Classification: UNCLASSIFIED Caveats: NONE From: Kennedy, Charles M USA CIV (US) [mailto:[email protected]] > This is all from a long time ago so my recollection may be slightly fuzzy and corrections are welcome.
Kermit's recollection agrees with mine. A note about those display technologies, which are probably not familiar to the younger generation: The Vector General was a "calligraphic" aka "stroke refresh" system. Before I came to BRL I developed software using a similar DEC system, their VS60. There were a few other contemporaneous (1970s-1980s) manufacturers of similar systems. These had various peripherals that could include joysticks, light pens, pushbutton keypads, knob arrays, keyboards, etc. (In my case, I interfaced a modified Talos digitizing tablet to the PDP-11 app via a DR11-C parallel port.) However, the distinctive feature was that they had programmable graphics processors which took their instructions from a portion of the PDP-11's RAM, called a "display list" or "display file". The majority of the display-list instructions specified vectors or character strings in absolute or relative coordinates, with parameters such as character size and vector intensity. There were also "jump" instructions of various sorts; e.g., the VS60 supported subroutines so one could define a subobject using all relative vectors and "call" it multiple times from different positions on the display. The graphics processor decoded the instructions and drove D/A converters to move the beam around on an CRT display (like X vs. Y mode on an oscilloscope, with Z for intensity). Some displays such as the VG could perform coordinate transformations, usually using "homogenous coordinates" which supports 3D perspective. Thus to move or rotate a subobject, one just updated its transformation matrix. (For the VS60 I had to do this via the PDP-11 CPU.) The result was real-time interaction with wireframe 3D displays. The Megatek had a similar display-list implementation, but it rasterized the vectors to a color frame buffer, which was concurrently displayed on a raster-scan monitor similar to what PCs now use. In addition to MGED, it inspired my "rayselect" tool suite which allowed interactive 3D viewing of user-selected, color-coded subsets of "shotlines" through target models. The ultimate system of this kind was the "Picture System" series produced by Evans & Sutherland. If you want more information, photos, etc. check out the *first* (1973) edition of Newman & Sproull's classic text "Principles of Interactive Computer Graphics". (The second [1979] edition was slanted more toward the raster-scan frame-buffer technology that was rapidly supplanting the stroke-refresh systems.) Several years ago, Phil Budne produced a DEC VT11 simulation for use with Bob Supnick's SIMH PDP-11 simulator. I worked with him and a couple of others to improve the VT11 simulation and add support for the VS60 (which was essentially a superset of the VT11). His original implementation is at URL http://ultimate.com/phil/xy/, but I don't think it was updated to include the later improvements. If you are interested, let me know and I'll send you my latest version, which can also be easily used in apps as a graphics subsystem entirely separate from SIMH. Mike Muuss and I had the notion that we could/should design an improved display-list oriented graphics subsystem, but we never got around to it. I also wanted to produce a similar subsystem for interactive 3D modeling on the Blit bit-mapped display terminals (AT&T/Teleype 5620 DMD and 630 MTG), which BRL used to have a lot of, but again it wasn't on my official task list and I never got around to it. The GPUs in today's PC video cards are programmable in a somewhat similar way to the display-list systems, but are much more oriented to 3D texture-mapped etc. models for FPS-style gaming. When we finally wrap up the Maximin implementation project, I plan to get back to my reconstruction of BRL/JHU PDP-11 Unix, at which time I may use the Budne-derived software as a base for a VG and/or VS60 emulation. Since much of the old hardware is no longer available/functional, and in many cases documentation seems to be lost, it is probably infeasible to reconstruct it in its original form. (If anybody knows where we can find any of this, please let me know. I know a fellow in California who has a VS60, and I have a bunch of boards for the VS11/VSV11 which is a raster system for the PDP-11/LSI-11 supporting a large subset of VT11 instructions.) - Douglas A. Gwyn, member of ARL Emeritus Corps Classification: UNCLASSIFIED Caveats: NONE
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