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Window-dependent buffer selection

  • US 5,001,469 A
  • Filed: 06/29/1988
  • Issued: 03/19/1991
  • Est. Priority Date: 06/29/1988
  • Status: Expired due to Term
First Claim
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1. A display system comprising:

  • A. an image generator, including a display screen and adapted to receive an image-data signal representing image data, for scanning locations on the screen in an ordered manner in successive scan frames and displaying in the scanned screen locations pixels having pixel values determined by the image-data signal received concurrently with the scanning of the screen locations;

    B. a plurality of frame buffers, each frame buffer containing image data representing a respective image and being operable to generate a frame-buffer output representing the image data;

    C. timing circuitry for operating the image generator and frame buffers in synchronism with each other;

    D. a selection-signal source for generating a selection signal having a plurality of states, each state designating a respective frame buffer, the selection-signal source including means for changing the selection-signal state in the midst of a scan frame, the selection-signal source comprising;

    i. a plurality of source-selection registers, each source-selection register being associated with a different one of a plurality of windows, for generating source-selection signals that designate the frame buffers from which data to be displayed in their associated windows are to be drawn;

    ii. counter means for generating address signals that represent the addresses of the pixels whose data are currently being represented by the image-data signal;

    iii. boundary registers, containing boundary data representing the locations of boundaries of the windows that can overlap so that a given scan location can fall into more than one window, for generating boundary signals that represent the boundary data;

    iv. comparison means, connected to receive the address and boundary signals, for comparing the address and boundary signals to determine whether the current scan location falls in any of the windows and generating ownership signals identifying all such windows simultaneously; and

    v. a selection-signal generator including priority means for assigning a predetermined priority to the windows and responsive to the ownership and source-selection signals to generate as the selection signal a signal designating the frame buffer designated by the source-selection register associated with the window that has the highest priority among those windows identified by ownership signals; and

    E. a multiplexer, connected for reception of the frame-buffer outputs and the selection signal, for producing and applying to the image generator as the image-data signal a multiplexer output determined by the frame-buffer output of the frame buffer that the selection signal designates.

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