JPH0734232B2 - Clipping device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clipping device of a graphic display device for displaying a polygon (hereinafter referred to as a polygon) forming a three-dimensional polyhedron on a two-dimensional screen while performing smooth shading. is there.

2. Description of the Related Art In a graphic display device in which an object defined in three dimensions is approximated to a polyhedron, and then coordinate conversion is performed to display it on a two-dimensional screen, the brightness of a display polygon is smoothly changed to give a stereoscopic effect. A so-called smooth shading method is sometimes used.

As for this smooth shading method, the method of Phong is
BT Phone, "Illumination for Computer Generated Pictures", Communications of
The ACM, 18 (6), July 1975, pp. 311-317.

FIG. 2 is a diagram for explaining the principle of this smooth shading method. First, the normal vectors ▲ ▼, ▲ ▼, ▲ ▼ given to each vertex of the polygon are linearly interpolated with respect to the ridge, and then the normal vectors ▲ ▼ and ▲ ▼ of the points where the ridge intersects the raster scan line are further linearly interpolated. Then, the normal vector ▲ ▼ of an arbitrary pixel is calculated. The brightness of the pixel can be calculated from the normal vector thus obtained, the position of the light source, and the position of the viewpoint. According to this method of Phong, a reflection effect such as specular reflection can be expressed and a realistic image can be obtained.

When displaying the polygon data on the three-dimensional coordinates defined in the database on the entire surface of the two-dimensional screen or in the rectangular window, a process called clipping is necessary in order to prevent the portion outside the display area from being displayed. Clipping means that when polygon vertex rows (P0, P1, P2 in Fig. 3) are sequentially input, and there is a point outside the display area, such as point P1, this portion is clipped and the result is Output the vertex sequence (P0, Pa, Pb, P2 ...) of the conventional clipping device, JF Brin et al.
"Clipping Using Homogeneous Coordinations", ACM, SIGGRAPH, Computer Graphics, 12 (3),
August 1978, pp.245-251, and further detailed in Fujio Yamaguchi, "Graphic Processing Engineering by Computer Display", Nikkan Kogyosha, 4.3.5 (pp.156-160), 1981. There is.

FIG. 4 is a diagram showing a processing flow of a conventional clipping device in consideration of performing smooth shading at the time of display. The clipping process is generally a method of calculating the intersection with one boundary surface at a time, and FIG. 4 shows the clipping process by the boundary surface of X / W = 1 in FIG. 3 (a) (see FIG. b)).

When the coordinates of the points P0 and P1 are given, the intersection of the straight line connecting them and the boundary surface X / W = 1 (that is, X−W = 0) is ▲ ▼ = ▲ ▼ + t ・ (▲ ▼-▲ ▼) However, it can be calculated by t = (X0−W0) / {(X0−W0) − (X1−W1)}, and once division is performed to obtain t, the addition and subtraction operations are then performed. The coordinate value of the intersection point Pa is calculated. At this time, the normal vector Na at the point Pa can be calculated by ▲ ▼ = ▲ ▼ + t ・ (▲ ▼-▲ ▼) from the nature of the above-mentioned linear interpolation, and the intersection point Pa is also calculated by addition / subtraction multiplication using t. The normal vector Na of can be calculated.
Therefore, it is suitable for processing by a sequential processor.

Problems to be Solved by the Invention However, in the above-mentioned configuration, since it is a sequential process and division is required even though it is performed once for each clipping process on one plane, there is a limit to the speeding up of the process. Had a point.

In view of such a point, the present invention provides a high-speed clipping device which is configured only by a subtraction (or addition) and a multiplication circuit, executes a clipping process in a pipeline, and can handle vertex normal information. With the goal.

Means for Solving Problems According to the present invention, a vector (X, Y, Z, Nx, Ny, Nz, W) in which not only the vertex coordinates of a polygon but also normal information of the vertex position is represented in a homogeneous coordinate system.
, A means for inputting in the order in which the vertices are connected, a subtracter (adder) for calculating the difference (or sum) between W and one of X, Y, and Z of the input vectors, and The first and second registers that sequentially latch the results output from the subtractor (adder) for the two vertices, and the consecutive two vertices to the subtracter (adder) of the input vector. First and second vector registers for sequentially latching six elements other than one of the two input coordinate values, contents of the second register and contents of the first vector register, and the first register And a vector subtractor that calculates the difference between the two multiplication results output from the vector multiplier, and serves as a boundary of the visible region. Chestnut And ping plane, with the intersection coordinates of the ridge line of the polygon, a clipping device also sequentially outputs the normal vector information of the intersection.

With the above-described structure, the present invention inputs the coordinates of the apex sequence of polygons and the vector having the normal line information as elements, and the coordinates and the normal line of the intersection of one gripping boundary surface and the ridge line of the polygon are input. Calculate information one after another.

Practical Example FIG. 1 is a block diagram showing a clipping device in an example of the present invention. The present embodiment is a clipping device that performs clipping by the boundary surface X / W = 1. In FIG. 1, 1 and 2 are registers, 3 to 8 are first vector registers, 9 to 14 are second vector registers, and 16 to 21 are first vectors.
Vector multiplier, 22 to 27 are second vector multipliers, 28
~ 33 is a vector subtractor.

The operation of the clipping device of the present embodiment configured as described above will be described below. Fig. 1 is the same as Fig. 3
This is a device that clips a polygon on a dimensional coordinate at the boundary plane X / W = 1, and the coordinates and normal information of the vertex sequence P0, P1, P2 of the polygon are vectors (X, Y, Z, Nx, Ny, Nz). , W) supplied from the outside.

Subtractor 15 calculates (X-W) and stores the result in register 1
Latch to. In the same cycle as this, input values (X, Y, Z, N
x, Ny, Nz) are latched in vector registers 3-8. The register 2 and the vector registers 9 to 14 latch the contents of the register 1 and the vector registers 3 to 8 one cycle later. FIG. 1 shows a state in which the coordinates / normal vectors of the first two points P0 and P1 of the vertex series have been input. That is, (X1
-W1) and (X0-X1), and (X1, Y1, Z1, Nx1, Ny1, Nz1) in vector registers 3-8 and vector registers 9-14.
And (X0, Y0, Z0, Nx0, Ny0, Nz0) are stored.

Multipliers 16 to 21 multiply the contents of vector registers 3 to 8 with the contents of register 2, and multipliers 22 to 27 similarly output the result of multiplying the contents of vector registers 9 to 14 with the contents of register 1. The subtracters 28 to 33 output the results of subtracting the output results of the multipliers 22 to 27 from the output results of the multipliers 16 to 21. This output value is now And this is That is, Is. In the homogeneous coordinate system, the same coordinate points are represented even if all vector elements are multiplied by the same value. Is However, it can be modified as t = (X0-W0) / {(X0-W0)-(X1-W1)} and is equivalent to the arithmetic expression shown in the conventional example. Therefore, it is output from the clipping device of the present invention. Is nothing but P, N.

In the next cycle register 1 and vector registers 3-8
Contents (X1-W1), X1, Y1, Z1, Nx1, Ny1, Nz1 are moved to register 2 and vector registers 9-14 respectively, and register 1
And vector registers 3 to 8 are newly added (X2 to W2), X2, Y
2, Z2, Nx2, Ny2, Nz2 are loaded respectively, and the clipping device of this embodiment uses the vector of the coordinates and the normal line of the intersection point Pb of the edge connecting the points P1 and P2 in FIG. 3 (b) and the clipping boundary surface. Is output.

If both connected two vertices exist inside or outside the boundary surface, that is, if the signs of the values stored in register 1 and register 2 are the same, the output result is not required and this output is rejected. do it.

In the above description, the value loaded into one of the vector registers 3 is X, but the other input to the subtractor 15, W, may be used, and the same result will be shown below. That is, the result obtained with such a substitution is Equation (1) can be derived by modifying this.

As described above, according to the present embodiment, by providing the vector register for the pipeline, the pipeline register for flowing (X-W) in the reverse direction, the vector multiplier, and the vector subtractor, the normal information of the vertex can be obtained. The included clipping processing can be executed at high speed in a pipeline manner.

Although the method of calculating the intersection with the boundary surface X / W = 1 has been described in the above embodiments, when calculating the intersection with X / W = -1, X + W is calculated instead of the subtractor. Adder, or the subtractor may be omitted at the intersection with X / W = 0. If you connect Y instead of X,
The intersections with Y / W = 1, Y / W = −1, Y / W = 0 can also be obtained, and the same applies to Z. It goes without saying that the result of clipping in the cubic region can be obtained by connecting in series a plurality of clipping devices of the present invention corresponding to six different boundary surfaces.

Further, although two vector multipliers are provided in the above embodiments, only one vector multiplier may be provided to perform the same calculation by time division.

EFFECTS OF THE INVENTION As described above, according to the present invention, clipping processing including vertex normal information can be executed at high speed by pipelined hardware, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a clipping device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of smooth shading, FIG. 3 is an explanatory diagram of clipping processing, and FIG. 4 is a processing flow diagram of a conventional clipping device. Is. 3-14 ... Vector register, 16-27 ... Vector multiplier, 28-33 ... Vector subtractor.

Claims (2)

[Claims] 1. In a graphic display device for displaying a three-dimensional polyhedral object on a two-dimensional screen, a vector (X, X, which represents the vertex coordinates of polygons forming the polyhedron as well as the normal information of the vertex positions in a homogeneous coordinate system. Y, Z, Nx, Ny, Nz, W) and means for inputting in the order in which the vertices are connected, and a subtracter for calculating the difference between W and one of X, Y, Z of the above input vectors. And the first and second registers that sequentially latch the results output from the subtractor for two consecutive vertices, and the two coordinates input to the subtractor in the input vector for the two consecutive vertices. First and second vector registers for sequentially latching six elements except one of the values, contents of the second register and contents of the first vector register, and contents of the first register and the first register. The contents of vector register 2 And a vector multiplier calculated to,
A vector subtractor for calculating a difference between two multiplication results output from the vector multiplier, and a clipping plane serving as a boundary of a visible region and an intersection point coordinate of ridge lines of polygons forming the polyhedron, and an intersection point A clipping device that also outputs normal information in sequence. 2. A graphic display device for displaying a three-dimensional polyhedron object on a two-dimensional screen, wherein a vector (X, X, which represents the vertex coordinates of polygons forming the polyhedron as well as the normal information of the vertex positions in a homogeneous coordinate system). Y, Z, Nx, Ny, Nz, W) and means for inputting in the order in which the vertices are connected, and an adder for calculating the sum of W and one of X, Y, Z of the above input vectors And first and second registers that sequentially latch the results output from the adder for two consecutive vertices, and the two coordinates of the two input vertices that are input to the adder in the input vector. First and second vector registers for sequentially latching six elements except one of the values, contents of the second register and contents of the first vector register, and contents of the first register and the first register. The contents of vector register 2 And a vector multiplier calculated to,
A vector subtractor for calculating a difference between two multiplication results output from the vector multiplier, and a clipping plane serving as a boundary of a visible region and an intersection point coordinate of ridge lines of polygons forming the polyhedron, and an intersection point A clipping device that also outputs normal information in sequence.