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

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Seiler, Larry D., Rose, Robert C., Pappas, James L.
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): HJERPE, RICHARD A
• Application Number:
  US07/212,819
• Time in Patent Office: 993 Days
• Field of Search: 340/721, 340/723, 340/724, 340/798, 340/799, 340/750, 340/747, 364/518, 364/521, 364/522
• US Class Current: 715/790
• CPC Class Codes: G09G 2340/12 Overlay of images, i.e. displayed pixel being the result of switching between the corresponding input pixels
• CPC Class Codes: G09G 5/14 Display of multiple viewports
• CPC Class Codes: G09G 5/397 Arrangements specially adapted for transferring the contents of two or more bit-mapped memories to the screen simultaneously, e.g. for mixing or overlay G09G5/02 takes precedence

Abstract

An image generator (38) in a workstation draws its image data from a pair of frame buffers (32 and 34). The selection between the frame buffers is made by a multiplexer circuit (42) that can switch between frame buffers (32 and 34) on a pixel-by-pixel basis, i.e., different frame buffers can be used during different parts of the same scan frame of a monitor (18) in the image generator (38). A selection-signal source (46), which provides the selection signals for the multiplexer circuit (42), includes a window detector (56), which compares the outputs of counters (72 and 74) that represent the monitor scan position with the outputs of registers (62, 64, 66, and 68) that represent the boundaries of windows used by respective applications that the workstation is running. The source (46) thereby identifies the windows in which the pixel currently being displayed is located, and it employs a priority circuit (76) to identify the one such window having the highest priority. Each software application deposits in a buffer register (70) the identity of the frame buffer (32 or 34) from which the data for its display should currently be drawn, and a priority circuit generates a BUFSEL signal to identify the buffer designated by the application associated with the highest-priority window. It uses BUFSEL to control the multiplexer circuit (42). In this way, all applications do not have to switch between buffers at the same time, so the complexity and lack of flexibility imposed by synchronizing between applications is avoided.

Claims

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.

2. A display system as defined in claim 1 further including validity means responsive to the comparison means to generate a validity signal that indicates whether, on the one hand, the current scan location falls in at least one of the windows or, on the other hand, it falls in none of the windows.

3. 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 selectionsignal 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 E. generating source-selection signals that designate the image-data sources 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. read/write boundary registers, containing boundary data representing the locations of boundaries of the windows, which boundary data can be changed to change the positions of the windows on the display, 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 an ownership signal identifying such a window; and

v. a selection-signal generator responsive to the ownership and source=selection signals to generate as the selection signal a signal designating the image-data source designated by the source selection register associated with the window identified by an ownership signal; and

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

4. 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, in buffer locations corresponding to the screen locations, image data representing a respective image and being operable to scan its buffer locations to generate a frame-buffer output representing the image data;

C. timing circuitry for operating the frame buffers to scan their respective buffer locations in synchronism with the scanning of the corresponding screen locations;

D. a selection-signal source for generating a selection signal having a plurality of states, each state designating a different respective frame buffer, the selection-signal source including means for changing the selection-signal state while the image data are being displayed; and

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

5. A display system as defined in claim 4 wherein the selection-signal source includes:

A. 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;

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

C. boundary registers, containing boundary data representing the locations of boundaries of the windows, for generating boundary signals that represent the boundary data;

D. 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 an ownership signal identifying such a window; and

E. a selection-signal generator 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 identified by an ownership signal.

6. A display system as defined in claim 5 further including validity means responsive to he comparison means to generate a validity signal that indicates whether, on the one hand, the current scan location falls in at least one of the windows or, on the other hand, it falls in none of the windows.

7. 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 image-data sources, each image-data source comprising means for generating an image-datasource signal containing image data representing pixels in a different respective image concurrently with the scanning by the image generator of locations corresponding to the locations of the represented pixels in the respective image;

C. a selection-signal source for generating a selection signal having a plurality of states, each state designating a respective image-data source, 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 image-data sources 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, 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 an ownership signal identifying such a window; and

v. a selection-signal generator responsive to the ownership and source-selection signals to generate as the selection signal a signal designating the image-data source designated by the source-selection register associated with the window identified by an ownership signal; and

D. a multiplexer, connected for reception of the imagedata-source and selection signals, for producing and applying to the image generator as the image-data signal a multiplexer output determined by the imagedata source signal generated by the image-data source that the selection signal designates.

8. A display system as defined in claim 7 further including validity means responsive to the comparison means to generate a validity signal that indicates whether, on the one hand, the current scan location falls in at least one of the windows or, on the other hand, it falls in none of the windows.

9. 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 image-data sources, each image-data source comprising means for generating an image-datasource signal containing image data representing pixels in a different respective image concurrently with the scanning by the image generator of locations corresponding to the locations of the represented pixels in the respective image;

C. a selection-signal source for generating a selection signal having a plurality of states, each state designating a respective image-data source, 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 image-data sources 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 sourceselection signals to generate as the selection signal a signal designating the image-data source designated by the source-selection register associated with the window that has the highest priority among these windows identified by ownership signals; and

D. a multiplexer, connected for reception of the imagedata-source and selection signals, for producing and applying to the image generator as the image-data signal a multiplexer output determined by the imagedata-source signal generated by the image-data source that the selection signal designates.

10. A display system as defined in claim 9 further including validity means responsive to the comparison means to generate a validity signal that indicates whether, on the one hand, the current scan location falls in at least one of the windows or, on the other hand, it falls in none of the windows.

11. 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 image-data sources, each image-data source comprising means for generating an image-datasource signal containing image data representing pixels in a different respective image concurrently with the scanning by the image generator of locations corresponding to the locations of the represented pixels in the respective image;

C. a selection-signal source for generating a selection signal having a plurality of states, each state designating a respective image-data source, 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 image-data sources 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. read/write boundary registers, containing boundary data representing the locations of boundaries of the windows, which boundary data can be changed in change the positions of the windows on the display, 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 an ownership signal identifying such a window; and

v. a selection-signal generator responsive to the ownership and source-selection signals to generate as the selection signal a signal designating the image-data source designated by the source-selection register associated with the window identified by an ownership signal; and

D. a multiplexer, connected for reception of the imagedata-source and selection signals, for producing and applying to the image generator as the image-data signal a multiplexer output determined by the imagedata-source signal generated by the image-data source that the selection signal designates.