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Fast Graphic Display

IP.com Disclosure Number: IPCOM000034666D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Related People

Tannhof, P: AUTHOR [+2]

Abstract

This article describes a method for reducing the delay of the display of a large number of points when using routines of a graphic control program such as GDDM* (Graphic Data Display Manager). When using such routines, we realize that the time necessary to construct a graphic with a large number of points becomes quickly prohibitive for an interactive program. a) The delay is not reduced when specifying a window where a few points are present. b) On the other hand, if one has to display a large number of points on a small area of the screen, all the points will be processed and displayed by GDDM even if a few points fall on the same pixel. According to this article, the principle is to sort the points before calling the graphic functions.

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Fast Graphic Display

This article describes a method for reducing the delay of the display of a large number of points when using routines of a graphic control program such as GDDM* (Graphic Data Display Manager). When using such routines, we realize that the time necessary to construct a graphic with a large number of points becomes quickly prohibitive for an interactive program. a) The delay is not reduced when specifying a window where a few points are present. b) On the other hand, if one has to display a large number of points on a small area of the screen, all the points will be processed and displayed by GDDM even if a few points fall on the same pixel. According to this article, the principle is to sort the points before calling the graphic functions. Two sorts are made: a) First, all the points that do not appear as a segment or a point within the display window are suppressed. b) Then, all the points that will fall on the same pixels of the screen are suppressed. In this way, plenty of time is saved when displaying curves or surfaces with a large number of points.

This method can be applied to any kind of display device. The principle of the display speed-up is based on the two previous remarks: first, the points that do not interact with the inside of the window are dropped; then, the points are sorted in order to have only one point per pixel. Fig. 1 gives an example of a curve displayed through a window. The problem is to eliminate the coordinates of the points that will not give any segment within the window. On the other hand, the time spent to sort the points should not be too long in order not to reduce the appeal of the method. A good compromise is to define 4 zones around the window: the A zone is defined by X < X1

the B zone is defined by X > X2

the C zone is defined by Y < Y1

the D zone is defined by Y > Y2 The first sort is made as follows: for each point that does not belong to the window, its two neighbors (the point before this one and the point after) are scanned. If the two adjacent points are in the same zone as the considered point, it can be suppressed. On Fig. 2, points 1, 2, 3, 10 and 11 are suppressed. In addition to all the points within the window, points 4, 8 and 9, necessary for drawing segmen...