JP2952585B1 - Image generation method - Google Patents

Abstract

An object of the present invention is to generate and display an image at high speed by extending a Z-buffer algorithm to reflection and refraction transmission when an object color is determined by a viewpoint and a positional relationship with another object. Make it an issue. SOLUTION: Specular reflection light vector 5 of object 1
Alternatively, the virtual screen 2 is provided so as to intersect orthogonally with the refracted transmitted light vector 7, the scene ahead of the vector is projected on the virtual screen 2 by the Z-buffer method, and the color of the projected image 10 is projected on the object 1. And add colors. Then, the color-added object 1 is displayed on the display 3 by the Z-buffer method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to computer graphics for displaying three-dimensionally input object data on a two-dimensional display, and more particularly to an image generation method in which the Z-buffer method is extended to reflection or refraction transmission light. About.

[0002]

2. Description of the Related Art As a so-called rendering method for displaying an object generated by three-dimensional computer graphics on a two-dimensional display, a scan line method, a ray tracing method, a Z buffer method and the like are well known. The scanline method examines the intersection of the viewpoint and the plane (scanline plane) containing the ray of light (scanline) on the display for an object displayed as a set of polygons (polygonal planes), This is a method in which erasure calculation is performed and colors of pixels on a display are determined one after another. The ray tracing method is a method in which light rays (rays) are reversely traced from the viewpoint to all the pixels on the display, and the color of the object in the scene is set to the pixel color.
Shading, reflection and refraction transmission calculations are performed simultaneously. The Z-buffer method is a method of calculating the depth of all objects (polygons) on a scene, and erasing the hidden surface by successively repainting the pixels in units of pixels. In addition, there are cases in which these methods are used alone to display on a two-dimensional display, and methods in which a part of the methods are changed and displayed as another method have been devised.

[0003]

However, the scan line method described above requires only a small amount of calculation because the calculation is performed only based on the relationship between the scan line and the polygon, so that relatively high-speed display is possible. Since the information obtained is only the proximity of the polygon on each scan line plane, it cannot deal with reflection / refraction or shadowing.

The ray tracing method is capable of displaying shadows and reflections, and displaying a translucent body, and is capable of coping with reflection and refraction. Therefore, a high-quality image can be generated. Since the intersection of a ray and an object is calculated and hidden surface elimination, shadowing, reflection, refraction, and transmission are calculated by the same algorithm, an enormous amount of calculation processing is required, and much processing time is required. The Z-buffer method has a simple algorithm and can perform high-speed processing with a small amount of time spent for calculation processing. However, since it is an algorithm using a mere overwriting principle, reflection, refraction, transmission, and shadowing can be performed. Can not.

[0005] As described above, each rendering algorithm has unique characteristics. Among them, the Z-buffer algorithm is merely a hidden surface elimination for judging the front and rear of a pixel based on the distance in the Z direction which is the depth of the object, and therefore, the reflection and refraction generated by the relationship between a plurality of objects and the viewpoint are used. Although no color can be represented, the intersection calculation found in the ray tracing method is not performed, so that the algorithm is simple and continuous processing is possible within the range of the pixel occupied by the object (or polygon).

Accordingly, the present invention focuses on the continuity, simplicity, and high speed of such processing, which are features of the Z-buffer method. When determined by the formula, an object is to generate an image by extending it to reflection, refraction, and transmission, and to display the image on a display.

[0007]

According to a first aspect of the present invention, there is provided an image generating method for displaying an object input three-dimensionally on a display, comprising: an environment light component and a diffuse reflection light component. A first step of calculating a basic color of each part of the object according to the above, a second step of providing a virtual screen on a plane orthogonal to a specular reflected light vector or a refracted transmitted light vector of the object, and A third step of displaying the scene ahead of the specular reflected light vector or the refracted transmitted light vector by the Z-buffer method, and projecting the color displayed on the virtual screen onto the object,
A fourth step of adding the basic color, and a fifth step of performing hidden surface removal processing on the added object by the Z-buffer method based on the display and displaying the result on the display. For objects having two or more specular reflected light or refracted transmitted light, the constituent surfaces of the object are grouped based on the similarity of the specular reflected light vector or refracted transmitted light vector, and a virtual screen is created for each group. Features.

[0008]

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart of an image generation method according to the present invention, and generates an image for an object input three-dimensionally according to the following flow. First, in step 1 (S1), among the colors of the object, the environment light component and the diffuse reflection light component are calculated, and the basic color of the object is obtained. Regarding the ambient light component, besides setting a constant value at any point on the object, if a plurality of objects influence each other, a known radiosity method or the like is used to perform complex secondary reflection between the objects. A method of adding a shadow may be used. For the diffuse reflection light component, the radiosity method may be used. Alternatively, for example, calculation may be performed by connecting a vertex of a polygon to a light source with a half line and determining whether there is an intersection with another polygon. Can be.

Next, in S2, it is determined whether or not the material of the object is specular reflection or refraction transmission. If the object is specular reflection or refraction transmission, the process proceeds to S3. In S3, the components are grouped. This is performed for an object that reflects or refracts and transmits in various directions as shown in FIG. 2 or an object composed of a plurality of objects, and is a specular reflection light vector or a refraction transmission light vector (hereinafter referred to as a reflection or transmission vector). Do)
Of these, the processing is performed to group constituent surfaces having vectors in similar directions and perform batch processing. By doing so, processing can be performed smoothly, and processing time can be reduced. In FIG. 2, 1 is an object, 4 is a normal vector, 5 is a specular reflection vector, 6 is a line-of-sight vector, 7 is a refraction transmission vector, and constituent planes are A and B similar to the normal vector 4. , C plane. However, if there is no vector in a similar direction, there is no need to perform grouping.

This grouping may be performed, for example, as follows. Assuming that the normal vectors of each component of the object are ω = (p, q, r) where ω = 1, A and B are defined for all the normal vectors by the following equation (1). Then, if the group is divided into m groups according to the size of A and n groups according to the size of B, the normal vectors can be divided into m × n groups as a whole. Note that the degree of division of A and B may be set so that m and n are appropriate numbers each time.

[0012]

(Equation 1)

Next, at step S4, a virtual screen orthogonal to the specular reflected light vector or the refracted transmitted light vector is provided. This virtual screen may be provided so as to be one surface of a rectangular parallelepiped or a polyhedron containing the object. Then, a coordinate system based on the virtual screen is set. In step S5, the coordinates of other objects or the like existing in the direction of the reflection or refraction vector are converted in the virtual screen coordinate system. In step S6, the reflection calculation of the scene in which these coordinates are converted is performed on the virtual screen by the Z-buffer calculation. .

In step S7, the image projected on the virtual screen is added to the component of the object to which the corresponding vector belongs by projecting it by orthographic projection or the like.
In addition, with respect to those processed in a group, the colors may be projected and added to the components to which the individual vectors belong.

FIG. 3 shows an example in which a virtual screen 2 orthogonal to the specular reflection light vector 5 is provided and a glass (reflection object 13) serving as a reflection source is projected, and FIG. In the case of a cylindrical shape, (b) shows a case where the object is a convex curved body. FIG.
Now, the reflection object 13 in front of the virtual screen 2
Are determined by setting four end points on the object 1 and using the four end reflection vectors 5a as they are in the four corners of the virtual screen 2, The image (color) reflected at that angle is projected onto the object 1 by orthographic projection.

The viewing angle of the virtual screen 2 may be obtained mechanically from the specular reflection vector 5 or the refraction transmission vector 7, or may be obtained by averaging four end points or a plurality of vectors. In addition, the size of the virtual screen 2 or the distribution and density of pixels may be arbitrarily set according to the size of the object, the degree of complexity of the surface, and the importance of the object in the scene.
Automatic calculation may be performed based on the ratio of the virtual screen to the final display surface or the like. In FIG. 3, 9 is a viewpoint,
10 is a projected image on the virtual screen, 11 is a projected image of the projected image 10 projected on the object 1,
12 is a line of sight.

When a plurality of groups are provided or when there are a plurality of types of reflection or refraction vectors, the above-mentioned S is used.
Steps 4 to S7 are executed for each group or each vector by imagining a rectangular parallelepiped or the like that includes them and providing and executing virtual screens, and projecting the obtained colors of each virtual screen to the constituent parts to which the group belongs. I just need.

In S8, hidden surface elimination processing is performed using the Z-buffer method in the original screen coordinate system based on the color of the object obtained and added by the above calculation processing, and the result is stored in the frame buffer. . And finally in S9,
Display the contents of the frame buffer on the display.

As described above, the color of the object is determined by adding and mixing the environment light component, the diffuse reflection light component, the specular reflection light component, and the refraction transmission light component, and the color displayed on the display exists in the virtual space. Can be obtained by calculating the color of the entire scene to be deleted and then removing the hidden surface.
By using the buffer method, it is possible to generate a high-quality image in consideration of specular reflection and refraction transmission.

At first glance, this method looks inefficient compared to a method of calculating only the color of a visible object, such as a ray tracing method. However, an object that cannot be seen is never produced, and the color calculation is not performed. If the result of (1) is the value of the object, for example, the value of the vertex of each polygon, or in the case of a large polygon, the polygon is subdivided into small polygons and held as the values of the vertices of the small polygon, the viewpoint moves in the virtual space In that case, the result can be used, so it is not inefficient as a whole. This is because if the result of the color calculation is stored separately for components that do not depend on the viewpoint, such as the ambient light component and the diffuse reflection light component, and components that depend on the viewpoint, such as the specular reflection light component and the refraction transmission light component, the viewpoint calculation can be performed. In the case of movement, only the latter needs to be calculated and only the former addition processing needs to be performed.

Since the Z-buffer algorithm originally performs high-speed calculations, the overall processing time can be reduced. Further, since this display method is a Z-buffer method, it can be executed using the conventional hardware capable of performing image processing by the Z-buffer method as it is, or a known hardware accelerator which is commercially available can be used. If so, each step of S6 and S8 in FIG. 1 can be further processed at high speed, which is an extremely practical image generation method.

When a part of the object, such as the shape or specular reflection, is a part of the object, the virtual screen does not necessarily need to be provided as an image of a cube having a size encompassing the entire object. The method of grouping and the number of groups may be arbitrarily specified, but may be automatically determined based on the number of polygons constituting the object.

[0023]

As described in detail above, according to the first aspect of the present invention, the processing time can be shortened by using the Z-buffer algorithm for performing high-speed processing, and the invention can cope with reflected and refracted light. Therefore, a higher quality image can be provided as compared with the existing Z buffer method.

Furthermore, even if the shape of the object is complicated, or if the object is composed of a plurality of objects, it can be processed smoothly.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a virtual screen.

FIG. 3 is an explanatory diagram of grouping.

[Explanation of symbols]

1. Object 2. Virtual screen 3. Display 5. Specular reflected light vector 7. Refracted transmitted light vector 9. View point 10. Projected image 1
1. Projection image.

Continuation of the front page (56) References JP-A-5-46782 (JP, A) JP-A-5-303652 (JP, A) JP-A-5-46780 (JP, A) JP-A-4-10178 (JP, A) , A) JP-A-1-224886 (JP, A) Kawabata et al., "High-speed image generation method using multi-pass rendering method", Information Processing Society of Japan Research Report, Information Processing Society of Japan, July 24, 1992, Vol. 92, No. 62 (Graphics and CAD 57-6), pp. 39-46 Shiono et al., “A Technique for Environmental Mapping”, Proc. Of the 42nd National Convention of IPSJ, IPSJ, February 25, 1991. , P. 2-287 to 2-288 (58) Fields surveyed (Int. Cl. ⁶ , DB name) G06T 15/50 G06T 15/40 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An image generation method for displaying a three-dimensionally input object on a display, comprising: a first step of calculating a basic color of each part of the object using an ambient light component and a diffuse reflection light component; A second step of providing a virtual screen on a plane orthogonal to the specular reflected light vector or the refracted transmitted light vector, and a Z-buffer method for setting a scene in front of the corresponding specular reflected light vector or refracted transmitted light vector on the virtual screen. A third step of projecting the color displayed on the virtual screen onto the object, and adding the basic color to the basic color; and displaying the display with respect to the added object. A fifth step of performing hidden surface removal processing by the Z-buffer method based on the reference and displaying the result on the display An object having two or more specular reflected light or refracted transmitted light groups the constituent surfaces of the object based on the similarity of the specular reflected light vector or refracted transmitted light vector, and creates a virtual screen for each group. Image generation method.