Hi,

When i try to compile the following code :

class Point {

 int x, y, z;
 
 Point(int _x, int _y) {
   x = _x;
   y = _y;
   z = 0;
 }
}

import JMyron.*;
JMyron m;
PImage img1, img2;
// img1 and img2 are the location to temporarily store the previous
// and current frame.
final int NROWS = 18;
final int NCOLS = 24;
final float LIMIT = 40.0;
int w, h;
// w and h are the size of the grid.

void initGrid() {
  for (int r=0;r<=NROWS;r++) {
     for (int c=0;c<=NCOLS;c++) {
        grid[r][c] = new Point(c*w,r*h);
     }
  }
}

void mapGrid(PImage _i) {
 noStroke();
 for (int r=0;r<NROWS;r++) {
   beginShape(QUAD_STRIP);
   texture(_i);
   for (int c=0;c<=NCOLS;c++) {
     vertex(grid[r][c].x,grid[r][c].y,grid[r][c].z,
     c*w,r*h);
     vertex(grid[r+1][c].x,grid[r+1][c].y,grid[r+1][c].z,
     c*w,(r+1)*h);
   }
   endShape();
 }
}

Point [][] grid = new Point[NROWS+1][NCOLS+1];

void setup() {
  size(320,240);
  m = new JMyron();
  m.start(width,height);
  println(m.getForcedWidth());
  println(m.getForcedHeight());
  m.findGlobs(0);
  img1 = createImage(width,height,ARGB);
  img2 = createImage(width,height,ARGB);
  noFill();
  stroke(255,200,0);
  smooth();
  frameRate(15);
  w = width/NCOLS;
  h = height/NROWS;
}

void draw() {
  background(0);
// copy the image from img1 to img2 - the previous frame.
  img2.copy(img1,0,0,img1.width,img1.height,
   0,0,img2.width,img2.height);
  img2.updatePixels();
  m.update();
// update the current frame to img1.
  m.imageCopy(img1.pixels);
  img1.updatePixels();
  image(img1,0,0);
  findFlow();
}

void findFlow() {
 int xOff = w/2;
 int yOff = h/2;
 for (int r=1;r<NROWS;r++) {
   for (int c=1;c<NCOLS;c++) {
     Point p1 = new Point(c*w, r*h);
     Point p2 = findPoint(p1.x, p1.y, xOff, yOff);
     drawLine(p1,p2);
     grid[r][c].z = int(dist(p1.x,p1.y,p2.x,p2.y));
   }
 }
}

void drawLine(Point _p, Point _q) {
// draw the arrow line from point _q to point _p.
  if (_p.x!=_q.x || _p.y!=_q.y) {
    line(_p.x,_p.y,_q.x,_q.y);
    float ang = atan2(_q.y-_p.y,_q.x-_p.x);
    float ln = w/3.0;
    float tx = _p.x + ln*cos(ang-PI/6);
    float ty = _p.y + ln*sin(ang-PI/6);
    line(_p.x,_p.y,tx,ty);
    tx = _p.x + ln*cos(ang+PI/6);
    ty = _p.y + ln*sin(ang+PI/6);
    line(_p.x,_p.y,tx,ty);
  }
  else {
    line(_p.x,_p.y,_q.x,_q.y);
  }
}

Point findPoint(int _x, int _y, int _xo, int _yo) {

// Given a pixel (_x, _y) in img1, we search the neighborhood of that
// pixel in img2 and try to find a matching colour.
//
// The neighborhood size is defined by (w x h) and the boundaries are
// x0 - left
// x1 - right
// y0 - top
// y1 - right

  int x0 = _x - _xo;
  int x1 = _x + _xo;
  int y0 = _y - _yo;
  int y1 = _y + _yo;

// Initialize the minimum difference to a high value.
// Loop through the pixels in img2 within the boundary.
// Find the pixel with minimum difference from the original one
// in img1.

  float minDiff = 999999999;
  Point p = new Point(_x,_y);
  color c1 = img1.pixels[_y*img1.width+_x];
  color c2 = img2.pixels[_y*img2.width+_x];
  if (!matchCol(c1,c2)) {
     for (int r=y0;r<y1;r++) {
       for (int c=x0;c<x1;c++) {
         c2 = img2.pixels[r*img2.width+c];
         float diff = dist(red(c1),green(c1),blue(c1),
         red(c2),green(c2),blue(c2));
         if (diff<minDiff) {
           minDiff = diff;
           p.x = c;
           p.y = r;
         }
       }
     }
  }
  return p;
}

boolean matchCol(color c1, color c2) {
// Compare two colour values and see if they are similar.
  float d = dist(red(c1),green(c1),blue(c1),
    red(c2),green(c2),blue(c2));
  return (d<LIMIT);
}



I get the following error :

Exception in thread "Animation Thread" java.lang.NullPointerException
     at TySke.findFlow(TySke.java:105)
     at TySke.draw(TySke.java:94)
     at processing.core.PApplet.handleDraw(PApplet.java:1406)
     at processing.core.PApplet.run(PApplet.java:1311)
     at java.lang.Thread.run(Thread.java:613)

Does anybody know what this means or how to fix it?