Browse Prior Art Database

Clipping and Overlay of Multiple Sources of Video and Graphics in Display Windows

IP.com Disclosure Number: IPCOM000105727D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

MacInnis, AG: AUTHOR

Abstract

Disclosed is a method to provide a combination on a per pixel basis of multiple real-time sources of multimedia video and graphics, within the same window and among different windows which may overlap. Windows may be of any shape and size. Overhead, performance and complexity are simultaneously optimized by distributing the function, as described below.

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Clipping and Overlay of Multiple Sources of Video and Graphics in Display Windows

      Disclosed is a method to provide a combination on a per pixel
basis of multiple real-time sources of multimedia video and graphics,
within the same window and among different windows which may overlap.
Windows may be of any shape and size.  Overhead, performance and
complexity are simultaneously optimized by distributing the function,
as described below.

      The combination and correct clipping of one or more multiple
windows, each of which may contain real-time motion imagery, is per-
formed by the following:

1.  Simple, coarse preclipping may be implemented at the source of
    data.  Window data are clipped at the source to the nearest
    practical geometrical shape to the actual window.  An exemplary
    design has the ability to exclude a small number (e.g., four
    rectangular regions) from a bounding rectangular region which
    contains the entire video source window.  This limits the amount
    of data that must be transferred to the mechanism that puts data
    into display memory.

2.  Portions of the window which are accurately preclipped by the
    source do not need to be checked by the CID mechanism (below),
    and they are not checked in implementations that obtain greater
    performance when CIDs are not checked for each pixel (this is
    typically the case).  Portions of the window that require
    additional pixel clipping or masking are checked using CIDs.

3.  Clipping IDs (CIDs), or the equivalent, are associated with each
    pixel in display memory.  Specific values of these CIDs are
    associated with identified video sources, and others are
    associated with other nonvideo sources.  A CID may consist of one
    or more bits.

4.  For each pixel to be written, if the CID value associated with
    the video data matches that of the target pixel address, the new
    value is written; otherwise, it is not.

5.  It is not necessary to use a specific bit to control the
    permission of each video source to write to display memory.
    Rather, values of combinations of CID bits are used supporting
    more sources with fewer bits.

6.  Persistent text and graphics are retained within windows being
    updated by video by checking via the CID mechanism.

7.  Pers...