Canvas How to - Draw rounded rectangle with bezier Curve

Question

We would like to know how to draw rounded rectangle with bezier Curve.

Answer


<!--  w w w. j a v  a 2  s  .  co m-->
<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'>
window.onload=function(){
    var K = 4 * (Math.SQRT2-1) / 3; //constant for circles using Bezier curve.
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext('2d');
    canvas.width = 400;
    canvas.height = 200;
    document.body.appendChild(canvas);
    rounded_rect(ctx,10,10,200,150,20);
    function rounded_rect(ctx,left,top, width, height, radius)
    {
        var right=left+width;
        var bottom=top+height;
        ctx.beginPath();
    // top left
        ctx.moveTo(left+radius,top);
    // top right
        ctx.lineTo(right-radius,top);
    //right top
        ctx.bezierCurveTo(right+radius*(K-1),top,right,top+radius*(1-K),right,top+radius);
    //right bottom
        ctx.lineTo(right,bottom-radius);
    //bottom right
        ctx.bezierCurveTo(right,bottom+radius*(K-1),right+radius*(K-1),bottom,right-radius,bottom);
    //bottom left
        ctx.lineTo(left+radius,bottom);
    //left bottom
        ctx.bezierCurveTo(left+radius*(1-K),bottom,left,bottom+radius*(K-1),left,bottom-radius);
    //left top
        ctx.lineTo(left,top+radius);
    //top left again    
        ctx.bezierCurveTo(left,top+radius*(1-K),left+radius*(1-K),top,left+radius,top);
        ctx.lineWidth=10;
        ctx.strokeStyle="rgb(0,0,0)";
        ctx.stroke();
    }
}
</script>
</head>
<body>
</body>
</html>

The code above is rendered as follows: