Graphics image relocation for display viewporting and pel scrolling

• US 4,663,617 A
• Filed: 02/21/1984
• Issued: 05/05/1987
• Est. Priority Date: 02/21/1984
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines SA (International Business Machines Corporation)
• Inventors: Stockwell, Dean A.
• Primary Examiner(s): Brigance, Gerald L.
• Application Number:
  US06/582,202
• Time in Patent Office: 1,169 Days
• Field of Search: 340/709, 340/724, 340/726, 340/723, 340/721
• US Class Current: 715/806
• CPC Class Codes: G09G 5/14 Display of multiple viewports
• CPC Class Codes: G09G 5/40 characterised by the way in which both a pattern determined by character code and another pattern are displayed simultaneously, or either pattern is displayed selectively, e.g. with character code memory and APA, i.e. all-points-addressable, memory

Abstract

By selecting the starting time of the display readout of a pel buffer raster generation, the pel data is mapped to a display screen with an arbitrary displacement with respect to the screen for relocation or scrolling of the pel image on the screen. To compensate for non-congruency between the pel data window and screen viewport definitions and to provide scrolling on a pel basis, the positioning of the window on the screen includes fine adjustment achieved by a determinable delay between the scanning of the buffer and the generation of the screen raster. The display circuits include means to extend the window background to fill in gaps between the edges of a window of pel data chosen to be displayed and a larger screen viewport in which it is to be displayed. System read/write access times to the buffer are interleaved with and synchronized to the data fetch times of the display.

Claims

1. A method of operating a display system for displaying a window of data from a pel buffer in a viewport on a display screen, wherein the display system includes first means defining the window with respect to the buffer and second means defining the viewport with respect to the screen,

characterized in that the first and second means operate on different radices, and in that the method comprises chossing a viewport at least as large as the window of data to be displayed, scanning the buffer and the screen at integrally related pel rates,

modifying the buffer addressing to bring the window of data approximately into desired registration with the viewport subject to the constraints imposed by the said different radices, and

providing a variable delay in the application of the pel data from the buffer to the screen to bring the window exactly into desired registration with the viewport.

2. The method of claim 1, additionally including the step of filling in a gap between the window and a boundary of the viewport with an extension of the pel background of the window.

3. The method of claim 2, additionally including the steps of providing access times to update the buffer interleaved with fetching of data from the buffer in the scanning of the window therein,

the access times being synchronized to the scanning to accommodate differences in the timing of the access and fetching operations.

4. The method of claim 1, additionally including the steps of providing access times to update the buffer interleaved with fetching of data from the buffer in the scanning of the window therein,

the access times being synchronized to the scanning to accommodate differences in the timing of the access and fetching operations.