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/*
 * Copyright (c) 2009-2022 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,
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package com.jme3.util;

import com.jme3.bounding.BoundingBox;
import com.jme3.bounding.BoundingSphere;
import com.jme3.bounding.BoundingVolume;
import com.jme3.math.FastMath;

/**
 * AreaUtils 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 4131 2009-03-19 20:15:28Z blaine.dev $
 */
public final class AreaUtils {
    /**
     * A private constructor to inhibit instantiation of this class.
     */
    private AreaUtils() {
    }
    
    /**
    * Estimate 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.getRadius() * 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.getXExtent() * bound.getXExtent()
                         + bound.getYExtent() * bound.getYExtent()
                         + bound.getZExtent() * bound.getZExtent();
        return ((radiusSquare * screenWidth * screenWidth) / (distance * distance * 4)) * FastMath.PI;
    }
}