Jump to content

Image of the Day

Working on #steam achievements!
#screenshotsaturday #indiegame #pixelart #NadiaWasHere #RPG #indiedev https://t.co/IcDuJSWsGK
IOTD | Top Screenshots

The latest, straight to your Inbox.

Subscribe to GameDev.net's newsletters to receive the latest updates and exclusive content.


Sign up now

Verlet particle sytem not working

4: Adsense

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.


  • You cannot reply to this topic
4 replies to this topic

#1 razaron   Members   

101
Like
0Likes
Like

Posted 13 January 2012 - 01:23 PM

I've a very basic particle system based on verlet intergration. It seems fine but the updateVerlet() function returns a nullpointer exception. I just can't find the problem.
Here's the source (exluding imports):

Main class,
public class ParticleSystem {
int lastFrame, width=800, height=600;
boolean simulating;
int ticker;


Vertex[] vertex = new Vertex[100];
int temp;


public void Start(){
 
  try {
   Display.setDisplayMode(new DisplayMode(width,height));
   Display.create();
  } catch (LWJGLException e) {
   e.printStackTrace();
   System.exit(0);
  }
 
 
 
  initGL();
 
  getDelta();
  boolean Close = Display.isCloseRequested();
 
  while(!Close){
   GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT); 
  
   int delta=getDelta();
   ticker+=delta;
  
   if(Keyboard.isKeyDown(Keyboard.KEY_ESCAPE) || Display.isCloseRequested())
    Close = true;
  
   if(Keyboard.isKeyDown(Keyboard.KEY_RETURN))
    simulating = true;
  
   if(temp <100 && Mouse.isButtonDown(0) && ticker>=100){
    vertex[temp]= new Vertex(Mouse.getX(), height-Mouse.getY());
    temp++;
    ticker=0;
   }
  
  
  
   if(simulating)
    logic(delta);
   renderer();
  
  
   Display.update();
  }
 
}

public void logic(int delta){
  for(int i=0;i<temp;i++){
   vertex[i].updateVerlet(delta);
  }
}

public void renderer(){
  for(int i=0;i<100;i++){
   if(vertex[i]!=null)
    vertex[i].draw();
  }
}

public int getDelta(){
  long time = getTime();
  int delta = (int) (time - lastFrame);
  lastFrame = (int) time;
 
  return delta;
}

public long getTime(){
  return (Sys.getTime()*1000)/Sys.getTimerResolution();
}

public void initGL(){
  GL11.glMatrixMode(GL11.GL_PROJECTION);
  GL11.glLoadIdentity();
  GL11.glOrtho(0, width, height, 0, 1, -1);
  GL11.glMatrixMode(GL11.GL_MODELVIEW);
}
public static void main(String args[]){
  ParticleSystem ps = new ParticleSystem();
  ps.Start();
}
}

Vertex class,
public class Vertex {
protected Point2D.Double pos;
protected Point2D.Double oldpos;
protected Point2D.Double acceleration;
protected Point2D.Double temp;

public Vertex(double x, double y){
  pos = new Point2D.Double(x,y);
  oldpos = new Point2D.Double(x,y);
}

public void updateVerlet(int delta){
  double t=((double)delta)/1000;
  temp.x=pos.x;
  temp.y=pos.y;
 
  pos.x += (pos.x - oldpos.x) + (acceleration.x*t*t);
  pos.y += (pos.y - oldpos.y) + (acceleration.y*t*t);
 
  oldpos.x=temp.x;
  oldpos.y=temp.y;
}

public void draw(){
  GL11.glColor3f(1f, 0f, 0f);
  GL11.glBegin(GL11.GL_QUADS);
   GL11.glVertex2d(pos.x-1, pos.y-1);
   GL11.glVertex2d(pos.x-1, pos.y+1);
   GL11.glVertex2d(pos.x+1, pos.y+1);
   GL11.glVertex2d(pos.x+1, pos.y-1);
  GL11.glEnd();
}
}

Thanks in advance.

#2 medv4380   Members   

98
Like
0Likes
Like

Posted 13 January 2012 - 02:23 PM

What does the null pointer exception say. Usually it give a line indication as to what's wrong.

#3 razaron   Members   

101
Like
0Likes
Like

Posted 13 January 2012 - 02:26 PM

Everything* in the updateVerlet() function except for the first line (the delta one) returns a nullpointer exception.

*I checked line by line.

#4 medv4380   Members   

98
Like
1Likes
Like

Posted 13 January 2012 - 02:32 PM

Usually you should stop at the first line the returns the error since that's probably where the error originates at.

When you get these kinds of problems there is a couple of ways to attack it. First thing to remember is that Null Pointer exceptions is reserved for objects only. So you just have to check each object that is in the line. Your first line in updateVerlet contains no object so that's why it's not throwing an exception since you can't not initialize a primitive.

Put this code at the first line of updateVerlet
	    if(temp  == null) System.out.println("Temp is NULL");
	    if(pos  == null) System.out.println("Pos is NULL");
	    if(oldpos  == null) System.out.println("OldPos is NULL");
	    if(acceleration  == null) System.out.println("Acceleration is NULL");

You probably have two uninitialized objects in the updateVerlet function.

#5 razaron   Members   

101
Like
0Likes
Like

Posted 13 January 2012 - 02:41 PM

Thank you. I wasn't initializing temp and acceleration. I assumed that they had already initialized as (0,0).




Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.