JS1k: The JavaScript code golfing competition

y=document;var b=y.getElementById("c"),c=b.width=window.innerWidth-24,f=b.height=window.innerHeight-24,g=b.getContext("2d");y.onmousemove=h;var j=true;y.onmouseover=function(){j=true};y.onmouseout=function(){j=false};var k=8,l=[];function m(a){return Math.floor(Math.random()*a)}function n(a){return m(a)*(Math.random()*2-1)}function o(){return"rgba("+m(256)+","+m(256)+","+m(256)+","+Math.random()+")"}var p=0,q=0;function h(a){p=a.pageX;q=a.pageY;if(p<0)p=0;if(q<0)q=0}var r=0;
function s(){for(var a=0;a<l.length;a++){var d;try{var e=g.getImageData(l[a].x+n(10),l[a].y+n(10),1,1).data;d="rgba("+e[0]+","+e[1]+","+e[2]+","+e[3]+")"}catch(t){d=o()}if(d.indexOf("rgba(0,0,0")>-1)d=l[a].b;g.fillStyle=d;if(j&&m(2)==1&&p>0&&q>0){d=p>l[a].x?1:-1;var i=q>l[a].y?1:-1;l[a].x+=m(3)*d;l[a].y+=m(3)*i}else{l[a].x+=n(3);l[a].y+=n(3)}g.fillRect(l[a].x,l[a].y,l[a].a,l[a].a)}if(l.length<1E3){a=m(c-k);d=m(f-k);i=m(k);e=g.fillStyle=o();g.fillRect(a,d,i,i);l[l.length]={x:a,y:d,a:i,b:e}}r++;setTimeout(s,
20)}s();

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// setup the canvas
        var c = document.getElementById("c");
        var a = c.width = window.innerWidth-24;
        var b = c.height = window.innerHeight-24;
        var x = c.getContext('2d');
        document.onmousemove = gm;
        var mio = true;
        document.onmouseover = function() { mio = true; };
        document.onmouseout = function() { mio = false; };
        
        var e = 8; // max object size
        var z = []; // object array
        
        // returns random number between 0 and 1
        function h() {
          return Math.random();
        }
        // returns random round number between 0 and g
        function f(g) {
          return Math.floor(h()*g);
        }
        // returns random number between -aa and aa
        function rn(aa) {
          return f(aa)*((h()*2)-1);
        }
        // returns random color
        function rc() {
          return "rgba("+f(256)+","+f(256)+","+f(256)+","+h()+")";
        }
        // return color of xx,yy coordinate
        // if something error happen, return random color
        function gc(xx,yy) {
          try {
            var pix = x.getImageData(xx,yy,1,1).data;
            return "rgba("+pix[0]+","+pix[1]+","+pix[2]+","+pix[3]+")";
          } catch (er) {
            return rc();
          }
        }
        // randomly returns true of false
        function tf() {
          return f(2)==1;
        }
        
        var tx = 0;
        var ty = 0;
        
        // retrieve mouse pos
        function gm(e) {
          tx = e.pageX;
          ty = e.pageY;
          if (tx < 0) tx = 0;
          if (ty < 0) ty = 0;
        }
        
        var cc = 0;
        
        // draw
        function d() {
          
          // alter existing objects
          for (var j = 0; j < z.length; j++) {
            // determine color
            var rg = gc(z[j].x+rn(10),z[j].y+rn(10));
            if (rg.indexOf("rgba(0,0,0") > -1) rg = z[j].c; //gc(z[j].x+1,z[j].y+1)
            x.fillStyle = rg;
            
            // move to mouse
            if (mio && tf() && tx > 0 && ty > 0) {
              var xd = tx > z[j].x ? 1 : -1;
            var yd = ty > z[j].y ? 1 : -1;
            z[j].x += f(3)*xd;
            z[j].y += f(3)*yd;
          }
          // or in a random direction
          else {
            z[j].x += rn(3);
            z[j].y += rn(3);
          }
          x.fillRect(z[j].x,z[j].y,z[j].w,z[j].w);
        }
        // generate new object
        if (z.length < 1000) {
          var u = f(a-e);
          var v = f(b-e);
          var w = f(e);
          var co = x.fillStyle = rc();
          x.fillRect(u,v,w,w);
          z[z.length] = {x:u,y:v,w:w,c:co};
        }
        cc++;
        setTimeout(d, 20);
        }
          d();