SG Window library defines two interfaces: IsgMessageSink and IsgPaintSink. If you implement these interfaces in a VB module and attach this implementation to the SG Window object, interface methods are called from the window object. That's why we call them callback interfaces.

IsgMessageSink

IsgMessageSink interface contains only one method: Message. This method is called when there is a new enabled message in the window's message queue.

IsgPaintSink

IsgPaintSink is interface specialized for window drawing. It's methods are called when window's client or frame should be painted.