Browse Prior Art Database

Insertion of Alphanumeric Characters on Display Screen

IP.com Disclosure Number: IPCOM000088147D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 84K

Publishing Venue

IBM

Related People

Hughes, MA: AUTHOR [+2]

Abstract

The vector graphics display system (Fig. 1) consists of display screen 1, associated display hardware 2 incorporating a display store for storing information displayed on screen 1, and a processor 3 for controlling the display system. Keystrokes can be entered into the system via keyboard 4 attached to processor 3. Keyboard code 5 converts the keystrokes into graphic commands which are issued as Vector Lists (VLs) to display hardware 2 via display code 6. Communication between the keyboard code and display code is accomplished by invoking appropriate Control Program macro-commands.

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Insertion of Alphanumeric Characters on Display Screen

The vector graphics display system (Fig. 1) consists of display screen 1, associated display hardware 2 incorporating a display store for storing information displayed on screen 1, and a processor 3 for controlling the display system. Keystrokes can be entered into the system via keyboard 4 attached to processor 3. Keyboard code 5 converts the keystrokes into graphic commands which are issued as Vector Lists (VLs) to display hardware 2 via display code 6. Communication between the keyboard code and display code is accomplished by invoking appropriate Control Program macro-commands.

Characters are displayed on the screen in a matrix of n rows by m columns, and an associated character buffer is maintained within 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 the screen as an underscore.

Each character is generated from a sequence of visible and invisible vector- stroke displacements permanently stored in the processor memory. Characters to be erased or drawn on the display screen must be erased from or written into the display store by the display hardware, and this is accomplished by issuing a Vector List to the display hardware.

Three types of Vector List operations are possible: `ERASE', `DRAW' and `ERASE & DRAW'. The Vector List format for `ERASE' and `DRAW' operations is identical and is illustrated in Fig. 2a. Two different formats are available for `ERASE & DRAW' operations, and these are illustrated in Figs. 2b and 2c. Each Vector List of the type illustrated in Fig. 2a contains a header specifying the type of operation (erase or draw) required, followed by a `SET X Y' command with x and y coordinates specifying the start position on display screen 1. The remainder of the Vector List is filled with a sequence of indirect pointers (one per character) to the vector-strokes. Further, `SET X Y' commands may be interspersed with these to accommodate line boundaries, etc. The `ERASE & DRAW' Vector List illustrated in Fig. 2b is essentially similar except that it consists of two sections separated by header information. The first section operates as an `ERASE' Vector List and the second as a `DRAW' Vector List. This is normally used when it is required to update a string of displayed characters in one operation.

In the normal mode of operation a keystroke causes the character at the cursor location to be replaced and the cursor to be moved to a new location. In order to accomplish this the cursor and old character must be erased, the new character must be drawn, and the cursor must be redrawn at its new location. The Vector List required to achieve this is reduced to that illustrated in Fig. 2c. Note that cursor generation does not advance the x position on the display screen, whereas generation of any other character does.

When inserting characters, each keystroke...