Morphic: A graphics model based on display trees, and a direct-manipulation user interface (UI) construction kit and library, under heavy development but now quite usable.
Morphic was originally developed as a prototype-based implementation, as part of the Self prototype-based object-oriented (OO) programming language project, at Sun Microsystems Laboratories, by John Maloney and Randy Smith.
Morphic is now in a class-based implementation as part of Squeak, an open source, open research, direct descendant of Smalltalk-80/Apple-Smalltalk, first at Apple Computers, then at Disney Corp., and now at the Viewpoints Research Institute, by the original Xerox PARC, Alan Kay team, with Dan Ingalls and John Malony.
Morphic is an alternative to the Model View Controller (MVC) graphics model used in many object-oriented languages: Java, Smalltalk. The Squeak team has replaced and obsoleted MVC with Morphic in Squeak Smalltalk.
Morphic's graphics model is portable and flexible: it was first implemented in Self as a prototype-based object system, and is now in Squeak as a class-based object system.
Morphic is much simpler and yet more general than the model used in many other object oriented languages: Model View Controller: MVC. It makes graphics far simpler to program, and eliminates many sources of bugs. One mail list posting said: "it makes syntax errors fly away."
Morphic looks like an important advance. It may have useful ideas for your project. Examine it for free. Since it is open source, it can be added to your project/language at no monetary cost, and easy licensing.