Vector screen

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Vector graphic screen: Vectrex Heads Up Action Soccer Game

A vector screen is a type of screen based on the cathode ray tube , which, unlike a television, does not build up the picture in rows and columns, but draws points and lines directly on the fluorescent screen with the cathode ray , like an oscilloscope . More complicated figures such as letters are composed of individual line segments. Vector screens were developed in the 1960s and could be found until the mid-1980s.

The general public encountered vector screens especially in computer games such as Lunar Lander , Asteroids and Spacewar! and the Vectrex game console .

functionality

Architecture of a typical vector graphics system

Typical vector graphics systems consist of a display processor connected to the main processor , a display buffer and a cathode ray tube . The display buffer stores a list of drawing commands with (x, y) - or (x, y, z) - end point coordinates as well as commands for text output. These commands are interpreted by the screen processor and converted by the vector generator into electrical voltages that ultimately control the position of the electron beam.

Since the luminosity of the phosphor decreases after excitation by the electron beam in a few tens or at most hundreds of microseconds, the screen processor has to go through the display buffer again and again in order to refresh the phosphor. This had to be done at least 40 times per second in order to keep the flickering tolerable, supported by medium-length photoluminescent screens. In the 1960s there were few and very expensive devices that could do this. In addition, only up to a few thousand lines could be displayed without flicker.

In the late 1960s, so-called Direct-View Storage Tubes (DVSTs) came onto the market, in which an image, once written, remained visible for several minutes. This made the display buffer obsolete; the display was always flicker-free. With this much cheaper technology, interactive computer graphics became affordable for many companies.

literature

  • James D. Foley et al: Computer Graphics: Principles and Practice. Pp. 9-11. Addison-Wesley, Reading 1995, ISBN 0-201-84840-6