This is a demonstration of how to use the quadraticCurveTo() function of the canvas 2D API. A quadratic curve is a type of curve which is available to you via the function built into the canvas API. The example here should help you to understand them because the control points (the coordinates that you give to the .quadraticCurveTo() function ) are illustrated and you can drag them around with your mouse - showing the effect on the curve. The resulting code is shown below.
This is the code that can be used to achieve the curve (the points are color coded to match the output above):
The quadraticCurveTo() function takes four arguments - ie two sets of X/Y coordinates. The curve is actually made up of three points - but the first point is the current point in your path. If you're starting a new path with the quadraticCurveTo() function then you need to use the moveTo function to move to the start point.