VAX Workstation Program

This document, "VAX Workstation Program System Display Architecture Revision 1.2," authored by Henry M. Levy and Daniel E. Ganek and dated October 27, 1982, describes a high-level programming interface designed for new generations of high-resolution, bit-mapped display terminals.

It addresses the need for a sophisticated interface to leverage advanced display capabilities such as screen sharing among multiple simultaneous activities (windows), graphics, multiple fonts, proportionally spaced text, and digitized images. A primary goal is to provide a high-level procedural interface that isolates application programmers from the physical characteristics and current state of the display device, enabling screen and keyboard multiplexing among independent processes and compatibility across varying display hardware.

The architecture is built upon a layered model, primarily defining two services:

• Virtual Display Service (VDS): Manages application-level objects for image composition. Key concepts include "Virtual Displays" (rectangular areas for text and graphics output), "Pasteboards" (2D coordinate spaces for arranging and combining virtual displays, potentially overlapping), and "Windows" (rectangular areas on a pasteboard that define what can be viewed on the screen).
• Virtual Screen Service (VSS): Manages user-level objects for arranging content on the physical screen. This includes "Virtual Screens" (a larger memory space where viewports reside) and "Viewports" (rectangular areas on the virtual screen that map a window's content to the physical display, allowing user control over image manipulation like moving, zooming, and panning).

The document also defines a comprehensive display vocabulary, specifies text management operations (lines, fields, subfields, characters, and various character renditions), details input device management (virtual keyboards and positioners like mice/touch pads), and notes that graphics management will be based on the proposed ANSI Virtual Device Interface (VDI). It concludes by discussing compatibility with other display architectures, such as Digital's Terminal Interface Architecture (TIA).