Monday, May 28, 2012

How to create Graphs using HTML5

To develop a small web application, I would like to use the data of students' grades and translate it into a graph bar.  But how can I do that?

With HTML5, using tag <canvas>, it is possible create a graph bar without third part software. The first thing to do is write some functions in JavaScript. Before you copy code, you have to understand the coordinates on Canvas. The next figure show how coordinates are designed. It is not the same of what we learned on Math classes.


JavaScript code:

<script type="text/javascript">


        function drawLine(context,startX,startY,endX,endY,color){
            context.beginPath();
            context.moveTo(startX,startY);
            context.lineTo(endX,endY);
            context.closePath();
            context.strokeStyle=color;
            context.stroke();
        }


        function drawRectangle(context,startX,startY,width,height,fill){
            context.beginPath();
            context.rect(startX,startY,width,height);
            context.closePath();
            context.stroke();
            if(fill) context.fill();
        }


        function clearCanvas(context){
            // Store the current transformation matrix
            context.save();
            // Use the identity matrix while clearing the canvas
            context.setTransform(1, 0, 0, 1, 0, 0);
            context.clearRect(0, 0, myCanvas.width, myCanvas.height);
            // Restore the transform
            context.restore();
        }


        function drawBarChart(context,data,startX,startY,endX,
endY,chartHeight,barWidth,markDataIncrementsIn,scale){
            //draw x-axis
            drawLine(context,startX,startY,endX,startY,"#000");
            //draw y-axis
            drawLine(context,startX,startY,startX,endY,"#000");


            var maxValue=0;
            for(var i=0;i<data.length;i++){
                //extract data
                var values = data[i].split(",");
                //column name
                var name=values[0];
                //column value
                var height=parseFloat(values[1])*scale;
                //find maximum value
                if(parseInt(height)>parseInt(maxValue)) maxValue=height;
                //write data to chart
                //fill rectangle with yellow color
                context.fillStyle="#ff0";
                drawRectangle(context,startX+(i*barWidth*2),(startY-height),barWidth,height,true);
                //add column title to x-axis
                context.textAlign="left";
                //text color is black
                context.fillStyle="#000";
                context.fillText(name,startX+(i*barWidth*2),(chartHeight-25),barWidth*2);
            }


            //add some data markers to y-axis
            var numMarkers = Math.ceil(maxValue/parseInt(markDataIncrementsIn));
            context.textAlign="right";
            context.fillStyle="#000";
            var markerValue=0;
            for(var i=0;i<=numMarkers;i++){
                context.fillText((markerValue/parseInt(scale)),(startX-5),(startY-markerValue),50);
                if(i==0){
                    drawLine(context,startX,(startY-markerValue),endX,(startY-markerValue),"#000");
                }else{
                    drawLine(context,startX,(startY-markerValue),endX,(startY-markerValue),"#00f");
                }
                markerValue+=parseInt(markDataIncrementsIn);
            }
        }


        function graph(scale){
            var s=0;
            var changed=false;
            document.getElementById("range").innerHTML=scale;
            if(scale==undefined){
                s=1;
                changed=false;
            }else{
                s=scale;
                changed=true;
            }
             
            var graphCanvas = document.getElementById("myCanvas");
            //ensure that element is available within DOM
            if(graphCanvas && graphCanvas.getContext){
                //open a 2d context within canvas
                var context = graphCanvas.getContext("2d");
                //bar chart data
                var data = new Array(5);
                data[0]="Bad,2";
                data[1]="Mediocre,0.45";
                data[2]="Sufficient,5.5";
                data[3]="Good,7.2";
                data[4]="Excelent,3.9";
                //draw bar chart
                if(!changed){
                    drawBarChart(context,data,35,560,750,50,myCanvas.height,30,s,s);
                }else{
                    //clear canvas to redrawing
                    clearCanvas(context);
                    //draw bar chart
                    drawBarChart(context,data,35,560,750,50,myCanvas.height,30,s,s);
                    
                }
            }
            return true;
        }
    </script>

The second thing to do is write some HTML tags.

<body onload="graph(1);">
        <div id="title">Grades</div>
        <table>
            <tr>
                <td><canvas id="myCanvas" width="800" height="600"></canvas><td>
            <td>
                <table>
                    <tr>
                        <td>Scale : <span id="range">1</span></td>
                    </tr>
                    <tr>
                        <td><input type="range" min="1" max="501" value="1" onchange="return graph(this.value)"/></td>
                    </tr>
                </table>
            </td>
        </tr>
    </table>
</body>


The third thing to do is write CSS.

<style type="text/css">
            #title{
                text-align: center;
            }
</style>

Now put together all three parts on a single page or you can create a file to JavaScript and another to CSS and then link them on HTML page. How you can do that? Copy the next code and you can change name files.

<head>
  <link rel="stylesheet" type="text/css" href="style.css" />
  <script type="text/javascript" src="functions.js"></script>
</head>



Attention
All this code is working on Google Chrome. Also works on Safari and Opera. If you will use Internet Explorer, you will have problems. For example, you can not use slide bar and you have to type a value instead.

Tuesday, May 1, 2012

How to install Oracle Database Express Edition


I heard talk about technology Oracle PL/SQL but I never tried it. To study PL/SQL it is necessary install software Oracle Database 11g Express Edition. Hereafter you have 3 minutes video showing all necessary steps to installation correct.