Browse Prior Art Database

Graphic Display List Structure

IP.com Disclosure Number: IPCOM000087647D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Murphy, AS: AUTHOR [+2]

Abstract

Digital graphic CRT display apparatus can be either of two basic types, raster scan or directed beam. In each case, a display controller accepts graphics commands and converts these into CRT beam information. In a directed-beam apparatus, the beam actually traces the designated shape on the screen, whereas with a raster scan display, the controller determines when a raster scanning beam must be turned on and off.

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Graphic Display List Structure

Digital graphic CRT display apparatus can be either of two basic types, raster scan or directed beam. In each case, a display controller accepts graphics commands and converts these into CRT beam information. In a directed-beam apparatus, the beam actually traces the designated shape on the screen, whereas with a raster scan display, the controller determines when a raster scanning beam must be turned on and off.

Conventional display controllers, whether for raster scan or directed-beam displays, normally include two registers which contain the current X and Y coordinate values, that is the current position of the beam on a line being traced. So long as only straight line segments are being described, there is no problem. However, as soon as an arc is introduced into the chain, a different type of sub- entity is created. By using the concept of "current direction" as well as "current position", arcs and straight lines can be used in a unified graphic command structure. The controller will, therefore, have three registers, X, Y and theta. In some implementations, however, the current angle theta may be more conveniently stored as two values P = cos theta and Q = sin theta.

Five basic drawing commands are postulated.

1. Absolute Point (x y). The current position registers are set to x and y,and the current direction register is set to Arctan deltay/deltax, where deltax and deltay is the difference between the current and new values X and Y.

2. Move by displacement (deltax d...