Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1995-03-31
2002-05-21
Nguyen, Phu K. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
Reexamination Certificate
active
06392643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image generation apparatus suitable for use with apparatuses utilizing computer graphics such as video game machines and graphic computers which must perform a high level of visualization using limited hardware resources. More particularly, the present invention relates to the so-called semitransparent process.
2. Description of the Related Art
In the art of computer graphics, the systems normally referred to as 3D (three-dimensional) graphics systems draw an image of an object which gives the sense of reality (hereinafter an object to be drawn will be simply referred to as an object) by first dividing the surface of the object into a plurality of polygons (“polygons” are the smallest units of figures treated by a drawing device (triangles and quadrangles)) and by drawing those polygons sequentially in a frame memory associated with a monitor display screen (herein after referred to as a frame buffer) to reconstruct an image which has a three-dimensional appearance.
In a normal image generation apparatus of this type, a dedicated drawing device is provided between the CPU and frame buffer in order to improve the processing speed. During the generation of an image, the CPU does not directly access the frame buffer, but generates commands (hereinafter simply referred to as draw commands) to draw basic figures such as triangles and quadrangles (polygons) and sends them to the drawing device. The drawing device interprets the draw commands and draws the figures in the frame buffer.
In computer graphics systems, the pixel data (throughout this specification, such data is constituted by, for example, data of three primary colors) of the image which has been previously displayed is mixed with the pixel data of the next image to be drawn in a predetermined ratio to perform a semitransparent process. The semitransparent process is performed by a drawing device, and a semi-transparent process portion of a drawing device has been configured as shown in
FIG. 11
in the prior art.
In
FIG. 11
,
10
designates a frame buffer and
20
designates a drawing device. The drawing device
20
includes a mixing circuit
21
for a semitransparent process, a read circuit
22
for reading pixel data from the frame buffer
10
, a write circuit
23
for writing pixel data in the frame buffer
10
, a draw command decoding portion
24
for decoding a draw command transmitted to the drawing device
20
, an image generation circuit
25
for generating an image in accordance with the draw command decoded by the draw command decoding portion
24
, a mixing ratio memory
26
, and a control portion
27
for controlling the transparent process as a whole.
A draw command includes the data of mixing ratios which is extracted by the draw command decoding portion
24
and is stored in the mixing ratio memory
26
. The mixing ratio memory
26
stores the mixing ratio for each of pixels which constitute the image generated. by the image generation portion
25
based on drawn pixel position information supplied by the image generation portion
25
.
The semitransparent process is performed as follows. The read circuit
22
reads the previous pixel data Vm in the pixel position in which drawing is to be performed from the frame buffer
10
and supplies the data to the mixing circuit
21
. Data Vc for the pixel to be newly drawn is supplied from the image generation portion
25
to the mixing circuit
21
. The mixing ratio a for the pixel to be newly drawn is read from the mixing ratio memory
26
and is supplied to the mixing circuit
21
.
In the mixing circuit
21
, the pixel data Vm and Vc are mixed in the mixing ratio &agr;. Specifically, mixed output pixel data Vo is obtained from a calculation:
(1−&agr;)
Vm+&agr;Vc=Vo
The pixel data as a result of the mixing is written back in the same address as that of the read pixel data Vm in the frame buffer
10
as described above by the write circuit
23
.
At this time, the color of the previous pixel remains on the new pixel in accordance with the mixing ratio &agr; and is displayed as a semitransparent color. If the mixing ratio &agr;=1, the color is fully opaque and, if the mixing ratio &agr;=0, the color is fully transparent.
The applicant has made the following Japanese patent applications which are related to the drawing device according to this application.
05-190763 (filed on Jun. 30, 1993)
05-190764 (filed on Jul. 2, 1993)
05-258625 (filed on Oct. 15, 1993)
06-027405 (filed on Jan. 31, 1994)
Each of the above applications is owned by the assignee of the present invention and is hereby incorporated by reference. (Applications for U.S. patent corresponding to these four Japanese patent applications are pending.)
As described above, in the conventional semitransparent process, a draw command includes the values of mixing ratios &agr; based on which a mixing ratio &agr; is stored in the mixing ratio memory
26
for each pixel. Therefore, when the mixing ratios are minutely set, the number of bits required for the mixing ratios &agr; becomes large. This results in an increase in the amount of data of a draw command which necessitates an increase in the capacity of the mixing ratio memory
26
.
In order to simplify the configuration of a drawing device, it is desirable to have the capability of the full transparent and full opaque processes included in the semitransparent process. As described above, however, in the semitransparent process, three steps of processing, i.e., reading from the frame buffer
10
, mixing, and writing back in the frame buffer
10
, must be performed for each pixel, and this results in a problem in that the processing time becomes relatively long.
It is an object of the present invention to provide an image generation apparatus which does not necessitate an increase in the amount of data of a draw command and which can employ a mixing ratio memory of a small capacity.
It is another object of the present invention to provide an image generation apparatus capable of performing full transparent and full opaque processes utilizing a semitransparent process at high speed.
SUMMARY OF THE INVENTION
In order to solve the above-described problem, according to the present invention, there is provided an image generation apparatus wherein draw commands generated by a CPU
42
are transferred to a drawing device portion
61
which generates an image on a frame buffer
63
by performing drawing sequentially in accordance with the draw commands, the drawing device portion
61
comprising a read means
102
for reading the pixel data of the image which has been previously drawn from the frame buffer
63
, a mixing circuit
101
for mixing the pixel data read from the frame buffer
63
and the pixel data of the corresponding position where the next drawing operation is to be performed in a specified mixing ratio, a write means
103
for writing pixel data as a result of the mixing at the mixing circuit
101
in the corresponding pixel position in the frame buffer
63
, a mixing ratio memory portion
106
for storing a plurality of the mixing ratios, and a selection means
107
for selecting the mixing ratio to be supplied to the mixing circuit
101
from the mixing ratio memory portion
106
according to mixing ratio selection information included in the draw command.
According to another aspect of the present invention, there is provided an image generation apparatus wherein draw commands generated by a CPU
42
are transferred to a drawing device portion
61
which generates an image on a frame buffer
63
by performing drawing sequentially in accordance with the draw commands, the drawing device portion
61
comprising a means
102
for reading the pixel data of the image which has been previously drawn from the frame buffer
63
, a mixing circuit
101
for mixing the pixel data read from the frame buffer
63
and the pixel data of the corresponding position where the next drawing operation is to be performed in a specified mixing ratio,
Furuhashi Makoto
Suzuoki Masakazu
Tanaka Masayoshi
Yutaka Teiji
Lerner David Littenberg Krumholz & Mentlik LLP
Nguyen Phu K.
Sony Computer Entertainment Inc.
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