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POGravity in processing (Floors)
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copied!<p>I'm using the <a href="http://www.processing.org" rel="nofollow">processing</a> java library to simulate a ball bouncing between two walls using Newtonian physics; horizontal velocity is a constant, as there is no acceleration. I got the simulation to work, however I would like to specify the height of the floor. However in my equations when I attempt to change direction when the ball is 10 pixels from the bottom of the screen, after every bounce, the ball gets lower and lower below the "floor". If I raise the floor to >20 pixels, the ball does not come to a halt and instead indefinitely bounces. Here is the pertinent code: Note that processing's coordinate system begins at the top and runs down and right. Thanks for the help in advance.</p> <pre><code>public class Testing extends PApplet { boolean inFloor=false; float xPosition=500; float yPosition=200; float xVelocity=25; float yVelocity=-80.0f; float yAccelleration=+10.0f; float elasticity=0.80f; public void setup (){ size(displayWidth,displayHeight); noStroke(); ellipseMode(RADIUS); frameRate(35); } public boolean sketchFullScreen() { return true; } public void draw(){ background(0); //Changes direction of motion when hitting a wall if(xPosition>=displayWidth||xPosition<0){ xVelocity=-xVelocity; } //supposed to change direction of motion when the ball hits the floor if(yPosition>=displayHeight-20){ yPosition=(displayHeight-20); yVelocity=-(yVelocity)*elasticity; if(yVelocity>=-1 && yVelocity<=0){ xVelocity=xVelocity*elasticity; yVelocity=0; yAccelleration=0; } } else{ yVelocity=yVelocity+yAccelleration; } yPosition=yVelocity+yPosition; xPosition=xPosition+xVelocity; ellipse(xPosition,yPosition,10,10); } </code></pre> <p><strong>Edit:</strong> Could this possibly be a timing issue?</p> <p><strong>Edit:</strong> Thank you for all the responses. Unfortunately I can't upvote any of them, (only 6 rep). I combined a mixture of @tobius_k's answer, @Roberto_Mereghetti's answer and some sample code from <a href="http://openprocessing.org/sketch/17115" rel="nofollow">OpenProcessing.org</a> and that solved it. In the solution provided below, because the canvas is measured in pixels (integer values), the use of floats to specify co-ordinates was causing graphical glitches in processing. So I implemented a system where float values were rounded, with decimal values being added to an accumulator ("xRounder" and "yRounder") which when were great than -1 or 1 were rounded and added to the Ball's current position. This gave me a floor!</p> <p><em>Final Code:</em></p> <pre><code> import processing.core.*; //import processing.xml.*; import java.applet.*; import java.awt.Dimension; import java.awt.Frame; import java.awt.event.MouseEvent; import java.awt.event.KeyEvent; import java.awt.event.FocusEvent; import java.awt.Image; import java.io.*; import java.net.*; import java.text.*; import java.util.*; import java.util.zip.*; import java.util.regex.*; public class Testing extends PApplet { int xPosition=500; int yPosition=200; float xRounder=0; float yRounder=0; float xVelocity=25; float yVelocity=-80.0f; float yAccelleration=+10.0f; float elasticity=0.80f; public void setup (){ size(displayWidth,displayHeight); noStroke(); ellipseMode(RADIUS); frameRate(15); } public boolean sketchFullScreen() { return true; } /* (non-Javadoc) * @see processing.core.PApplet#draw() */ public void draw(){ background(0); yPosition=round(yVelocity)+yPosition; yRounder+=(yVelocity-round(yVelocity)); xPosition=round(xVelocity)+xPosition; xRounder+=(xVelocity-round(xVelocity)); if(xRounder>=1||xRounder<=-1){ xPosition=xPosition+round(xRounder); xRounder=xRounder-round(xRounder); } if(yRounder>=1||yRounder<=-1){ yPosition+=round(yRounder); yRounder=yRounder-round(yRounder); } if(yPosition>displayHeight-50 && yVelocity>0){ yPosition=displayHeight-50; yVelocity=-(yVelocity)*elasticity; xVelocity=xVelocity*elasticity; } if(xPosition>=displayWidth||xPosition<0){ xVelocity=-xVelocity; } yVelocity=yVelocity+yAccelleration; ellipse(xPosition,yPosition,10,10); } static public void main(String args[]) { PApplet.main(new String[] { "--bgcolor=#ECE9D8", "Testing" }); // new Testing().setVisible(true); } } </code></pre>

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