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Buffer Mechanism for Pel Positioning of Multiple Video Images, Including Overlapping, on a Raster-Scan CRT

IP.com Disclosure Number: IPCOM000038976D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Brown, MW: AUTHOR [+2]

Abstract

A buffer mechanism allows multiple video images to be individually positioned at any pel location on the screen of a raster-scan CRT. The images may overlap each other and do so in a controlled manner. The buffer mechanism (Fig. 1) has five parts: the Loader 11, the VDE Buffer 12, the Transformer 13, the Scan Buffer 14, and the Displayer 15. Loader 11 adds VDEs to VDE Buffer 12. VDEs are stored in the Buffer 12 for as long as they are needed by Transformer 13 and are then discarded to make room for new VDEs. Transformer 13 uses the VDEs to generate the pels (picture elements) for a full scan and stores them in Scan Buffer 14. Displayer 15 reads and displays the Scan Buffer contents. The information in or associated with each VDE is the image origin, OI = (XI, YI) and dimensions, WI x HI, shown in Fig. 2.

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Buffer Mechanism for Pel Positioning of Multiple Video Images, Including Overlapping, on a Raster-Scan CRT

A buffer mechanism allows multiple video images to be individually positioned at any pel location on the screen of a raster-scan CRT. The images may overlap each other and do so in a controlled manner. The buffer mechanism (Fig. 1) has five parts: the Loader 11, the VDE Buffer 12, the Transformer 13, the Scan Buffer 14, and the Displayer 15. Loader 11 adds VDEs to VDE Buffer 12. VDEs are stored in the Buffer 12 for as long as they are needed by Transformer 13 and are then discarded to make room for new VDEs. Transformer 13 uses the VDEs to generate the pels (picture elements) for a full scan and stores them in Scan Buffer 14. Displayer 15 reads and displays the Scan Buffer contents. The information in or associated with each VDE is the image origin, OI = (XI, YI) and dimensions, WI x HI, shown in Fig. 2. OI is specified by the X,Y coordinates of the first pel to be scanned by the CRT raster.

(Image Omitted)

VDEs are loaded in the same order as the OIs are scanned by the CRT raster. This order is defined as increasing Y and, within each YI, increasing X, as symbolized in Fig. 3. In this example, the correct order for loading the VDEs is indicated by the numbers alongside the image origins. This ordering minimizes the amount of lead time and buffering necessary for the Loader to stay ahead of the Transformer. A "slot" is a storage partition in the VDE Buffer which can contain a single VDE. Associated with each slot is a pointer to another slot. The pointers are initialized so that they link the slots together into a single chain or list (Fig. 4). This initial linked list is the Empty List since none of the slots are occupied. As VDEs are added to the VDE Buffer, they are appended to the end of a second list called the Full List. The new VDEs occupy slots which were originally part of the Empty List. Therefore, the Full List grows in length at the expense of the Empty List. When the Empty List reaches zero length, the Loader must wait until the list length is greater than zero. When a VDE is no longer needed by the Transformer, its slot is removed from the Full List and appended to the Empty List. The Full List is relinked without affecting the relative order of the remaining occupied slots (Fig. 5). In this way, the order in which the VDEs were originally loaded into the Full List is retained at all times.

(Image Omitted)

Transformer 13 (Fig. 1) fetches the video contents of a complete horizontal scan by going through the "active" part of the Full List. All VDEs for which the relation YI & S YI + HI is true (where S is the Y value for the current scan) are "active" ...