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Deletion of Alphanumeric Characters from Display Screen

IP.com Disclosure Number: IPCOM000088149D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Johnson, JS: AUTHOR [+2]

Abstract

Fig. 1 illustrates a vector graphics display system in which characters can be displayed on display screen 1. Associated with screen 1 is display hardware 2 which includes a display store for storing the displayed information. The display operates under command of controlling processor 3. Characters can be entered on to screen 1 via keyboard 4 connected to processor 3. Processor 3 performs any necessary processing and updates the display store, as necessary.

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Deletion of Alphanumeric Characters from Display Screen

Fig. 1 illustrates a vector graphics display system in which characters can be displayed on display screen 1. Associated with screen 1 is display hardware 2 which includes a display store for storing the displayed information. The display operates under command of controlling processor 3. Characters can be entered on to screen 1 via keyboard 4 connected to processor 3. Processor 3 performs any necessary processing and updates the display store, as necessary.

Characters are displayed in a matrix of n rows by m columns and are stored in a character buffer within controlling processor 3 as a contiguous list of m x n eight-bit character codes. A cursor is used to point to one of the m x n character buffer locations and is displayed on screen 1 as an underscore.

Characters to be erased or drawn on display screen 1 must be erased from or written into the display store. Each character is generated from a sequence of visible and invisible vector-stroke displacements permanently stored in the processor memory. All characters, with the exception of the cursor, advance the x position on display screen 1 to the start of the next character. A string of characters is erased or drawn by issuing a Vector List to display hardware 2. The Vector List contains a header followed by a sequence of indirect pointers (one per character) to the vector strokes. The header specifies the type of operation (erase or draw) required and specifies the x and y coordinates of the start position. Once an erase or draw operation has been started, display hardware 2 may access the character vector strokes directly without further program intervention until the operation is complete. Vector List loading is carried out in the keyboard code. Vector Lists are transmitted to the display code by invoking appropriate control program macro-commands and are then issued to the display hardware by the display code.

A character delete operation occurs as a result of a delete key depression on attached keyboard 4. This causes the character at the cursor location to be deleted and all characters to t...