# A Bar chart with a rotating background

This is the single canvas version of this demo that only uses a single canvas. The background rotates and the Bar chart is drawn on top. Because of the constant updating its not conducive to interactive features - for that you'll want the two canvas version .

This goes in the documents header:

    <script src="RGraph.common.core.js"></script>
    <script src="RGraph.bar.js"></script>

Put this where you want the chart to show up:

    <canvas id="cvs" width="750" height="250">[No canvas support]</canvas>

This is the code that generates the chart:

    <script>
        color1    = 'white';
        color2    = 'rgba(255,0,0,0.25)';
        increment = 0.0005;
        radius    = 500; // The gradient radius

        ca    = document.getElementById('cvs'),
        co    = ca.getContext('2d'),

        cx    = ca.width / 2,
        cy    = ca.height / 2,
        angle = 0,

        bar = new RGraph.Bar({
            id: 'cvs',
            data: [1,5,3,2,5,6,8],
            options: {
                colors: ['Gradient(#fcc:red)'],
                labels: ['Monday','Tuesday','Wednesday','Thursday','Friday','Saturday','Sunday'],
                backgroundGrid: false,
                shadow: true,
                shadowOffsetx: 1,
                shadowOffsety: 1,
                shadowBlur:3
            }
        });

        function draw ()
        {
            co.clearRect(-5000,-5000,10000,10000);

            co.translate(cx,cy);
            co.rotate(increment);
            co.translate(cx * -1,cy * -1);

            // Keep a record of what the angle used is
            angle += increment;

            for (var i=0; i<6.28; i+=(6.28 / 15)) {

                var endpoint1 = RGraph.getRadiusEndPoint(cx, cy, i - 0.1, 10000 * angle * 4);
                var endpoint2 = RGraph.getRadiusEndPoint(cx, cy, i + 0.1, 10000 * angle * 4);

                co.beginPath();
                    co.fillStyle = color2;
                    co.moveTo(cx,cy);
                    co.lineTo(endpoint1[0],endpoint1[1]);
                    co.lineTo(endpoint2[0],endpoint2[1]);
                    co.lineTo(cx,cy);
                co.fill();
            }

            // Draw a circular gradient from the center outwards
            var grad = co.createRadialGradient(cx, cy, 0, cx, cy, 1000);
                grad.addColorStop(0, 'rgba(255,255,255,1)');
                grad.addColorStop(0.25, 'rgba(255,255,255,0.5)');
                grad.addColorStop(0.5, 'rgba(255,255,255,0)');

            co.fillStyle = grad;
            RGraph.path2(
                co, 'b a % % % % % % f',
                cx, cy,
                1000,
                0,
                2 * Math.PI,
                -1
            );

            drawChart()

            setTimeout(draw, 25);

            // This function draws the chart
            function drawChart ()
            {
                // Rotate the canvas back so when drawn the chart appears straight
                co.translate(cx,cy);
                co.rotate(0-angle);
                co.translate(cx * -1,cy * -1);

                bar.draw();

                // Rotate the canvas again
                co.translate(cx,cy);
                co.rotate(angle);
                co.translate(cx * -1,cy * -1);
            }
        }

        draw();
    </script>