index.html

<html>
    <head>
        <style>
            
            /*basic reset */
            
            *{
                margin: 0;
                padding: 0;
            }
            
           

            body {background: black;}
            canvas {display:block;}
        
        </style>
    </head>
    <body>
    
        <canvas id="c"></canvas>
        
        <script>
        // geting canvas by id c
        var c = document.getElementById("c");
        var ctx = c.getContext("2d");

        //making the canvas full screen
        c.height = window.innerHeight;
        c.width = window.innerWidth;

        //chinese characters - taken from the unicode charset
        var matrix = "AﾎｹBCｽDEF:・.\"=*ﾕﾗ+-<>GHIJｶKLﾋMNOﾊﾐｰｳﾅﾓﾆｻﾂｵﾘｱﾒｴｷｾﾈﾀﾇﾍPQRﾜSｼTUVﾏWXYZ123ﾑ4567ﾃ89";
        //converting the string into an array of single characters
        matrix = matrix.split("");

        var font_size = 12;
        var columns = c.width/font_size; //number of columns for the rain
        //an array of drops - one per column
        var drops = [];
        //x below is the x coordinate
        //1 = y co-ordinate of the drop(same for every drop initially)
        for(var x = 0; x < columns; x++)
            drops[x] = 1; 

        var once = false;    
        var myTimer;
        //drawing the characters
        function draw()
        {
            //Black BG for the canvas
            //translucent BG to show trail
            ctx.fillStyle = "rgba(0, 0, 0, 0.04)";
            ctx.fillRect(0, 0, c.width, c.height);
            
            if(once == false)
            {
                ctx.fillStyle = "#000";            
            }
            else
            {              
                ctx.fillStyle ="#0F0";
            }
            
            ctx.font = font_size + "px arial";

            for(var i = 0; i < drops.length; i++)
            {               
                var text = matrix[Math.floor(Math.random()*matrix.length)];
                //x = i*font_size, y = value of drops[i]*font_size     

                ctx.fillText(text, i*font_size, drops[i]*font_size);                             

                if(drops[i]*font_size > c.height && Math.random() > 0.975)
                {  
                    drops[i] = 0;

                    if(once === false)
                    {
                       clearInterval(myTimer);
                       myTimer = setInterval(draw, 60);
                    }

                     once = true;                     
                }
                
                drops[i]++;               
            }
        }
       
        myTimer = setInterval(draw, 1);              
        
        </script>
    </body>
</html>﻿

<!--

 if(once == true && i < columns)
                { 
                   ctx.fillStyle = "#fff";
                }
                else    
                {
                  ctx.fillStyle = "#0F0";
                  console.log(columns + " " + i);
                }

                 -->