polyline.java

来自「纯java操作系统jnode,安装简单和操作简单的个人使用的Java操作系统」· Java 代码 · 共 120 行

/*
 * $Id: PolyLine.java,v 1.1 2003/11/25 11:51:42 epr Exp $
 */
package org.jnode.awt.geom;

import java.awt.geom.Rectangle2D;

/**
 * @author Ewout Prangsma ([e-mail])
 */
public class PolyLine {

	/**
	 * Does the polyline described by the given line points contain
	 * (x,y)
	 * @param linePoints
	 * @param x
	 * @param y
	 * @return True if the point is contained, false otherwise
	 */
	public static boolean contains(double[] linePoints, double x, double y) {
		int wind = 0;
		final int cnt = linePoints.length;
		double lastX = linePoints[cnt - 2];
		double lastY = linePoints[cnt - 1];
		int oldquad = whichquad(lastX, lastY, x, y); /* get starting angle */
		for (int i = 0; i < cnt; i += 2) { /* for each point in the polygon */
			final double thisX = linePoints[i];
			final double thisY = linePoints[i + 1];
			final int newquad = whichquad(thisX, thisY, x, y);
			if (oldquad != newquad) { /* adjust wind */
				/*
				 * use mod 4 comparsions to see if we have
				 * advanced or backed up one quadrant 
				 */
				if (((oldquad + 1) & 3) == newquad)
					wind++;
				else if (((newquad + 1) & 3) == oldquad) {
					wind--;
				} else {
					/*
					* upper left to lower right, or
					* upper right to lower left. Determine
					* direction of winding  by intersection
					*  with x==0.
					*/
					double a = lastY - thisY;
					a *= (x - lastX);
					double b = lastX - thisX;
					a += lastY * b;
					b *= y;
					if (a > b) {
						wind += 2;
					} else {
						wind -= 2;
					}
					//System.out.println("x=" + x + "\ty=" + y + "\ta=" + a + "\tb=" + b + "\twind=" + wind);
				}
			}
			lastX = thisX;
			lastY = thisY;
			oldquad = newquad;
		}
		return (wind != 0); /* non zero means point in poly */

	}

	/**
	 * Gets the bounding box of a PolyLine.
	 * @param linePoints
	 * @return The calculated bounding box
	 */
	public static Rectangle2D getBounds(double[] linePoints) {
		double minX = Double.MAX_VALUE;
		double minY = Double.MAX_VALUE;
		double maxX = Double.MIN_VALUE;
		double maxY = Double.MIN_VALUE;

		final int cnt = linePoints.length;
		for (int i = 0; i < cnt; i += 2) {
			final double x = linePoints[i];
			final double y = linePoints[i + 1];
			minX = Math.min(minX, x);
			minY = Math.min(minY, y);
			maxX = Math.max(maxX, x);
			maxY = Math.max(maxY, y);
		}

		final double w = (maxX - minX) + 1;
		final double h = (maxY - minY) + 1;
		return new Rectangle2D.Double(minX, minY, w, h);
	}

	/**
	 * Figure out which quadrent pt is in with respect to orig
	 * @param x
	 * @param y
	 * @param origX
	 * @param origY
	 * @return The quadrant
	 */
	private static int whichquad(double x, double y, double origX, double origY) {
		final int quad;
		if (x < origX) {
			if (y < origY) {
				quad = 2;
			} else {
				quad = 1;
			}
		} else {
			if (y < origY) {
				quad = 3;
			} else {
				quad = 0;
			}
		}
		return quad;
	}
}