Browse Prior Art Database

Magnifying Cursor

IP.com Disclosure Number: IPCOM000059808D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Murphy, AS: AUTHOR

Abstract

In a graphics display system having a cursor movable by a cursor control device, software is used to expand and display a predetermined area around the cursor to provide a simulated magnifying lens in front of the screen. This assists in the accurate positioning of the cursor relative to an image on the screen. The magnification may be accomplished by simple image expansion or by reducing from a display list. In the following description the magnifying lens is square (21x21 pels) and has a magnifying ratio of 3. Other shapes, sizes and magnifications are possible. Suppose that the cursor is at the coordinate (X,Y). A rectangular display screen area extending from pel positions (X-11, Y-11) to (X+11, Y+11) inclusive is saved in a cursor shadow buffer and the screen area cleared.

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Magnifying Cursor

In a graphics display system having a cursor movable by a cursor control device, software is used to expand and display a predetermined area around the cursor to provide a simulated magnifying lens in front of the screen. This assists in the accurate positioning of the cursor relative to an image on the screen. The magnification may be accomplished by simple image expansion or by reducing from a display list. In the following description the magnifying lens is square (21x21 pels) and has a magnifying ratio of 3. Other shapes, sizes and magnifications are possible. Suppose that the cursor is at the coordinate (X,Y). A rectangular display screen area extending from pel positions (X-11, Y-11) to (X+11, Y+11) inclusive is saved in a cursor shadow buffer and the screen area cleared. (Note: For a fuller explanation of the shadow buffer technique as used in displays, see [*].) The data occupying the area (X-3, Y-3) to (X+3, Y+3) is now drawn with a 3 times magnification in the cleared screen area and the cursor exclusive ORed onto it. The cleared area is 2 pels wider and deeper than the space required for the magnified image - this is to allow for the lens border lines
(i.e., cursor box). The original image can be restored to the screen by rewriting the image buffer with the data previously stored in the shadow buffer. Cursor movement is accomplished by first restoring the original image, moving the cursor position and then drawing the magnified image as outlined above. There are two methods that can be adopted for drawing the magnified image within the cleared area: 1.Simple Image Expansion The pels within the area (X-3, Y-3) to (X+3, Y+3) are expanded and redrawn such that each source pel now occupies 3 x 3 pels in the expanded image. This method is suitable for display terminal without a high performance drawing engine. It operates independently of the size of the display list, but does not produce the same quality of result as the other method described below. Fig. 1 shows the pel patterns of three vectors (AA, BB and CC), while Fig. 2 shows a cursor with box 1 and cros...