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Canvas mit JavaScript

Submitted by Erik Wegner on So., 17.03.2013 - 17:49

Canvas stellt die Möglichkeit bereit, mit JavaScript zur Laufzeit Bilder und Animationen auf einer Webseite zu erzeugen. In diesem Beispiel wird eine Sinus-Welle angezeigt.

Demo

Quellcode

<!DOCTYPE html>
<html><head><title>Canvas demo</title></head>
<body>

<canvas id="canvas1" width="100" height="50">C A N V A S</canvas>

<script type="text/javascript">
if ( window.addEventListener ) {
addEventListener( "load", draw, false ); } else { attachEvent( "onload", draw );
}

var width = 0;
var height = 0;
var amplitude = 0;
var deg = 0;
var deginc = 1;
var starty = 0;
var stretch = 1.3;

function draw(){
    prepare();
    window.setInterval(timerEvent, 66);
}

function prepare() {
    var canvas = document.getElementById('canvas1');
    if (canvas) {
        width = canvas.width;
        height = canvas.height;
        amplitude = height / 2 - 3;
        starty = height / 2;
    }
}

function timerEvent() {
    var canvas = document.getElementById('canvas1');
    if (canvas.getContext) {
        canvas = canvas.getContext('2d');
        //canvas.fillStyle = "rgb(255,255,255)";
        //canvas.fillRect( 0, 0, width, height);

        canvas.clearRect(0, 0, width, height);
        // Create gradient
        var grd=canvas.createLinearGradient(0,0,width,0);
        grd.addColorStop(0,"white");
        grd.addColorStop(0.1,"red");
        grd.addColorStop(0.9,"red");
        grd.addColorStop(1,"white");

        // Fill with gradient
        canvas.strokeStyle=grd;
        
        canvas.lineWidth = 5;
        canvas.fillStyle = "rgb(250,0,0)";
        canvas.beginPath();
        canvas.moveTo(0, starty);
        starty = height / 2 + Math.sin((deg + deginc) * 6.28 / width / stretch) * amplitude;
        for (x = 0; x < width; x += 2) {
            var y = height / 2 + Math.sin((deg + x) * 6.28 / width / stretch) * amplitude;
            canvas.lineTo(x,y);
        }
        canvas.stroke();
    }
    deg+=deginc;
    while(deg > width * stretch) deg -= width * stretch;
}
</script>
</body>
</html>

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