//The following two lines are needed to open and close a window.
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

//The following two lines are needed to let the window repaint itself.
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;

//The following two lines are needed for what we want to draw in the window.
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.GC;

public class DominicanSWT {
	public static void main(String[] args) {

		// The following two lines are needed to open the window.
		final Display display = new Display();
		final Shell shell = new Shell(display);

		// Everything from Point A to Point B will be executed
		// whenever the window needs to be redrawn.
		shell.addPaintListener(new PaintListener() {
			public void paintControl(PaintEvent e) {

				// Point A
				GC gc = e.gc; // Graphics Context: the pen you draw with
				final int width = 400; //in pixels
				final int height = width * 5 / 8; //in pixels
				final int stripe = height / 5;	//width of white stripes, in pixels

				//Convenient to put the origin (0, 0) at center of flag.
				final int ymax = height / 2;
				final int ymin = ymax - height;
				final int xmax = width / 2;
				final int xmin = xmax - width;
				final int s = stripe / 2;

				final int radius = s;	//of yellow circle in center

				for (int x = xmin; x < xmax; ++x) {
					for (int y = ymin; y < ymax; ++y) {
						Color color;

						// The last three arguments of Color are the amount of
						// red, green, blue:
						// minimum amount is zero, maximum is 255.

						// && means "and", || means "or".

						if (Math.hypot(x, y) < radius) {
							//could also say if (Math.sqrt(x * x + y * y) < radius) {
							//yellow circle in center
							color = new Color(display, 255, 255, 0);
						} else if (Math.abs(x) < s || Math.abs(y) < s) {
							//white horizontal an vertical stripes
							color = new Color(display, 255, 255, 255);
						} else if (x > 0 && y > 0 || x < 0 && y < 0) {
							//upper right or lower left: red
							color = new Color(display, 255, 0, 0);
						} else {
							//lower right or upper left: blue
							color = new Color(display, 0, 0, 255);
						}

						gc.setForeground(color);

						/*
						Change the pixel at location x, y to the foreground color.

						Our x's run from xmin (on the left) to xmax-1 (on the right).
						But the first argument of drawPoint must run from zero (on the
						left) to width-1 (on the right), so we subtract xmin.

						Our y's run from ymin (on the bottom) to ymax-1 (on the top).
						But the second argument of drawPoint must run from zero (on the
						top) to height-1 (on the bottom), so we add height and ymin
						to -y.
						*/

						gc.drawPoint(x - xmin, height - y + ymin);

						color.dispose(); // don't need this color any more
					}
				}

				gc.dispose(); // don't need gc any more
				// Point B
			}
		});

		shell.setText("Dominican flag");
		shell.open();

		// The following six lines are needed to close the window.
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}
		display.dispose();
	}
}