JPS6314286A - Circle depiction system - Google Patents

Abstract

PURPOSE:To depict a natural circle with a thick line without striping the thick line by using an algorithm where the center of the circle is successively shifted inward to describe arcs having the same radius and this operation is repeated to depict the circle with the thick line. CONSTITUTION:A CPU 1 outputs an arc description instruction, which has coordinates of the center of an arc, coordinates of the depiction start point, the number of clockwise traversed picture elements, and the number of picture elements to be depicted as parameters, to a picture processor. The processor 3 obtains the number of picture elements to be depicted or an outside circle in accordance with these parameters to depict this circle, and the center is shifted inward to describe an arc with the same radius. The number of picture elements of the following arc is obtained for the purpose of synchronizing depiction with error correction of the processor 3 to depict an arc having the same radius. In this system, stripes which appear for depiction of a thick line are eliminated and the circle is depicted in a two-dimensional picture memory space with the thick line of a single picture element. As the result, the circle which looks natural is depicted with the thick line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a circle drawing method suitable for use in a graphic manual system.

(Prior art) It is difficult to draw an arc with a graphics device using a rask scanning type CRT display.
This means that data is modified bit by bit for the bitmap memory with k. Originally, arcs are analog objects whose values change continuously, so the drawing device must perform some processing to approximate and quantize them as dots on the crosspoints of a grid.

Normally, a two-dimensional image space is created within the one-dimensional address space of the storage device, and the center coordinates of the circle and the radius are manually input to that space.
The coordinates of the arc are determined from the main meter and drawn.

(Problem to be Solved by the Invention) By the way, in the above-described drawing device, when drawing a circle indicated by a thick line, after drawing one circle, draw another circle that is concentric and has a radius one pixel smaller. This is handled by drawing, and this situation is shown in FIG. However, in this case, as shown by points b1 to b6 in the figure, white pixels are crowded into the thick line, and this appears as a striped pattern on the thick line, which is undesirable from a visual perspective. The purpose of this paper is to provide a circle drawing method that draws natural thick-line circles using a full two-dimensional image memory by adopting a new drawing algorithm for thick-line circle drawing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention involves drawing an arc of the same radius inside a circle while shifting the center of the circle, and repeating this process. An algorithm for drawing a thick line circle is adopted, and a stroke 1-grain processor capable of drawing a single arc is used, and this algorithm is realized under CPU control.

(Function) First, the CPU sends the image processor an arc-centered image, drawing start point coordinates 9 clockwise υ movement liT + prime number.

Outputs an arc drawing command with the number of pixels to be drawn as a parameter. The image processor calculates the number of pixels to draw the outer circumferential circle according to the above parameters, draws the circle, and draws an arc with the same radius while shifting the center inside this circle. Then, in order to synchronize with the image processor's error correction, the number of pixels in the arc is calculated and arcs with the same radius are drawn.

This eliminates the appearance of striped patterns on the thick lines, making it possible to draw circles with thick lines that look natural.

(Example) Hereinafter, examples of the present invention will be described in detail using the drawings. 1. La- is a block diagram showing all embodiments of the present invention. In the figure, 1 is a CPU that outputs all drawing instructions to an image processor 3, which will be described later, and 2 is a main memory that stores the program. 3 is an image processor that draws an arc into the image memory 4; 4 is an image memory. 5 is a CrLT monitor, and 6 is a display controller (CRTC) that controls when image data stored in the image memory 4 is displayed on 5. CPU mentioned above 1. Main memory 2° Image processor 31 Image memory 4. Display controller 6 is commonly connected to system bus 7.

FIG. 2 shows the parameters of the arc drawing command that the CPU 1 outputs to the image processor 3, the drawn arc that the image processor 3 writes to the image memory 4, and the parameters that the image processor 3 outputs to the CPU 1. They are shown below. In the figure, a is the center coordinate of the arc, b is the starting point coordinate of the arc drawing, C is the end point coordinate after the arc drawing, Nl
is the number of clockwise moving pixels, N2 is the number of pixels drawn after Nl
The number of i pixels is shown. The parameter of the arc drawing command is 'e b a NIN2. The arc drawn is
This is the part corresponding to N2 between 6 and 0. The output parameter of the arc drawing command is ``g''.

Figure 3 shows the number of pixels drawn for a circle. Since the number of pixels drawn is determined by the number of coordinate grid lines (raster) that the arc crosses, in the areas 1 and ■, the number of pixels drawn in the horizontal direction is The number of intersections between the vertical grid line and the circular arc, and in the areas (■) and (■), the number of intersections between the vertical grid line and the circular arc is the number of pixels to be drawn.

Therefore, the number of pixels for drawing a circle is r, n, tII, and the number of skill marks in the area.

FIG. 4 shows a method for obtaining the number of pixels of a circumference, in which the CPU 1 sends the image processor 3 the arc center coordinates d (N2.Y,?) and the drawing start point coordinates s (N2゜y2+r) 1 Indicates the drawing end point coordinate f(N3.Y, 1) which is the output of the image processor 3 when all the arc drawing commands are output according to the clockwise movement pixel number 0 and the drawing pixel number r. .

FIG. 5 shows a method for drawing thick circles.

2 is a circle with center coordinates (x, y) and radius r. J is center coordinates (X, Y-1), radius r (l/8 circle-1 pixel)
It is an arc of . K, center coordinates (X+r, Y), radius r
It is a circular arc of (1/4-2i elements). L is the center coordinate (X
, Y-r), (1/4 circle-21F!ili chord) of radius r
It is an arc of . (2) is an arc of (1/4 circle - 2 pixels) with center coordinates (X-r, Y) and radius r. N is the center coordinate (X, Y+r).

It is an arc of radius r (178 circles - 1 pixel).

Figure 6 shows one control of circle drawing! shows the program flow.

Specifically, this operating procedure is stored in the main memory 2 shown in FIG. 1 in the form of a program, and the image processor 3 successively executes this program.

Hereinafter, the operation of the embodiment of the present invention will be explained in detail.

A method for obtaining the number of pixels to draw a circle using Figs. 3 and 4 will be described. CPU at the parameter shown in Figure 4
1 is 1! It is assumed that an arc drawing command is output to the II image processor 3. In this case, the image processor? The output of
From the relationship between the f parameter and the relationship shown in FIG. 3, the number of pixels drawn in a circle with radius r: t is ((r+Y, y-Y2-1)X4).

Next, we will discuss the method of drawing thick lines, which is the gist of the present invention.

This will be explained using FIGS. 5 and 6. First, the image processor 3 draws a circle based on the following meters. The parameters are center coordinates (X = Y) e drawing start point coordinates (X, Y-) - r), number of clockwise moving pixels O1, number of drawing pixels t. Then, draw the arc J using the following parameters. The parameters are the center coordinates (X, Y-1
), drawing start point coordinates (X.

Y-1+r), number of clockwise moving pixels O, number of drawing pixels ((
t/8)-1). In order to synchronize with the error correction of the image processor 3, the number of pixels in the arc: 61.
= ((Y4-Y) X-1, Y+r)
, ``\f Number of pixels per clockwise movement t/8° Number of pixels drawn 11.

Next, draw the arc using the following serameter.

The parameters are center coordinates (X, Y+1), drawing start point coordinates (x, y+t+r), number of clockwise movement pixels (t/2-C1/8-1)), number of drawing pixels ((Otsu/4)-2 ). In addition, the following! Draw an arc M using a metric. The parameters are center coordinates (x-t, y),
Drawing start point coordinates (X-1, Y+r), number of clockwise moving pixels ((t/2)+(/=+8)), number of drawing pixels 61
It is.

Then, arc M is drawn using the following A' parameters.・! Lameter is the center coordinate (X-1, Y), the drawing start point coordinate (X-
1, Y+r), number of clockwise moving pixels ((t/2)
+ (t/8)), and the number of pixels to be drawn is 11.

Then, arc N is drawn using the following parameters.

The parameters are the center coordinates (X, Y-1), the coordinates of the starting point of one drawing plane (X, Y-1+r), and the number of clockwise moving pixels (L - (
z,,'s -1)) #number of drawing pixels ((t-8)-1)
It is.

It goes without saying that if you want to make one circle even thicker, you can draw a smaller circle inside while shifting the center further using the method described above.

[Effects of the Invention] According to the present invention as explained above, the striped pattern that appears when drawing a thick line is eliminated, and it becomes possible to draw a circle with a single pixel thick line in the two-dimensional image memory space, which improves the appearance. You can expect natural thick circle drawing.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, and Figs. 2 to 5 are diagrams cited to explain the operation of the embodiment of the present invention, and each is used in the embodiment of the present invention. Examples of parameters, a diagram showing pixels to draw a circle, a diagram to show how to obtain the number of pixels to draw on the circumference, and a diagram to show how to obtain a thick-line circle drawing. FIG. 6 is a diagram showing the operating procedure of the embodiment of the present invention, and FIG. 7 is a diagram showing an example of conventional thick-line circle drawing. 1... CPU, 2... Memory, 3... Image processor, 4... [1iii Image memory. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 7 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] The CPU is connected to an image processor that operates based on image processing instructions issued from the CPU, and draws a circle, and draws an arc with the same radius while shifting the center inside the circle. The image processor includes a memory in which a processing procedure is programmed to draw a thick line circle by drawing, and an image memory, and when the CPU outputs a thick line circle drawing command, the image processor executes the process stored in the memory. A circle drawing method characterized in that a thick line circle is drawn in the image memory according to a procedure.