Canvas reference: The quadraticCurveTo function

The quadraticCurveTo function can be used to add curves to your chart. It uses the existing pen position as the start point and then the first two coordinates as the mid-point and the last two coordinates that you give it as the end point. The curve that is drawn will not necessarily pass through the mid-point.

Arguments to the function

• The X1 coordinate (of the mid-point, P1 on the diagram)
• The Y1 coordinate (of the mid-point, P1 on the diagram)
• The X2 coordinate (of the end-point, P2 on the diagram)
• The Y2 coordinate (of the end-point, P2 on the diagram)

P0 is not specified on the quadraticCurveTo function - this is done by a moveTo call before the quadraticCurveTo call. As shown below.

An example

<script>
    window.onload = function ()
    {
        var canvas  = document.getElementById("cvs");
        var context = canvas.getContext('2d');

        context.beginPath();
        
        // This is where the curve begins (P0)
        context.moveTo(100, 100);
    
        context.quadraticCurveTo(150, 50, 200, 100);
    
        context.stroke();
    }
</script>

See also:

• An example of the HTML5 canvas quadraticCurveTo function