Browse Prior Art Database

Graphic Correlate Improvement

IP.com Disclosure Number: IPCOM000050392D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Murphy, AS: AUTHOR

Abstract

This article describes a method for improving the efficiency of the Graphic Correlate Operation in a display terminal or graphic drawing engine which stores a complete description of a graphic picture in a segmented display file and allows the user to view only a selected window of the picture. It is important that segment correlation be performed rapidly and efficiently so that an appropriate echo response can be made to the user. (Note: Correlation is the process of determining which segment lies within a specified distance of a given coordinate (x,y).)

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 2

Graphic Correlate Improvement

This article describes a method for improving the efficiency of the Graphic Correlate Operation in a display terminal or graphic drawing engine which stores a complete description of a graphic picture in a segmented display file and allows the user to view only a selected window of the picture. It is important that segment correlation be performed rapidly and efficiently so that an appropriate echo response can be made to the user. (Note: Correlation is the process of determining which segment lies within a specified distance of a given coordinate (x,y).)

Consider a graphic drawing engine which is capable of storing a complete graphic picture in a segmented display file. The operator is allowed to select any 'window' within this graphic picture, and the drawing engine will then draw this selected part within a 'viewport' on the display screen. The display mechanism is equipped with a mechanism for 'clipping' the window (x1,y1,x2,y2) from the picture space, transforming it to the screen coordinate system, and drawing it on the screen.

A simple method for performing the correlate operation is to redefine the clipping window as the 'trap-aperture' (i.e., a small rectangular area surrounding the correlate point (x,y)) and then to perform a pseudo drawing operation. The display list is processed a second time by the drawing engine. The engine performs the clipping operation using the trap aperture and notes any segment which falls within this tiny window. The names of all such segments (or possibly only the first one encountered) are returned as the result of the correlate process.

In order to speed the correlate operation up, it should be noted that the trap- aperture must lie within the original screen viewport. Thus, it is only necessary to correlate over those segments which were originally drawn...