Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1998-07-06
2002-12-03
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
Reexamination Certificate
active
06489966
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a graphic processing device for generating a computer graphics (CG) screen on a display, such as a CRT (Cathode Ray Tube), and in particular to a graphic processing device which divides an object into multiple polygons and performs a geometric process on the polygons, and then for rasterizes pixels that constitute each polygon. More specifically, the present invention pertains to a graphic processing device for performing an anti-aliasing process to remove aliasing at the edges of polygons, and in particular to a graphic processing device for performing anti-aliasing in accordance with a percentage (i.e., a coverage) of sub-pixels, included in a pixel, that are covered by a polygon.
2. Related Art
In accordance with recent technical progression, application fields for computers have expanded. The preparation and processing of graphic forms and images using computers, i.e., computer graphics (CG), is one of examples. Recently, in accordance with improvements in the display capabilities of computers, and functional enhancements of graphic processes, “three-dimensional graphics” that generate two-dimensional images of three-dimensional objects and display them has been focused on. Three-dimensional graphics is a technique whereby an arithmetic model is employed to represent an optical phenomenon of a three-dimensional object when it is illuminated by a light source, and that performs shading of the surface of the object based on the arithmetic equation model, or that puts a pattern to a two-dimensional image to generate a graphic image that has a more realistic appearance and has three dimensions. The three-dimensional graphic techniques have become more popular for the CAD/CAM in science, engineering, manufacturing and other application fields, and in various software development fields.
The graphic processing system generally comprises a “geometry sub-system” that is regeared as a front end and a “raster sub-system” that is regarded as a back end.
The geometry sub-system is a system for performing a geometric process to determine the position of an object on a computer screen. In the geometry sub-system, generally, an object is treated as a set of multiple polygons (normally triangles), and processing is performed for each polygon. That is, geometric calculations, such as “coordinate transformation,” “clipping” and “calculation relative to a light source,” are performed for each vertex that defines a polygon. “Coordinate transformation” is a process for transforming the coordinates of each vertex of a provided polygon in accordance with the position of a viewpoint. “Clipping” is a process for detecting and removing a portion of a polygon that is outside the boundaries of the edge of a computer screen. “Calculation relative to a light source” is a process for acquiring the luminance of each vertex based on the positional relationship with a light source.
The raster subsystem is a system for generating pixels that constitute an object. The rasterization process is generally performed by interpolating image parameters for all pixels in the polygon, with employing an image parameter that is obtained for each vertex of a polygon. The image parameters are color data represented by RGB and a Z value representing the depth. For the latest three-dimensional graphic process, an f (fog), to express a distance, and a t (texture), to express a material or a pattern on the surface of an object to provide reality, are included as image parameters. These image parameters are also calculated for each pixel.
Almost all data in the computer engineering field are represented as digital values. Therefore, so-called aliasing, which is an undesirable phenomenon, frequently appears during the conversion of an analog phenomenon in the natural world into discontinuous digital values. In computer graphic processing, aliasing is perceived as being the zig-zag edges of a polygon, or as a graphic form that has an inaccurate shape. This phenomenon is also caused because the pixels of a display are too large or the resolution is insufficiently high in comparison with the visual acuity of a person.
The process employed for removing the aliasing phenomenon is generally called anti-aliasing. The anti-aliasing process in the computer graphic field can be performed, for example, by dividing a pixel, which is the minimum unit for a drawing process, into multiple sub-pixels and by re-evaluating image data (color data, etc.) concerning the pixel obtained during the rasterization process. In other words, in the anti-aliasing process, a pixel that is cut across by the edges of polygons is divided into 4×4, 8×8 or 16×16 sub-pixels, and the value of the color data provided for a pixel is adjusted in accordance with the percentage of sub-pixels covered by a polygon (the sub-pixels to be painted), i.e., the coverage of the sub-pixels.
In the example shown in
FIG. 5
, a part of a pixel is covered with a polygon having a linear edge. When the pixel is divided into 4×4 sub-pixels, the coverage is 14/16. In the example shown in
FIG. 6
, a part of a pixel is covered with a polygon having an arced edge. When the pixel is divided into 4×4 sub-pixels, the coverage is 14/16. In these examples, instead of determining the color data for a pixel to be discontinuous values based on whether or not a pixel is covered by a polygon, the graduation should be adjusted in accordance with the extent of the coverage of the pixel. As a result, discontinuity at the edge will be reduced and the display quality will be enhanced. A graduation substantially similar to a natural phenomenon may be added to the edges of the polygon by performing anti-aliasing. For example, a three-dimensional wire frame model generated by CAD can be drawn as a continuous smooth line with no zig-zags. In addition, an image can be drawn for which there is less smearing of color at the edge of a polygon.
For the coverage calculations for acquiring the percentage of sub-pixels covered, whether the sub-pixels of a pixel are positioned inside a polygon, along an edge line, or outside the polygon must be determined. In other words, for the coverage calculation, a processing function (edge function) must be performed to determine the position of each sub-pixel, either above, below or on an edge line that defines the boundary of a polygon.
It would be easily understood by one having ordinary skill in the art that the edge function is represented by geometric calculation expressions that include several terms. Since the edge function processing is conventionally performed by software, fast calculation is difficult. It is preferable for fast anti-aliasing that a specific hardware circuit (e.g., an LSI) be used and that parallel processing be performed. However, the edge function processing involves multiple multiplications and divisions, and a relatively large gate size is required for implementing the hardware that performs such calculation (well known). Therefore, the size of the LSI chip would become larger and accordingly, the manufacturing costs would increase.
SUMMARY OF THE INVENTION
It is, therefore, one object of the present invention to provide a superior graphic processing device to perform an anti-aliasing process for removing aliasing that occurs at the edges of polygons.
It is another object of the present invention to provide a superior graphic processing device that performs anti-aliasing in accordance with a percentage (coverage) of the sub-pixels, included in a pixel, that are covered by a polygon.
It is an additional object of the present invention to provide a superior graphic processing device that performs parallel and rapid processing to acquire a coverage required for an anti-aliasing process.
It is a further object of the present invention to provide a superior graphic processing device on which an LSI having a relatively small gate size can be implemented to acquire the coverage required for anti-aliasing.
To achieve the above objects, a
Kanzaki Eisuke
Takagaki Shunichi
Yasuda Hiroaki
Blackman Anthony J.
Brier Jeffery
Drumheller Ronald L.
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