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Polygon.java
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1998-09-22
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/*
* @(#)Polygon.java 1.18 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.awt;
/**
* The <code>Polygon</code> class encapsulates a description of a
* closed, two-dimensional region within a coordinate space. This
* region is bounded by an arbitrary number of line segments, each of
* which is one side of the polygon. Internally, a polygon
* comprises of a list of (<i>x</i>, <i>y</i>) coordinate pairs,
* where each pair defines a <i>vertex</i> of the polygon, and two
* successive pairs are the endpoints of a line that is a side of the
* polygon. The first and final pairs of (<i>x</i>, <i>y</i>)
* points are joined by a line segment that closes the polygon.
*
* @version 1.18, 07/01/98
* @author Sami Shaio
* @author Herb Jellinek
* @since JDK1.0
*/
public class Polygon implements Shape, java.io.Serializable {
/**
* The total number of points.
* @since JDK1.0
*/
public int npoints = 0;
/**
* The array of <i>x</i> coordinates.
* @since JDK1.0
*/
public int xpoints[] = new int[4];
/**
* The array of <i>y</i> coordinates.
* @since JDK1.0
*/
public int ypoints[] = new int[4];
/*
* Bounds of the polygon.
*/
protected Rectangle bounds = null;
/*
* JDK 1.1 serialVersionUID
*/
private static final long serialVersionUID = -6460061437900069969L;
/**
* Creates an empty polygon.
* @since JDK1.0
*/
public Polygon() {
}
/**
* Constructs and initializes a polygon from the specified
* parameters.
* @param xpoints an array of <i>x</i> coordinates.
* @param ypoints an array of <i>y</i> coordinates.
* @param npoints the total number of points in the polygon.
* @exception NegativeArraySizeException if the value of
* <code>npoints</code> is negative.
* @since JDK1.0
*/
public Polygon(int xpoints[], int ypoints[], int npoints) {
this.npoints = npoints;
this.xpoints = new int[npoints];
this.ypoints = new int[npoints];
System.arraycopy(xpoints, 0, this.xpoints, 0, npoints);
System.arraycopy(ypoints, 0, this.ypoints, 0, npoints);
}
/**
* Translates the vertices by <code>deltaX</code> along the
* <i>x</i> axis and by <code>deltaY</code> along the
* <i>y</i> axis.
* @param deltaX the amount to translate along the <i>x</i> axis
* @param deltaY the amount to translate along the <i>y</i> axis
* @since JDK1.1
*/
public void translate(int deltaX, int deltaY) {
for (int i = 0; i < npoints; i++) {
xpoints[i] += deltaX;
ypoints[i] += deltaY;
}
if (bounds != null) {
bounds.translate(deltaX, deltaY);
}
}
/*
* Calculate the bounding box of the points passed to the constructor.
* Sets 'bounds' to the result.
*/
void calculateBounds(int xpoints[], int ypoints[], int npoints) {
int boundsMinX = Integer.MAX_VALUE;
int boundsMinY = Integer.MAX_VALUE;
int boundsMaxX = Integer.MIN_VALUE;
int boundsMaxY = Integer.MIN_VALUE;
for (int i = 0; i < npoints; i++) {
int x = xpoints[i];
boundsMinX = Math.min(boundsMinX, x);
boundsMaxX = Math.max(boundsMaxX, x);
int y = ypoints[i];
boundsMinY = Math.min(boundsMinY, y);
boundsMaxY = Math.max(boundsMaxY, y);
}
bounds = new Rectangle(boundsMinX, boundsMinY,
boundsMaxX - boundsMinX,
boundsMaxY - boundsMinY);
}
/*
* Update the bounding box to fit the point x, y.
*/
void updateBounds(int x, int y) {
if (x < bounds.x) {
bounds.width = bounds.width + (bounds.x - x);
bounds.x = x;
}
else {
bounds.width = Math.max(bounds.width, x - bounds.x);
// bounds.x = bounds.x;
}
if (y < bounds.y) {
bounds.height = bounds.height + (bounds.y - y);
bounds.y = y;
}
else {
bounds.height = Math.max(bounds.height, y - bounds.y);
// bounds.y = bounds.y;
}
}
/**
* Appends a point to this polygon.
* <p>
* If an operation that calculates the bounding box of this polygon
* has already been performed, such as <code>getBounds</code>
* or <code>contains</code>, then this method updates the bounding box.
* @param x the <i>x</i> coordinate of the point.
* @param y the <i>y</i> coordinate of the point.
* @see java.awt.Polygon#getBounds
* @see java.awt.Polygon#contains
* @since JDK1.0
*/
public void addPoint(int x, int y) {
if (npoints == xpoints.length) {
int tmp[];
tmp = new int[npoints * 2];
System.arraycopy(xpoints, 0, tmp, 0, npoints);
xpoints = tmp;
tmp = new int[npoints * 2];
System.arraycopy(ypoints, 0, tmp, 0, npoints);
ypoints = tmp;
}
xpoints[npoints] = x;
ypoints[npoints] = y;
npoints++;
if (bounds != null) {
updateBounds(x, y);
}
}
/**
* Gets the bounding box of this polygon. The bounding box is the
* smallest rectangle whose sides are parallel to the <i>x</i> and
* <i>y</i> axes of the coordinate space, and that can completely
* contain the polygon.
* @return a rectangle that defines the bounds of this polygon.
* @since JDK1.1
*/
public Rectangle getBounds() {
return getBoundingBox();
}
/**
* @deprecated As of JDK version 1.1,
* replaced by <code>getBounds()</code>.
*/
public Rectangle getBoundingBox() {
if (bounds == null) {
calculateBounds(xpoints, ypoints, npoints);
}
return bounds;
}
/**
* Determines whether the specified point is inside the Polygon.
* Uses an even-odd insideness rule (also known as an alternating
* rule).
* @param p the point to be tested
*/
public boolean contains(Point p) {
return contains(p.x, p.y);
}
/**
* Determines whether the specified point is contained by this polygon.
* <p>
* (The <code>contains</code> method is based on code by
* Hanpeter van Vliet [hvvliet@inter.nl.net].)
* @param x the <i>x</i> coordinate of the point to be tested.
* @param y the <i>y</i> coordinate of the point to be tested.
* @return <code>true</code> if the point (<i>x</i>, <i>y</i>)
* is contained by this polygon;
* <code>false</code> otherwise.
* @since JDK1.1
*/
public boolean contains(int x, int y) {
return inside(x, y);
}
/**
* @deprecated As of JDK version 1.1,
* replaced by <code>contains(int, int)</code>.
*/
public boolean inside(int x, int y) {
if (getBoundingBox().inside(x, y)) {
int hits = 0;
int ySave = 0;
// Find a vertex that's not on the halfline
int i = 0;
while (i < npoints && ypoints[i] == y) {
i++;
}
// Walk the edges of the polygon
for (int n = 0; n < npoints; n++) {
int j = (i + 1) % npoints;
int dx = xpoints[j] - xpoints[i];
int dy = ypoints[j] - ypoints[i];
// Ignore horizontal edges completely
if (dy != 0) {
// Check to see if the edge intersects
// the horizontal halfline through (x, y)
int rx = x - xpoints[i];
int ry = y - ypoints[i];
// Deal with edges starting or ending on the halfline
if (ypoints[j] == y && xpoints[j] >= x) {
ySave = ypoints[i];
}
if (ypoints[i] == y && xpoints[i] >= x) {
if ((ySave > y) != (ypoints[j] > y)) {
hits--;
}
}
// Tally intersections with halfline
float s = (float)ry / (float)dy;
if (s >= 0.0 && s <= 1.0 && (s * dx) >= rx) {
hits++;
}
}
i = j;
}
// Inside if number of intersections odd
return (hits % 2) != 0;
}
return false;
}
}