JS1k: The JavaScript code golfing competition

var c=document.body.children[0],d=c.getContext('2d'),w=100,p=5E3,i,x,y,u,v,t=[],m=[],n=[],F=Math.floor,R=Math.random;d.globalAlpha=0.8;for(i=-1;++i<p;){m[i]=n[i]=0;t[i]=9*(i%2E3<1E3?i%20<10:i%20>9)}setInterval(function(){for(i=-1;++i<p;){n[i]=(m[(p+i-1)%p]+m[(i+1)%p]+m[(p+i-w)%p]+m[(i+w)%p]>>1)-n[i];n[i]-=n[i]>>5}for(i=-1;++i<p;){x=m[(p+i-1)%p]-m[(i+1)%p]>>9;y=m[(p+i-w)%p]-m[(i+w)%p]>>9;u=(x<0?8:x>7?15:x+8).toString(16);v=t[((w*y)+x+i+p)%p];d.fillStyle='#'+u+v+u+'ff'+v;d.fillRect(i%w*3,F(i/w)*3,3,3)}x=m;m=n;n=x},20);function W(z){m[z+1]=m[z-1]=m[z+w]=m[z-w]=m[z]-=p}c.onmousemove=function(e){W(F(e.offsetX/3)+w*F(e.offsetY/3))};(function X(){W(F(R()*p));setTimeout(X,F(R()*p))})()

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// Simple cellular-automata based water simulation,
// http://iobound.com/2010/08/js1k/

// Based on Hugo Elias' algorithm at: 
// http://freespace.virgin.net/hugo.elias/graphics/x_water.htm

// Variable lookup:
//
// c  - Canvas
// d  - 2D Context
// w  - Pixels across (150)
// p  - Total pixels (150*100)
// m  - First water buffer
// n  - Second water buffer
// t  - Texture buffer
// x,y,u,v  - Temp vars

// Function lookup:
//
// W  - Disturb water
// F  - Math.floor
// R  - Math.random

// To compress (hat tip to Paul Hammond, http://phmmnd.me/1k):
// perl -p -0 -e 's!(//[^\n]*)?\n\s*!!g;s!;}!}!g;s!;+!;!g' <script.js >compressed.js

// Initialise variables
var c=document.body.children[0],
  d=c.getContext('2d'),
  w=100,
  p=5E3,
  i,x,y,u,v,t=[],m=[],n=[],
  F=Math.floor,
  R=Math.random;

// Use alpha to take edge off pixellyness
d.globalAlpha=0.8;

// Clear water buffers.
// Initialise background checkerboard texture.
for(i=-1;++i<p;){
  m[i]=n[i]=0;
  t[i]=9*(i%2E3<1E3?i%20<10:i%20>9)
}

// Tick the simulation and render
setInterval(function(){

  // Update water height map - see algorithm for explanation
  for(i=-1;++i<p;){

    // Calculate new value based on previous 2 frames
    n[i]=(m[(p+i-1)%p]+
            m[(i+1)%p]+
            m[(p+i-w)%p]+
            m[(i+w)%p]>>1)-n[i];

    // Apply damping
    n[i]-=n[i]>>5
  }

  // Render pixels
  for(i=-1;++i<p;){

    // Get X and Y wave gradient by comparing height with neighbours
    x=m[(p+i-1)%p]-m[(i+1)%p]>>9;
    y=m[(p+i-w)%p]-m[(i+w)%p]>>9;

    // Use X gradient to pick a reflection map value
    // (Fake environment map)
    u=(x<0?8:x>7?15:x+8).toString(16);

    // Use X and Y gradients as offsets into texture array
    // (Fake refraction)
    v=t[((w*y)+x+i+p)%p];
    
    // Use these components to make a bluish hex value
    d.fillStyle='#'+u+v+u+'ff'+v;

    // Draw a 3x3 pixel
    d.fillRect(i%w*3,F(i/w)*3,3,3)
  }

  // Swap water buffers over
  x=m;
  m=n;
  n=x
},20);

// Disturb water at position z
function W(z){

  // Perturb a cross of pixels centered on z
  m[z+1]=m[z-1]=m[z+w]=m[z-w]=m[z]-=p
}

// Register mouse handler to stir water
c.onmousemove=function(e){
  W(F(e.offsetX/3)+w*F(e.offsetY/3))
};

// Make it rain
(function X(){
  W(F(R()*p));
  setTimeout(X,F(R()*p))
})()