          // cA.set(normal).mulLocal(scalar).addLocal(clipPoint);
          // cB.set(normal).mulLocal(radiusB).subLocal(clipPoint).negateLocal();
          // points[i].set(cA).addLocal(cB).mulLocal(0.5f);

          final float scalar =
              radiusA
                  - ((clipPoint.x - planePoint.x) * normal.x + (clipPoint.y - planePoint.y)
                      * normal.y);

          final float cAx = normal.x * scalar + clipPoint.x;
          final float cAy = normal.y * scalar + clipPoint.y;

          final float cBx = -normal.x * radiusB + clipPoint.x;
          final float cBy = -normal.y * radiusB + clipPoint.y;

          points[i].x = (cAx + cBx) * .5f;
          points[i].y = (cAy + cBy) * .5f;
          separations[i] = (cBx - cAx) * normal.x + (cBy - cAy) * normal.y;
        }
      }
        break;
      case FACE_B:
        final Vec2 planePoint = pool3;
        Rot.mulToOutUnsafe(xfB.q, manifold.localNormal, normal);
        Transform.mulToOut(xfB, manifold.localPoint, planePoint);

        // final Mat22 R = xfB.q;
        // normal.x = R.ex.x * manifold.localNormal.x + R.ey.x * manifold.localNormal.y;
        // normal.y = R.ex.y * manifold.localNormal.x + R.ey.y * manifold.localNormal.y;
        // final Vec2 v = manifold.localPoint;
        // planePoint.x = xfB.p.x + xfB.q.ex.x * v.x + xfB.q.ey.x * v.y;
        // planePoint.y = xfB.p.y + xfB.q.ex.y * v.x + xfB.q.ey.y * v.y;

        final Vec2 clipPoint = pool4;

        for (int i = 0; i < manifold.pointCount; i++) {
          // b2Vec2 clipPoint = b2Mul(xfA, manifold->points[i].localPoint);
          // b2Vec2 cB = clipPoint + (radiusB - b2Dot(clipPoint - planePoint,
          // normal)) * normal;
          // b2Vec2 cA = clipPoint - radiusA * normal;
          // points[i] = 0.5f * (cA + cB);

          Transform.mulToOut(xfA, manifold.points[i].localPoint, clipPoint);
          // cB.set(clipPoint).subLocal(planePoint);
          // float scalar = radiusB - Vec2.dot(cB, normal);
          // cB.set(normal).mulLocal(scalar).addLocal(clipPoint);
          // cA.set(normal).mulLocal(radiusA).subLocal(clipPoint).negateLocal();
          // points[i].set(cA).addLocal(cB).mulLocal(0.5f);

          // points[i] = 0.5f * (cA + cB);

          //
          // clipPoint.x = xfA.p.x + xfA.q.ex.x * manifold.points[i].localPoint.x + xfA.q.ey.x *
          // manifold.points[i].localPoint.y;
          // clipPoint.y = xfA.p.y + xfA.q.ex.y * manifold.points[i].localPoint.x + xfA.q.ey.y *
          // manifold.points[i].localPoint.y;

          final float scalar =
              radiusB
                  - ((clipPoint.x - planePoint.x) * normal.x + (clipPoint.y - planePoint.y)
                      * normal.y);

          final float cBx = normal.x * scalar + clipPoint.x;
          final float cBy = normal.y * scalar + clipPoint.y;

          final float cAx = -normal.x * radiusA + clipPoint.x;
          final float cAy = -normal.y * radiusA + clipPoint.y;

          points[i].x = (cAx + cBx) * .5f;
          points[i].y = (cAy + cBy) * .5f;
          separations[i] = (cAx - cBx) * normal.x + (cAy - cBy) * normal.y;
        }
        // Ensure normal points from A to B.
        normal.x = -normal.x;
        normal.y = -normal.y;
        break;
    }
  }
}