JP2001005996A - Graphic data processor in ray tracing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smooth the luminance change of curved surfaces approximated by a plurality of polygons and to prevent the boundaries of the polygons from being conspicuous in ray tracing. SOLUTION: A viewpoint is set, a ray generating part 10 generates a ray passing through pixels on a screen from the viewpoint, an intersection calculating part 12 calculates the intersection of the ray and a polygon, an interpolation vector calculating part 14 allocates a temporary vector on each vertex of the polygon, interpolates the vector and calculates an interpolation vector. A luminance calculating part 16 calculates the luminance on the intersection from the interpolation vector and defines the luminance as the luminance of a pixel on the screen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphic display device for calculating the luminance to be drawn on a pixel on a screen and performing shading (shading) when displaying a three-dimensional graphic in two dimensions using ray tracing. The present invention relates to a graphic data processing device in ray tracing to be used.

[0002]

2. Description of the Related Art Three-dimensional computer graphics (C)
As a general method of expressing a curved surface in G), a method of approximating a three-dimensional figure by a plurality of polygons is known.
By projecting these polyhedra on a two-dimensional image, C
A three-dimensional figure is drawn on a screen such as an RT screen.

FIG. 4 is an explanatory diagram of ray tracing.
3 composed of multiple polygons by ray tracing
When a dimensional figure is displayed on a CRT screen or the like, a viewpoint 20 is set at an arbitrary position in a three-dimensional space as shown in FIG. The screen 22 corresponds to a CRT screen. A ray 26 is generated that passes through one square of the screen 22 divided by vertical and horizontal pixels (pixels) 24. A pixel originally represents an element that is two-dimensionally arranged on the screen 22 that displays an image, and can be called a pixel only after an image is drawn. However, in this specification, a pixel that can be called a pixel equivalent position before image drawing is also called a pixel. The intersection point 30 between the ray 26 and the polygon 28 is obtained, the brightness at the intersection point 30 is calculated, and the calculated brightness is set as the brightness of the pixel 24 on the screen 22. Ray 26
Intersects a plurality of polygons 28, the intersection 30 closest to the viewpoint 20 is used.

[0004] In addition to projection onto a two-dimensional image, expression of a three-dimensional effect on a curved surface is performed by calculation of luminance, that is, brightness, such as shading. Generally, a model that considers ambient light, diffuse reflected light, and specular reflected light is used for calculating luminance. FIG. 5 is an explanatory diagram of a vector used for luminance calculation. N is a normal vector of the plane P, L is a unit vector in the direction of the light source, R is a unit vector in the direction of light reflected from the light source,
V is a unit vector in the line-of-sight direction. The incident angle between L and N and the reflection angle between R and N are the same angle θ. The reflectance is K _a , the intensity of ambient light is I _a , the diffuse reflectance is K _d , the intensity of incident light is I _l , the specular reflectance is K _s , and the parameters for determining the spread of the highlight portion are n, When the distance and the attenuation coefficient due to the light distribution and d, using the _{I = K a I a + {} K d I l (L · n) + K s I l (R · V) n} / d ... (1), The luminance I at the point Q on the plane P when there is one light source can be obtained. (L · N) and (R · V) represent the inner product of L and N and the inner product of R and V, respectively.
By considering these luminance calculations for each of R (red), G (green), and B (blue), the color at point Q is determined.

A conventional method of calculating the luminance in ray tracing is to calculate the normal vector of each polygon, and calculate for each polygon using, for example, equation (1) to determine the luminance. It is. For example, the intersection is the surface T _{1 in} FIG.
Brightness on the intersection of the cases in the above can be obtained by substituting the normal vector N ₁ in the formula (1).

FIG. 6 is a schematic diagram showing a configuration of a conventional graphic data processing apparatus in ray tracing. The intersection of the ray and the polygon generated by the ray generation unit 10 is calculated by the intersection calculation unit 12, and the ID of the polygon including the intersection coordinates and the intersection is sent to the luminance calculation unit 16. The luminance calculation section 16 performs luminance calculation and outputs luminance data.

[0007]

In the Z-buffer method, a phon shading method (smooth shading method of phon) or a Gouraud shading method is used for calculating the luminance. However, in a graphic display device that displays a graphic by ray tracing, the normal vector on the intersection used when calculating the luminance at the intersection between the polygon and the ray uses the normal vector of the polygon as it is. Is common. The second term of the expression (1), which is a diffuse reflection component of luminance, includes the inner product of the unit vector L and the normal vector N of the polygon in the direction of the light source, and thus varies depending on the angle between L and N. That is, only one luminance is determined for a plane having only one normal. On the other hand, adjacent polygons have different normal vectors N, and thus have different luminances. Therefore, the curved surface is approximated by a polygon having an intermittent change in luminance at the boundary, and the luminance at the boundary of the polygon changes abruptly, and furthermore, the boundary of the polygon becomes conspicuous due to the Mach band effect.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention provides a graphic data processing apparatus in ray tracing for use in a graphic display apparatus that makes a boundary of a polygon generated on a curved surface approximated by a plurality of polygons inconspicuous. It is intended to be.

[0009]

In order to achieve the above object, according to the present invention, a viewpoint is set, a ray passing from a viewpoint to a pixel on a screen is generated, and an intersection between the ray and a polygon is calculated. Temporary vectors are allocated to each vertex of the polygon, and these temporary vectors are interpolated to calculate an interpolation vector on the intersection, and further, the brightness on the intersection from the interpolation vector is calculated to obtain the pixel brightness and I do.

That is, according to the present invention, a viewpoint is set,
A ray generation unit that generates a ray passing through a pixel on the screen from the viewpoint, an intersection calculation unit that calculates an intersection between the ray and a polygon approximating a three-dimensional figure to be displayed, and each vertex of the polygon An interpolated vector calculation unit that allocates a temporary vector on the top, and calculates the interpolation vector on the intersection by interpolating the temporary vector, and a brightness calculation unit that calculates the brightness on the intersection from the interpolation vector And a luminance data output unit that outputs the luminance as the luminance of the pixel.

It is a preferred embodiment of the present invention that the present invention further provides that a vector obtained by averaging normal vectors of polygons surrounding the vertices is assigned as a temporary vector on the vertex.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a drawing data processing apparatus in ray tracing according to the present invention will be described below with reference to the drawings. FIG. 2 is a flowchart showing an embodiment of the graphic data processing apparatus in ray tracing according to the present invention. Before executing the steps of this flowchart, it is assumed that the surface of the three-dimensional figure has already been approximated by pasting polygons by a conventional method.

In FIG. 2, at step S10, an intersection of a ray and a polygon generated from a ray generation unit on the screen is calculated by an intersection calculation unit, and an intersection coordinate and a polygon including the intersection coordinates are determined. In step S12, step S
A temporary vector is allocated to each vertex of the polygon determined in step 10. In step S14, the temporary vector on each vertex allocated in step S12 is interpolated as a base vector, and an interpolation vector on the coordinates of the intersection in the polygon is obtained. In step S16, the luminance is calculated by the above-described equation (1) using the interpolation vector on the intersection coordinates in the polygon obtained in step S14 as the normal vector N at that point. In step S18, the luminance obtained in step S16 is output as luminance data of a pixel on the screen corresponding to the intersection coordinates. By repeating the process from step S10 to step S18 for each point on the screen, the luminance at all points on the screen can be determined.

FIG. 3 is a schematic diagram for explaining temporary vectors allocated on vertices. This explains the operation of step S12 in FIG. Now, an example will be described in which a temporary vector is assigned to a vertex A when a curved surface is approximated by bonding a plurality of triangles.
The triangles T _{1 to} T ₆ surrounding the vertex A have normal vectors N _{1 to} N ₆ , respectively. The average of the normal vectors N _{1 to} N ₆ is calculated, and the resulting vector is assigned to the vertex A to be a temporary vector N _A. At this time, the temporary vector N _A
Can be obtained by using the normalized normal vectors N _{1 to} N ₆ , and after taking the sum of the normal vectors N _{1 to} N ₆ , the temporary vector N _A is normalized. It is also possible.

The correspondence between the vectors in FIG. 3 and the flowchart in FIG. 2 will be described. Step S12 calculates the average of the normal vectors N ₁ to N ₆ of FIG. 3, in which assigned as the temporary vector N _A on the vertex A. Step S1
For example, when obtaining a normal vector at a point D in T ₁ , the tentative vectors N _B and N _C are obtained for the vertices B and C by performing the same operation as the vertex A, and the tentative vector N _a, N _B, by interpolating the N _C, and calculates the interpolation vector at point D.

FIG. 1 is a schematic diagram showing the configuration of a graphic data processing apparatus in ray tracing according to the present invention. An intersection of the ray and the polygon generated by the ray generation unit 10 is calculated by an intersection calculation unit 12, and the intersection coordinates and the I of the polygon including the intersection are calculated.
D is sent to the interpolation vector calculation unit 14. The interpolation vector calculation unit 14 calculates an interpolation vector at the intersection, and sends it to the luminance calculation unit 16 together with the intersection coordinates and the polygon including the intersection.
The luminance calculation unit performs luminance calculation using the interpolation vector and outputs luminance data.

In the above embodiment, the brightness is calculated by using a calculation formula called a phone model shown in equation (1). However, the brightness may be calculated by using, for example, a Cook model. It is also possible to add a term that takes into account the effects of secondary reflection and the like to equation (1).
It is also possible to omit the inside attenuation coefficient.

[0018]

As described above, according to the present invention,
Set the viewpoint, generate rays passing through the pixels on the screen from the viewpoint, calculate the intersection of the ray and the polygon, assign temporary vectors to each vertex of the polygon, and insert these temporary vectors inside. Interpolation to calculate the interpolation vector on the intersection, and then calculate the brightness on the intersection from the interpolation vector to obtain the brightness of the pixel on the screen, so that the brightness change of the curved surface approximated by multiple polygons is smoothed. Thus, it is possible to realize a graphic data processing device in ray tracing used for a graphic display device that makes the boundaries of polygons inconspicuous.

Further, in addition to the above configuration, if a vector obtained by averaging the normal vectors of the polygons surrounding the vertices is assigned as a temporary vector on the vertices, the boundaries of the polygons can be made less noticeable. A graphic data processing device in ray tracing used for a graphic display device can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a graphic data processing apparatus in ray tracing according to the present invention.

FIG. 2 is a flowchart illustrating an embodiment of a graphic data processing apparatus in ray tracing according to the present invention.

FIG. 3 is a schematic diagram illustrating a temporary vector allocated on each vertex.

FIG. 4 is an explanatory diagram of ray tracing.

FIG. 5 is an explanatory diagram of a vector used for luminance calculation.

FIG. 6 is a schematic diagram showing a configuration of a conventional graphic data processing device in ray tracing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ray generation part 12 Intersection calculation part 14 Interpolation vector calculation part 16 Luminance calculation part 20 Viewpoint 22 Screen 24 Pixel 26 Ray 28 Polygon 30 Intersection

Claims (2)

[Claims] 1. A ray generation unit for setting a viewpoint and generating a ray passing through a pixel on a screen from the viewpoint, and an intersection for calculating an intersection between the ray and a polygon approximating a three-dimensional figure to be displayed. A calculating unit, an interpolating vector calculating unit that allocates a tentative vector on each vertex of the polygon, and calculates an interpolating vector on the intersection by interpolating the tentative vector; A graphic data processing apparatus in ray tracing, comprising: a luminance calculation unit that calculates the luminance described above; and a luminance data output unit that outputs the luminance as the luminance of the pixel. 2. The graphic data processing apparatus according to claim 1, wherein a vector obtained by averaging normal vectors of a polygon surrounding the vertices is assigned as the temporary vector.