Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-05-18
2001-12-04
Vo., Cliff N. (Department: 2171)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C345S440000
Reexamination Certificate
active
06326969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to managing display images.
2. Related Art
Asynchronous rendering of background images and foreground images (foreground overlays) is known. Rendering of the images is typically accomplished by writing data representative of the images in an on-screen area of memory such as a frame buffer. A single frame buffer may be used to store the background image and foreground overlays. The background image is rendered before rendering a foreground overlay over a specified portion of the background image (overlay area). The overlay area is not stored or constantly kept up to date after the corresponding foreground overlay has been written into it.
Since the overlay area is not constantly kept up to date, re-rendering the background image with one or all foreground overlays removed requires at least one additional step of updating the overlay map with up-to-date background image information before transferring the updated overlay area to the frame buffer. This slows down the re-rendering of background images when a foreground overlay is removed, since the overlay area needs to be updated before it can be transferred into the frame buffer.
One solution that avoids the additional step of updating the overlay area with up-to-date background image information is to use multiple frame buffers. But this incurs the additional expense of adding memory management features to coordinate which images in the frame buffers to display, besides the expense of the additional frame buffers.
Accordingly, it would be desirable to provide an apparatus and method for managing the rendering of background images and foreground overlays that keep the overlay area of the background image up to date.
SUMMARY OF THE INVENTION
The invention provides an apparatus and method for managing background and foreground display images. Graphics memory for images which are rendered in software is referenced by a processor using an MMU (memory mapping unit) having MMU tables. The graphics memory includes a portion for on-screen display, and a portion which can be written into but which is not displayed.
When a background image is overlaid by a foreground image, the portion of the background image overlaid is copied to a save-away area, and the MMU tables are altered so that software rendering of the background image automatically occurs in the save-away area. However, the foreground image is written directly into the on-screen display area by rendering hardware. This allows the software-rendered image to be kept up to date, and allows data for the software-rendered image not to be lost during the time, the background image is covered up.
When the background image is no longer overlaid by the foreground image, the portion of the background image which was overlaid is copied back from the save-away area to the on-screen display area. The MMU tables are altered so that software rendering of the background image thereafter automatically occurs in the on-screen display area. This allows the software-rendered image to be quickly displayed on screen in its updated form.
The invention can be used in conjunction with other inventions relating to text and graphic element displays, such as inventions described in the following patent applications: Provisional Patent Application to Serial No. 60/046,750 filed May 16, 1997, entitled “IMPROVED TV QUALITY”.
These applications are hereby incorporated by reference as if filly set forth herein.
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Helman Jim
Vickers Mark A.
Glenn Michael A.
Liberate Technologies
Vo. Cliff N.
LandOfFree
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