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Buffer Mechanism for Pel Positioning of Multiple Video Images on a Raster Scan CRT

IP.com Disclosure Number: IPCOM000047725D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Pavicic, MJ: AUTHOR

Abstract

This buffer mechanism allows individual positioning of multiple video images at any pel (picture element) position on the screen of a raster-scan CRT. This is accomplished by providing, in addition to the standard regeneration buffer, a second buffer which stores information units called video data elements a short time before they begin to be displayed and retains them only so long as they are needed for display. The buffer mechanism has three parts: the Loader, the Buffer and the Displayer. The Loader puts information into the Buffer, and the Displayer takes it out. The information being managed describes a video image in terms of video data elements. The information in each video data element is the image origin OI and image height HI, if it is variable.

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Buffer Mechanism for Pel Positioning of Multiple Video Images on a Raster Scan CRT

This buffer mechanism allows individual positioning of multiple video images at any pel (picture element) position on the screen of a raster-scan CRT. This is accomplished by providing, in addition to the standard regeneration buffer, a second buffer which stores information units called video data elements a short time before they begin to be displayed and retains them only so long as they are needed for display. The buffer mechanism has three parts: the Loader, the Buffer and the Displayer. The Loader puts information into the Buffer, and the Displayer takes it out. The information being managed describes a video image in terms of video data elements. The information in each video data element is the image origin OI and image height HI, if it is variable. The image origin is specified by the X, Y screen coordinates of the first pel to be scanned by the CRT raster. Video data elements are loaded in the Buffer in the same order as the image origins OI are scanned by the CRT raster. This order is defined as increasing Y and, within each Y, increasing X.

The Buffer is partitioned in slots. Each slot can contain one or more video data elements. There is a one-to-one relationship between the slots and imaginary columns on the display of width W pels. The X coordinate is used to determine which slot a particular video data element is to be loaded into. If W is constant, then the slot number can be calculated as the integer part of X/W. Video data elements are loaded into "not full" slots in the Buffer. A slot is "not full" when it can accept at least one more video data element. If a target slot is full, the Loader must wait until it is "not full" again. The video data elements in a given slot are retrieved by the Displayer in the same order in which they were loaded. The result of these orderings is that the slots t...