Java Games Continued: Fun with Polygons - Pro Android Games - page 86

Constructors : The default constructor will create a four-sided polygon. You can
also define an N-sided polygon by giving two arrays representing the X0,X1,. . .Xn
and Y0,Y1,. . .Yn coordinates of the vertices where (X0,Y0) represents the
coordinates of the first vertex and so forth, The constructor also takes the number
of sides.

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calculateBounds(int xpoints[], int ypoints[], int npoints) : This method
calculates the bounds of the polygon given a set of X and Y coordinates and
number of points with respect to maximum integer values.

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addPoint(int x, int y) : This one adds a point to the polygon given its X and Y
coordinates.

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updateBounds(int x, int y) : This method updates the bounds of the polygon to
include a new point (X,Y).

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getBoundingBox() : This returns the rectangular bounds of the polygon.

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contains(int x, int y) : This one checks if the polygon contains a given point
(X,Y).

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float[] getPoints() : This method returns the X and Y coordinates of the vertices
of the polygon.
Both the Polygon and Rectangle classes are used by the next class, PolygonSprite , to define all game
objects.

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Listing 4-2. The Polygon Class for Asteroids

package ch04.common;

public class Polygon {

public int npoints;
public int[] ypoints;
public int[] xpoints;

protected Rectangle bounds;

public Polygon() {
xpoints = new int[4];
ypoints = new int[4];
}

public Polygon(int xpoints[], int ypoints[], int npoints) {
// Fix 4489009: should throw IndexOutofBoundsException instead
// of OutofMemoryException if npoints is huge
// and > {x,y}points.length
if (npoints > xpoints.length || npoints > ypoints.length) {
throw new IndexOutOfBoundsException(
"npoints > xpoints.length || npoints > ypoints.length");
}