The hardworking Microsoft Visio product development team have worked hard to almost match all of the functionality of the old server-side Visio services control, but they haven’t quite got everything. So I cheered when I hear that support for html overlays are in the roadmap to be supported! All I ask for now (almost) is layer control, and I will be very happy.
They also stated that they will be enabling all this functionality for non-SharePoint web sites in the future!
Go to http://aka.ms/voapireference got more details.