Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
2000-12-29
2004-07-13
Nguyen, Phu K. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
Reexamination Certificate
active
06762760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of computer graphics and, more particularly, to high performance graphics systems.
2. Description of the Related Art
A computer system typically relies upon its graphics system for producing visual output on the computer screen or display device. Early graphics systems were only responsible for taking what the processor produced as output and displaying it on the screen. In essence, they acted as simple translators or interfaces. Modern graphics systems, however, incorporate graphics processors with a great deal of processing power. They now act more like coprocessors rather than simple translators. This change is due to the recent increase in both the complexity and the amount of data being sent to the display device. For example, modern computer displays have many more pixels, greater color depth, and are able to display images that are more complex with higher refresh rates than earlier models. Similarly, the images displayed are now more complex and may involve advanced techniques such as anti-aliasing and texture mapping.
As a result, without considerable processing power in the graphics system, the CPU would spend a great deal of time performing graphics calculations. This could rob the computer system of the processing power needed for performing other tasks associated with program execution and thereby dramatically reduce overall system performance. With a powerful graphics system, however, when the CPU is required to draw a box on the screen, the CPU is freed from having to compute the position and color of each pixel. Instead, the CPU may send a request to the graphics system stating, “draw a box at these coordinates”. The graphics system then draws the box, thereby freeing the CPU to perform other tasks.
Generally, a graphics system in a computer system is a type of video adapter that contains its own processor to boost performance levels. These processors are specialized for computing graphical transformations, so they tend to achieve better results than the general-purpose CPU used by the computer system. In addition, they free up the computer's CPU to execute other commands while the graphics system is handling graphics computations. The popularity of graphical applications, and especially multimedia applications, has made high performance graphics systems a common feature of computer systems. Most computer manufacturers now bundle a high performance graphics system with their systems.
Since graphics systems typically perform only a limited set of functions, they may be customized and therefore be far more efficient at graphics operations than the computer's general-purpose central processor. While early graphics systems were limited to performing two-dimensional (2D) graphics, their functionality has increased to support three-dimensional (3D) wire-frame graphics, 3D solids, and now includes support for 3D graphics with textures and special effects such as advanced shading, fogging, alpha-blending, and specular highlighting.
The processing power of 3D graphics systems has been improving at a breakneck pace. A few years ago, shaded images of simple objects could only be rendered at a few frames per second, while today's systems support rendering of complex 3D objects at 60 frames per second or higher.
In order to render a 3D object, the 3D object must be organized or projected, in the mathematical sense, from 3D space onto a 2D display device. The display device can be the retina of the human eye, the film of a photographic camera, a projector screen, a head-mounted display, or a computer display screen. Typically, computer graphics systems use a “perspective projection” that mimics the way a human eye and the way a photographic camera project 3D images onto a 2D plane. Computer graphics systems project the 3D world onto a viewport, an imaginary 2D surface between the 3D world and the viewpoint. The viewpoint represents the assumed position of a viewer. The projected image may then be transformed for viewing on a computer display screen.
FIGS. 1A and 1B
are used to provide definitions for the coordinate system that is typically used to represent the distance of an object from the viewpoint for a particular viewport.
FIG. 1A
is a top view from above viewport
100
, and
FIG. 1B
is a view from behind viewpoint
102
and viewport
100
. As shown in
FIGS. 1A and 1B
, distance x is the horizontal distance from object
103
to viewpoint
102
, distance y is the vertical distance from object
103
to viewpoint
102
, and distance z is the depth distance from object
103
to viewpoint
102
. Furthermore, note that the horizontal distance x is measured along a direction parallel to the top and bottom edges of viewport
100
, the vertical distance y is measured along a direction parallel to the left and right edges of viewport
100
, and the depth distance z is measured along a direction perpendicular to the surface of viewport
100
.
While the number of pixels is an important factor in determining graphics system performance, another factor of equal import is the quality of the image. One visual effect used by graphics systems to increase the realism of computer images is called “fogging”. Fogging is a technique by which the color of objects can be reduced in intensity or blended with other colors so that the objects appear to be buried in fog, mist, or smoke. To give the impression of an object obscured by fog, the graphics system typically blends constant fogging color values with the color values of the object. The resulting fog-shaded color typically retains some of the object's original color. The weight of the constant fogging color in the blending, which also represents the amount of fogging applied, is typically a function of the distance of the object from the viewpoint. The further away that an object is from the assumed location of the viewer, the more fog-shaded the object appears. Beyond a certain distance, the object may appear to be totally occluded by the fog, mist, or smoke. In these cases, the object may simply be assigned the color of the fog. Note that, as used herein, the word fog is used to also refer to mist, smoke, or any other phenomenon that has the effect of reducing visibility.
In prior art graphics systems, the amount of fogging depends on the depth distance z from the object to the viewpoint. Since the depth distance z does not represent the actual distance from the viewpoint to the object, certain limitations exist for prior art graphics systems that use the depth distance z for implementing fogging. These limitations and other artifacts associated with using the depth distance z to implement fogging are described below with the aid of
FIGS. 2A & 2B
.
FIG. 2A
shows 2D viewport
100
with 3D space
116
located behind viewport
100
. Objects that are located in 3D space
116
, such as objects
108
&
110
, are projected onto viewport
100
to form images that may be later transformed so that they may be displayable on a computer display screen. For the projection, the graphics system assumes that a viewer is located at viewpoint
102
. For this discussion, a typical fogging model is assumed for the prior art graphics system where fogging is applied according to fogging plane
104
that is located a certain depth distance z
F
from viewpoint
102
. A full amount of fogging is applied to objects that have depth distance z greater than z
F
, and no fogging is applied to objects that have depth distance z less than z
F
. Applying no fogging is implemented by displaying the color values of objects unchanged. Applying a full amount of fogging is implemented by discarding the color values of an object and replacing the object's color values with the constant fogging color values. As shown in
FIG. 2A
, object
108
has a z value that is less than z
F
and as a result is displayed without any fogging applied, and object
110
has a z value that is greater than z
F
and as a result is displayed with a full amount of fog
Hood Jeffrey C.
Meyertons Hood Kivlin Kowert & Goezel, P.C.
Nguyen Phu K.
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