// Based on example from the book _Java in a Nutshell_ by David Flanagan. // Written by David Flanagan. Copyright (c) 1996 O'Reilly & Associates. import java.applet.*; import java.awt.*; import java.net.*; import java.lang.*; public class kepler extends Applet implements Runnable { //PlanckCanvas panel; planckSlider slide1; static double slideval; static final int nsteps = 400; // Time steps per revolution static final int pixelWidth = 250; // Width of ellipse in pixels // Conversion factors from Kepler natural units to CGS and basic constants static final double secyear=3.155815e+7; static final double AUcm = 1.496e+13; static final double Msolar = 1.989e+33; static final double G = 6.67259e-8; // Input data double a = 2.0; double acm = AUcm * a; double pixelScale = (double)pixelWidth/a/2.0; // Scale AU --> pixels int apixel = (int)(pixelScale*a); double e = 0.2; double b = Math.sqrt(a*a*(1.0-e*e)); int bpixel = (int)(pixelScale*b); double M = 3.0; double Mgrams = M * Msolar; double P; double Psec; double r = a*(1.0 - e); double rcm = acm*(1.0 - e); double theta = 0.0; double dtheta; double t = 0.0; double dt; int xshift; int yshift; Image sun; Image planet; int sizeSun; int sizePlanet; int x = 0; int y = 0; Color c1 = new Color(0x000000); Color c2 = new Color(0xffffff); Font font = new Font("Helvetica", Font.BOLD, 12); Image offscreen; int imagewidth, imageheight; Thread animator = null; boolean please_stop = false; boolean show_orbit = true; // Measure size of images being animated. We need this // information later to do clipping. public void init() { URL codeBase = getCodeBase(); sun = getImage(codeBase,"siriusA.jpg"); planet = getImage(codeBase,"siriusB.jpg"); // Following two methods seem to work with appletviewer, but // not with browsers (?). When run under browsers they tend to return // -1 for the size. Replaced with hard-wired sizes // sizeSun = sun.getWidth(this); //sizePlanet = planet.getWidth(this); sizeSun = 28; sizePlanet = 15; // Calculate period in years from Kepler's 3rd Law and // convert to CGS units (seconds). Then calculate the length of // a timestep in seconds. P = Math.sqrt(a*a*a/M); Psec = secyear * P; dt = Psec/((double) nsteps); // Lay out the GUI setLayout(new BorderLayout()); //panel = new planckCanvas(); //add("Center",panel); Panel pb = new Panel(); add("South",pb); pb.setBackground(Color.white); pb.add(slide1=new planckSlider((int)(e*100.),0,95)); slideval=planckSlider.slideval; e = slideval; System.out.println("e="+e); resize(400,320); } // Start the animation public void start() { e = planckSlider.slideval; animator = new Thread(this); animator.start(); } // Stop it. public void stop() { if (animator != null) animator.stop(); animator = null; } // Stop and start animating on mouse clicks. public boolean mouseDown(Event e, int x, int y) { // if running, stop it. Otherwise, start it. if (animator != null) please_stop = true; else { please_stop = false; start(); } return true; } // Draw the applet background void drawBackground(Graphics gr, Color c1) { e = planckSlider.slideval; Dimension size = this.size(); int w = size.width; int h = size.height; gr.setColor(c1); gr.fillRect(0, 0, w, h); xshift = w/2 + (int)(e*a*pixelScale); yshift = h/2 - 10; gr.drawImage(sun, xshift - sizeSun/2, yshift - sizeSun/2, this); if (show_orbit == true){ gr.setColor(c2); gr.drawOval(w/2 - apixel, yshift - bpixel, 2*apixel, 2*bpixel); gr.setFont(font); gr.setColor(Color.yellow); gr.drawString("e = "+e,350,20); gr.drawString("a = "+a,350,36); gr.drawString("M = "+M,350,52); } } // This method draws the background and image at its current position. public void paint(Graphics g) { drawBackground(g, c1); g.drawImage(planet, x-sizePlanet/2, y-sizePlanet/2, this); } // Main animator thread. public void run() { while(!please_stop) { Dimension d = this.size(); // Create offscreen image at the right size. if ((offscreen == null) || ((imagewidth != d.width) || (imageheight != d.height))) { // if (offscreen != null) offscreen.flush(); offscreen = this.createImage(d.width, d.height); imagewidth = d.width; imageheight = d.height; } // Set up clipping. We only need to draw within the // old rectangle that needs to be cleared and the new // one that is being drawn. // the old rectangle Rectangle oldrect = new Rectangle(x-sizePlanet/2, y-sizePlanet/2, sizePlanet, sizePlanet); // Update the coordinates for animation. // Update time and theta t = t + dt; dtheta = Math.sqrt(G*Mgrams*acm*(1.0 - e*e))*dt/rcm/rcm; theta = theta + dtheta; // Calculate r r = a*(1.0 - e*e)/(1.0 + e*Math.cos(theta)); rcm = AUcm * r; // Calculate relative x and y in pixels int xrel = (int)(r * Math.cos(theta) * pixelScale); int yrel = (int)(r * Math.sin(theta) * pixelScale); //x = xrel + xshift - sizePlanet/2; //y = yrel + yshift - sizePlanet/2; x = xrel + xshift; y = yrel + yshift; // the new rectangle Rectangle newrect = new Rectangle(x-sizePlanet/2, y-sizePlanet/2, sizePlanet, sizePlanet); // Compute the union of the rectangles Rectangle r = newrect.union(oldrect); // Use this rectangle as the clipping region when // drawing to the offscreen image, and when copying // from the offscreen image to the screen. Graphics g = offscreen.getGraphics(); // g.clipRect(r.x, r.y, r.width, r.height); // Draw into the off-screen image. paint(g); // Copy it all at once to the screen, using clipping. g = this.getGraphics(); // g.clipRect(r.x, r.y, r.width, r.height); g.drawImage(offscreen, 0, 0, this); // wait then draw it again try { Thread.sleep(20); } catch (InterruptedException e) { ; } } animator = null; } } /****************************************************************** // // // // Class planckSlider implements a slidebar for input of the // // temperature. Class has its own event processor that sets the // // class float variable "slideval" equal to the value of the // // slidebar when it is moved. This variable may then be accessed // // from another class as "planckSlider.slideval". // // // // Mike Guidry Feb. 20, 1997 // // // // *******************************************************************/ class planckSlider extends Panel { Scrollbar slider; Label value; static double slideval; Font font = new Font("Helvetica", Font.BOLD, 12); public planckSlider(int i, int min, int max) { setFont(font); setLayout(new GridLayout(1,3,15,15)); add(value = new Label("e: ",Label.RIGHT)); value.setForeground(Color.red); add(slider = new Scrollbar(Scrollbar.HORIZONTAL, i, 100, min, max)); slider.setBackground(Color.gray); add(value = new Label(String.valueOf((float)i/100.),Label.LEFT)); value.setForeground(Color.red); slideval=(double)i/100.; } public boolean handleEvent(Event evt) { if (evt.target.equals(slider)) { int i = slider.getValue(); value.setText(String.valueOf((float)i/100.)); slideval=(double)i/100.; // kepler keplerStart = new kepler(); // keplerStart.stop(); // keplerStart.init(); // keplerStart.start(); } return true; } // Rescale the preferred size of buttons in the layouts public Dimension preferredSize() { return new Dimension(600, 18); } } // ----- End class planckSlider -----