Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
2001-11-19
2004-05-18
Zimmerman, Mark (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
C345S426000
Reexamination Certificate
active
06738061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates a method, an apparatus, a storage medium, a program, and a program product, for displaying a plurality of transparent primitive surfaces (transparent primitive surfaces or translucent primitive surfaces) provided in a virtual three-dimensional space.
2. Description of Related Art
Conventionally, a game apparatus for displaying a virtual three-dimensional space created by three-dimensional computer graphics is known. Such a game apparatus arranges objects consisting of a plurality of polygons (primitive surfaces) in a virtual three-dimensional space represented in a world coordinate system, and generates images viewed from a view point in the virtual three-dimensional space.
That is, the game apparatus operates coordinate values and a direction of each object (polygons constituting each object, vertexes constituting each polygon) in the world coordinate system. Then, the game apparatus determines a view point, an eyes direction, and a view volume (a field of view; a pyramid determined by a field of view angle and a Z direction depth of field) of the view point, and transforms the coordinate values and the direction of each object represented in the world coordinate system to those represented in a viewing coordinate system. Then, the game apparatus performs a hidden surfaces processing to the polygons, and perspective projects the polygons in a screen coordinate system. Thereby, the game apparatus decides a color of each pixel of a frame buffer (a screen).
As one algorithm of the hidden surfaces processing, it is a Z buffer algorithm. In order to perform the Z buffer algorithm, the game apparatus prepares a Z buffer that is a storage area therein. The Z buffer is a storage area storing Z values in the screen coordinate system, corresponding to pixels stored in the frame buffer, respectively. According to the Z buffer algorithm, the game apparatus perspective projects all polygons on the screen in voluntary order. Herein, when perspective projecting any one of polygons on the screen, the game apparatus performs the following processing.
That is, in case Z values of pixels occupied by the perspective projected polygon are not stored in the Z buffer, the game apparatus stores the color of the point of the polygon corresponding to each pixel in the frame buffer, in the pixel of the frame buffer. On the other hand, in case Z values of pixels occupied by the polygon are stored in the Z buffer, the game apparatus compares the Z value of the point of the polygon corresponding to each pixel with the Z value of the pixel. Then, in case the Z value of the point of the polygon is smaller than the Z value of the pixel corresponding to the point, the game apparatus rewrites the Z value of the pixel to the Z value of the point, stores the Z value of the point in the Z buffer, and provides the color of the point to the pixel. On the other hand, in the case the Z value of the point of the polygon is larger than the Z value of the pixel corresponding to the point, the game apparatus does not rewrite the Z value of the pixel, and does not provide the color of the point to the pixel. When the game apparatus outputs values stored in the frame buffer after performing the above-described processing to each pixel, it is possible that the game apparatus performs the hidden surfaces processing to all polygons.
As another algorithm of the hidden surfaces processing, it is a back surfaces clipping algorithm. The back surfaces clipping algorithm is an algorithm of performing the hidden surfaces processing without perspective projecting all polygons. According to the back surfaces clipping algorithm, the game apparatus performs the following processing to each object provided in the virtual three-dimensional space.
That is, the game apparatus determines whether each polygon constituting the object is at the view point side (the front) of the object or the opposite side (the back) to the view point, on the basis of an eyes direction and direction of a normal of each polygon. More specifically, the game apparatus operates an angle between a normal vector of each polygon and an eyes vector, decides that the polygon is at the back in case the angle is an acute angle, and decides that the polygon is at the front in case the angle is an obtuse angle. Then, the game apparatus transforms only the polygons at the front to those represented in the screen coordinate system, and thereby determines the color of each pixel stored in the frame buffer. Therefore, because the game apparatus displays only the front of each object, it is possible that the game apparatus performs the hidden surfaces processing to all polygons.
By the way, in order to display more realistic images on a display screen, there is a case a transparent object or a translucent object such as a window glass or a water surface is provided in the virtual three-dimensional space. Hereinafter, the transparent object and the translucent object will be called a transparent object. The game apparatus displays the transparent object on the screen by performing the following processing.
That is, the game apparatus perspective projects the transparent object on the screen coordinate system, and determines colors of pixels corresponding to points included in each transparent polygon of the transparent object, according to an alpha value of the transparent object. More specifically, the game apparatus composes the color of each pixel decided before displaying the transparent polygon on the screen and the color of the transparent polygon, according to the alpha value, and thereby determines each pixel of the frame buffer. When the game apparatus performs the above-described processing to all transparent polygons constituting the transparent object, the transparent object is displayed on the screen.
In the game apparatus according to an earlier development, there are the following problems in case the game apparatus performs the hidden surfaces processing to the transparent polygon.
When the game apparatus carries out the hidden surfaces processing according to the Z buffer algorithm, because the game apparatus perspective projects all polygons in voluntary order, there is a case the display on the screen is influenced by the projection order. For example, in case another polygon is provided at the far side of the transparent polygon in the eyes direction, there is a difference in the display on the screen between the case the game apparatus perspective projects the transparent polygon first and the case the game apparatus perspective projects another polygon first.
That is, in case the game apparatus perspective projects the transparent polygon after perspective projecting another polygon first, because the Z value of the point included in the transparent polygon is smaller than the Z value of the pixel stored in the frame buffer, that is the Z value of the point included in another polygon, the game apparatus composes the color of the transparent polygon and the color of the frame buffer, that is the color of another polygon. Therefore, the images are displayed on the display screen so that another polygon is always at the far side of the transparent polygon. On the other hand, in case the game apparatus perspective projects another polygon after perspective projecting the transparent polygon first, because the Z value of the point included in another polygon is larger than the Z value of the pixel stored in the frame buffer, that is the Z value of the point included in the transparent polygon, the game apparatus does not provide the color of another polygon to the pixel. Therefore, in spite of the transparent polygon, the color of another polygon is not reflected in the transparent polygon on the display screen.
Further, according to the Z buffer algorithm, even if another object is not provided at the far side of the transparent object in the eyes direction, there is a difference in displaying the transparent object on the screen between the case the game apparatus perspective projects
Cao Huedung X.
NAMCO Ltd.
Oliff & Berridg,e PLC
Zimmerman Mark
LandOfFree
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