import java.util.Arrays;

/**

* A polygon that rotates around its center.

*/

public class RotatingPolygon extends RegularPolygon {

private int xmid;

private int ymid;

private int angle; // in degrees

private int[] x0; // original xpoints

private int[] y0; // original ypoints

/**

* Constructs a rotating polygon.

*

* @param nsides the number of sides

* @param radius from center to vertex

*/

public RotatingPolygon(int nsides, int radius) {

super(nsides, radius);

center();

}

/**

* Sets the rotation point to the middle.

*/

public void center() {

// find the average x and y values

int xsum = 0;

int ysum = 0;

for (int x : xpoints) {

xsum += x;

}

for (int y : ypoints) {

ysum += y;

}

xmid = (int) Math.round(xsum / npoints);

ymid = (int) Math.round(ysum / npoints);

// reset the rotation direction

angle = 359;

// save the original x and y points

x0 = Arrays.copyOf(xpoints, npoints);

y0 = Arrays.copyOf(ypoints, npoints);

}

@Override

public void step() {

// update the rotation angle

angle = (angle + 1) % 360;

final double RAD = Math.toRadians(angle);

final double COS = Math.cos(RAD);

final double SIN = Math.sin(RAD);

// translate the polygon points

for (int i = 0; i < npoints; i++) {

double t = x0[i] - xmid;

double v = y0[i] - ymid;

xpoints[i] = (int) Math.round(xmid + t * COS - v * SIN);

ypoints[i] = (int) Math.round(ymid + t * SIN + v * COS);

}

}

@Override

public void translate(int deltaX, int deltaY) {

super.translate(deltaX, deltaY);

center();

}

}