For help with anything that CEGUI doesn't offer straight out-of-the-box, e.g.: - Implementation of new features, such as new Core classes, widgets, WindowRenderers, etc. ... - Modification of any existing features for specific purposes - Integration of CEGUI in new engines or frameworks and writing of new plugins (Renderer, Parser, ...) or modules
To do something like in the image posted you just ensure your 'fill' image is circular also, and just treat the thing as a square otherwise. Since you have transparent regions, it shows as circular, and this is the way probably 99% of these things are handled. To have actual circular windows, where child content is clipped to the inner edge of the circle is not currently supported.