Method and system for rendering overlapping opaque graphical objects in graphic imaging systems

• US 6,268,859 B1
• Filed: 06/06/1995
• Issued: 07/31/2001
• Est. Priority Date: 06/06/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Andresen, Kevin W., Chen, Kok S.
• Primary Examiner(s): ZIMMERMAN, MARK K
• Application Number:
  US08/473,651
• Time in Patent Office: 2,247 Days
• Field of Search: 395/121, 395/122, 395/135, 345/421, 345/422, 345/435
• US Class Current: 345/421
• CPC Class Codes: G06T 15/40 Hidden part removal

Abstract

Objects in an image are rendered in a manner which dynamically avoids the rendering of obscured objects. Data pertaining to one object is stored in a designated memory location, such as a cache memory. Data for a subsequent object is compared with the stored data, and the area of intersection between the two objects is determined. This area of intersection is subtracted from the first object, and the data for the second object is added to the memory. As the memory is filled, the data for the oldest object is removed and the object is rendered. After all objects in the list have been processed in this manner, those which remain in the memory are also rendered, and removed from the memory. At each step of the process, the portions of an object which are obscured by later-generated objects are eliminated, and thereby unnecessary rendering of obscured objects is avoided.

Claims

1. A method for generating a graphic image, comprising the steps of:

generating data which describes objects in the graphic image;

storing the data for multiple objects in a memory;

comparing the stored data for a first object with data for a second object to identify any area of intersection of said objects;

modifying the stored data for the first object by removing and identified area of intersection;

repeating said comparing and modifying steps for successive objects whose data is stored in the memory;

determining whether said memory is full;

rendering the modified stored data for the first object, to create a pixel map which defines portions of said object that are not obscured by said second object, when the memory is determined to be full; and

creating an image in accordance with the rendered data.

2. The method of claim 1 further including the step of replacing the data in said memory for said first object with the data for said second object after said modifying step.

3. The method of claim 1 wherein said first object, whose modified data is rendered, is an object whose data has been stored in said memory for the longest period of time when the memory is determined to be full.

4. A graphic imaging system, comprising:

means for generating data which describes objects in an image;

a memory for storing data pertaining to a plurality of objects;

means for comparing data pertaining to a first object with the data for a second object and modifying the data for the first object to remove any common areas of said first and second objects;

means for determining when said memory is full;

means for selecting data for one of the objects stored in said memory when the memory is determined to be full;

a rendering device for creating a pixel map corresponding to the modified data for the selected object; and

an image output device for generating an image in accordance with the pixel map.

5. The graphic imaging system of claim 4 wherein the data that is selected pertains to an object whose data has been stored in the memory the longest.

6. The graphic imaging system of claim 4 wherein said image output device comprises a print engine for a printer.

7. The graphic imaging system of claim 4 wherein said image output device comprises a computer monitor.

8. A method for producing an image containing multiple objects, comprising the following steps:

storing data in a first memory which describes the area covered by each of plural objects in the image;

retrieving data from said first memory that describes the area covered by a first object and storing said data in a second memory;

retrieving data from said first memory that describes the area covered by a second object;

determining whether there is a common area of intersection for the areas covered by said first and second objects;

modifying the data stored in said second memory to remove the common area of intersection from the description of the area covered by said first object;

rendering the modified data stored in said second memory that describes the area covered by the first object; and

generating an image in accordance with the rendered data.

9. A method for producing an image containing multiple objects, comprising the following steps:

a) storing data in a first memory which describes the area covered by each of plural objects in the image;

b) retrieving data from said first memory that describes the area covered by a first object and storing said data in a second memory;

c) retrieving data from said first memory that describes the area covered by a second object;

d) determining whether there is a common area of intersection for the areas covered by said first and second objects;

e) modifying the data stored in said second memory to remove the common area of intersection from the description of the area covered by said first object;

f) repeating steps c), d) and e) for successive objects whose data is stored in said first memory;

g) rendering the modified data stored in said second memory that describes the area covered by the first object; and

h) generating an image in accordance with the rendered data.

10. The method of claim 9 wherein the data that is retrieved for each of the objects is stored in said second memory and modified in accordance with the data of successive objects, and further including the steps of determining when said second memory is full, selecting the modified data for one of said objects, and rendering the data for the selected object in step g).

11. The method of claim 10, wherein the selected object is the object whose data has been stored in said second memory for the longest period of time.