hi,  
I've been trying to learn processing and like most people I'm waiting for Shiffman's book to come out but until then I'm trying to work out as much as possible on my own. I found this code on the net that someone posted. Its a water simulation. I tried to get it to go fullscreen and add a background image to get a handle on the syntax. The code is fairly simple to understand but why my additions will not work is not.I thought I inserted screen.width and screen.height into the maps and size command. can someone help me fix this code to go full screen and display a background image?

color col;
int i,j,g;
float osc=0;
int x=0;
int y=0;
float c=0;

float newmap[]=new float[width*height];
float currentmap[]=new float[width*height];
float prevmap[]=new float[width*height];
//my addition-changed 500*500 on the maps to width*height  




void setup(){
 size(screen.width, screen.height,P3D);
 loadPixels();
 //colorMode(RGB,2.0,1.0,1.0);
//commented out colormode for PImage
 noCursor();
PImage w;  
w = loadImage("Worn wall.jpg");  
 image(w, 0, 0);  
//My addition- changed 500*500 to screen.width and  
screen.height
//added PImage code
//get a null pointer exception on image(w, 0, 0) why?
 
 
 
 for(g=0;g<width*height;g++){
   currentmap[g]=0;
   newmap[g]=0;
 }
}

float lu(int x, int y, float array[]){ // look up a table
 return(array[(y*width)+x]);
}


void draw(){
 x=mouseX;
 y=mouseY;
 osc+=.2;
 splash(x,y,.6);
 
if(mousePressed);
   line(mouseX, mouseY, pmouseX, pmouseY);
 for(i=155;i>100;i--){
for(j=100;j<155;j++){
 //     currentmap[(width*j)+i]=.7;//
}
 }
//splash(160,100,100.,1)
 for(j=2;j<height-1;j++){
 for(i=1;i<width-1;i++){

   newmap[i+(j*width)]=.99*
   (((
lu(i+1, j,   currentmap)+
lu(i-1, j,   currentmap)+
lu(i,   j+1, currentmap)+
lu(i,   j-1, currentmap)+
lu(i+1, j+1, currentmap)+
lu(i+1, j-1, currentmap)+
lu(i-1, j+1, currentmap)+
lu(i-1, j-1, currentmap))/4.)-lu(i,j,prevmap));
  // newmap[i+(j*width)]=    newmap[i+(j*width)]-    (newmap[i+(j*width)]*16);
   }
 }

for(g=400;g<(width*height)-2222;g++) {

 //   c=(newmap[g+width+1]-newmap[g-width-1]);
 //  pixels[g]=color(0,0,atan2(.15,c));

   pixels[g]=color((.1)*(1.-abs((newmap[g]))),(.7)*(.6-abs(newmap[g])), 1.-abs(newmap[g]));
 }

arraycopy(currentmap,prevmap);

arraycopy(newmap,currentmap);
// currentmap=newmap;


 updatePixels();
}




void splash(int x, int y, float power){
int sqsize=3; //intensity
float a,b;

if(x>=sqsize && y>=sqsize && x<width-sqsize && y<height-sqsize){
  for(int xx=-sqsize;xx<sqsize;xx++){
 for(int yy=-sqsize;yy<sqsize;yy++){
     a=xx;
     b=sqsize;
currentmap[((y+yy)*width)+x+xx]-=power;//(power-((a/b)*power));

 }
  }
}
}

FYI The code you have there is some of my really old code for a  water effect.  I have a newer version up that is much cleaner and probably 5-10 times faster.  

http://viz.nu/programming/processing/splish

wow movax, great code! I checked out your new simulation and it is really awesome! Thanks for posting that and the code with it! I thought your new code was much easier to read with the notes and very helpful. It certainly clarifies alot more of processing's syntax for a beginner like me. I wish everyone put such well organized commentary into their code. Until Daniel shiffmans book comes out I think alot of beginners like myself are relying on other processing artists code to learn the basics of structure, making their comments critical to the novices learning experience. I know every artist codes differently but it helps to see how things were organized and simplified if you are a beginner without a background in code. anyway, thanks again.