Moving a ball over a rotateable line.

ppl = people

ur = your

wud = would

You *are* using a regular size keyboard, right?

To your question - this has nothing to do with Java, you just need the right physics simulation. Draw a diagram on a piece of paper, brush up on a little trigonometry from school and that's it. Nothing to do with Robot or intersects().

kirillga at 2007-7-14 21:14:25 >

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import javax.swing.*;

import javax.swing.event.*;

public class LocationTest extends JPanel implements ChangeListener

{

Ellipse2D.Double ball;

Line2D.Doubleline;

JSlider translate;

doublelastTheta = 0;

public void stateChanged(ChangeEvent e)

{

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

String name = slider.getName();

int value = slider.getValue();

if(name.equals("rotation"))

tilt(Math.toRadians(value));

else if(name.equals("translate"))

moveBall(value);

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);

}

private void initGeom()

{

int w = getWidth();

int h = getHeight();

int DIA = 30;

int padFromEnd = 5;

line = new Line2D.Double(w/4, h*15/16, w*3/4, h*15/16);

double x = line.x2 - padFromEnd - DIA;

double y = line.y2 - DIA;

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

// update translate slider values

int max = (int)line.getP1().distance(line.getP2());

translate.setMaximum(max);

translate.setValue(max-padFromEnd);

}

private void tilt(double theta)

{

// rotate line from left end

Point2D pivot = line.getP1();

double lineLength = pivot.distance(line.getP2());

Point2D.Double p2 = new Point2D.Double();

p2.x = pivot.getX() + lineLength*Math.cos(theta);

p2.y = pivot.getY() + lineLength*Math.sin(theta);

line.setLine(pivot, p2);

// find angle from pivot to ball center relative to line

// ie, ball center -> pivot -> line end

double cx = ball.getCenterX();

double cy = ball.getCenterY();

double pivotToCenter = pivot.distance(cx, cy);

// angle of ball to horizon

double dy = cy - pivot.getY();

double dx = cx - pivot.getX();

// relative angle phi = ball_to_horizon - last line_to_horizon

double phi = Math.atan2(dy, dx) - lastTheta;

// rotate ball from pivot

double x = pivot.getX() + pivotToCenter*Math.cos(theta+phi);

double y = pivot.getY() + pivotToCenter*Math.sin(theta+phi);

ball.setFrameFromCenter(x, y, x+ball.width/2, y+ball.height/2);

lastTheta = theta; // save theta for next time

}

private void moveBall(int distance)

{

Point2D pivot = line.getP1();

// ball touches line at distance from pivot

double contactX = pivot.getX() + distance*Math.cos(lastTheta);

double contactY = pivot.getY() + distance*Math.sin(lastTheta);

// find new center location of ball

// angle lambda = lastTheta - 90 degrees (anti-clockwise)

double lambda = lastTheta - Math.PI/2;

double x = contactX + (ball.width/2)*Math.cos(lambda);

double y = contactY + (ball.height/2)*Math.sin(lambda);

ball.setFrameFromCenter(x, y, x+ball.width/2, y+ball.height/2);

}

private JPanel getControls()

{

JSlider rotate = getSlider("rotation angle", "rotation", -90, 0, 0, 5, 15);

translate = getSlider("distance from end", "translate", 0, 100, 100,25, 50);

JPanel panel = new JPanel(new GridLayout(0,1));

panel.add(rotate);

panel.add(translate);

return panel;

}

private JSlider getSlider(String title, String name, int min, int max,

int value, int minorSpace, int majorSpace)

{

JSlider slider = new JSlider(JSlider.HORIZONTAL, min, max, value);

slider.setBorder(BorderFactory.createTitledBorder(title));

slider.setName(name);

slider.setPaintTicks(true);

slider.setMinorTickSpacing(minorSpace);

slider.setMajorTickSpacing(majorSpace);

slider.setPaintLabels(true);

slider.addChangeListener(this);

return slider;

}

public static void main(String[] args)

{

LocationTest test = new LocationTest();

JFrame f = new JFrame();

f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

f.getContentPane().add(test);

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

f.setSize(400,400);

f.setLocation(200,200);

f.setVisible(true);

}

}

74philipa at 2007-7-14 21:14:25 >

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import java.text.MessageFormat;

import javax.swing.*;

public class LocationTest2 extends JPanel

{

JLabel lineAngle;

Ellipse2D.Double ball;

Line2D.Double line;

Point origin = new Point();

double theta = 0;

double thetaInc = Math.toRadians(1);

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();

AffineTransform at =

AffineTransform.getRotateInstance(theta, origin.x, origin.y);

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

g2.draw(at.createTransformedShape(line));

g2.setPaint(Color.red);

g2.draw(at.createTransformedShape(ball));

showLineAngle(at);

}

private void showLineAngle(AffineTransform at)

{

Point2D p1 = line.getP1();

Point2D p2 = line.getP2();

Point2D xfp1 = new Point2D.Double();

Point2D xfp2 = new Point2D.Double();

at.transform(p1, xfp1);

at.transform(p2, xfp2);

double dy = xfp2.getY() - xfp1.getY();

double dx = xfp2.getX() - xfp1.getX();

double degrees = Math.toDegrees(Math.atan2(dy, dx));

if(degrees < 0)

degrees += 360;

String s = MessageFormat.format("{0,number,0.#}", degrees);

lineAngle.setText(s);

}

public void spin(Point origin)

{

this.origin = origin;

theta += thetaInc;

repaint();

}

private void initGeom()

{

int w = getWidth();

int h = getHeight();

int DIA = 30;

int padFromEnd = 5;

line = new Line2D.Double(w/4, h/2, w*3/4, h/2);

double x = line.x2 - padFromEnd - DIA;

double y = line.y2 - DIA;

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

}

private JPanel getLabel()

{

lineAngle = new JLabel(" ");

Dimension d = lineAngle.getPreferredSize();

d.width = 35;

lineAngle.setPreferredSize(d);

JPanel panel = new JPanel();

panel.add(new JLabel("line angle "));

panel.add(lineAngle);

return panel;

}

public static void main(String[] args)

{

LocationTest2 test = new LocationTest2();

test.addMouseListener(new SpinController());

JFrame f = new JFrame();

f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

f.getContentPane().add(test);

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

f.setSize(400,400);

f.setLocation(200,200);

f.setVisible(true);

}

}

class SpinController extends MouseAdapter implements Runnable

{

LocationTest2 panel;

Point spinOrigin;

Thread thread;

boolean spinning = false;

public void mousePressed(MouseEvent e)

{

if(panel == null)

panel = (LocationTest2)e.getSource();

spinOrigin = e.getPoint();

if(!spinning)

{

spinning = true;

thread = new Thread(this);

thread.setPriority(Thread.NORM_PRIORITY);

thread.start();

}

}

public void mouseReleased(MouseEvent e)

{

spinning = false;

thread = null;

}

public void run()

{

while(spinning)

{

try

{

Thread.sleep(40);

}

catch(InterruptedException ie)

{

System.out.println("interrupt");

spinning = false;

}

panel.spin(spinOrigin);

}

}

}

74philipa at 2007-7-14 21:14:25 >

Some comments:

1 — Here's an attempt at showing how to accurately locate a falling ball as it

contacts a plane that can have an arbitrary rotation (about the view axis).

2 — I drew the floor in blue to help see the placement. The green line is the

rotating/tilted line. To keep things simple and restrict the focus to the ball–line

contact I did not implement any lateral displacement.

3 — There may be a lot of ways of doing this placement and you may find one that

suits you better. I have not included any construction lines or details to show how I did

the figuring in the tilt method.

4 — When the animation is not running the slider shows the ball tangent to both the

(green) line and (blue) floor through a range of rotation. Reset will get it ready for a

drop event.

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import javax.swing.*;

import javax.swing.event.*;

public class TrueContact extends JPanel implements ActionListener, ChangeListener

{

DropController dropController = new DropController(this);

Ellipse2D.Double ball;

Line2D.Doubleline;

doubleinitialX;

doublefloor;

doublelastTheta = 0;

doubleg = 3.0;

doubledLast;

doublevLast;

doublerestitution = 0.75;

public void actionPerformed(ActionEvent e)

{

String ac = e.getActionCommand();

if(ac.equals("drop"))

dropController.start();

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

{

dropController.stop();

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

vLast = 0;

dLast = 0;

repaint();

}

}

public void stateChanged(ChangeEvent e)

{

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

int value = slider.getValue();

tilt(Math.toRadians(value));

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);

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*7/8, w*3/4, h*7/8);

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);

// Stop animation if rebound height is small.

if(reboundHeight < 1.0)

{

dropController.stop();

y = floor - ball.height;

}

}

return y;

}

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)

{

TrueContact test = new TrueContact();

JFrame f = new JFrame();

f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

f.getContentPane().add(test);

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

f.setSize(400,400);

f.setLocation(200,200);

f.setVisible(true);

}

}

class DropController implements Runnable

{

TrueContact trueContact;

Thread thread;

boolean animating;

public DropController(TrueContact 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.dropBall();

}

}

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; }

}

74philipa at 2007-7-14 21:14:25 >