Package net.phys2d.raw.strategies

Source Code of net.phys2d.raw.strategies.QuadSpaceStrategy

/*
* Phys2D - a 2D physics engine based on the work of Erin Catto.
*
* This source is provided under the terms of the BSD License.
*
* Copyright (c) 2006, Phys2D
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
*  * Redistributions of source code must retain the above
*    copyright notice, this list of conditions and the
*    following disclaimer.
*  * Redistributions in binary form must reproduce the above
*    copyright notice, this list of conditions and the following
*    disclaimer in the documentation and/or other materials provided
*    with the distribution.
*  * Neither the name of the Phys2D/New Dawn Software nor the names of
*    its contributors may be used to endorse or promote products
*    derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
* OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
* OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
* TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
* OF SUCH DAMAGE.
*/
package net.phys2d.raw.strategies;

import java.util.ArrayList;

import net.phys2d.raw.Body;
import net.phys2d.raw.BodyList;
import net.phys2d.raw.BroadCollisionStrategy;
import net.phys2d.raw.CollisionContext;
import net.phys2d.raw.shapes.AABox;

/**
* A strategy that divides the space into 4 repeatedly until either
* the target number of bodies is reached or the a given level of
* subdivisions is reached.
*
* @author Kevin Glass
*/
public class QuadSpaceStrategy implements BroadCollisionStrategy {
  /** The spaces dervied */
  private ArrayList spaces = new ArrayList();
  /** The number of sub divisions allows */
  private int maxLevels;
  /** The maximum number of bodies in a given space acceptable */
  private int maxInSpace;
 
  /**
   * Create a new strategy
   *
   * @param maxInSpace The maximum number of bodies in a given space acceptable
   * @param maxLevels The number of sub divisions allows
   */
  public QuadSpaceStrategy(int maxInSpace, int maxLevels) {
    this.maxInSpace = maxInSpace;
    this.maxLevels = maxLevels;
  }
 
  /**
   * @see net.phys2d.raw.BroadCollisionStrategy#collideBodies(net.phys2d.raw.CollisionContext, net.phys2d.raw.BodyList, float)
   */
  public void collideBodies(CollisionContext context, BodyList bodies, float dt) {
    spaces.clear();
   
    Space space = new Space(0,0,0,0);
   
    for (int i=0;i<bodies.size();i++) {
      Body body = bodies.get(i);
     
      space.addAABox(body.getShape().getBounds(),
               body.getPosition().getX(),
               body.getPosition().getY());
      space.addBody(body);
    }
   
    splitSpace(space, 0, maxInSpace, spaces);
   
    for (int i=0;i<spaces.size();i++) {
      context.resolve((Space) spaces.get(i), dt);
    }
  }

  /**
   * Get the spaces dervied in the quad process
   *
   * @return The list of spaces dervied (QuadSpaceStrategy.Space)
   */
  public ArrayList getSpaces() {
    return spaces;
  }
 
  /**
   * Considering splitting a space into 4 sub-spaces
   *
   * @param space The space to subdivide
   * @param level The number of levels of subdivision allowed
   * @param target The target number of bodies per space
   * @param spaceList The list of spaces to populate
   * @return True if the target has found
   */
  private boolean splitSpace(Space space, int level, int target, ArrayList spaceList) {
    if (space.size() <= target) {
      spaceList.add(space);
      return true;
    }
    if (level > maxLevels) {
      spaceList.add(space);
      return true;
    }
   
    Space[] spaces = space.getQuadSpaces();
    for (int j=0;j<4;j++) {
      splitSpace(spaces[j], level+1, target, spaceList);
    }

    return false;
  }
 
  /**
   * A single space within the quad-tree
   *
   * @author Kevin Glass
   */
  public class Space extends BodyList {
    /** The top left x coordinate */
    public float x1;
    /** The top left y coordinate */
    public float y1;
    /** The bottom right x coordinate */
    public float x2;
    /** The bottom right y coordinate */
    public float y2;
   
    /**
     * Create a space within the quad tree
     *
     * @param x The x position of the space
     * @param y The y position of the space
     * @param width The width of the space
     * @param height The height of the space
     */
    public Space(float x, float y, float width, float height) {
      this.x1 = x;
      this.y1 = y;
      this.x2 = x + width;
      this.y2 = y + height;
    }
   
    /**
     * Add a pody to the space
     *
     * @param body The body to add to the space
     */
    public void addBody(Body body) {
      add(body);
    }
   
    /**
     * Sub-divide this space into four seperate sub-spaces dolling
     * out the bodies into each space
     *
     * @return The spaces created by the subdivision (always length 4)
     */
    public Space[] getQuadSpaces() {
      Space[] spaces = new Space[4];
      float width = (this.x2 - this.x1) / 2;
      float height = (this.y2 - this.y1) / 2;
     
      spaces[0] = new Space(x1,y1,width,height);
      spaces[1] = new Space(x1,y1+height,width,height);
      spaces[2] = new Space(x1+width,y1,width,height);
      spaces[3] = new Space(x1+width,y1+height,width,height);
     
      for (int i=0;i<size();i++) {
        Body body = get(i);
        for (int j=0;j<4;j++) {
          if (spaces[j].touches(body.getShape().getBounds(),
                      body.getPosition().getX(),
                      body.getPosition().getY())) {
            spaces[j].add(body);
          }
        }
      }

      return spaces;
    }
   
    /**
     * Combine this space with another box
     *
     * @param box The box to include in this space
     * @param xp The x position of the box
     * @param yp The y position of the box
     */
    public void addAABox(AABox box, float xp, float yp) {
      float x1 = xp - box.getWidth();
      float x2 = xp + box.getWidth();
      float y1 = yp - box.getHeight();
      float y2 = yp + box.getHeight();
     
      this.x1 = Math.min(x1,this.x1);
      this.y1 = Math.min(y1,this.y1);
      this.x2 = Math.max(x2,this.x2);
      this.y2 = Math.max(y2,this.y2);
    }
   
    /**
     * Check if this space touches a box
     *
     * @param box The box to check against
     * @param xp The x position of the box to check
     * @param yp The y position of the box to check
     * @return True if the box touches these space
     */
    public boolean touches(AABox box, float xp, float yp) {
      float thisWidth = (this.x2 - this.x1) / 2;
      float thisHeight = (this.y2 - this.y1) / 2;
      float thisCx = this.x1 + thisWidth;
      float thisCy = this.y1 + thisHeight;
     
      float x1 = xp - (box.getWidth()/2);
      float x2 = xp + (box.getWidth()/2);
      float y1 = yp - (box.getHeight()/2);
      float y2 = yp + (box.getHeight()/2);
     
      float otherWidth = (x2 - x1) / 2;
      float otherHeight = (y2 - y1) / 2;
      float otherCx = xp;
      float otherCy = yp;
     
      float dx = Math.abs(thisCx - otherCx);
      float dy = Math.abs(thisCy - otherCy);
      float totalWidth = thisWidth + otherWidth;
      float totalHeight = thisHeight + otherHeight;
     
      return (totalWidth > dx) && (totalHeight > dy);
    }
   
    /**
     * Get the top left x coordinate of this space
     *
     * @return The top left x coordinate of this space
     */
    public float getX1() {
      return x1;
    }

    /**
     * Get the bottom right x coordinate of this space
     *
     * @return The bottom right x coordinate of this space
     */
    public float getX2() {
      return x2;
    }

    /**
     * Get the top left y coordinate of this space
     *
     * @return The top left y coordinate of this space
     */
    public float getY1() {
      return y1;
    }

    /**
     * Get the bottom right y coordinate of this space
     *
     * @return The bottom right y coordinate of this space
     */
    public float getY2() {
      return y2;
    }
   
    /**
     * @see java.lang.Object#toString()
     */
    public String toString() {
      return "[Space "+x1+","+y1+" "+x2+","+y2+" "+size()+" bodies]";
    }
  }
}
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