JP2002109553A - Polygon plotting method by triangulation avoiding edge overlapping, and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polygon plotting device by triangulation avoiding edge overlapping. SOLUTION: In triangle plotting processing, when a triangle is halved and plotted, plotting of a right edge and a left edge is controlled respectively, to thereby avoid overlapped processing with an edge of a triangle plotted beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for dividing and drawing a polygon into triangles.

[0002]

2. Description of the Related Art In recent years, computer graphics (C
G) is applied in a very large number of fields, and its drawing method also varies widely depending on the application. Above all, various algorithms have been devised for rendering polygons, and in car navigation systems in particular, since map data is composed of polygons, a faster rendering method is desired. It is rare.
The polygon drawing algorithm can be roughly classified into two methods. One is to draw the outline of a polygon and then fill the inside, and the other is to draw it by dividing it into simpler figures. For the former, there is a method of preparing a work area other than a seed fill algorithm or a drawing surface and using the work area to create and transfer a polygonal outer shape. Although this method has a drawback that the apparatus becomes complicated, it can be said that it is suitable for general polygon drawing such that processing can be performed regardless of the complexity of the polygon. In the latter method, it is generally often divided into triangles. In this case, a triangular drawing device can be easily implemented, but there is a problem of overhead involved in polygon division processing.
However, polygons that can be drawn are limited to convex figures,
Since the division process itself can be omitted by devising the order of the vertices to be given, it is often implemented as a simple method. The present invention is an improvement of this method.

[0003]

In CG, drawing is performed by rewriting a memory corresponding to a point on the screen called a pixel. Normal drawing is performed by replacing the color code of the color you want to write to the corresponding memory, but applying certain processing to the color code of the original pixel, such as color inversion processing and translucent drawing Sometimes you want to get special effects. Here, if this effect is to be obtained at the time of polygonal division drawing, a problem arises because the divided edge portions are processed in an overlapping manner. In the part where the edge overlaps, the color returns to the original color in the case of the color inversion processing, and the part is drawn with a dark color in the translucent drawing.

Conventionally, there have been two methods for solving this problem. One is a method of preparing a work area for storing a flag corresponding to each pixel, and setting a flag at a point where the processing has been performed once to avoid overlapping processing. This method is not efficient because the result is the same as the method of drawing the outline of the polygon on the work. The other is to not draw the right (or left) edge of each split triangle. Although this method can be implemented very easily, it is necessary to repaint the edges later to draw a polygon having a desired outer shape. At this time, if the right edge (or left edge) of the polygon is not determined, a problem of the overlapping process occurs.

[0005]

In order to solve the above-mentioned problems, the present invention provides a process of dividing a polygon into triangles, a process of dividing a triangle into upper and lower trapezoids, and drawing left and right edges of the trapezoid. And a step of performing drawing while avoiding overlapping drawing processing.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a polygon drawing apparatus according to an embodiment of the present invention. In the conventional polygon drawing method based on triangulation, there is a portion that is subjected to overlap processing at a pixel corresponding to an edge portion of the division. However, according to the present invention, processing for each pixel can be performed only once. This makes it possible to efficiently perform processing such as translucent drawing. Further, it is not necessary to redraw the edge portion later to draw a desired figure. As shown in FIG. 1, this is realized by controlling the drawing of the portion corresponding to the edge of the triangle to be drawn to avoid the overlapping processing.

(1) Details of Drawing Unit FIG. 8 is a block diagram of a drawing apparatus for realizing the present invention. The drawing unit includes a drawing control unit N2b, a rendering unit N2a, and a video memory N2c, and operates according to a drawing command from the control unit. What kind of command the drawing unit has
Depends on system design. In many car navigation systems, many graphic commands such as points, straight lines, polygons, and characters are prepared. Here, only the portions relevant to the present invention will be described. Also, the function of the rendering unit differs depending on the design. The rendering unit draws a figure by hardware, but the same processing can be performed in software drawing by the drawing control unit, although the processing speed is different. That is, everything described here can also be realized by software.

(1-1) Video Memory A video memory is used in various ways such as a frame buffer, a Z buffer, and a work. Here, a case where only a frame buffer is handled will be described. The extension is also possible when using a Z buffer and a work. The frame buffer is an area for storing an image to be displayed itself, and is formed of a two-dimensional array in which color codes corresponding to the pixels are stored. The video output signal section converts the content in the frame buffer into a video output signal and outputs the video output signal.
Here, the horizontal right direction is the X axis, the vertical downward direction is the Y axis, and F
Let [x, y] denote the color code corresponding to the pixel at coordinates (x, y). Normal point drawing processing is realized by writing a color code to be drawn into a memory area corresponding to coordinates at which to draw. F [x, y] = C Color inversion and translucent processing are realized by adding various processing to the original point color. If the size of the color code corresponds to the brightness of the color, F [x, y] = Cmax-CF [x, y] = αC + (1-α) F [x, y] (0 ≦ α ≦ 1).

(1-2) Polygon drawing procedure (FUN) In the map data of the car navigation system, the terrain and the shape of the building are treated as polygons, and the number of vertices and the vertex coordinates are recorded in order. I remember the shape. In a general map format, there is no particular restriction on the shape of a polygon. Therefore, when drawing is performed by a polygon drawing method based on triangulation, it is necessary to perform triangulation without contradiction in advance. Here, assuming that these operations have already been performed, the polygon data is provided by a structure called a fan. According to this structure, rendering of the polygon is Δ123, Δ134, Δ145,…,
If it is performed in the order of Δ1 n-1 n, the process is completed. At this time, in the second and subsequent triangles, if the drawing of the edge connecting the first vertex and the second vertex can be suppressed, the overlapping process can be avoided.
FIG. 2 shows this processing in a flowchart. Triangles are given to the next procedure, a triangle drawing procedure TRI, in the order shown above. At this time, a flag that suppresses drawing of an edge connecting the first vertex and the second vertex is also passed.
The present invention can be applied to any data structure that can determine the edge whose drawing should be suppressed from the arrangement of the vertices, even if it is not a fan structure.

(1-3) Triangle Drawing Procedure (TRI) FIG. 3 is a flowchart of the triangle drawing procedure. Here, description will be made with reference to this figure. According to the present invention, this triangle drawing procedure is performed in two steps.

(1-3-1) Vertex Sorting First, a process of rearranging the vertices of a given triangle in ascending order of the Y coordinate is performed. This corresponds to the processing of S21 to S27 in FIG. At this time, the location of the edge connecting the given first vertex and the second vertex is stored using the flags f1 to f3. However, these flags are reset in S28 and S29 when it is not particularly necessary to suppress edge drawing.

(1-3-2) Judgment and Drawing of Triangle Shape Subsequently, the shape of a triangle is judged. For the edge connecting the vertices (X1, Y1) and (X3, Y3) obtained by sorting,
The processing branches depending on whether (X2, Y2) is on the right or on the left. Specifically, a horizontal line and side (X1, Y2) passing through (X2, Y2)
1), intersection (X4, Y2) of (X3, Y3) is found (S211b), X2 and X4
The branch determination S212 is performed based on the magnitude relation. FIG. 4 shows the positional relationship between the vertices and the sides whose drawing is suppressed in each case. However, if all the vertices are on the same Y coordinate, the division cannot be performed, so the processing is performed in S211a. By these processes, the triangle specified to be drawn is
It can be divided into a part above and below the horizontal line passing through (X2, Y2).
Drawing is performed by TRAP. At this time, the flags f1 to f3
Adjusts the drawing position passed to TRAP, thereby avoiding edge overlap processing. Here, if the argument passed to TRAP cannot be calculated due to division by 0, an appropriate value may be passed.

(1-4) Trapezoidal Drawing Procedure (TRAP) FIG. 5A is a flowchart of trapezoidal drawing. S34, S3
The horizontal line segment is drawn by repeating step 5, and the trapezoidal drawing as shown in FIG. 5B can be performed by repeatedly drawing the line segment. Such a trapezoidal drawing algorithm is based on the fact that elements in the X-axis direction are assigned to consecutive addresses in a general two-dimensional array of frame buffers. Drawing of straight lines continuous in the X direction can be speeded up by various measures. Where transc (n) is the real number n rounded down to the decimal point, DOT
(x, y) represents the point drawing process as described in (1-1).

With the above procedure, a polygon rendering apparatus based on triangulation which avoids edge overlap as described in this specification can be realized.

(2) System Using the Polygon Drawing Method FIG. 6 shows a car navigation system as an example of a system using the polygon drawing method in the present embodiment. The present polygon drawing method can be applied to most other cases where computer graphics are generated, such as a personal computer and a video game. The car navigation system includes a car navigation device 1, a liquid crystal display device 2, a GPS receiving device 3, a VICS receiving device 4, a vehicle speed sensing device 5, a navigation software 6, and a remote control device 7. The car navigation device 1 senses a signal from the remote control operating device 7 from the light receiving unit 8 attached to the liquid crystal display device 2 and performs a designated operation. Specifically, the data from the various signal receiving devices 3, 4, and 5 are analyzed, and the current position and the surrounding road conditions are determined, and then information such as a map around the user is output to the liquid crystal display device 2. . Data that cannot be obtained in real time, such as a map, is written as navigation software 6 on a medium such as a CD-ROM or DVD-ROM, and the car navigation device 1 obtains necessary data by reading out the contents thereof. .

FIG. 7 is a block diagram showing a hardware configuration of the car navigation device 1. As shown in FIG. The car navigation device 1 includes a control unit N1, a drawing unit N2, a disk reading unit N3, a video signal output unit N4, and various signal input units N5, each of which is connected via a bus. Control unit N1
Has a CPU N1a and a main memory N1b, and controls the entire system by executing a program stored in the main memory N1b. The drawing unit N2 is a rendering unit N2.
a, a drawing control unit N2b, and a video memory N2c, which process an image drawing command sent from the control unit N1. Screen drawing is writing to the video memory N2c corresponding to each pixel on the screen.The rendering unit N2a is a video memory that responds to drawing commands for very basic figures such as points and straight lines. Write to the N2c address. On the other hand, the drawing control unit N2b decomposes a complicated figure into simple figures and causes the rendering unit N2a to draw. The polygon drawing method according to the present invention is realized by a combination of the drawing control unit and the rendering unit. Further, in a simple system, the rendering control unit N2b and the rendering unit N2a in this system may be performed only by the CPU N1a. In such a case, the present polygon rendering method is the same. The disk reading unit N3 reads data from the disk under the control of the CPU N1a. The video output signal section N4 is
The content of the video memory N2c is converted into a video output signal at regular intervals and output. Various signal input parts are GPS, VICS,
An input from the vehicle speed sensing device remote controller is received and stored in the main memory. This stored signal is processed by the CPU N1a.

[0017]

As described above, according to the present invention, when a polygon is drawn by triangulation, the drawing can be performed without overlapping the edge portions. This makes it easy to perform color code inversion processing and translucent composite drawing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state in which a triangle edge is drawn during polygon drawing according to the present invention.

FIG. 2 is a flowchart showing a procedure for drawing a polygon in an expression using a FUN structure.

FIG. 3 is a flowchart of a triangle drawing procedure according to the present invention.

FIG. 4 is a diagram showing a positional relationship between a vertex and a flag in a triangle drawing procedure.

FIG. 5 is a flowchart of a trapezoidal drawing procedure according to the present invention.

FIG. 6 is a configuration diagram of a car navigation system.

FIG. 7 is a block diagram showing a configuration of the car navigation device 1.

FIG. 8 is a block diagram showing a configuration in a drawing unit N2.

[Explanation of symbols]

 1 Car navigation device 2 Liquid crystal display device 3 GPS receiving device 4 VICS receiving device 5 Vehicle speed sensing device 6 Navigation software 7 Remote control device 8 Light receiving unit N1 Control unit N1a CPU N1b Main memory N2 Drawing unit N2a Rendering unit N2b Drawing control unit N2c Video Memory N3 Disk reader N4 Video signal output N5 Various signal input

Claims (3)

[Claims] 1. A drawing method for generating a polygon from given vertex coordinates, comprising: a step of dividing the polygon into triangles; a step of dividing the triangles into upper and lower trapezoids; A polygon drawing method comprising a step of controlling drawing of an edge and performing drawing while avoiding overlapping drawing processing. 2. A drawing method for generating a trapezoid from a given vertex and the inclination of both edges, wherein the drawing of an edge is controlled by adjusting the position of the vertex to the left and right. . 3. A drawing apparatus for generating a polygon from given vertex coordinates, comprising: means for dividing the polygon into triangles; means for dividing the triangle into upper and lower trapezoids; A polygon drawing device, comprising: means for controlling drawing of an edge and performing drawing while avoiding overlapping drawing processing.