Display controller with enhanced video window clipping

• US 5,768,491 A
• Filed: 06/07/1995
• Issued: 06/16/1998
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Fong, Kai-Fat, Lobodzinski, Mark A.
• Primary Examiner(s): Feld, Joseph H.
• Assistant Examiner(s): BUCHEL JR, RUDOLPH JOHN
• Application Number:
  US08/476,099
• Time in Patent Office: 1,105 Days
• Field of Search: 395/134, 395/162, 395/164, 395/119, 395/339-345, 395/508
• US Class Current: 345/620
• CPC Class Codes: G09G 2340/125 wherein one of the images is motion video
• CPC Class Codes: G09G 5/14 Display of multiple viewports
• CPC Class Codes: G09G 5/393 Arrangements for updating the contents of the bit-mapped memory

Abstract

A computer system includes a display controller which supports video display. The display controller includes circuitry for determining which portions of one or more video windows should be written to the frame buffer responsive to the locations of other screen objects which may overlie the video window on the display. An unused portion of frame buffer memory is used to stored a plurality of transition groups, each group defining which portions of the video window are visible within a range of scanlines. The transition information is used by clipped circuitry to enable or disable writing of video information to the frame buffer.

Claims

1. A display controller having capability to display a predefined region of video on a computer display, comprising:

a first memory portion in a frame buffer memory for storing information for display;

a second memory portion in a frame buffer memory for storing at least one group of transition information defining points of said predefined video region at which screen objects overlay said predefined video region, and wherein said group of transition information includes a first transition word for specifying a scanline at which the transition information in said group of transition information is no longer valid; and

video control circuitry for reading said transition information from said second memory portion and enabling or disabling writing of video information to said first memory portion responsive thereto.

2. The display controller of claim 1 wherein said group of transition information further includes one or more second transition words for specifying one or more points along a scanline where a transition occurs between enabling and disabling writing of video information for said predefined video region to said first memory portion.

3. The display controller of claim 2 wherein said group of transition information further includes a transition count value for specifying the number of second transition words specified in said group of transition information.

4. The display controller of claim 2 wherein said second transition word is a predetermined code specifying that said screen objects completely overlay said predefined video region.

5. The display controller of claim 2 wherein said first transition word is a Y coordinate in world coordinates and said second transition word is an X coordinate in world coordinates.

6. The display controller of claim 2 wherein said first transition word and said one or more second transition words are each doubleword values and said first transition word of each group of video information is aligned on a double word boundary.

7. The display controller of claim 6 wherein a word of dummy data is inserted following an odd number of second transition words such that said first transition word of a next group of transition information is aligned on a double word boundary.

8. The display controller of claim 1 wherein said at least one group of transition information defining points of said predefined video region at which screen objects overlay said predefined video region comprises a first set of transition information and further including a second set of transition information comprising at least one group of transition information for defining points of a second predefined video region at which screen objects overlay said second predefined video region.

17. The display controller of claim 2 wherein a first of said one or more second transition words specifies a first point along a scanline where writing of video information for said predefined video region to said first memory portion is enabled.

9. A computer system comprising:

a processor;

a main memory coupled to said processor;

a computer display; and

a display controller coupled to said processor and to said computer display for displaying a predefined region of video on said computer display, comprising;

a first memory portion in a frame buffer memory for storing information for display on said computer display;

a second memory portion in a frame buffer memory for storing at least one group of transition information defining points of said predefined video region at which screen objects overlay said predefined video region, and wherein said group of transition information includes a first transition word for specifying a scanline at which the transition information in said group of transition information is no longer valid; and

video control circuitry for reading said transition information from said second memory portion and enabling or disabling writing of video information to said first memory portion responsive thereto.

10. The computer system of claim 9 wherein said group of transition information further includes one or more second transition words for specifying one or more points along a scanline where a transition occurs between enabling and disabling writing of video information to said first memory portion.

11. The computer system of claim 10 wherein said group of transition information further includes a transition count value for specifying the number of second transition words specified in said group of transition information.

12. The computer system of claim 10 wherein said second transition word is a predetermined code specifying that said screen objects completely overlay said predefined video region.

13. A method of displaying a predefined video region on a computer display, comprising:

storing video information for display in a first portion of a frame buffer memory;

storing at least one video group of transition data for defining points of said predefined video region at which screen objects overlay said predefined video region in a second portion of said frame buffer memory, wherein said step of storing a video group of transition data comprises the step of storing a first transition word for signifying a scanline at which said video group of transition data is no longer valid; and

reading said video group of transition data from said second portion of said frame buffer memory and enabling or disabling writing of video information for said predefined video region to said first portion of said frame buffer memory responsive thereto.

14. The method of claim 13 wherein said step of storing a video group of transition data further comprises the step of storing one or more second transition words wherein each second transition word specifies a point along a range of scanlines where a transition occurs between enabling and disabling writing of video information for said predefined region to said first portion of said frame buffer memory.

15. The method of claim 14 wherein said step of storing a video group of transition data further comprises the step of storing a transition count wherein each transition count specifies a number of said second transition words.

16. The method of claim 13 wherein said step of storing a video group of transition data further comprises the step of storing a predetermined code which specifies that said screen objects completely overlay said predefined video region.