US 5,745,095 A · Compositing digital information on a display screen based on screen descriptor

Abstract

A method and system for producing a composite image of two or more graphic objects. In a set top box (44) designed to be used with a television receiver or video monitor (40), an application specific integrated circuit (ASIC) (76) is provided that includes a dynamic composition engine (DCE) (84), which generates a composite image for display on the screen of the television receiver. The composite image is based upon Screen Descriptor data that include a Line Descriptor defining each scan line using Span Descriptors. A Span Descriptor defines the portion of a line occupied by one of the objects that will comprise the composite image and specifies how that object will be combined with other objects on the line. A line buffer is filled with the pixels for the scan line next to be displayed while data in a second line buffer are written to the display screen. The two line buffers are then switched, enabling the next line to be composed in one line buffer while the data in the other line buffer are written to the screen. A new Screen Descriptor is produced if a change in the composite image occurs. When the last Line Descriptor in the current Screen Descriptor is processed, a pointer to the new Screen Descriptor is passed to the DCE to enable the new Screen Descriptor to be used for generating the next frame on the display screen.

Claims30

Dependent claims

A method for displaying objects on a screen as an image that comprises a plurality of scan lines, comprising the steps of:

(a) storing bitmap data in a memory for each object to be displayed on the screen;
(b) creating a data structure based on the bitmap data for each object, said data structure describing each object to be displayed on the screen and including a Screen Descriptor referencing a plurality of Line Descriptors that define the composition of each scan line of the screen, providing a composite of any objects that overlap on the scan line;
(c) storing the data structure in the memory;
(d) processing the data structure to produce video data for each scan line to be displayed on the screen;
and
(e) generating an image on the screen using the video data for the scan lines of the screen, said image displaying the composite of any overlapping objects on the scan lines.

3 more elements

A system adapted for controlling the display of objects on a screen as an image comprising a plurality of scan lines, comprising:

(a) a memory for storing bitmap data for each of the objects and machine instructions controlling the operation of the system;
(b) a processor, coupled to the memory, for executing the machine instructions so as to implement a plurality of functions used for controlling the display of the objects, said plurality of functions including producing control signals for a dynamic composition engine, said dynamic composition engine producing video signals that are adapted to drive the screen to display the objects in response to the control signals, said dynamic composition engine including:
(i) means for creating a data structure based upon the bitmap data for each of the objects to be displayed, said data structure being stored in the memory, describing each object to be displayed on the screen, and including a Screen Descriptor referencing a plurality of Line Descriptors that define the composition of each scan line of the screen providing a composite of any objects that overlap on the scan line;
and
(ii) means for processing the data structure to produce video data for each scan line to be displayed on the screen;
and
(c) said system further including means for generating an image on the screen using the video data for the scan lines of the screen, said image displaying the composite of any overlapping objects on the scan lines.

4 more elements

Dependencies are inferred from the claim text.

Compositing digital information on a display screen based on screen descriptor

Life of this patent

Compositing digital information on a display screen based on screen descriptor

Life of this patent

Abstract

Claims30