Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1998-11-06
2001-12-04
Nguyen, Phu K. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
Reexamination Certificate
active
06326964
ABSTRACT:
TECHNICAL FIELD
The invention generally relates to graphics processing, and more specifically relates to rendering object geometry in a graphics scene to image regions called “chunks.”
BACKGROUND
With the widespread use of computers in all aspects of modem life, there is an increasing demand to improve the human-machine interface through the use of visual information. Advances in graphical software and hardware have already improved the human-machine interface drastically. Interactive graphics such as windowing environments for desk-top computers, for example, have improved the ease of use and interactivity of computers drastically and are commonplace today. As the price-performance ratio of hardware drops, the use of computer generated graphics and animation will become even more pervasive. Unfortunately, the cost of producing truly interactive and realistic effects has limited its application. There is a need, therefore, for new graphics processing techniques and architectures that provide more interactive and realistic effects at a lower cost.
Although there are numerous ways to categorize graphics processing, one common approach is to describe an image in terms of the dimensions of the objects that it seeks to represent. For example, a graphics system may represent objects in two dimensions (e.g., having x and y coordinates); in which case the graphics are said to be “two-dimensional”, and three dimensions (e.g., having x, y, and z coordinates), in which case the graphics are said to be “three-dimensional” (“3-D”).
Since display devices such as cathode ray tubes (CRTs) are two-dimensional (“2-D”), the images displayed by computer graphic systems are generally 2-D. As discussed in greater detail below, however, if the computer maintains a graphical model representing the imaged object in three-dimensional space, the computer can alter the displayed image to illustrate a different perspective of the object in 3-D space. In contrast, although a 2-D graphic image can be transformed prior to display (e.g., scaled, translated, or rotated), the computer can not readily depict the object's appearance from a different perspective in 3-D space.
The increasing ability of modern computers to efficiently handle 2-D and, particularly, 3-D graphics has resulted in a growing variety of applications for computers, as well as fundamental changes in the interface (UI) between computers and their users. The availability of 3-D graphics is becoming increasingly important to the growth of entertainment related applications including production quality film animation tools, as well as lower resolution games and multimedia products for the home. A few of the many other areas touched by 3-D graphics include education, video conferencing, video editing, interactive user interfaces, computer-aided design and computer-aided manufacturing (CAD/CAM), scientific and medical imaging, business applications, and electronic publishing.
A graphics processing system may be thought of as including an application model, application program, graphics subsystem, as well as the conventional hardware and software components of a computer and its peripherals.
The application model represents the data or objects to be displayed, assuming of course that the image processing is based upon a model. The model includes information concerning primitives such as points, lines, and polygons that define the objects' shapes, as well as the attributes of the objects (e.g., color). The application program controls inputs to, and outputs from, the application model—effectively acting as a translator between the application model and graphics sub-system. Finally, the graphics sub-system is responsible for passing user inputs to the application model and is responsible for producing the image from the detailed descriptions stored by the application model.
The typical graphics processing system includes a physical output device which is responsible for the output or display of the images. Although other forms of display devices have been developed, the predominant technology today is referred to as raster graphics. A raster display device includes an array of individual points or picture elements (i.e., pixels), arranged in rows and columns, to produce the image. In a CRT, these pixels correspond to a phosphor array provided on the glass faceplate of the CRT. The emission of light from each phosphor in the array is independently controlled by an electron beam that “scans” the array sequentially, one row at a time, in response to stored information representative of each pixel in the image. Interleaved scanning of alternate rows of the array is also a common technique in, for example, the television environment. The array of pixel values that map to the screen is often referred to as a bitmap or pixmap.
One problem associated with raster graphics devices is the memory required to store the bitmap for even a single image. For example, the system may require 3.75 megabytes (Mb) of random access memory to support a display resolution of 1280×1024 (i.e., number of pixel columns and rows) and 24 bits of color information per pixel. This information, which again represents the image of a single screen, is stored in a portion of the computer's display memory known as a frame buffer.
Another problem with conventional raster graphics devices such as CRTs is the relatively quick decay of light emitted by the device. As a result, the display must typically be “refreshed” (i.e., the raster rescanned) at a rate approaching 60 Hz or more to avoid “flickering” of the image. This places a rigorous demand on the image generation system to supply image data at a fixed rate. Some systems address this problem by employing two frame buffers, with one of the buffers being updated with pixmap information corresponding to subsequent image frame, while the other buffer is being used to refresh the screen with the pixmap for the current image frame.
The demands placed upon the system are further exacerbated by the complexity of the information that often must be processed to render an image from the object stored by the application model. For example, the modeling of a three-dimensional surface is, in itself, a complex task. Surface modeling is performed by the application model and may involve the use of polygon meshes, parametric surfaces, or quadric surfaces. While a curved surface can be represented by a mesh of planar polygons, the “smoothness” of its appearance in the rendered image will depend both upon the resolution of the display and the number of individual polygons that are used to model the surface. The computations associated with high resolution modeling of complex surfaces based upon polygon meshes can be extremely resource intensive.
As intimated above, there is a demand to produce more realistic and interactive images. The term, “real-time,” is commonly used to describe interactive and realistic image processing systems. In a “real-time” system, the user should perceive a continuous motion of objects in a scene. In a video game having real-time capabilities, the active characters and view point should respond with minimal delay to a user's inputs, and should move smoothly.
To produce such real-time effects, an image rendering system has to generate a new image at a sufficiently high rate such that the user perceives continuous motion of objects in a scene. The rate at which a new image is computed for display is referred to as the “computational” rate or the “computational frame” rate. The computational rate needed to achieve realistic effects can vary depending on how quickly objects move about the scene and how rapidly the viewing perspective changes. For a typical application, a real-time graphics system recomputes a new image at least twelve times a second to generate a series of images that simulate continuous motion. For high-quality animation applications, however, the computational rate must be significantly higher.
Another critical issue for real-time systems is transport delay. Transport delay is the time
Elliott Conal M.
Snyder John M.
Klarquist & Sparkman, LLP
Microsoft Corporation
Nguyen Phu K.
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