Nick Dunn

package solarsystem;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.util.Observable;
import java.util.Observer;
import java.util.Random;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/**
 *
 * @author NDUNN
 * @date Jan 29, 2010
 */
public class SolarSystemView extends JComponent implements Observer {

    // Make the sun this proportion of screen DEFAULT_WIDTH
    private static final double SUN_RADIUS_PROPORTION = 0.2;
    private static final double EARTH_RADIUS_PROPORTION = .3 * SUN_RADIUS_PROPORTION;
    private static final double MOON_RADIUS_PROPORTION = .2 * EARTH_RADIUS_PROPORTION;

    private static final double EARTH_DISTANCE_PROPORTION_SCREEN = 0.4;
    private static final double MOON_DISTANCE_PROPORTION_SCREEN = 0.1;

    private static final int DEFAULT_WIDTH = 640;
    private static final int DEFAULT_HEIGHT = 640;

    private static final int NUM_STARS = 100;
    private static final int MAX_STAR_RADIUS = 3;

    private static final double TWO_PI = 2.0 * Math.PI;

    private SolarSystemModel model;
    private Random random = new Random();

    private int[] starX;
    private int[] starY;
    private int[] starRadius;

    public SolarSystemView(SolarSystemModel model) {
        super();
        this.model = model;
        setPreferredSize(new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT));

        createStarField(DEFAULT_WIDTH, DEFAULT_HEIGHT, MAX_STAR_RADIUS);
    }

    /**
     * Creates and populates our arrays of star x values, star y values, and
     * star radii
     * @param width     what is max x value we should consider for star
     * @param height    what is max y value we should consider for star
     */
    private void createStarField(int width, int height, int maxRadius) {
        // Create the arrays
        starX = new int[NUM_STARS];
        starY = new int[NUM_STARS];
        starRadius = new int[NUM_STARS];
        // Fill them in with random values
        for (int i = 0; i < NUM_STARS; i++) {
            starX[i] = random.nextInt(width);
            starY[i] = random.nextInt(height);
            starRadius[i] = random.nextInt(maxRadius);
        }
    }


    /**
     * Draws a black backdrop with star field
     * @param g2
     */
    private void drawSpaceBackdrop(Graphics2D g2) {
        // Draw background as black
        g2.setColor(Color.BLACK);
        g2.fillRect(0, 0, getWidth(), getHeight());

        g2.setColor(Color.WHITE);
        for (int i = 0; i < NUM_STARS; i++) {
            g2.fillOval(starX[i], starY[i], starRadius[i], starRadius[i]);
        }

    }

    /**
     *
     * @param g2 graphics context with (0,0) in center of screen (where sun will
     * be centered)
     */
    private void drawSun(Graphics2D g2) {
        int sunRadius = (int) (SUN_RADIUS_PROPORTION * getWidth());
        GradientPaint sunColor = new GradientPaint(0, 0, Color.YELLOW, 0, sunRadius, Color.RED);
        g2.setPaint(sunColor);
        g2.fillOval(-sunRadius/2, -sunRadius/2, sunRadius, sunRadius);
    }


    /**
     * Draws the earth to the screen, whose position is dependent upon the
     * day of the year
     * @param g2 the graphics context with its origin in the center of the sun
     */
    private void drawEarth(Graphics2D g2) {
        // Draw the earth
        // Calculate what portion along its orbit the earth is, and thus how
        // far to rotate about our centerpoint
        double earthTheta = map(model.getDay(), 0, SolarSystemModel.DAYS_PER_EARTH_REVOLUTION_AROUND_SUN, 0, TWO_PI);

        // Rotate our coordinate system by that much
        g2.rotate(earthTheta);
        // Translate the earth
        int distanceFromEarthToSun = (int) (EARTH_DISTANCE_PROPORTION_SCREEN * getWidth());
        g2.translate(distanceFromEarthToSun, 0);

        int earthRadius = (int) (EARTH_RADIUS_PROPORTION * getWidth());
        GradientPaint earthColor = new GradientPaint(0, 0, Color.BLUE, 0, earthRadius, Color.GREEN.darker(), true);
        g2.setPaint(earthColor);

        g2.fillOval(-earthRadius/2, -earthRadius/2, earthRadius, earthRadius);
    }

    /**
     * Draw the moon to the screen, whose position is dependent upon that of
     * the earth and the day of the year, which dictates its position along
     * its orbit around earth
     * @param g2 the graphics context with its origin in the center of the earth
     */
    private void drawMoon(Graphics2D g2) {
        double moonTheta = map(model.getDay(), 0, SolarSystemModel.DAYS_PER_MOON_ORBIT_AROUND_EARTH, 0, TWO_PI);

        int moonRadius = (int) (MOON_RADIUS_PROPORTION * getWidth());
        g2.setColor(Color.WHITE);
        g2.rotate(moonTheta);
        int distanceFromEarthToMoon = (int) (MOON_DISTANCE_PROPORTION_SCREEN * getWidth());
        // Translate the earth
        g2.translate(distanceFromEarthToMoon, 0);
        g2.fillOval(-moonRadius/2, -moonRadius/2, moonRadius, moonRadius);
    }


    @Override
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;

        drawSpaceBackdrop(g2);

        // Set the origin to be in the center of the screen
        g2.translate(getWidth()/2, getHeight()/2);

        // Order matters, since the earth placement is dependent upon the sun
        // placement, and the moon placement is dependent upon the earth placement
        drawSun(g2);

        drawEarth(g2);

        drawMoon(g2);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Solar System");

        final SolarSystemModel model = new SolarSystemModel();
        final SolarSystemView view = new SolarSystemView(model);
        model.addObserver(view);

        JPanel panel = new JPanel();
        panel.add(view);

        final JSlider daySlider = new JSlider(0,SolarSystemModel.DAYS_PER_EARTH_REVOLUTION_AROUND_SUN);
        daySlider.setPaintLabels(true);
        daySlider.setPaintTicks(true);
        daySlider.setMajorTickSpacing(100);
        panel.add(daySlider);
        daySlider.addChangeListener(new ChangeListener() {
            public void stateChanged(ChangeEvent e) {
                model.setDay(daySlider.getValue());
            }
        });
        frame.add(panel);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }


    public void update(Observable o, Object arg) {
        repaint();
    }


    /**
     * @param value The incoming value to be converted
     * @param low1  Lower bound of the value's current range
     * @param high1 Upper bound of the value's current range
     * @param low2  Lower bound of the value's target range
     * @param high2 Upper bound of the value's target range
     */
    public static final double map(double value, double low1, double high1, double low2, double high2) {

        double diff = value - low1;
        double proportion = diff / (high1 - low1);

        return lerp(low2, high2, proportion);
    }

    // Linearly interpolate between two values
    public static final double lerp(double value1, double value2, double amt) {
        return ((value2 - value1) * amt) + value1;
    }


}