Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1997-03-19
2001-01-30
Brier, Jeffery (Department: 2779)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C345S503000, C345S506000
Reexamination Certificate
active
06181346
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a graphics system for displaying computer graphics (CG) on a display screen. More particularly, it relates to a graphics system that includes a geometric sub-system for dividing a graphic object into multiple polygons and for performing geometric processing only on the vertexes of the polygons. Furthermore, it relates to such a graphic system that also includes a raster sub-system for interpolating image data for pixels in the polygons. Specifically, the present invention pertains to a graphics system as described above in which the geometric sub-system performs parallel processing.
DESCRIPTION OF THE BACKGROUND
The generation and processing of graphic images using computers (so-called “computer graphics (CG)”) is an example of the expansion in the use of computers. Recently, as the capabilities of computer displays have been improved, and their graphic functions enhanced, the focus has been placed on “3D Graphics”, whereby a three-dimensional object is rendered on a two-dimensional medium for display on a screen. With the 3D graphics, an optical phenomenon of a 3D object when it is irradiated by a light source is provided by using a mathematical model, and based on the model, the surface of the object is described by using shading or perspective, or a pattern is used to represent the surface, for the display of a more realistic and colorful 3D image. The 3D graphic techniques have been used more frequently for CAD/CAM in science, in engineering, in manufacturing, and in other application fields, and for the development of various software applications.
Graphics System
The graphics system comprises a “geometric sub-system”, generally as a front-end, and a “raster sub-system”, generally as a back-end.
The geometric sub-system regards a graphic object as a set of polygons (normally, triangles), and performs schematic geometric processing for each polygon. The geometric processing performed by the geometric sub-system determines the position of an object on a computer screen. More specifically, geometric calculations, such as coordinate transformation, clipping, and light source calculation, are performed only on the coordinates of the individual vertexes defining the polygons. Coordinate transformation is a process for transforming the coordinates for the vertexes of a given polygon in accordance with the position of a visual point. Clipping is a process for removing portions of a polygon that lie outside the limits of a computer screen. Light source calculation is a process for calculating a luminance at each vertex based on its positional relationship with a light source.
The raster sub-system interpolates image parameters for all the pixels in a polygon by using image parameters acquired for the vertexes of the polygon. The image parameters are color data indicated by RGB, and a Z value representing the distance in the direction of the depth. In the latest highly colorful 3D graphic processing, fog “f” to represent distance and texture t to represent a material and a pattern on the surface of an object are included as image parameters, which are also calculated for each pixel. The polygon is represented in two dimensions and an object without a texture is merely an inorganic image obtained by shifting each plane in parallel or rotating it in accordance with a visual point. Therefore, the processing for putting texture on the surface of an object (texture mapping) is very important for the quality and the realism of an object. However, the amount of bit mapped texture data required for surface patterns is generally enormous, and a huge memory resource is thus required.
Parallel processing for graphics system
Since the capabilities of signal processing are limited when a large amount of calculations must be performed in real time, a multiprocessing technique that performs parallel processing using a plurality of node processors has been used. Since 3D graphic processing requires an enormous amount of calculations and data for image generation, parallel processing is used for enhancement of functions and performances.
In the above described graphics system, while the geometric sub-system performs calculations for each polygon, the raster sub-system performs calculations for each pixel in a polygon. In other words, the processing unit at the front-end and the back-end differ from each other. The sub-systems at the front-end and at the back-end frequently have separate inherent parallel structures to independently provide improved functions and performances. A system design in which the sub-systems adopt different parallel structures is described in, for example, Chapter 18 of “Computer Graphics” (J. D. Foley: second edition, Addison-Wesley).
FIG. 6
is a schematic diagram illustrating a hardware arrangement for a graphics system that comprises two different parallel structures. The graphics system includes a dispatch processor
10
; a plurality of geometry node processors
20
; a merge processor
30
; a plurality of raster node processors
40
; and a frame buffer
50
.
The dispatch processor
10
distributes drawing instructions sets for the geometric processing of a 3D object to each of the geometry node processors
20
. More specifically, the dispatch processor
10
is connected to another host computer system (not shown) via a bus. On the bus, the dispatch processor
10
sequentially receives a set of drawing instructions (also called a “data set”), and distributes the data sets so as to equalize the work loads imposed on the respective node processors
20
. In other words, an data set is the unit to be distributed to the node processors
20
. A data set is generally a set of data for defining one polygon (or a part of a polygon) and includes coordinate values for the vertexes, and attribute information, such as line widths, line types and texture IDs for specifying texture.
The geometry node processors
20
, which constitute the core of the geometric sub-system, perform parallel geometric calculations for a 3D object. Each of the geometric node processors
20
performs coordinate transformation, clipping, and light source calculation for a received data set, and outputs the results to the merge processor
30
.
The merge processor
30
merges the data sets transmitted from the geometry node processors
20
, and imposes on the succeeding raster sub-system the rasterization of the data sets. The raster sub-system shown in
FIG. 6
has a parallel structure including a plurality of raster node processors
40
. The merge processor
30
also serves as a dispatch processor for the raster sub-system. That is, when the merge processor
30
receives a data set that has been geometrically processed, it distributes, to the raster node processors
40
, the pixels in the screen regions defined by the data sets.
The raster node processors
40
, which constitute the core of the raster sub-system, rasterize the distributed pixels. Since data sets are distributed to the raster node processors
40
as pixel units, which are smaller than data set units, more raster node processors
40
are provided than the geometry node processors
20
. The raster node processors
40
employ image parameters (color data, such as RGB and fog) that have been acquired for each vertex to interpolate the image parameters for distributed pixels and to put texture image (texture mapping).
The results obtained by the raster node processors
40
are appropriately written to corresponding addresses in the frame buffer
50
. The drawing information is read from the frame buffer
50
and is displayed on an attached display
60
.
Problems with parallel graphics system
In a parallel geometric sub-system, several problems have arisen at the front-end.
One of these problems is the maintenance of the drawing order for drawing data sets. The problem concerns serialization. The data sets for geometric processing for a 3D object are distributed to the geometry node processors
20
as polygon units. However, the geometry node processors
20
do not always terminate their proce
Moriyama Takao
Ohtani Munetaka
Ono Makoto
Takatsu Yoshihisa
Brier Jeffery
Good-Johnson Motilewa
International Business Machines - Corporation
Sbrollini Jay P.
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