I am using the Highcharts js library and rendering my users' avatars on the canvas using the Highcharts Renderer methods. I need the avatars to be rendered with rounded corners rather than square, unfortunately I am obtaining the avatars through Gravatar, so it is not possible to modify the images beforehand.
My question is similar to this one, except that I haven't been able to figure out how to implement it using the Highcharts API.
var xpos = chart.chartWidth/2;
var ypos = chart.plotTop + chart.plotSizeY/2;
chart.renderer.image('http://www.gravatar.com/avatar/2ce72b95b9ed68d79a99d717b58ec64c?s=70', xpos-35, ypos-35, 70, 70).add();