Browse Prior Art Database

Video Window Address Generation Circuit using X,Y Locator

IP.com Disclosure Number: IPCOM000116123D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 6 page(s) / 174K

Publishing Venue

IBM

Related People

Lee, WR: AUTHOR [+2]

Abstract

This circuit calculates the proper location for a video co-processor to begin writing of video pixel data into video memory. This is performed for many screen resolutions and color depths. This implementation uses minimal area because of the amount of time available to perform this calculation.

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Video Window Address Generation Circuit using X,Y Locator

      This circuit calculates the proper location for a video
co-processor to begin writing of video pixel data into video memory.
This is performed for many screen resolutions and color depths.  This
implementation uses minimal area because of the amount of time
available to perform this calculation.

      Once this calculation is performed, video pixel data is written
into the frame buffer using this calculated memory location.  The
video window may occupy some or all of the screen.  It may be of any
size rectangle, and it may be located anywhere on the screen.

Figure 1.  X,Y Coordinate Based Address Calculation Circuit.  Diagram
of Output Video Window on Computer Screen

      This circuit implements in hardware the calculation of the
proper starting address of the video window.  It uses X,Y
coordinate-based inputs to determine the window location relative to
the top-left corner of the computer screen.  This circuit also
calculates the proper address offset to implement vertical and
horizontal "flipping" of the video image.  Vertical flipping makes
the image appear upside-down, and horizontal flipping makes the image
appear as a mirror reflection.  The video window height and width
input parameters are used to properly implement flipping.  Fig. 1
shows the video window on a screen.  The window, screen, and offset
inputs to the circuit are listed in Table 1.
                      Table 1. Inputs to Address
                      Calculation Circuit
                      Name in Diagram      Description
                      XCOORD               X-Coordinate
                                           Offset
                      YCOORD               Y-Coordinate
                                           Offset
                      OWW                  Output
                                           Window Width
                      OWH                  Output
                                           Window Height
                      OSW                  Output
                                           Screen Width
                      SOS                  Start of
                                           Screen Address

      All values except for SOS are in pixels, and all values are
inputs to the circuit.

      XCOORD and YCOORD are 0-based, so an X,Y value of 0,0
corresponds to the top-left corner of the...