areautils.java

来自「java 3d game jme 工程开发源代码」· Java 代码 · 共 84 行

/*
 * Copyright (c) 2003-2009 jMonkeyEngine
 * 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 'jMonkeyEngine' 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
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package com.jme.util;

import com.jme.bounding.BoundingBox;
import com.jme.bounding.BoundingSphere;
import com.jme.bounding.BoundingVolume;
import com.jme.math.FastMath;

/**
 * <code>AreaUtils</code> is used to calculate the area of various objects, such as bounding volumes.  These
 * functions are very loose approximations.
 * @author Joshua Slack
 * @version $Id: AreaUtils.java,v 1.12 2006/01/13 19:39:24 renanse Exp $
 */

public class AreaUtils {

  /**
   * calcScreenArea -- in Pixels
   * Aproximates the screen area of a bounding volume.  If the volume isn't a
   * BoundingSphere, BoundingBox, or OrientedBoundingBox 0 is returned.
   *
   * @param bound The bounds to calculate the volume from.
   * @param distance The distance from camera to object.
   * @param screenWidth The width of the screen.
   * @return The area in pixels on the screen of the bounding volume.
   */
  public static float calcScreenArea(BoundingVolume bound, float distance, float screenWidth) {
    if (bound.getType() == BoundingVolume.Type.Sphere)
      return calcScreenArea((BoundingSphere)bound, distance, screenWidth);
    else if (bound.getType() == BoundingVolume.Type.AABB)
      return calcScreenArea((BoundingBox)bound, distance, screenWidth);
    return 0.0f;
  }

  private static float calcScreenArea(BoundingSphere bound, float distance, float screenWidth) {
    // Where is the center point and a radius point that lies in a plan parallel to the view plane?
//    // Calc radius based on these two points and plug into circle area formula.
//    Vector2f centerSP = null;
//    Vector2f outerSP = null;
//    float radiusSq = centerSP.subtract(outerSP).lengthSquared();
    float radius = (bound.radius * screenWidth) / (distance * 2);
    return radius * radius * FastMath.PI;
  }

  private static float calcScreenArea(BoundingBox bound, float distance, float screenWidth) {
      // Calc as if we are a BoundingSphere for now...
      float radiusSquare=bound.xExtent*bound.xExtent+
          bound.yExtent*bound.yExtent+
          bound.zExtent*bound.zExtent;
        return ((radiusSquare*screenWidth*screenWidth)/(distance*distance*4))*FastMath.PI;
  }
}