Browse Prior Art Database

Low-Cost Addressing of Frame Buffer for a Multi-Media Rasterizer

IP.com Disclosure Number: IPCOM000113408D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 92K

Publishing Venue

IBM

Related People

Roberson, J: AUTHOR [+2]

Abstract

Many Graphic Controllers for the UNIX/X Windows environment support multiple pixel types. The Frame Buffer may contain multiple windows, each with a different pixel type. The Graphics Controller will format the Frame Buffer to support these multiple pixel types simultaneously. This will often require the actual pixel data format to be different than the logical pixel data format that a given application might expect. This can pose a problem when an application performs a Direct Frame Buffer Access (DFA) operation. This invention allows the graphics programmer to make a DFA call and use the pixel data format that corresponds to the applications logical view of the Frame Buffer. This is accomplished by emulating frame buffer formats.

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Low-Cost Addressing of Frame Buffer for a Multi-Media Rasterizer

      Many Graphic Controllers for the UNIX/X Windows environment
support multiple pixel types.  The Frame Buffer may contain multiple
windows, each with a different pixel type.  The Graphics Controller
will format the Frame Buffer to support these multiple pixel types
simultaneously.  This will often require the actual pixel data format
to be different than the logical pixel data format that a given
application might expect.  This can pose a problem when an
application performs a Direct Frame Buffer Access (DFA) operation.
This invention allows the graphics programmer to make a DFA call and
use the pixel data format that corresponds to the applications
logical view of the Frame Buffer.  This is accomplished by emulating
frame buffer formats.  The emulation process involves 3 modules which
are (1) BLT Format Conversion, (2) Data Format Conversion, and (3)
Memory Controller (Fig.  1).  The DFA data is sent to the emulator in
the standard address,data format.  The emulator receives the data and
converts the data stream to a Bit BLT  (BLT Format Conversion).
Next, the Data Format Conversion hardware converts the data into an
internal format.  (see next section for details).  Finally, the data
is forwarded to the memory controller so the frame buffer can be
updated.

      Data Format Conversion involves 2 distinct operations which
are:  (1) data rearrangement (2) screen alignment.  Both operations
take data from the system (we will call this external format) and
convert it to a format the rasterizer can understand (internal
format).  The internal format varies from rasterizer to rasterizer.
The pixel data includes color and alpha informa- tion.  The data
rearrangement operation simply reorders the color/alpha information
when converting from external to internal format.  For example an
external format may be ordered as Alpha, Red, Green, Blue.  However,
the internal format may require an ordering of Alpha, Blue, Green,
Red.  For 12 bit data, the data must be shifted into the correct
color channel.  Se...