Browse Prior Art Database

Smooth Travel of Crosshair Cursor on Display Screen

IP.com Disclosure Number: IPCOM000046317D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Hawes, AJ: AUTHOR [+2]

Abstract

There are two modes of operation for a crosshair cursor, single pel movement and repeat action rate with an accelerating condition from prolonged key depression. The movement of the cursor is controlled by north, south, east and west keys. In a cathode ray tube (CRT) video display which uses interlace, it is usual practice to "refresh" the screen on even fields, have a flyback period, and then refresh the odd fields. At the end of each refresh cycle there is a vertical synchronization time where nothing is refreshed. It is, therefore, very convenient to use this time to update the crosshair cursor position. However, it would be more desirable to update the cursor with its new position at the end of one complete screen "frame", i.e., when both odd and even fields have been refreshed.

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Smooth Travel of Crosshair Cursor on Display Screen

There are two modes of operation for a crosshair cursor, single pel movement and repeat action rate with an accelerating condition from prolonged key depression. The movement of the cursor is controlled by north, south, east and west keys. In a cathode ray tube (CRT) video display which uses interlace, it is usual practice to "refresh" the screen on even fields, have a flyback period, and then refresh the odd fields. At the end of each refresh cycle there is a vertical synchronization time where nothing is refreshed. It is, therefore, very convenient to use this time to update the crosshair cursor position. However, it would be more desirable to update the cursor with its new position at the end of one complete screen "frame", i.e., when both odd and even fields have been refreshed. This ensures that the entire crosshair cursor disappears and re- appears in its new position and does not become pel fragmented due to updates occurring after odd and even field refresh.

Updating the crosshair cursor in a single pel movement is easy.

However, an accelerating cursor creates a problem if it needs to be smooth and predictable.

It is now assumed that updating will occur at the end of screen frame time. Having established that the cursor is in acceleration mode under a repeat action key, the updating of the cursor must be integrated over each accelerated step. An example of acceleration would be to move the cursor 2 extra pels per keystroke up to a maximum of, say, 2l, i.e., l, 3, 5, 7, etc.

Once a maximum of, say, 2l pels per keystroke, the cursor would jump 2l pels per keystroke across the screen, without giving a smooth movement. However...