Download source: collide.zip
collide.java
import javafx.animation.Animation; import javafx.application.Application; import javafx.stage.Stage; import javafx.animation.KeyFrame; import javafx.animation.Timeline; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.scene.Scene; import javafx.scene.Node; import javafx.scene.layout.Pane; import javafx.scene.paint.Color; import javafx.util.Duration; import java.util.*; class TestPanel extends Pane { ArrayList<Ball> balls; ArrayList<Collision> collisions; double width, height; TestPanel() { Ball ball1, ball2; setStyle("-fx-background-color: honeydew;"); balls = new ArrayList<Ball>(); collisions = new ArrayList<Collision>(); balls.add(new Ball()); balls.add( new Ball(330,80,-5,8,Color.BLUE)); balls.add(new Ball(30,200,-9,7,Color.GREEN)); for (Ball b: balls) getChildren().add(b.circle); //for (Ball b: balls) System.out.println(b); //for (Node n: getChildren()) System.out.println(n); } public void update_collision_list(double tstep) { Collision c; collisions.clear(); for (Ball ball: balls) { c = intersect_window(ball,tstep); if (c!=null) collisions.add(c); } int nballs = balls.size(); for (int i=0; i<nballs-1; i++) { for (int j=i+1; j<nballs; j++) { Ball b1 = balls.get(i); Ball b2 = balls.get(j); c = intersect_balls(b1,b2,tstep); if (c!=null) collisions.add(c); } } } public void update() { width = getWidth(); height = getHeight(); double tstep, tmore; tmore = 1.0; while (tmore>0.0) { update_collision_list(tmore); if (collisions.size()>0) { java.util.List<Collision> list = collisions; Collections.<Collision>sort(list); Collision c = collisions.get(0); tstep = c.timestep; tmore = tmore - tstep; for (Ball ball: balls) ball.move(tstep); c.update_velocity(); } else { tstep = tmore; tmore = 0.0; for (Ball ball: balls) ball.move(tstep); } } } Collision intersect_window(Ball ball, double tstep) { double [] t = new double[4]; double tmax = 1000; if (ball.vx<0) { t[0] = (ball.px-ball.radius)/(-ball.vx); } else t[0] = tmax; if (ball.vx>0) { t[1] = (width - ball.px - ball.radius)/(ball.vx); } else t[1] = tmax; if (ball.vy<0) { t[2] = (ball.py-ball.radius)/(-ball.vy); } else t[2] = tmax; if (ball.vy>0) { t[3] = (height - ball.py - ball.radius)/ball.vy; } else t[3] = tmax; int idx = 0; double tx = t[0]; for (int i=1; i<4; i++) { if (t[i]>tx) continue; tx = t[i]; idx = i; } if (tx>tstep) { return null; // does not intersect } return new Collision(tx,ball,idx); } Collision intersect_balls(Ball ball1, Ball ball2, double tstep) { // relative velocity double rx = ball2.vx - ball1.vx; double ry = ball2.vy - ball1.vy; // relative position double px = ball2.px - ball1.px; double py = ball2.py - ball1.py; // test radius double r = ball1.radius + ball2.radius - 1; double C = px*px + py*py - r*r; if (C<0) return null; // already intersecting double B = rx*px+ry*py; double A = rx*rx+ry*ry; if (A<=0.0) return null; // no relative velocity // quadratic At^2 + 2Bt + C = 0 double radical = B*B-A*C; if (radical<=0.0) return null; // no intersection (balls miss) double R = Math.sqrt(radical); double t; if (B>0) t = (-B + R)/A; else t = -(B+R)/A; if (t<=0.0 || t>tstep) return null; // no intersection within time limit return new Collision(t,ball1,ball2); } } public class collide extends Application { ArrayList<Ball> balls = new ArrayList<Ball>(); @Override // Override the start method in the Application class public void start(Stage primaryStage) { // Create a pane TestPanel pane = new TestPanel(); // Create a handler for animation EventHandler<ActionEvent> eventHandler = e -> { pane.update(); }; // Create an animation Timeline animation = new Timeline( new KeyFrame(Duration.millis(30), eventHandler)); animation.setCycleCount(Timeline.INDEFINITE); animation.play(); // Start animation // Create a scene and place it in the stage Scene scene = new Scene(pane, 400, 400); primaryStage.setTitle("colliding balls"); // Set the stage title primaryStage.setScene(scene); // Place the scene in the stage primaryStage.show(); // Display the stage } public static void main(String args[] ) { launch(args); } }
Maintained by John Loomis, updated Thu Feb 15 20:09:59 2018