trig.java

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/*
	Netwar
	Copyright (C) 2002  Daniel Grund, Kyle Kakligian, Jason Komutrattananon, & Brian Hibler.

	This file is part of Netwar.

	Netwar is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	Netwar is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with Netwar; if not, write to the Free Software
	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package netwar.utils;

/** This is a purely static class used to perform trigonometric calculations rapidly.
 * To accomplish this, Trig uses a static array of precalculated results,
 * and merely performs an array look-up when the actual value is needed.
 * As a result, Trig.initialize() must be called once before any of the Trig methods are called.
 * Features like error trapping and automatic initialization at the first use were left out,
 * because it would slow the performance of the methods, which are intended to be called up to
 * several thousand times per second.
 * @author Group N2 - Project Netwar
 * @author Daniel Grund
  * @author Kyle Kakligian
 */
public class Trig {
  /** This is the number of angular units in a full circle.
    * Since the value is currently 360, they will be referred to as degrees.
    * This value can be changed to use another form of angular unit.
    * Note that the resolution of the sin/cos methods in Trig is equal to one angular unit.
    */
  public static final int fullCircle = 360;
  /** This is the number of angular units in a right angle.
    * If this is not exactly one fourth of fullCircle, it will cause miscalculations.
    * This is pre-calculated, to prevent an unnecessary divide from being added to each cos call.
    */
  public static final int right = 90;
  private static float sine[] = null;
  /** Sets up the Trig lookup table.
   */
  static {
    int i;
    if(sine == null) {
      sine = new float[fullCircle];
      for(i = 0; i < fullCircle; i++)
        sine[i] = (float)Math.sin((float)i / fullCircle * 2 * Math.PI);
    }
  }
  /** Returns the sine of the angle.
   * @param a The angle, in degrees.
   * @return The sine of a.
   * @see normalize(int)
   */
  public static float sin(int a) {return sine[a];}
  /** Returns the cosine of the angle.
   * @param a The angle, in degrees.
   * @return The cosine of a.
   * @see normalize(int)
   */
  public static float cos(int a) {
    if(a <= right)
      return sine[right - a];
    return sine[fullCircle + right - a];
  }
  /** Returns the measure of an angle in angular units (degrees) which has a measure of factor times pi radians.
   * Example: a factor of 1 corresponds to an angle of pi radians, which is 180 degrees, so pi(1) returns 180.
   * @param factor A number to multiply by PI to get the radian measure of an angle.
   * @return The degree measure of that angle.
   */
  static public int pi(float factor) {
    return (int)((long)(fullCircle * factor / 2) % (fullCircle));
  }
  /** Returns an angle equivalent to a, but guaranteed to be within the range [0, fullCirlce).
   * If an angle is less than 0 or greater than or equal to fullCircle,
   * it will cause an array out of bounds exception when you call Trig.sin or Trig.cos.
   * Use this method to ensure that your angle can be used with Trig.sin and Trig.cos.
   * @param a The angle to correct.
   * @return The corrected angle.
   */
  static public int normalize(int a) {
    a %= fullCircle;
    if(a < 0) a+= fullCircle;
    return a;
  }
}