[5168] in java-interest
Bouncing Ball...take 2...
daemon@ATHENA.MIT.EDU (Paul Benati)
Tue Jan 30 16:01:54 1996
Date: Tue, 30 Jan 1996 14:25:48 -0500
To: java-interest@java.sun.com
From: Paul Benati <benatip@pcd.kodak.com>
Group,
I have another question. In the bouncing ball program (attached below)
when the user depresses the mouse the ball stops its movement. When the
ball is stopped, then the user can depress the <CTRL> and mouse button
to draw a line from the ball's origin to the mouse cursor location. My
question is, why doesn't the event's (x,y) location equate to the location
of the cursor? [I'm on a Windows95 box.]
Paul
-----------------------------[ code below ]------------------------------
import java.awt.*;
import java.lang.*;
// ------------------------------------------------------------------------
// ------------------------------------------------------------------------
public class Bounce extends Frame
{
private static final int TimeInterval = 75;
private static Ball ball = new Ball();
private Panel mainPanel = new Panel();
private long time = 0;
private boolean doQuit = false;
private boolean moveBall = true;
private Dimension frameSize;
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
public
Bounce(String title)
{
setTitle(title);
setCursor(CROSSHAIR_CURSOR);
setBackground(Color.red);
add("Center", ball);
}
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
public
void go()
{
time = System.currentTimeMillis();
while(doQuit != true)
{
if((moveBall) && ((time + TimeInterval) <= System.currentTimeMillis()))
{
frameSize = size();
ball.moveBall(frameSize.width, frameSize.height);
time = System.currentTimeMillis();
}
}
}
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
public
boolean handleEvent(Event e)
{
boolean handled = false;
int modifiers = e.modifiers;
switch (e.id)
{
case e.MOUSE_DOWN:
{
if((moveBall == false) && (modifiers == 2))
{
ball.drawVelocityVector(e.x, e.y);
}
else
{
if(moveBall)
moveBall = false;
else
moveBall = true;
}
break;
}
case e.MOUSE_UP:
{
break;
}
case e.KEY_PRESS:
{
System.exit(0);
break;
}
case e.WINDOW_DESTROY:
{
System.exit(0);
break;
}
} // end of switch statement
return handled;
}
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
public
static void main(String args[])
{
Bounce bounce = new Bounce("Bounce");
bounce.pack();
bounce.show();
bounce.go();
}
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
public
Dimension preferredSize()
{
return(new Dimension(200, 300));
}
}
// ------------------------------------------------------------------------
// ------------------------------------------------------------------------
class Ball extends Panel
{
private static double Gravity = 1.0; // pid/cron^2
private static double TimeUnit = 1.0; // cron
private boolean velocityVector = false;
private int oldX2 = -1;
private int oldY2;
private int newX2;
private int newY2;
private int radius;
private int diameter;
private int xOrigin;
private int yOrigin;
private int xVelocity;
private int yVelocity;
public
Ball()
{
xOrigin = 50;
yOrigin = 50;
radius = 20;
diameter = radius*2;
xVelocity = 5;
yVelocity = 0;
setBackground(Color.white);
resize(200, 300);
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
void calculateBallPosition(int windowWidth, int windowHeight)
{
xOrigin += (int) (xVelocity + 0.5*Gravity*TimeUnit*TimeUnit);
yOrigin += (int) (yVelocity + 0.5*Gravity*TimeUnit*TimeUnit);
// ------------------------------------------------------------------
// Reflect ball from wall if necessary!
// ------------------------------------------------------------------
if((xOrigin + radius) >= windowWidth)
{
xOrigin = windowWidth - ((xOrigin + radius) - windowWidth + radius);
xVelocity = -(Math.abs(xVelocity) - 1);
}
else if((xOrigin - radius) <= 0)
{
xOrigin = -((xOrigin - radius) - radius);
xVelocity = (Math.abs(xVelocity) - 1);
}
// ------------------------------------------------------------------
// Reflect ball from wall if necessary!
// ------------------------------------------------------------------
if((yOrigin + radius) >= windowHeight)
{
yOrigin = windowHeight - ((yOrigin + radius) - windowHeight + radius);
yVelocity = -(Math.abs(yVelocity) - 1);
}
else if((yOrigin - radius) <= 0)
{
yOrigin = -((yOrigin - radius) - radius);
yVelocity = (Math.abs(yVelocity) - 1);
}
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
void calculateBallVelocity()
{
yVelocity = yVelocity + (int) (Gravity*TimeUnit);
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
void calculateBallVelocity(int xPosition1, int yPosition1,
int xPosition2, int yPosition2)
{
xVelocity = (xPosition2 - xPosition1)/10;
yVelocity = (yPosition2 - yPosition1)/10;
}
public
void drawVelocityVector(int x, int y)
{
velocityVector = true;
newX2 = x;
newY2 = y;
repaint(1);
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
void moveBall(int windowWidth, int windowHeight)
{
repaint(1, xOrigin - radius, yOrigin - radius, diameter+1, diameter+1);
calculateBallVelocity();
calculateBallPosition(windowWidth, windowHeight);
repaint(1, xOrigin - radius, yOrigin - radius, diameter+1, diameter+1);
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
void paint(Graphics g)
{
g.setXORMode(getBackground());
if(velocityVector)
{
// if(oldX2 != -1)
// {
// g.drawLine(xOrigin, yOrigin, oldX2, oldY2);
System.out.println("origin = ("+xOrigin+","+yOrigin+")");
System.out.println("new = ("+newX2+","+newY2+")");
g.drawLine(xOrigin, yOrigin, newX2, newY2);
oldX2 = newX2;
oldY2 = newY2;
// }
// else
// {
// g.drawLine(xOrigin, yOrigin, newX2, newY2);
//
// oldX2 = newX2;
// oldY2 = newY2;
// }
velocityVector = false;
}
g.drawOval(xOrigin - radius, yOrigin - radius, diameter, diameter);
g.fillOval(xOrigin, yOrigin, 2, 2);
}
// --------------------------------------------------------------------
// --------------------------------------------------------------------
public
Dimension preferredSize()
{
return(new Dimension(200, 300));
}
}
Paul Benati
Digital Imaging Evangelist
Software Engineer/Imaging Scientist
Eastman Kodak Company benatip@kodak.com
http://www.kodak.com/ ftp.kodak.com
901 Elmgrove Road (716) 253 - 1775 (EP Office)
Rochester, NY 14653-5555 (716) 726 - 7295 (EP Fax)
233 - 1775 (KMX/Internal)
"I know that you believe you understand what you think I said, but
I am not sure you realize that what you heard is not what I meant."
-- by unknown author.
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