/*
 * stars.java
 *
 * Created on 31 December 2003, 12:06
 */

import java.awt.*;
import java.awt.image.*;
import java.awt.color.*;
import java.applet.*;

/**
 *
 * @author  Allen
 */
public class starsApplet extends Applet {

	public void init()
	{
		initForm();

		// TODO: Add any constructor code after initForm call.
	}

	
	private static class myPoint {
		int x;
		int y;
		int z;
	}
	
	
	private final static int NUM_STARS = 600;   // must be final static for use to dimension arrays !
	private final static boolean SHOW_FRAME_TIME = false;	// show frame time or fps
	private final static int SCALE = 1;	// make the final drawn image bigger (or smaller!)

	private static myPoint[] stars = new myPoint[NUM_STARS];

	private final static int SLEEP_TIME = 20;	// period of thread sleep in ms
	private static int FRAMES_TO_CHECK = 100;	// how many frames to average the frame time over
	private static int width = 320;
	private static int half_w = width / 2;
	private static int height = 240;
	private static int half_h = height / 2;
	private static long frameTime, timeTemp;
	private static int frameCount = 0;
	private static float fps = (float)0.0;
	private static BufferedImage img;
	private static Graphics g;
	


	/** Creates new form stars */
	void initForm() {

		int loop;

//		initComponents();
		
		// set the number of frames to do the timing over (aim for 2 second update based on sleep time)
		FRAMES_TO_CHECK = 2000 / SLEEP_TIME;
		
//		setTitle("Stars");
//		setSize(width * SCALE, height * SCALE);
		
		setVisible(true);
		setBackground(Color.black);
		img = new BufferedImage(width, height, ColorSpace.TYPE_RGB);

		for(loop = 0; loop < NUM_STARS; loop++) {
			stars [loop] = new myPoint();
			// putting the x, y coords in as double width/height may give a better spread of distant stars
			// but makes them look dimmer ?
			stars [loop].x = my_random(width);
			stars [loop].y = my_random(height);
			stars [loop].z = loop + 1;
		}

		g = this.getGraphics();
		timeTemp = System.currentTimeMillis();


		for(;;) {
		
			try { Thread.sleep(SLEEP_TIME); } catch (Exception e) {}
			repaint();


		}
	}
	
	

	/** This method is called from within the constructor to
	 * initialize the form.
	 * WARNING: Do NOT modify this code. The content of this method is
	 * always regenerated by the Form Editor.
	 */
/*	private void initComponents() {//GEN-BEGIN:initComponents
		
		addWindowListener(new java.awt.event.WindowAdapter() {
			public void windowClosing(java.awt.event.WindowEvent evt) {
				exitForm(evt);
			}
		});
		
		pack();
	}//GEN-END:initComponents

*/

	/** Exit the Application */
	private void exitForm(java.awt.event.WindowEvent evt) {//GEN-FIRST:event_exitForm
		System.exit(0);
	}//GEN-LAST:event_exitForm



	/**
	* @param args the command line arguments
	*/
	public static void main(String args[]) {
		new stars().show();
	}
	

	public void paint(Graphics g) {
	
		int greyscale_method = 2;	// use to try alternate greyscale technique
	
		int loop, x, y;
		double z_div;
		int g_scale;
		int star_colour = 0;	// bloody compiler, might be used uninitialised
		
		
		z_div = (double)NUM_STARS / 255;	// shades of grey (255 max!)
		g_scale = 0x010101;
		
		if(img != null) {
			// draw stars in black
			// (translating to x,y screen coords for each, simple z division)
			for(loop=0; loop < NUM_STARS; loop++)
			{
				x = ((stars[loop].x << 7) / stars[loop].z) + half_w;
				y = ((stars[loop].y << 7) / stars[loop].z) + half_h;
				if((x > 0) && ( x < width) && ( y > 0) && (y < height))
   		        	img.setRGB(x, y, 0x000000);	// set to black
			}
			// move stars and draw in white
			for(loop = 0; loop < NUM_STARS; loop++)
			{
				stars[loop].z = stars[loop].z - 2;
				if(stars[loop].z < 1)
					stars[loop].z = stars[loop].z + NUM_STARS;

				x = ((stars[loop].x << 7) / stars[loop].z) + half_w;
				y = ((stars[loop].y << 7) / stars[loop].z) + half_h;
				if((x > 0) && ( x < width) && ( y > 0) && (y < height))
				{
					//two choices of greyscale technique,
					if(greyscale_method == 1) {
						// 1: from the number of stars (and therefore max Z) and divide by the number
						// of shades of grey
						star_colour = (int)(256 - (stars[loop].z / z_div)) ;
					}
					if(greyscale_method == 2) {
						// 2: only shade the nearest 256(ish) Z values (so only around 200 visible at
						// any time, but looks better because there is no distant block of stars)
						if(stars[loop].z > 254) {
							star_colour = 1;
						}
						else
						{
							star_colour = 255 - stars[loop].z;
						}
					}
					star_colour = star_colour * g_scale;
   		        	img.setRGB(x, y, star_colour);	// set to z defined shade of grey
   		        }
			}

			// draw the scaled image
			g.drawImage(img, 0, 0, width * SCALE, height * SCALE, 0, 0, width, height, this);

			g.setColor(Color.white);
			frameCount++;
			if(SHOW_FRAME_TIME) {
				if(frameCount > FRAMES_TO_CHECK) {
					frameCount = 0;
					frameTime = System.currentTimeMillis() - timeTemp;
					timeTemp = System.currentTimeMillis();
				}
				g.drawString("Frame time: "+ (((float)frameTime / FRAMES_TO_CHECK) - SLEEP_TIME) +" ms (+ " + SLEEP_TIME + "ms)", 10, (height * SCALE) - 10);
			}
			else
			{
				if(System.currentTimeMillis() > timeTemp + 2000) {	// check fps every two secs
					frameTime = System.currentTimeMillis() - timeTemp;
					fps = (float)frameCount / frameTime * 1000;
					frameCount = 0;
					timeTemp = System.currentTimeMillis();
				}
				g.setColor(Color.white);
				g.drawString("FPS: "+ fps, 10, (height * SCALE) - 10);
			}
		}
	}
		
		
	
	public void update(Graphics g) {
			paint(g);
	}
	
	

	// generate a random number between -(n/2) and (n/2) (but not 0)
	private int my_random(int n) {
	
		int rnumber = 0;
		
		while(rnumber == 0) {
			rnumber = (int)((Math.random() * n) - (n / 2));
		}
	
		return(rnumber);
	}
	
	// Variables declaration - do not modify//GEN-BEGIN:variables
	// End of variables declaration//GEN-END:variables

}