JP3644460B2 - Von shading circuit - Google Patents

Description

The present invention relates to hardware implementation of a phone shading model, which is known as one of computer graphics rendering technologies considering light sources, and is used in a computer graphics video high-speed generation device. .
[0001]
[Conventional technology]
Conventionally, a method for realizing phone shading by hardware is disclosed in Japanese Patent Application No. 4-255313. In this method, the surface inclination (normal vector) and the incident angle from the light source are defined by two components, the horizontal and vertical angles with respect to the viewpoint coordinate axis, and diffusion and specular reflection are simultaneously performed independently for each component. In the storage element, these independent gradient components are synthesized by averaging and final data is obtained. Since diffusion and specular reflection calculations were obtained for each of these components using a set of memory elements, the circuit was suitable for LSI implementation. On the other hand, in the von shading model, the reflected light Ip to be obtained is defined as the sum of the diffuse component and the specular reflection component. Conventionally, as described above, the horizontal component Iph and the vertical component Ipv are obtained for each component in order to obtain this Ip. However, the diffusion and specular reflection components in one table are obtained simultaneously for each inclination component, and the method of averaging and combining them is a specific inclination condition (one is close to 0 ° and the other is close to 90 °). This results in an error with respect to the value obtained from the true phone shading model. An object of the present invention is to provide a circuit for minimizing this error.
[0002]
[Means for solving problems]
In the present invention, a new mathematical model is defined in which the inclination of the surface is defined by two components, Nh and Nv, horizontal and vertical, while the variables form the function terms independently from each other in the equation from the von shading model. As a result, each function term is calculated by using a storage element in which the range of the input variable is within one variable, and the diffusion term component and the specular reflection component are obtained using a multiplier and an adder. It is. This mathematical model is expressed as follows. The direction cosine cos θ is cos θ = cos Nv {cos Lv [cos (Lh−Nh) −1]} + cos (Lv−Nv) (1) with respect to the angle θ between the light source incident angle and the normal vector of the surface.
Here, Lh and Lv represent the incident angle from the light source as horizontal Lh and vertical angle Lv components with respect to the viewpoint coordinate axis. Further, regarding the difference α between the viewpoint axis and the reflection angle, cos α = 2 cos Nh · cos Nv · cos θ−cos Lh · cos Lv
Or cos α≈ (cos θ + cos NH · cos Nv) / 2 (2)
It becomes. Here, since the incident angles Lh and Lv of the light from the light source are unique for each frame and can be regarded as a constant value in terms of the circuit configuration, each triangular function term in the equations (1) and (2) is one each. It is established with input variables. That is, when the function values are tabulated in the ROM, the addresses remain within one variable range such as Nh or Nv. Reflected light Ip by the von shading model is Id = Id · cos θ + Ir · cos ⁿ α (3) ^where Id is the diffusion coefficient, Ir is the specular reflection coefficient, and n is the reflectance.
The Ip value can be easily obtained by performing trigonometric function conversion with a storage element from the equations (1), (2) and (3), and multiplying and adding using a multiplication and addition circuit. (Cos α) ^{n is} also converted by a memory element having cos α as an address. As is clear from the equations (1), (2) and (3), the feature of the present invention is that the reflected light Ip by the von shading model is received at each point by the storage element, multiplier and adder using the normal of the curved surface as input. It can be obtained within one clock every time. The calculation delay is only the switching speed of each circuit element, and a plurality of clocks are not required for each calculation.
[0003]
[Example]
FIG. 1 shows a fogging circuit according to the present invention based on the above equations (1), (2) and (3). The input variables of the circuit are the slopes Nh and Nv of the curved surface defined by the horizontal and vertical angles, respectively. Direction cosines cos θ and cos α are generated. The storage element 1 stores cosLv [cos (Lh−Nh) −1], the storage elements 2 and 4 store cosNv and cosNh, respectively, and the storage element 3 stores cos (Lv−Nv). The storage elements 2 and 4 are usually constituted by a ROM (Read only Memory) 1 and 3 by a RAM (Random Access Memory). As is clear from the variable of the triangular function, each of them has only one of the surface inclination components Nh and Nv, and the other is constant. This means that the capacity of the triangular function RAM or ROM is within the range that one input variable can take, and the capacity can be reduced. In FIG. 1, cos θ is obtained at the output of the adder 6a and cos α is obtained at the adder 6b by hardware implementation of the equation (2). 1/2 in the figure means 1-bit shift down of the connection. The diffusion component is multiplied by the coefficient Id and cos θ by the multiplier 5c, while the specular reflection component is passed through the storage element RAM 7 for generating cos ⁿ α using the specular reflectance n and then multiplied by the reflection coefficient Ir by the multiplier 5d. Get by multiplication. From the above, the final luminance Ip can be obtained by adding Id · cos θ and Ir · cos ⁿ α by the adder 6c based on the equation (3).
[0004]
[The invention's effect]
According to the present invention, a hardware circuit of a von shading model with a small calculation error can be configured. As a result, it is possible to display a three-dimensional object having a highlighting effect in real time, and it plays an important role in the technology for realizing virtual reality by computer graphics.
[Brief description of figure]
FIG. 1 shows a phone shading circuit according to the present invention.
1 cosLv [cos (Lh-Nh) -1] storage element 2 cosNv storage element 3 cos (Lv-Nv) storage element 4 cosNh storage element 5a, 5b, 5c, 5d multipliers 6a, 6b, 6c adder 7 cos ⁿ α memory element

Claims (1)

The normal vector and the light source incident angle on the curved surface are defined as the horizontal and vertical angles with respect to the viewpoint coordinate axis, respectively, and the horizontal and vertical angles are determined in the von shading circuit that calculates the diffuse and specular reflection light using the normal vector of the surface as the input variable. As a means to obtain the diffuse light component and the specular reflection component from the surface inclination and incidence angle, and the cosine of the viewing axis and the reflection angle, respectively, using an independent storage element for each input variable Is a phone shading circuit which passes through a specular reflectance conversion circuit comprising a memory element and then multiplies the specular reflection coefficient and diffused light by the diffusion coefficient and adds these two components to obtain reflected light.

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