Browse Prior Art Database

Independent Pixel Interpretation for Windowed Overlays/Underlays

IP.com Disclosure Number: IPCOM000116469D
Original Publication Date: 1995-Sep-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 107K

Publishing Venue

IBM

Related People

Grupp, R: AUTHOR [+4]

Abstract

This article describes a way in which internal RAMDAC hardware is added that makes it possible for overlay/underlay graphics memory to have separate pixel interpretations in independent windows of arbitrary shape relative to the frame buffer. This capability also makes it possible to vary the visibility priorities relative to frame buffer, transparent overlay, opaque overlay, and underlay pixels.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Independent Pixel Interpretation for Windowed Overlays/Underlays

      This article describes a way in which internal RAMDAC hardware
is added that makes it possible for overlay/underlay graphics memory
to have separate pixel interpretations in independent windows of
arbitrary shape relative to the frame buffer.  This capability also
makes it possible to vary the visibility priorities relative to frame
buffer, transparent overlay, opaque overlay, and underlay pixels.

      In graphics systems, there may be separate memories for the
frame buffer and the overlay/underlay (ovl/und) buffer.  The frame
buffer is 'windowed' in that pixels in different areas (windows) of
the video monitor are interpreted (mapped) in many different ways
depending on the usage.  These windows can have any arbitrary shape
where the simplest is a rectangle and one of the more complex is a
circle.

      The overlay buffer is provided primarily for the display of
transient data without disturbing the underlying frame buffer data
which may be very difficult to generate.  The use of overlays,
therefore, reduces the number of re-draw occurrences, thereby
improving performance.  The ovl/und buffer, however, has historically
been 'full screen' where all pixels on the screen are interpreted in
a single way via a single color palette.  With current hardware, the
overlay pixels always have the highest visibility priority.  This is
not sufficient if overlays are generalized for windowed user
applications because, in the event that another window obscures a
overlayed window, the obscured overlay pixels must not be visible in
order to satisfy user visibility expectations.  Because of these
limitations, applications for overlays have been limited primarily to
simple uses such as menus, system messages, etc., which do not
require large numbers of colors and/or color visual modes.

      This article describes a way in which color mapping hardware is
added to the RAMDAC in such a way that overlay and/or underlay
visuals are totally independent of frame buffer visuals.  These
visuals
(characteristics which affect the way the graphics data looks)
includes
the following:
  1.  Color visual - Pseudo, grey-scale, direct, or true color
  2.  Color palette selection
  3.  Number of bit planes per pixel (8pbb, 16pbb, 24pbb)
  4.  Buffer selection for double buffered...