Browse Prior Art Database

Prioritizing Video Pixel Selection

IP.com Disclosure Number: IPCOM000100401D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 137K

Publishing Venue

IBM

Related People

Bealkowski, R: AUTHOR [+2]

Abstract

A technique is described whereby a number of semi-independent video subsystems are able to compete for the right to output a pixel to a displayed video image, as used in computer systems.

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This is the abbreviated version, containing approximately 50% of the total text.

Prioritizing Video Pixel Selection

       A technique is described whereby a number of
semi-independent video subsystems are able to compete for the right
to output a pixel to a displayed video image, as used in computer
systems.

      The concept allows for the composition of a single video
display image, to occur on a pixel-by-pixel basis, from separate and
semi-independent video subsystems.  A priority video pixel selection
mechanism provides a means of combining multiple video subsystems for
"windowing", so that a single computer system is capable of
supporting multiple logical screens, of potentially differing video
modes, on a single display simultaneously.

      Typically, windowing is used in personal computer systems to
allow portions of logically separate screens to be shown on a single
display.  Generally, this is accomplished entirely through software.
However, the processing of the software uses valuable processing
time, due to the many screen maintenance activities.

      The ability to provide a number of semi-independent video
subsystems, each with its own memory, in a single computer allows
more tasks to have access to the hardware. Direct access to the
hardware, when performed in ways that are compatible with exisiting
systems, enhances performance and software portability.  However, in
systems with only one display, each video subsystem must serially
share the display.

      The concept described herein provides a means of combining
multiple subsystems with hardware support for windowing so that a
system is capable of producing multiple logical screens on a single
display simultaneously.

      The first step is to define the hardware windowing support
which spans a number of separate semi-independent video subsystems.
This is done by means of prioritizing video pixel selection.  Each
video subsystem is defined as one component of the entire display.
For each pixel of the display image, a decision is made as to which
subsystem is to provide a specific pixel.  The drawing illustrates
the elements of the video subsystem and main control block.  The
video subsystem has the configuration registers on the left and
interacts with the main control block.

      The priority level of each subsystem is the level at which its
window is stacked relative to all other windows. This value is
programmable and is used to change which window appears on top of
other windows.

      The X and Y clock inputs are counted by the subsystem and are
used in determining when the subsystem's window is active.  The X and
Y reset lines instruct the subsystem to clear its respective counts.

      The (ulx,uly) values are the upper-left-x and the upper-left-y
pixel values and are used with (lrx,lry) the lower-right-x and lower-
right-y pixel values in determining when the subsystems window is
active.  These values relate directly to the external X,Y count.
When the external X,Y count falls within the upp...