A Window Architecture Providing Predictable Temporal Performance

Programs running on high performance workstations are beginning to require the ability to perform precise temporal synchronization for applications that range from process and system visualization to video games like flight simulators. Unfortunately, the architecture of operating systems and graphics makes this capability very hard to achieve. This paper describes the architecture and implementation of SLwindows, a window system that provides all the usual facilities of overlapping windows in addition to real-time performance controllable from within the individual applications. It does so by making use of graphics hardware that duplicates context within the graphics system, allowing the implementation of independent graphics data paths that run from each application all the way to the digital-toanalogue converters. The window system written to take advantage of this hardware allows individual application tasks direct access to all the graphics hardware, giving them real-time control of the graphical output. In doing so it eliminates much of the time-consuming overhead that exists in current window systems, such as damage repair. The implementation was performed using a decadeold graphics system, combined with custom-built hardware. But the capabilities of commercial graphics subsystems are improving in ways that make widespread implementation of similar systems possible in the near future. They will be essential as application programs begin to use facilities like multi-media that require tight control of temporal synchronization among a variety of output streams.