JPH01283679A - Circle clip processing system - Google Patents

Abstract

PURPOSE:To perform a clip processing of a circle at a low cost and at a high speed by deciding a display area by a regular square frame segment circumscribed to its circle and executing the clip processing of the circle of the outside of the display area, at the time of executing a display processing of the circle. CONSTITUTION:At the time of executing a display processing of a circle, a clip processing of the circle of the outside of a display area is executed by deciding the display area by regular square A-D segments circumscribed to its circle. That is, before converting the circle to a polygon or a sequence of points, the regular square frame segments circumscribed to the circle are generated, and whether this circle exists in the display area or not is decided in advance by bringing these regular squares A-D to clip processing. In case when the circle does not exist in the display area, a command processing of the circle is ended without converting the circle to a polygon or a sequence of points. In such a way, the clip processing of the circle which does not exist in the display area can be executed at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circular clip processing method in a circular display device.

[Prior Art] FIG. 2 is a block diagram showing the configuration of a conventional rask scan type circular display device. In the figure, l is an interface circuit, and 2 is a computer (
A controller 3 converts display data and display commands sent from a controller (not shown) into an internal format, and a storage H 3 stores display data and display commands that have been converted into the internal format. The control device 2 analyzes the display commands stored in the storage device 3 and generates coordinate values for display. The coordinate values generated by the control device 2 are transferred to a coordinate conversion circuit 4 and a clip circuit 5 based on instructions from the control device 2.
is applied to the straight line generator 6 via. Further, in the figure, 7 is a frame buffer, 8 is a CRT (cathode ray tube), and 9 is an input device.

FIG. 3 is a flowchart showing circle command processing by the circular display device of FIG.

Next, circle command processing by the conventional circular display device will be described. When the control device 2 receives the circle command, the center coordinate value of the circle and the radius of the circle are read as parameters. If a circle is approximated as a polygon, the number of angles is determined by the radius of the circle and the expansion and contraction terms of coordinate transformation. If a circle is created as a sequence of points, calculate the coordinate values of the corner points. The coordinate values of the polygon line segment sequence or point sequence generated by the above processing are input to the coordinate conversion circuit 4. The corresponding coordinate values after coordinate transformations such as enlargement, reduction, rotation, and movement are performed in the coordinate transformation circuit 4 are input to the clipping circuit 5 for determining the display area, and the clipping process of the circle by the clipping circuit 5 is performed. As a result, only the line segment sequence or dot sequence displayed on the CRT 8 is sent to the straight line generator 6. In this way, the circle command processing is completed.

[Problems to be Solved by the Invention] Since the conventional circular display device described above is configured as described above, the circle clipping process is performed for each line segment sequence and point sequence after coordinate transformation, so that the conventional circular display device shown in FIG. As shown in the circle display example, if there are fewer circles within the display area than circles outside the display area,
The time required to clip the coordinate values of circle line segments and point sequences outside the display area, which should not be necessary, becomes longer.
As a result, there is a problem in that it takes a long time to perform the entire display process.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a circle clipping method that easily and quickly clips circles outside the display area.

[Means for Solving the Problems] The circle clip processing method according to the present invention, when displaying a circle, determines the display area based on the square frame line circumscribing the circle, thereby clipping the area outside the display area. It is designed to perform circle clipping processing.

[Operation] The circle clip processing method in this invention creates a square frame line segment circumscribing the circle after converting a circle into a polygon or a point sequence, and clips this square, thereby
It is determined in advance whether the relevant circle is within the display area, and if the relevant circle is outside the display area, the circle command processing is terminated without converting the circle to a polygon or point sequence. Try to speed up the circle clipping process.

[Embodiment FIG. 5 is a diagram showing an example of the definition of a square frame circumscribing a circle. In the figure, PX and PY are the center points of the circle, and are values calculated in advance as movement terms during coordinate transformation. R
is the radius of the circle, and is a value calculated in advance as an expansion and contraction term during coordinate transformation. Vertices A, B of the square frame,
C, D are (PX+R, PY+R), (PX-R,
PY+R).

(PX-R, PY-R), (PX+R, PY-R)
It is indicated by.

FIG. 1 is a flowchart showing circle command processing in a circle clip processing method according to an embodiment of the present invention. In the circle command processing according to the present invention, coordinate transformation and clip processing are first performed on the apex A (PX+R, PY+R) of the square frame shown in FIG. Perform occurrence processing. If the apex A (PX + R, PY + R) of the square frame is outside the display area, clip the square frame lines according to the flowchart shown in Figure 1, and display even one of the four square frame lines. If it falls within the area, the same circle generation process as in the conventional example described above is performed. If all the square frame line segments are outside the display area, the corresponding circle is also outside the display area, so the circle command processing ends at this point.

[Effects of the Invention] As described above, according to the circle clip processing method of the present invention, when displaying a circle, the display area is determined by the square frame lines circumscribing the circle. Since the outer circle is clipped, the circle can be clipped at low cost and at high speed, and the overall processing speed can be reduced, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a second flowchart showing circle command processing in the circle clip processing method which is an embodiment of the present invention.
The figure shows the configuration of a conventional rask scan type circular display device, FIG. 3 shows flowchart 1 showing the circle command processing by the circular display device of FIG. 2, and FIG. 4 shows an example of displaying a circle. FIG. 5 is a diagram showing an example of the definition of a square frame circumscribing a circle. In the figure, 1... interface circuit, 2... control device, 3... storage device, 4... coordinate conversion circuit, 5
...Clip circuit, 6...Line line generator, 7...Frame buffer, 8...CRT, 9...Input device
It is. In addition, the same symbols in the figures indicate the same or equivalent parts. Agent Masuo Oiwa @＋
Figure 3 fj4t, Figure 5 Showa year month day

Claims (1)

[Claims] A function that generates a circle, a polygonal line segment sequence of a circle, or a polygon by inputting the radius and center coordinates of the circle, and coordinates for enlarging, contracting, rotating, and moving the output circle component coordinate values. In a circular display device that is equipped with a function to perform conversion and a function to perform clipping processing by determining the display area for each coordinate point after coordinate conversion, clipping of a circle is determined using square frame line segments circumscribing the circle. A circle clipping method characterized by comprising means for clipping a circle outside a display area.