递归算法(2) - 勾股树

先来看一下效果：

实现代码：

/**
 * 勾股树
 * @param g Graphics
 * @param p1 起始点1
 * @param p2 起始点2
 * @param angle 每次迭代时的偏移角（弧度）
 * @param n 迭代次数
 */
function gouguTree(g:Graphics, p1:Point, p2:Point, angle:Number, n:int):void {
 /*
  *    p5
  *    /\
  * p3/A \p4
  *  +---+
  *  |   |
  *  +---+
  * p1   p2
  */
 var p3:Point, p4:Point, p5:Point;
 var length:Number;
 var p1_p2:Point = p2.subtract(p1);
 var baseAngle:Number = Math.atan2(p1_p2.y, p1_p2.x); 
 length = p1_p2.length;
 p3 = p1.add( Point.polar(length, baseAngle + Math.PI/2) );
 p4 = p3.add(p1_p2);
 g.moveTo(p1.x, p1.y);
 g.lineTo(p2.x, p2.y);
 g.lineTo(p4.x, p4.y);
 g.lineTo(p3.x, p3.y);
 g.lineTo(p1.x, p1.y);
 if(n > 0) {
 //if(length > 10) { //改为此句将会当长度小于10时结束。
  /*
   * cosA = |p3_p5| / |p3_p4|
   * |p3_p5| = cosA * |p1_p2| (p3_p4 = p1_p2)
   */
  var p3_p4:Point = p4.subtract(p3);
  var l_p3_p5:Number = Math.cos(angle) * length;
  p5 = p3.add( Point.polar(l_p3_p5, baseAngle + angle) );
  trace("@l_p3_p5",l_p3_p5);
  n--;
  gouguTree(g, p3, p5, angle, n);
  gouguTree(g, p5, p4, angle, n);
 }
}