JP2002260005A - Image plotting method and program used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image plotting method capable of plotting a natural curved surface without having the possibility of generating clearance between the edges in a boundary part changing in a dividing level. SOLUTION: When plotting an image by dividing a continuous surface such as a water surface and a ground surface into a plurality of curved surfaces mutually different in a polygon dividing level by using a computer, in an adjacent boundary part of the two curved surfaces 1A and 1B mutually different in the dividing level, coordinates are arithmerically operated on the partial apex P1, P3, P5, P7 and P9 among the apexes P1 to P9 of a polygon 2 to be defined on the edge 3B of the higher level side curved surface. The other apexes P2, P4, P6 and P8 are set in the same as the coordinates calculated on the apex adjacent to the same edge to be matched with the number of apparent apexes on the edge of the curved surface different in the dividing level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing an image for expressing a continuous surface such as a ground surface or a water surface by using computer graphics technology.

[0002]

2. Description of the Related Art When expressing a water surface or a terrain using an interpolation surface such as a patch surface, an LO that switches a division level of the surface in accordance with an appropriate condition (for example, a distance from a viewpoint).
A technique called D (abbreviation of Level Of Details) may be used.

[0003]

However, when the division level of a curved surface is dynamically changed by the LOD, the edge of the curved surface is not connected at a portion where the division level is switched, and an unnatural gap may occur.

Accordingly, the present invention provides a method for drawing an image capable of drawing a natural curved surface without a risk of creating a gap between edges at a boundary portion where the division level changes, and a computer program used for realizing the method. The purpose is to:

[0005]

Hereinafter, the present invention will be described. In addition, in order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are added in parentheses, but the present invention is not limited to the illustrated embodiment.

An image drawing method according to the present invention is a method for drawing an image by using a computer to divide a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels. In a boundary portion where two curved surfaces (1A, 1B) different from each other are adjacent to each other, among the vertices (P1 to P9) of the polygon (2) to be defined on the edge (3B) of the curved surface on the higher level side For some vertices (P1, P3, P5, P7, P9), the coordinates are calculated, and for other vertices (P2, P4, P6, P8), the coordinates calculated for adjacent vertices on the same edge are calculated. By setting the same, the number of apparent vertices on the edge of a curved surface having a different level of division is matched.

According to the image drawing method of the present invention, the apparent numbers of vertices defined on the edges of curved surfaces having different division levels match, so that both edges are connected without gaps. Thus, a continuous curved surface can be drawn naturally.

Another image drawing method according to the present invention is a method for drawing an image by using a computer to divide a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels. The level of polygon division on each surface is set so that the number of divisions per unit area is limited to a power of two, and the number of divisions per unit area is not more than two levels apart between adjacent curved surfaces. When two curved surfaces (1A, 1B) having different levels are adjacent to each other, the edge (3) of the curved surface (1B) on the higher level is used.
B) When determining the vertex coordinates of the polygon (2) above, the vertices (P1 to P9) of the polygon that should exist on the edge
Of the vertices (P1, P3, P5, P7, P9) to be defined every other from one end of the edge, and the coordinates of the other vertices (P2, P4, P6, P8) are The coordinates are set to be the same as the coordinates calculated for the adjacent vertices on the edge.

According to this image drawing method, two vertices of a polygon to be defined on an edge of a curved surface having a higher division level are placed at the same position in a portion where curved surfaces having different polygon division levels are adjacent to each other. And the number of vertices on that edge is substantially halved. On the other hand, the number of divisions per unit area in each curved surface is limited to a power of two, and the difference between the division levels between adjacent curved surfaces is within one stage as the number of divisions per unit area, in other words,
The exponent of power of 2 is limited to 1 or less. Therefore, the apparent numbers of vertices respectively defined by the edge of the curved surface having a high division level and the edge of the curved surface having a low division level match, and both edges are connected without a gap. This allows
A continuous curved surface can be drawn naturally.

In the image drawing method of the present invention,
It is desirable that the calculation of the coordinates related to the vertices is performed such that the vertices approximate points on a curved surface to be represented by the polygon.

The program according to the present invention is a program for converting a predetermined continuous surface into a plurality of curved surfaces (1A,
1B) is a program for causing a computer to execute a process of drawing by dividing the two curved surfaces (1A, 1B) having different levels of division from each other. Of the vertices (P1 to P9) of the polygon (2) to be defined on the edge (3B) of the boundary portion of the curved surface, the curved surface (1B) having the higher level of division among the curved surfaces is targeted. Some vertices (P
1, P3, P5, P7, P9), calculate their coordinates, and set the other vertices (P2, P4, P6, P8) to the same as the coordinates calculated for adjacent vertices on the same edge. And causing the computer to execute the procedure of matching the number of apparent vertices on the edge of a curved surface having a different level of division.

Another program of the present invention is a program for causing a computer to execute a process of drawing a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels from each other. A procedure for setting the level of division such that the number of divisions per unit area is limited to a power of two and the number of divisions per unit area does not deviate by two or more levels between adjacent curved surfaces; Two different curved surfaces (1A, 1
B) are adjacent to each other, the curved surface (1
When determining the vertex coordinates of the polygon (2) on the edge (3B) of B), every other vertex (P1 to P9) of the polygon to be present on that edge is counted from one end of the edge. Vertices to be defined (P1, P3, P5, P
7, P9), and calculate the other vertices (P2, P9).
The coordinates of (4, P6, P8) are set to be the same as the coordinates calculated for the vertices adjacent on the edge, and the computer is made to execute the procedure.

By reading and executing these programs by a computer, the image drawing method of the present invention can be implemented.

In the program according to the present invention, the coordinates of the vertices may be calculated such that the vertices approximate a point on a curved surface to be represented by the polygon.

Further, the program of the present invention may be recorded on a storage medium and provided to the user, or may be provided to the user on a wired or wireless transmission medium. In addition,
In the present invention, the apparent number of vertices refers to the number of vertices when the number of vertices is counted by regarding one vertex having the same coordinates as one.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows a polygon model drawn by using the LOD method in order to represent a wavy surface of a water surface as a continuous surface in one embodiment of the present invention. The LOD method is a method of switching a polygon division level based on a predetermined parameter (typically, depth from a viewpoint). The level of polygon division here means the number of divisions of polygons per unit area, that is, the degree of fineness when a model placed in a virtual three-dimensional space is decomposed into polygons. Generally,
Since it is less necessary to display details as the object is seen farther away, drawing is performed with a lower division level as the depth increases. Also in the model of FIG. 1, it can be observed that the division level is set higher on the near side and lower on the back side. FIG. 2 shows a part of FIG. 1 in an enlarged manner, and the boundaries of the division levels are shown by thick lines.

The polygon model shown in FIG. 1 is drawn by interpolating the patch surface 1 shown in FIG.
The patch surface 1 has coordinates of the vertices P01 to P04 of the four corners,
It is defined by a mathematical expression (hereinafter, referred to as a curved surface expression formula) that expresses a curved surface surrounded by them. The vertex coordinates and the surface expression are defined, for example, according to the UV coordinate system set for the patch surface 1. When the polygon model of FIG. 1 is generated, the surface shape of the water surface to be expressed is divided into a number of patch surfaces, and each patch surface 1 is approximately represented by a polygon 2.

In order to express the patch surface 1 as a set of polygons 2, the division level of the patch surface 1 is first determined, and then the UV coordinates of the vertices of the polygon 2 in a number corresponding to the division level are expressed in a curved surface. Determine according to the formula. In the case of performing such division, as apparent from FIG. 2, the number of vertices arranged along the boundary line is different at the boundary where the patch surfaces 1 having different division levels are adjacent to each other. If there is, the polygons 2 are not connected well, and a gap occurs when a texture is pasted on the polygons 2 to generate an unnatural image. In order to avoid such inconvenience, in the present embodiment, the patch surface 1 is divided into polygons 2 under the following conditions.

First, when dividing the patch surface 1 into a plurality of polygons 2 along the direction of each side, the number of divisions per unit area is limited to a power of two. For example, assuming that the patch surface 1 shown in FIG. 3 is equal to the unit area, the patch surface 1 is a power of 2, that is, 1, 2, 4, 8, 1
It is assumed that the polygons 2 are divided by any one of 6, 32,. Further, when the patch surface 1 is divided by, for example, 16 polygons 2, the number of polygon divisions of another patch surface 1 adjacent thereto is within one level with respect to the exponent, that is, 8, 16, or 32. Is limited to any one of the division numbers.

Further, when two patch surfaces having different division levels are adjacent to each other, when determining the vertex coordinates of the polygon on the edge of the patch surface having the higher division level, they should be present on the edge. Calculate the coordinates of the vertices of the polygon vertices that should be defined every other count from one end of the edge, and set the coordinates of the other vertices to be the same as the coordinates calculated for the adjacent vertices on the edge . This will be described with reference to FIG.

FIG. 4 shows a patch surface 1A in which the division level is N, that is, the number of polygon divisions per unit area is set to N.
And a boundary portion between the patch curved surface 1B and the patch surface 1B whose division level is set to N + 1, which is higher by one level. In order to facilitate understanding, the edges 3A and 3B of the curved surfaces 1A and 1B are separated from each other. As illustrated in FIG. 4, the edge 3 of the patch curved surface 1B on the higher division level side
Vertices P1 to P9 are defined in B from one end to the other end. Originally, these vertices P1 to P9 are arranged so as to have an appropriate interval along the edge 3B. However, the edge 3A to be connected to the edge 3B has only vertices defined according to the division level N, and the number is substantially half (strictly, one more than half). Therefore, the vertices P1 to P9
Are arranged at substantially equal intervals along the edge 3B,
Due to the difference in the number of vertices, the edges 3A and 3B are not completely connected, and a gap is left between the polygons 2.

Therefore, in the present embodiment, among the vertices arranged on the edge 3B on the higher division level side, the edge 3
The vertices P2, P4, P6, and P8 to be defined as even numbers counted from the vertex P1 at one end of B are moved to positions that match the immediately preceding vertices P1, P3, P5, and P7. . As a result, the edge 3B has the edge 3
Only the vertices having substantially the same number as A are present, and both are connected without any gap.

Next, a specific procedure for realizing the above-described drawing method will be described with reference to FIGS. Although the image drawing method of the present invention can be used in three-dimensional image processing in various fields, an example in which the drawing method of the present invention is implemented in a game machine using a computer will be described below as an example.

FIG. 5 is a block diagram of a typical control system of a game machine using a computer. As is well known, the game machine 10 as a computer executes a predetermined game in accordance with a game program recorded on a storage medium (for example, a DVD-ROM) 25, and includes a CPU 11 mainly including a microprocessor. A ROM 12 and a RAM 13 as main storage devices for the CPU 11, an image processing device 14 and a sound processing device 16 for performing processing suitable for image processing and sound processing based on an instruction from the CPU 11, and reading data and the like from a storage medium. And a storage medium reading device 18. R
In the OM 12, an operating system as a program necessary for controlling the overall operation of the game machine 10 is written. A DVD-RO as a storage medium is stored in the RAM 13.
The game program and data read from M25 are written as needed.

The image processing device 14 renders a predetermined image on the buffer memory 15 in accordance with an instruction from the CPU 11, converts the rendered image data into a predetermined video reproduction signal, and outputs it to the monitor 19 at a predetermined timing. I do. Depending on the game machine, the image processing device 1
4 may be equipped with a graphics accelerator function for executing an advanced three-dimensional operation, and what kind of processing each of the CPU 11 and the image processing device 14 bears greatly differs depending on the hardware configuration. . Therefore, in the present embodiment, the description will be continued by regarding the CPU 11 and the image processing apparatus 14 as an integrated computer. Although the buffer memory 15 is an example provided in the image processing apparatus 14 as a memory dedicated to drawing, a buffer memory may be secured on the RAM 13 as a main memory.

The sound processing device 16 is a DVD-ROM
The data such as voice and musical sound read from the speaker 25 and the sound source data are reproduced and output from the speaker 20. The reading device 18 is a DVD-ROM according to an instruction from the CPU 11.
It reads the program and data recorded on 25 and outputs a signal corresponding to the read content. DVD-
The ROM 25 stores programs and data necessary for implementing the image drawing method according to the present invention. Monitor 1
9 is a home-use television receiver, and the speaker 20 is a built-in speaker of the television receiver. Further, an input device 22 and an external storage device 23 are connected to the CPU 11 via a bus 24. The external storage device 23 is a rewritable storage device such as a nonvolatile semiconductor memory, a hard disk, and a magneto-optical disk. Such a configuration is merely an example, and the configuration of a computer to which the image drawing method of the present invention is applied may be appropriately changed.

The program recorded on the DVD-ROM 25 as a storage medium includes a module describing a procedure necessary for drawing a surface by dividing it by the above-described method. The data recorded on the DVD-ROM 25 includes, as data necessary for implementing the above-described method, data on polygon models constituting various objects and data on various textures.

A program module for dividing and drawing a patch surface is called up and executed by the CPU 11 when it is necessary to draw a curved surface according to the present invention in the process of generating image data of each frame.
It should be noted that a known technique can be used as it is for the processing other than the part related to the drawing of the curved surface, and the description thereof will be omitted in this specification.

FIG. 6 is a flowchart showing a procedure of processing executed by the computer of the game machine to draw one patch surface 1.

In this processing, based on the shape of the water surface to be drawn in the next frame, each vertex position P01 to P04 (see FIG. 3) which is a control point of the patch surface 1 is determined (step S1). The position of the camera for photographing the water surface is determined (step S2). Subsequently, an appropriate LOD level (level of polygon division) in each patch surface (that is, each patch surface constituting the water surface) is set based on the distance from the viewpoint of the camera (step S3).
At this time, as described above, the level is limited so that the number of divisions per unit area is a power of two.

Next, it is checked whether or not the difference between the LOD levels of adjacent patch surfaces is within 1, and the level is corrected for a portion having a difference of two or more levels, while the level of each patch surface is low. A flag is set for an edge that is a boundary with the patch surface (step S4). Thereafter, one patch surface to be processed later is selected from the patch surfaces forming the water surface (step S5). Thereafter, the process proceeds to step S6 in FIG. 7, and the number of divisions of the patch surface selected as the processing target is set for the surface according to the LOD level set in step S3. Next, along the specific direction (for example, the U-axis direction) on the patch surface to be processed, the number of lines corresponding to the number of divisions is set, and one of them is selected as the processing target (step S
7). For example, when selecting a line in the U-axis direction,
Lines with smaller V-axis coordinates are sequentially selected as processing targets.

In order to define vertices according to the number of divisions on the line to be processed, first, a vertex to be defined is selected (step S8), and the vertex is set to a vertex on the edge for which the flag is set in step S4. Is determined (step S
9). If it is not a vertex on the edge on which the flag is set, the process proceeds to step S11. If it is a vertex on the edge on which the flag is set, the process proceeds to step S10. In step S10, it is determined whether or not the selected vertex is an even number (the vertex at the edge of the edge is the first) counted from the edge of the edge. If the result is negative, the coordinates of the vertex are determined. The calculation is performed based on the surface expression for the patch surface (step S11). In this case, the coordinates of a point approximate to a point on the patch surface are calculated.

On the other hand, if it is determined in step S10 that the selected vertex is an even-numbered vertex, the coordinates of the immediately preceding vertex on the same edge are copied as the coordinates of the selected vertex (step S12). . By these processes, among the vertices located on the edge 3B as shown in FIG. 4, the odd-numbered vertices P1, P3, P5
The coordinates of P7 and P9 are calculated according to the surface expression of the patch surface 1B, and the coordinates of the even-numbered vertices P2, P4, P6 and P8 are the same as the coordinates of P1, P3, P5 and P7, respectively. As a result, the number of apparent vertices on the edge 3B becomes equal to the number of vertices on the edge 3A, and both edges 3A, 3
B is connected without any gap. Even if a line in the U-axis direction, which is the second or later line counted from the U-axis, is selected as a processing target, if a flag is set for an edge extending in the V-axis direction, for example, Step S9 is affirmed when obtaining the vertex located at. If the vertex is an even number counted from the edge of the edge (V-axis direction), the coordinates of the immediately preceding point on the edge are copied in step S12.

In the following step S13, it is determined whether or not the coordinates of all the vertices on one line have been determined. If not, the processing from step S8 is repeated. When the processing of one line is completed, the process proceeds to step S14, and the loop processing of steps S7 to S14 is performed for one patch surface by two.
It is determined whether it is the first time or later. If it is the second time or later, since the vertex coordinates on the two lines have already been determined,
The polygon 2 sandwiched between these lines is drawn in the buffer memory 15 (step S15). After the drawing, it is determined whether or not the processing has been completed for all the lines (step S
16) If there is any unprocessed line, step S
7 and the following processes are repeated. When the processing of all the lines is completed, the process proceeds to step S17, and it is determined whether there is an unprocessed patch surface. If there is any unprocessed one, step S5 in FIG.
The following processing is repeated. Then, when there is no more unprocessed patch surface, the above processing is terminated.

The above embodiment is merely an example of the present invention, and the present invention may be embodied in various forms. For example, in the above embodiment, the coordinates of the vertices on the edge of the patch
The apparent number of vertices of each adjacent curved surface is matched by matching the coordinates of the vertices in front of every other, but the present invention is not limited to this, and matches the apparent number of vertices. The coordinates of the vertices may be set using various methods as far as possible. In the present embodiment, a water surface is assumed as a continuous surface, but various continuous surfaces such as a ground surface can be represented by the present invention.

According to the above-described embodiment, a patch surface can be drawn by a relatively simple algorithm. Therefore, there is an advantage that even a processor having a limited memory, such as a DSP (for example, called a vector operation unit) attached to a CPU of a game machine, can be executed relatively easily.

[0037]

As described above, according to the image drawing method of the present invention, the apparent numbers of vertices defined on the edges of curved surfaces having different division levels coincide with each other.
Both edges are connected without a gap. Thus, a continuous curved surface can be drawn naturally.

[Brief description of the drawings]

FIG. 1 is a diagram showing a polygon model configured to represent a water surface in one embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG. 1;

FIG. 3 is a diagram showing a correspondence between a patch surface and a polygon approximating the surface.

FIG. 4 is a diagram conceptually illustrating a process performed to match the apparent number of vertices between edges of two curved surfaces having different polygon division levels.

FIG. 5 is a block diagram of a game machine which is an example of a computer for implementing the present invention.

FIG. 6 is a flowchart showing a procedure of a curved surface drawing process executed by the game machine of FIG. 5;

FIG. 7 is a flowchart following FIG. 6;

[Explanation of symbols]

 1, 1A, 1B patch surface 2 polygon 3A, 3B edge 10 game machine

Claims (6)

[Claims] 1. A method for drawing an image using a computer by drawing a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels, wherein the two curved surfaces having different division levels are different from each other. In the adjacent boundary portion, among the vertices of the polygon to be defined on the edge of the curved surface on the higher level, the coordinates of some vertices are calculated, and the other vertices are adjacent on the same edge. A method of drawing an image, wherein the number of apparent vertices on the edge of a curved surface having a different level of division is matched by setting the same as the coordinates calculated for the vertices. 2. A method of drawing an image by using a computer to divide a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels and draw the image. The number of divisions per unit is limited to a power of two, and the number of divisions per unit area is set so as not to be separated by two or more levels between adjacent curved surfaces, and two curved surfaces having different levels of division are adjacent to each other When determining the vertex coordinates of the polygon on the edge of the curved surface on the higher level, among the vertices of the polygon to be present on the edge, the vertices to be defined every other from one end of the edge , And setting the coordinates of other vertices to be the same as the coordinates calculated for vertices adjacent on the edge. 3. The image drawing method according to claim 1, wherein the calculation of the coordinates related to the vertices is performed such that the vertices approximate points on a curved surface to be represented by the polygon. Method. 4. A program for causing a computer to execute a process of drawing a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels from each other, wherein the two curved surfaces having different division levels are in contact with each other. A step of specifying a boundary portion to be performed; and, among the two curved surfaces, a curved surface having a higher division level as an object, and one of vertexes of a polygon to be defined on an edge of the boundary portion of the curved surface. The coordinates of the vertices of the part are calculated, and the other vertices are set to be the same as the coordinates calculated for the adjacent vertices on the same edge. A program for causing a computer to execute the procedure for matching the number of images. 5. A program for causing a computer to execute a process of drawing a predetermined continuous surface into a plurality of curved surfaces having different polygon division levels from each other, wherein the level of polygon division on each curved surface is determined per unit area. The number of divisions is limited to a power of two, and the number of divisions per unit area is not more than two levels apart between adjacent curved surfaces; and two curved surfaces having different levels of division are adjacent to each other In determining the vertex coordinates of the polygon on the edge of the curved surface on the higher level, every other vertex of the polygon to be present on the edge should be defined by counting from one end of the edge. Calculating the coordinates of the vertices, and setting the coordinates of the other vertices to be the same as the coordinates calculated for the adjacent vertices on the edge. Graphics programs for drawing, characterized in that it is configured to row. 6. The image drawing apparatus according to claim 4, wherein the calculation of the coordinates regarding the vertices is performed such that the vertices approximate points on a curved surface to be represented by the polygon. Program.