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Draw a bar chart using HTML5 Canvas

阿神Original: 2017-03-21 10:08:344080browse

Rendering:

<!DOCTYPE>
 <html>
  <head>
   <title>Bring Your Charts to Life</title>
  <script type="text/javascript">

        // chart sample data
        var arrVisitors = new Array();
        arrVisitors[0] = "2007, 750";
        arrVisitors[1] = "2008, 425";
        arrVisitors[2] = "2009, 960";
        arrVisitors[3] = "2010, 700";
        arrVisitors[4] = "2011, 800";
        arrVisitors[5] = "2012, 975";
        arrVisitors[6] = "2013, 375";
        arrVisitors[7] = "2014, 775";
        var canvas;
        var context;
        // chart properties
        var cWidth, cHeight, cMargin, cSpace;
        var cMarginSpace, cMarginHeight;
        // bar properties
        var bWidth, bMargin, totalBars, maxDataValue;
        var bWidthMargin;
        // bar animation
        var ctr, numctr, speed;
        // axis property
        var totLabelsOnYAxis;
        // barchart constructor
        function barChart() {
            canvas = document.getElementById(&#39;bchart&#39;);
            if (canvas && canvas.getContext) {
                context = canvas.getContext(&#39;2d&#39;);
            }
            chartSettings();
            drawAxisLabelMarkers();
            drawChartWithAnimation();
        }
        // initialize the chart and bar values
        function chartSettings() {
            // chart properties
            cMargin = 25;
            cSpace = 60;
            cHeight = canvas.height - 2 * cMargin - cSpace;
            cWidth = canvas.width - 2 * cMargin - cSpace;
            cMarginSpace = cMargin + cSpace;
            cMarginHeight = cMargin + cHeight;
            // bar properties
            bMargin = 15;
            totalBars = arrVisitors.length;
            bWidth = (cWidth / totalBars) - bMargin;
            // find maximum value to plot on chart
            maxDataValue = 0;
            for (var i = 0; i < totalBars; i++) {
                var arrVal = arrVisitors[i].split(",");
                var barVal = parseInt(arrVal[1]);
                if (parseInt(barVal) > parseInt(maxDataValue))
                    maxDataValue = barVal;
            }
            totLabelsOnYAxis = 10;
            context.font = "10pt Garamond";
            
            // initialize Animation variables
            ctr = 0;
            numctr = 100;
            speed = 10;
        }
        // draw chart axis, labels and markers
        function drawAxisLabelMarkers() {
            context.lineWidth = "2.0";
            // draw y axis
            drawAxis(cMarginSpace, cMarginHeight, cMarginSpace, cMargin);
            // draw x axis
            drawAxis(cMarginSpace, cMarginHeight, cMarginSpace + cWidth, cMarginHeight);
            context.lineWidth = "1.0";
            drawMarkers();
        }
        // draw X and Y axis
        function drawAxis(x, y, X, Y) {
            context.beginPath();
            context.moveTo(x, y);
            context.lineTo(X, Y);
            context.closePath();
            context.stroke();
        }
        // draw chart markers on X and Y Axis
        function drawMarkers() {
            var numMarkers = parseInt(maxDataValue / totLabelsOnYAxis);
            context.textAlign = "right";
            context.fillStyle = "#000";;
            // Y Axis
            for (var i = 0; i <= totLabelsOnYAxis; i++) {
                markerVal = i * numMarkers;
                markerValHt = i * numMarkers * cHeight;
                var xMarkers = cMarginSpace - 5;
                var yMarkers = cMarginHeight - (markerValHt / maxDataValue);
                context.fillText(markerVal, xMarkers, yMarkers, cSpace);
            }
            // X Axis
            context.textAlign = &#39;center&#39;;
            for (var i = 0; i < totalBars; i++) {
                 arrval = arrVisitors[i].split(",");
                 name = arrval[0];
                 markerXPos = cMarginSpace + bMargin 
                              + (i * (bWidth + bMargin)) + (bWidth/2);
                 markerYPos = cMarginHeight + 10;
                 context.fillText(name, markerXPos, markerYPos, bWidth);
            }
            context.save();
            // Add Y Axis title
            context.translate(cMargin + 10, cHeight / 2);
            context.rotate(Math.PI * -90 / 180);
            context.fillText(&#39;Visitors in Thousands&#39;, 0, 0);
            context.restore();
            // Add X Axis Title
            context.fillText(&#39;Year Wise&#39;, cMarginSpace + 
                        (cWidth / 2), cMarginHeight + 30 );
        }
        function drawChartWithAnimation() {
            // Loop through the total bars and draw
            for (var i = 0; i < totalBars; i++) {
                var arrVal = arrVisitors[i].split(",");
                bVal = parseInt(arrVal[1]);
                bHt = (bVal * cHeight / maxDataValue) / numctr * ctr;
                bX = cMarginSpace + (i * (bWidth + bMargin)) + bMargin;
                bY = cMarginHeight - bHt - 2;
                drawRectangle(bX, bY, bWidth, bHt, true);
            }
            // timeout runs and checks if bars have reached
            // the desired height; if not, keep growing
            if (ctr < numctr) {
                ctr = ctr + 1;
                setTimeout(arguments.callee, speed);
            }
        }
        function drawRectangle(x, y, w, h, fill) {
            context.beginPath();          
            context.rect(x, y, w, h);          
            context.closePath();
            context.stroke();
            if (fill) {
                var gradient = context.createLinearGradient(0, 0, 0, 300);
                gradient.addColorStop(0, &#39;green&#39;);
                gradient.addColorStop(1, &#39;rgba(67,203,36,.15)&#39;);
                context.fillStyle = gradient;
                context.strokeStyle = gradient;
                context.fill();
            }
        }
</script>
 <noscript>
  This chart is unavailable because JavaScript is disabled on your computer. Please enable
  JavaScript and refresh this page to see the chart in action.
 </noscript>
</head>
 <body onLoad="barChart();">
   <canvas id="bchart" height="400" width="600">Your browser does not support HTML5 Canvas
   </canvas>
</body>
</html>

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