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POSimulate the gravitational pull of a star?
 

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  1. POSimulate the gravitational pull of a star?
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    <p>I'm making a game where the player will (<em>on release of mouseclick</em>) shoot a "star" in a certain direction at an initial speed determined by how far he dragged the mouse before releasing. I have a "planet" (<em>stationary circle</em>) on the canvas that I want to exert a gravitational pull on the moving planet. I believe I'm using the right formulas for gravitational force and such, and I have it partially working - the planet affects the planet's trajectory up until a certain point, when the star seems to endlessly speed up and stop changing direction based on it's angle to the star. <strong>Any advice</strong>? (<em>I know that stars aren't supposed to orbit planets, it's the other way around. I coded the whole thing with the names interchanged so forgive that</em>).</p> <p>main class:</p> <pre><code> import acm.graphics.GCompound; import acm.graphics.GImage; import acm.graphics.GLabel; import acm.graphics.GLine; import acm.graphics.GMath; import acm.graphics.GObject; import acm.graphics.GPen; import acm.graphics.GPoint; import acm.graphics.GRect; import acm.graphics.GOval; import acm.graphics.GRectangle; import acm.program.GraphicsProgram; import acm.util.RandomGenerator; import java.awt.Color; import java.awt.event.MouseEvent; import java.util.*; public class Space extends GraphicsProgram { public static int APPLICATION_WIDTH = 1000; public static int APPLICATION_HEIGHT = 1000; private int size = 15; public static double pMass = 1000; public static int sMass = 20; public static double G = 200; private RandomGenerator rand = new RandomGenerator(); GOval planet, tempstar; shootingStar star; GLine line; double accel, xAccel, yAccel, xspeed, yspeed, angle; public void init(){ planet = new GOval(APPLICATION_WIDTH/2, APPLICATION_HEIGHT/2, 30, 30); planet.setFilled(true); planet.setFillColor(rand.nextColor()); add(planet); } public void mousePressed(GPoint point) { // draw a line tempstar = new GOval(point.getX() - size/2, point.getY() - size/2, size, size); tempstar.setFilled(true); tempstar.setColor(rand.nextColor()); add(tempstar); line = new GLine(tempstar.getX() + size/2, tempstar.getY() + size/2, point.getX(), point.getY()); add(line); line.setVisible(true); } public void mouseDragged(GPoint point) { line.setEndPoint(point.getX(), point.getY()); } public void mouseReleased(GPoint point){ xspeed = -.05*GMath.cosDegrees(getAngle(line))*GMath.distance(line.getStartPoint().getX(), line.getStartPoint().getY(), line.getEndPoint().getX(), line.getEndPoint().getY()); yspeed = .05*GMath.sinDegrees(getAngle(line))*GMath.distance(line.getStartPoint().getX(), line.getStartPoint().getY(), line.getEndPoint().getX(), line.getEndPoint().getY()); System.out.println(xspeed + " " + yspeed); star = new shootingStar(xspeed, yspeed, this); if(xspeed != 0) add(star, tempstar.getX(), tempstar.getY()); new Thread(star).start(); remove(tempstar); remove(line); } private double getAngle(GLine line) { return GMath.angle(line.getStartPoint().getX(), line.getStartPoint().getY(), line.getEndPoint().getX(), line.getEndPoint().getY()); } public void checkPlanet(){ accel = .06*GMath.distance(star.getX(), star.getY(), planet.getX(), planet.getY()); angle = correctedAngle(GMath.angle(planet.getX(), planet.getY(), star.getX(), star.getY())); xAccel = accel*GMath.cosDegrees(GMath.angle(planet.getX(), planet.getY(), star.getX(), star.getY())); yAccel = accel*GMath.sinDegrees(GMath.angle(planet.getX(), planet.getY(), star.getX(), star.getY())); double newX = xspeed - xAccel*.01; double newY = yspeed + yAccel*.01; xspeed = newX + xAccel*Math.pow(.01, 2)/2; yspeed = newY + yAccel*Math.pow(.01, 2)/2; star.setSpeed(xspeed, yspeed); } public double correctedAngle(double x) { return (x%360.0+360.0+180.0)%360.0-180.0; } } </code></pre> <p>Pertinent parts of shootingStar class:</p> <pre><code> public void run() { // move the ball by a small interval while (alive) { oneTimeStep(); } } // a helper method, move the ball in each time step private void oneTimeStep() { game1.checkPlanet(); shootingStar.move(xSpeed, ySpeed); pause(20); } public void setSpeed (double xspeed, double yspeed){ xSpeed = xspeed;; ySpeed = yspeed; } } </code></pre> <hr> <p>EDIT:</p> <p>Current Main Class Method:</p> <pre><code> public void checkPlanet(){ double xDistance = star.getX() - planet.getX(); double yDistance = star.getY() - planet.getY(); double distance = Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2)); accel = G*pMass/Math.pow(distance, 2); xAccel = accel * xDistance/distance; yAccel = accel * yDistance/distance; xspeed += xAccel; yspeed += yAccel; star.setSpeed(xspeed, yspeed); } </code></pre> <p>Current Star class Method:</p> <pre><code> public void run() { while (alive) { oneTimeStep(); } } private void oneTimeStep() { game1.checkPlanet(); shootingStar.move(xSpeed, ySpeed); pause(20); } public void setSpeed (double xspeed, double yspeed){ xSpeed = xspeed;; ySpeed = yspeed; } } </code></pre>
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    1. USuser1811903
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    1. COAfter a whole day of reading TDWTF, eventually stopping at [this](http://thedailywtf.com/Articles/Divine-by-Zero.aspx), I momentarily felt obligated to ask whether you wanted to simulate the gravitational pull or just the math behind it.
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      1. POSimulate the gravitational pull of a star?
      1. USTheodoros Chatzigiannakis
 

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