NEED HELP WITH MY GAME "FREEFALL"

is this Philip?

Yes.

When the ball starts moving down the line the x and y axis increments are not accurate enough for the ball to move along the line. Can you tell me how i can achieve this.

The inclined plane part is a little different than the falling ball. But the locating of the ball is pretty close in both cases.

Try this:

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import javax.swing.*;

import javax.swing.event.*;

public class TC extends JPanel implements ActionListener, ChangeListener {

DropController dropController = new DropController(this);

Ellipse2D.Double ball;

Line2D.Doubleline;

doubleinitialX;

doublefloor;

doublelastTheta = 0;

doubleg = 3.0;

doubledLast;

doublevLast;

doublexLast;

doublexVelocity;

doublerestitution = 0.75;

boolean isFalling;

boolean isRolling;

public void actionPerformed(ActionEvent e) {

String ac = e.getActionCommand();

if(ac.equals("drop")) {

isFalling = true;

dropController.start();

} else if(ac.equals("reset")) {

dropController.stop();

double pivotX = line.getX1() + (line.getX2() - line.getX1())/2;

double pivotY = line.getY1() + (line.getY2() - line.getY1())/2;

double verticalOffset = (ball.height/2)*(1.0 - 1.0/Math.cos(lastTheta));

double dx = pivotX - initialX - ball.getWidth()/2;

double rotationOffset = dx*Math.tan(lastTheta);

floor = pivotY + verticalOffset - rotationOffset;

ball.setFrame(initialX, 0, ball.width, ball.height);

vLast = 0;

dLast = 0;

isFalling = false;

isRolling = false;

repaint();

}

}

public void stateChanged(ChangeEvent e) {

JSlider slider = (JSlider)e.getSource();

int value = slider.getValue();

tilt(Math.toRadians(value));

repaint();

}

public void step() {

if(isFalling)

dropBall();

else if(isRolling) {

if(!hasClearedPlane())

rollBall();

else {

isRolling = false;

xVelocity = vLast*Math.cos(lastTheta);

vLast *=Math.sin(lastTheta);

xLast = 0;

dLast = 0;

freeFall();

}

} else

freeFall();

}

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Graphics2D g2 = (Graphics2D)g;

g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

if(ball == null)

initGeom();

g2.setPaint(Color.green.darker());

g2.draw(line);

g2.setPaint(Color.red);

g2.fill(ball);

g2.setPaint(Color.blue);

int w = getWidth();

g2.draw(new Line2D.Double(w/4, floor, w*3/4, floor));

}

private void initGeom() {

int w = getWidth();

int h = getHeight();

int DIA = 30;

line = new Line2D.Double(w/4, h*3/4, w*3/4, h*3/4);

floor = line.getY1();

// Near the center is best for initial x value.

initialX = w*7/12.0;

double y = 0;

ball = new Ellipse2D.Double(initialX, y, DIA, DIA);

vLast = 0;

dLast = 0;

}

private void tilt(double theta) {

// Rotate line at its center.

Point2D p1 = line.getP1();

Point2D p2 = line.getP2();

double length = p1.distance(p2);

Point2D.Double pivot = new Point2D.Double();

pivot.x = p1.getX() + (p2.getX() - p1.getX())/2;

pivot.y = p1.getY() + (p2.getY() - p1.getY())/2;

double x = pivot.getX() + (length/2)*Math.cos(theta);

double y = pivot.getY() + (length/2)*Math.sin(theta);

p2.setLocation(x, y);

x = pivot.x + (length/2)*Math.cos(theta+Math.PI);

y = pivot.y + (length/2)*Math.sin(theta+Math.PI);

p1.setLocation(x, y);

line.setLine(p1, p2);

// Adjust floor/ball height on tilted line in two parts:

// Locate ball center above the intersection of the tilted line

// and the vertical line that passes through the ball center.

double verticalOffset = -(ball.height/2)/Math.cos(theta) + ball.height/2;

// Find vertical displacement of intersection of tilted line

// and vertical line caused by rotation angle of tilted line.

double dx = pivot.x - ball.getCenterX();

double rotationOffset = dx*Math.tan(theta);

// Find floor == point of contact between ball and the horizontal.

floor = pivot.y + verticalOffset - rotationOffset;

// If the animation is not running we can adjust the

// vertical position of ball to rest on floor.

if(!dropController.isRunning())

ball.y = floor - ball.height;

lastTheta = theta;

}

public void dropBall() {

// v = v0t + gt; t = 1

// d = d0 + v0t + (v - v0)t/2

double v = vLast + g;

double d = dLast + (v + vLast)/2.0;

double x = ball.getX();

double y = checkForContact(d);

ball.setFrameFromDiagonal(x, y, x + ball.width, y + ball.height);

repaint();

// If there was no contact with line, update state variables.

if(y == d) {

dLast = d;

vLast = v;

}

}

private double checkForContact(double y) {

if(y + ball.height >= floor) { // contact

// Find velocity at contact.

// v^2 = v0^2 + 2gd

// v = sqrt(v0*v0 + 2gd)

double distanceToContact = floor - ball.height - dLast;

double contactVelocity = Math.sqrt(vLast*vLast + 2.0*g*distanceToContact);

// Apply coefficient of restitution to kinetic energy.

// ke = (mv^2)/2

double ke = (contactVelocity*contactVelocity)/2.0;

double keAfter = restitution*ke;

// Calculate new rebound velocity.

double reboundVelocity = -Math.sqrt(2.0*keAfter);

// Reset variables to reflect the contact with line.

y = floor - ball.height;

vLast = reboundVelocity;

dLast = y;

// Determine the rebound height after contact.

// v2^2 = v1^2 + 2gd

// d = (v1^2)/2g

double reboundHeight = (reboundVelocity*reboundVelocity)/(2.0*g);

// Switch from falling to rolling/stop if rebound height is small.

if(reboundHeight < 1.0) {

isFalling = false;

if(lastTheta == 0.0)

dropController.stop();

else {

vLast = 0;

dLast = 0;

isRolling = true;

}

y = floor - ball.height;

}

}

return y;

}

private void rollBall() {

// v = v0t + gt*sin(theta); t = 1

// d = d0 + v0t + (v - v0)t/2

double v = vLast + g*Math.sin(lastTheta);

double d = dLast + (v + vLast)/2.0;

double x = ball.getX() + d*Math.cos(lastTheta);

double y = ball.getY() + d*Math.sin(lastTheta);

ball.setFrameFromDiagonal(x, y, x + ball.width, y + ball.height);

floor = ball.getY() + ball.getHeight();

repaint();

dLast = d;

vLast = v;

}

private boolean hasClearedPlane() {

if(lastTheta < 0.0)

return ball.getCenterX() < line.getX1();

else

return ball.getCenterX() > line.getX2();

}

private void freeFall() {

// v = v0t + gt; t = 1

// d = d0 + v0t + (v - v0)t/2

double v = vLast + g;

double d = dLast + (v + vLast)/2.0;

xLast += xVelocity;

double x = ball.getX() + xLast;

double y = ball.getY() + d;

ball.setFrameFromDiagonal(x, y, x + ball.width, y + ball.height);

floor = ball.getY() + ball.getHeight();

repaint();

if(ball.getY() > getHeight())

dropController.stop();

else {

dLast = d;

vLast = v;

}

}

private JPanel getControls() {

JSlider slider = new JSlider(JSlider.HORIZONTAL, -45, 45, 0);

slider.setPaintTicks(true);

slider.setMinorTickSpacing(5);

slider.setMajorTickSpacing(15);

slider.setPaintLabels(true);

slider.addChangeListener(this);

JButton drop = new JButton("drop");

drop.setActionCommand("drop");

drop.addActionListener(this);

JButton reset = new JButton("reset");

reset.setActionCommand("reset");

reset.addActionListener(this);

JPanel panel = new JPanel(new GridBagLayout());

GridBagConstraints gbc = new GridBagConstraints();

gbc.insets = new Insets(1,0,1,0);

gbc.weightx = 1.0;

panel.add(drop, gbc);

gbc.gridwidth = gbc.REMAINDER;

panel.add(reset, gbc);

gbc.gridwidth = 2;

gbc.fill = gbc.HORIZONTAL;

panel.add(slider, gbc);

return panel;

}

public static void main(String[] args) {

TC test = new TC();

JFrame f = new JFrame();

f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

f.getContentPane().add(test);

f.getContentPane().add(test.getControls(), "Last");

f.setSize(500,500);

f.setLocation(200,100);

f.setVisible(true);

}

}

class DropController implements Runnable {

TC trueContact;

Thread thread;

boolean animating;

public DropController(TC tc) {

trueContact = tc;

animating = false;

}

public void run() {

while(animating) {

try {

Thread.sleep(100);

} catch(InterruptedException ie) {

System.out.printf("sleep interrupted%n");

animating = false;

}

trueContact.step();

}

}

public void start() {

if(!animating) {

animating = true;

thread = new Thread(this);

thread.setPriority(Thread.NORM_PRIORITY);

thread.start();

}

}

public void stop() {

if(animating) {

animating = false;

thread.interrupt();

thread = null;

System.out.printf("thread stopped%n");

}

}

public boolean isRunning() { return animating; }

}

crwooda at 2007-7-15 4:24:12 >

rotate the line so that the slope is inverted and then invert the slope again...

Think there is solution for that?

To change the angle of rotation of the line while the ball is moving. To do this I

started with a new app that focuses on the ball rolling on an inclined plane. Along

the way I found some errors in TC above; I'll try to list them in an edit to that reply.

This is a bit choppy at times but I think you will be able to work with it.

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import javax.swing.*;

import javax.swing.event.*;

public class RollingBall extends JPanel implements ActionListener, ChangeListener {

RollController rollController = new RollController(this);

Ellipse2D.Double ball;

Line2D.Doubleline;

Point2D.Doublepivot;

doubleinitialX;

doubleinitialY;

doublefloor;

doubleg = 1.25;

doubletheta = 0;

doublevLast;

public void actionPerformed(ActionEvent e) {

String ac = e.getActionCommand();

if(ac.equals("roll")) {

rollController.start();

} else if(ac.equals("reset")) {

rollController.stop();

double verticalOffset = (ball.height/2)*(1.0 - 1.0/Math.cos(theta));

double dx = pivot.x - initialX - ball.getWidth()/2;

double rotationOffset = dx*Math.tan(theta);

floor = pivot.y + verticalOffset - rotationOffset;

ball.setFrame(initialX, initialY, ball.width, ball.height);

initialize();

repaint();

}

}

public void stateChanged(ChangeEvent e) {

JSlider slider = (JSlider)e.getSource();

theta = Math.toRadians(slider.getValue());

tilt();

repaint();

}

public void roll() {

if(isOverLine())

rollBall();

else {

rollController.stop();

initialize();

}

}

private void initialize() {

positionBall();

vLast = 0;

repaint();

}

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Graphics2D g2 = (Graphics2D)g;

g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

if(ball == null)

initGeom();

g2.setPaint(Color.green.darker());

g2.draw(line);

g2.setPaint(Color.red);

g2.fill(ball);

g2.setPaint(Color.blue);

double cx = ball.getCenterX();

g2.draw(new Line2D.Double(cx-50, floor, cx+50, floor));

}

private void initGeom() {

int w = getWidth();

int h = getHeight();

int DIA = 30;

Point2D p1 = new Point2D.Double(w/16, h*7/12);

Point2D p2 = new Point2D.Double(w*15/16, h*7/12);

line = new Line2D.Double(p1, p2);

double x = p1.getX() + (p2.getX() - p1.getX())/2;

double y = p1.getY() + (p2.getY() - p1.getY())/2;

pivot = new Point2D.Double(x, y);

floor = line.getY1();

initialX = w/2.0;

initialY = line.getY1() - DIA;

ball = new Ellipse2D.Double(initialX, initialY, DIA, DIA);

initialize();

}

private void tilt() {

// Rotate line at its center.

Point2D p1 = line.getP1();

Point2D p2 = line.getP2();

double length = p1.distance(p2);

double x = pivot.getX() + (length/2)*Math.cos(theta);

double y = pivot.getY() + (length/2)*Math.sin(theta);

p2.setLocation(x, y);

x = pivot.x + (length/2)*Math.cos(theta+Math.PI);

y = pivot.y + (length/2)*Math.sin(theta+Math.PI);

p1.setLocation(x, y);

line.setLine(p1, p2);

positionBall();

}

private void positionBall() {

setFloor();

// Make sure ball contact is between ends points of line.

if(!isOverLine())

moveBallOverLine();

// If the animation is not running we can adjust the

// vertical position of ball to rest on floor.

if(!rollController.isRunning())

ball.y = floor - ball.height;

}

private void setFloor() {

// Adjust floor/ball height on tilted line in two parts:

// Locate ball center above the intersection of the tilted line

// and the vertical line that passes through the ball center.

double verticalOffset = (ball.height/2)*(1.0 - 1.0/Math.cos(theta));

// Find vertical displacement of intersection of tilted line

// and vertical line caused by rotation angle of tilted line.

double dx = pivot.x - ball.getCenterX();

double rotationOffset = dx*Math.tan(theta);

// Find floor == point of contact between ball and the horizontal.

floor = pivot.y + verticalOffset - rotationOffset;

}

private void rollBall() {

// v = v0t + gt*sin(theta); t = 1

// d = d0 + v0t + (v - v0)t/2

double v = vLast + g*Math.sin(theta);

double d = (v + vLast)/2.0;

double x = ball.getX() + d*Math.cos(theta);

double y = getBallY() + d*Math.sin(theta);

ball.setFrameFromDiagonal(x, y, x + ball.width, y + ball.height);

floor = ball.getY() + ball.getHeight();

repaint();

vLast = v;

}

private double getBallY() {

double phi = theta + Math.PI/2;

double contactX = ball.getCenterX() + (ball.getWidth()/2)*Math.cos(phi);

double contactY = ball.getCenterY() + (ball.getHeight()/2)*Math.sin(phi);

double normalX = ball.getCenterX() + 200*Math.cos(phi);

double normalY = ball.getCenterY() + 200*Math.sin(phi);

Point2D.Double intxn = getIntersection(normalX, normalY);

double dy = intxn.y - contactY;

return ball.getY() + dy;

}

private Point2D.Double getIntersection(double endX, double endY) {

double x1 = line.getX1();

double y1 = line.getY1();

double x2 = line.getX2();

double y2 = line.getY2();

double x3 = ball.getCenterX();

double y3 = ball.getCenterY();

double x4 = endX;

double y4 = endY;

double aDividend = (x4 - x3)*(y1 - y3) - (y4 - y3)*(x1 - x3);

double aDivisor = (y4 - y3)*(x2 - x1) - (x4 - x3)*(y2 - y1);

double ua = aDividend / aDivisor;

double bDividend = (x2 - x1)*(y1 - y3) - (y2 - y1)*(x1 - x3);

double bDivisor = (y4 - y3)*(x2 - x1) - (x4 - x3)*(y2 - y1);

double ub = bDividend / bDivisor;

Point2D.Double p = new Point2D.Double();

p.x = x1 + ua * (x2 - x1);

p.y = y1 + ua * (y2 - y1);

return p;

}

private boolean isOverLine() {

// find contact point of ball with (infinite) line

double phi = theta + Math.PI/2;

double contactX = ball.getCenterX() + (ball.getWidth()/2)*Math.cos(phi);

double contactY = ball.getCenterY() + (ball.getHeight()/2)*Math.sin(phi);

double d1 = pivot.distance(contactX, contactY);

double d2 = pivot.distance(contactX, contactY);

double pivotToEnd = pivot.distance(line.getP1());

return pivotToEnd > (d1 < d2 ? d1 : d2);

}

private void moveBallOverLine() {

double d1 = line.getP1().distance(ball.getCenterX(), ball.getCenterY());

double d2 = line.getP2().distance(ball.getCenterX(), ball.getCenterY());

double phi = theta - Math.PI/2;

if(d1 < d2) {

ball.x = line.getX1()+1;

ball.y = line.getY1()+1;

} else if(d1 > d2) {

ball.x = line.getX2()-1;

ball.y = line.getY2()-1;

}

ball.x += (ball.getWidth()/2)*Math.cos(phi) - ball.getWidth()/2;

ball.y += (ball.getHeight()/2)*Math.sin(phi) - ball.getHeight()/2;

setFloor();

}

private JPanel getControls() {

JSlider slider = new JSlider(JSlider.HORIZONTAL, -45, 45, 0);

slider.setPaintTicks(true);

slider.setMinorTickSpacing(5);

slider.setMajorTickSpacing(15);

slider.setPaintLabels(true);

slider.addChangeListener(this);

JButton roll = new JButton("roll");

roll.setActionCommand("roll");

roll.addActionListener(this);

JButton reset = new JButton("reset");

reset.setActionCommand("reset");

reset.addActionListener(this);

JPanel panel = new JPanel(new GridBagLayout());

GridBagConstraints gbc = new GridBagConstraints();

gbc.insets = new Insets(1,0,1,0);

gbc.weightx = 1.0;

panel.add(roll, gbc);

gbc.gridwidth = gbc.REMAINDER;

panel.add(reset, gbc);

gbc.gridwidth = 2;

gbc.fill = gbc.HORIZONTAL;

panel.add(slider, gbc);

return panel;

}

public static void main(String[] args) {

RollingBall test = new RollingBall();

JFrame f = new JFrame();

f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

f.getContentPane().add(test);

f.getContentPane().add(test.getControls(), "Last");

f.setSize(500,500);

f.setLocation(200,100);

f.setVisible(true);

}

}

class RollController implements Runnable {

RollingBall rollingBall;

Thread thread;

boolean animating;

public RollController(RollingBall br) {

rollingBall = br;

animating = false;

}

public void run() {

while(animating) {

try {

Thread.sleep(50);

} catch(InterruptedException ie) {

System.out.printf("sleep interrupted%n");

animating = false;

}

rollingBall.roll();

}

}

public void start() {

if(!animating) {

animating = true;

thread = new Thread(this);

thread.setPriority(Thread.NORM_PRIORITY);

thread.start();

}

}

public void stop() {

if(animating) {

animating = false;

thread.interrupt();

thread = null;

System.out.printf("thread stopped%n");

}

}

public boolean isRunning() { return animating; }

}

crwooda at 2007-7-15 4:24:12 >

Hey Philip!!! awesome man!! Your code is perfect!! I am not able to assign you the remaining duke dollars cause the icon is not showing. Anyways thanks a lot. I have a few doubts which you could probably help me out with. Can you give me a detailed explanation of what is beiing done in the following part of your code. I know its the key to solving the problem I faced in my code. I see a lot of calculations. Are these to get rid of all the offsets. It would be really helpful if you just give me an explanation on the technique you have used. Specially the use of variables aDividend, aDivisor, bDivident and bDivisor. Thanks again.

private void rollBall() {

// v = v0t + gt*sin(theta); t = 1

// d = d0 + v0t + (v - v0)t/2

double v = vLast + g*Math.sin(theta);

double d = (v + vLast)/2.0;

double x = ball.getX() + d*Math.cos(theta);

double y = getBallY() + d*Math.sin(theta);

ball.setFrameFromDiagonal(x, y, x + ball.width, y + ball.height);

floor = ball.getY() + ball.getHeight();

repaint();

vLast = v;

}

private double getBallY() {

double phi = theta + Math.PI/2;

double contactX = ball.getCenterX() + (ball.getWidth()/2)*Math.cos(phi);

double contactY = ball.getCenterY() + (ball.getHeight()/2)*Math.sin(phi);

double normalX = ball.getCenterX() + 200*Math.cos(phi);

double normalY = ball.getCenterY() + 200*Math.sin(phi);

Point2D.Double intxn = getIntersection(normalX, normalY);

double dy = intxn.y - contactY;

return ball.getY() + dy;

}

private Point2D.Double getIntersection(double endX, double endY) {

double x1 = line.getX1();

double y1 = line.getY1();

double x2 = line.getX2();

double y2 = line.getY2();

double x3 = ball.getCenterX();

double y3 = ball.getCenterY();

double x4 = endX;

double y4 = endY;

double aDividend = (x4 - x3)*(y1 - y3) - (y4 - y3)*(x1 - x3);

double aDivisor = (y4 - y3)*(x2 - x1) - (x4 - x3)*(y2 - y1);

double ua = aDividend / aDivisor;

double bDividend = (x2 - x1)*(y1 - y3) - (y2 - y1)*(x1 - x3);

double bDivisor = (y4 - y3)*(x2 - x1) - (x4 - x3)*(y2 - y1);

double ub = bDividend / bDivisor;

Point2D.Double p = new Point2D.Double();

p.x = x1 + ua * (x2 - x1);

p.y = y1 + ua * (y2 - y1);

return p;

}

MyJavaStorya at 2007-7-15 4:24:12 >