Debugging Interactive Applications

Although interactive, direct manipulation applications are known to be difficult to design and implement, the toolkits with which they are built generally do not contain any particular support for debugging. The Amulet toolkit contains a comprehensive collection of monitoring and debugging tools, including an interactive ‘‘Inspector.’’ These tools are provided in a machine-independent way in C++ without using hooks into the compiler, symbol tables or the run-time stack. Some of these capabilities are based on well-known techniques, but others are innovations that have never been provided before. Based on our experience with writing and debugging interactive applications, we have provided tools to address the most common and difficult programming bugs. The capabilities include: viewing values of objects as they change; breaking into the debugger when values change; viewing the inheritance and grouping hierarchies of objects; feedback for why objects are not visible or not interactive; tracing of constraint dependencies; and various techniques to search for objects. In addition, programmers can edit the values displayed in the Inspector, supporting rapid prototyping without requiring a C++ interpreter. These features make debugging interactive applications written using Amulet is substantially easier than with other toolkits.