JPH04291685A - Clip tester circuit and clip testing method - Google Patents

Abstract

PURPOSE:To obtain a circuit for finding out relation between a display area whose border is indicated by a clip frame on a display screen and a straight line to be displayed and relation between the klip frame and the straight line. CONSTITUTION:This clip tester circuit is constituted of a start point register 11 for storing the start point of a straight line, an end point register 12 for storing an end point, a klip frame register 13 for storing clip frame data, a comparing circuit 14 for comparing the data of the register 13 with the data of respective registers 11, 12, and a logical synthesis circuit 15 for synthesizing the outputs of the circuit 14.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to a graphic display device that displays straight lines, etc. on a screen. , or not included (hereinafter referred to as clip-out), or whether a part of the straight line is included (hereinafter referred to as actual clip), and in the case of actual clipping, determines the clip frame that intersects with the straight line. The present invention relates to a clip tester circuit for performing a clip test and a clip test method.

0002

2. Description of the Related Art Conventionally, when displaying a figure included in a designated display area in a graphic display device, a method for determining whether the figure is included in the display area has been used.
An approach was taken using Ohen-Sutherland's domain coding. Literature “Interactive Computer Graphics” McGraw-Hill Publishing PP. 74-77 describe the algorithm in detail.

FIG. 4 shows the Cohen-Sutherland
It is a figure which shows the clip code of. The display area is four clip frames X=Xmax X=Xmin Y=Yma
It is a rectangular area surrounded by x Y=Ymin. Clip codes are assigned to nine areas divided by four clip frames, and when performing a clip test,
Use the clip code to which the start and end points of the straight line belong.

Next, the clip code will be explained. The clip code is composed of 4 bits, which are called 0th bit, 1st bit, 2nd bit, and 3rd bit from the right. The 0th bit is the clip frame X=Xmin, the 1st bit is the clip frame X=Xmax, the 2nd bit is the clip frame Y=Ymin, the 3rd bit is the clip frame Y
This shows the relationship between =Ymax and a point.

FIG. 5 is a flowchart of clip code generation. The procedure for generating clip code bits will be explained using FIG. 5. The 0th bit of the clip code is the point X
Compare the coordinates and the clipping frame X=Xmin, and if X coordinate < Xmin ■1", X coordinate ≥
If n, the first bit of the clip code compares the X coordinate of the point with the clip frame X = Xmax, and if the X coordinate > Xmax, it is "1", and the
max is “0”, the second bit of the clip code compares the Y coordinate of the point and the clip frame Y=Ymin, and calculates Y
“1” if coordinate < Ymin, Y coordinate ≧
If Ymin, the third bit of the clip code compares the Y coordinate of the point with the clip frame Y=Ymax, and if Y coordinate > Ymax, it is "1", and if Y coordinate ≦
In the case of Ymax, it becomes "0". In this way, a clip code is generated by comparing the X and Y coordinates of a point with the clip frame.

FIG. 6 is a flowchart of a clip test method using a clip code. A clip test method using a clip code will be explained with reference to FIG. The clip code (hereinafter referred to as Scod) of the starting point obtained using the above method
e) and the end point clip code (hereinafter referred to as Eco
e), the relationship between the straight line and the display area is determined by the following logical operation.

[0007] Find the logical sum (Scode OREcode) of the clip codes at the starting point and ending point of the straight line, and find out that the value is "
0000", it is a clip-in in which a straight line exists in the display area. If it is not a clip-in, the logical product (Scode AND) of the above clip codes of the start point and end point is
If the value is not "0000", there is a straight line outside the display area, indicating clip-out. Clips that are not clip-in or clip-out are real clips where a straight line intersects the display area.

[0008] Furthermore, data indicating the relationship between the straight line and the clip frame can be obtained by calculating the exclusive OR (Scode The 0th bit of the data indicating the relationship between this straight line and the clipping frame is X=Xmin, and the 1st bit is X=X
max, the second bit indicates Y=Ymin, and the third bit indicates the relationship between the clip frame and the straight line of Y=Ymax,
When the bit is "0", it does not intersect with the clip frame, and when the bit is "1", it indicates that it intersects with the clip frame. As described above, a clip test can be performed to examine the relationship between a straight line and a clip frame by logically calculating the clip codes at the start and end points of the straight line.

Conventionally, such clip code generation and clip testing have been processed by software.

0010

[Problem to be Solved by the Invention] To perform the clip test using the above clip code using software,
A comparison operation that compares the X and Y coordinates of the starting point and ending point of a straight line with each of the four clip frames to generate a clip code, and a comparison operation that compares the starting point and ending point of the straight line to find the relationship between the straight line and the display area. There is a problem in that a logical product, a logical sum operation, and an exclusive logical sum operation of the clip codes of the starting point and the ending point of the straight line must be performed to find the relationship between the straight line and the clipping frame, and the processing time is large.

The present invention was made to solve the above-mentioned problems, and it is possible to quickly obtain the clip codes of the starting point and end point of a straight line, the relationship between the straight line and the display area, and the relationship between the straight line and the clip frame. The object of the present invention is to obtain a clip tester circuit and a clip test method that can perform the following steps.

0012

[Means for Solving the Problems] A clip tester circuit according to the present invention includes a start point register that holds the starting point coordinates of a straight line, an end point register that holds the end point coordinates of the straight line, and a clip frame that indicates the boundary of a display area. A plurality of comparators that compare the held clip frame register, the start point coordinate data of the above start point register, the end point coordinate data of the end point register, and the clip frame data of the clip frame register, and the start point of the straight line output from the above comparator. , a logic synthesis circuit that generates data indicating the relationship between the straight line and the display area and the relationship between the straight line and the clipping frame from data on the relationship between the end point and the display area.

The clip test method according to the present invention includes a comparison step of simultaneously comparing the starting point coordinates of a straight line, the ending point coordinates of a straight line, and the coordinates of a clipping frame indicating the boundary of a display area on the screen using a plurality of comparators. , A process of generating data indicating that the straight line is inside the display area from data indicating the positional relationship between the coordinates of the start point and the end point and the display area output from the above comparison process, and that the straight line is outside the display area. The present invention includes a logical synthesis process that simultaneously performs processing for generating data indicating the line and data indicating the type of clip frame that intersects the straight line when the line intersects the display area.

[0014]

[Operation] In the clip tester circuit according to the present invention, the starting point register holds the starting point coordinates of the input straight line, the ending point register holds the ending point coordinates of the straight line, and the clipping frame coordinates indicating the boundary of the display area are held in the clipping frame register. holds. A comparator compares data in the start point register and data in the clip frame register to generate a clip code for the start point, and a comparator compares data in the end point register and data in the clip frame register to generate a clip code for the end point. A clip code indicating the relationship between the starting point and end point of the straight line and the display area is input to a logic synthesis circuit, and data indicating the relationship between the straight line and the display area and data indicating the relationship between the straight line and the clip frame are generated.

[0015] In the clip test method according to the present invention, the comparison step includes the coordinates of the starting point of the straight line, the coordinates of the ending point of the straight line,
Since the coordinates of the clip frames that indicate the boundaries of the display area on the screen are compared simultaneously using multiple comparators, the X and Y coordinates of the starting point and end point of the straight line are compared with each of the four clip frames to generate a clip code. Comparison operations that perform the following are executed simultaneously and at high speed. Then, the logic synthesis process generates data indicating that the straight line is inside the display area from the data indicating the coordinates of the start point and end point output from the comparison process and the positional relationship of the display area, and the process of generating data indicating that the straight line is inside the display area. The process of generating data indicating that the line is outside the display area and the process of generating data indicating the type of clipping frame that intersects the line when the line intersects the display area are executed at the same time. The AND operation and OR operation of the clip codes at the start point and end point of a straight line to find the relationship between the straight line and the exclusive OR operation of the clip codes at the start point and end point of the straight line to find the relationship between the straight line and the clip frame are performed. executed at high speed at the same time.

[0016]

[Example] Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a clip tester circuit according to the present invention. 11 is a start point register that holds the starting point coordinates of a straight line; 12 is an end point register that holds the end point coordinates of the straight line; 13 is a clip frame register that holds clip frame coordinates that indicate the boundary of the display area; and 14 is provided with a plurality of comparators. , Comparison of data in start point register 11 and data in clip frame register 13, and comparison of data in start point register 11 and end point register 1
15 is a comparison circuit that compares the data of 2 and the data of the clip frame register 13; 15 is the output data of the comparison circuit 14, which is a clip code that indicates the relationship between the start point and end point of the straight line and the display area; and 15, the clip code that indicates the relationship between the straight line and the clip frame. This is a logic synthesis circuit that converts data into data. 141, 142, 143, 144,
Comparators 145, 146, 147, and 148 constitute the comparison circuit 14. 161, 162, 163, and 164 are output lines of comparators 141, 142, 143, and 144, respectively. 165, 166, 167, and 168 are output lines of comparators 145, 146, 147, and 148, respectively.

FIG. 2 is a diagram showing an example of a logic synthesis circuit according to the present invention. 21 is a clip-in determination circuit that determines whether a straight line is clip-in based on the clip codes at the start and end points of the straight line, and 22 is a clip-out determination circuit that determines whether the straight line is clip-out from the clip codes at the start and end points of the straight line. A circuit 23 is an actual clip frame discrimination circuit that generates data indicating the clip frame crossed by the straight line from the clip codes at the start and end points of the straight line.

The operation of this embodiment configured as described above will be explained. First of all, the clip frame
X=Xmin, X=Xmax, Y=Ymin, Y=Ym
The value of ax is set in the clip frame register 13, the X coordinate data and Y coordinate data of the starting point of the straight line are set in the starting point register 11, and the X coordinate data and Y coordinate data of the ending point of the straight line are set in the ending point register 12. .

The comparator 141 receives the X coordinate data (Sx) of the starting point register 11 and the clip frame X=Xmin data of the clip frame register 13, and compares the two data. If the comparison result is Sx ≧ Xmin, the comparator 141 outputs "0" to the output line 161, and S
If x < Xmin, comparator 141 connects output line 16
Output “1” to 1. The comparator 142 contains the X coordinate data (Sx) of the start point register 11 and the clip frame register 13.
Clip frame X=Xmax data is input, and the above two data are compared. The comparison result is Sx ≦ Xm
ax, the comparator 142 outputs “0” to the output line 162, and when Sx > Xmax, the comparator 142 outputs “0” to the output line 162.
outputs “1” to the output line 162. The Y coordinate data (Sy) of the start point register 11 and the clip frame Y=Ymin data of the clip frame register 13 are input to the comparator 143, and the two data are compared. The comparison result is S
If y≧Ymin, the comparator 143 outputs the output line 163
If Sy < Ymin, the comparator 143 outputs “1” to the output line 163. The comparator 144 contains the Y coordinate data (Sy) of the start point register 11 and the clip frame of the clip frame register 13. Y=Ymax
Data is input and the two data are compared. If the comparison result is Sy ≦ Xmax, the comparator 14
4 outputs "0" to the output line 164, and Sy > Ym
In the case of ax, the comparator 144 outputs "1" on the output line 164.

The comparator 145 receives the X coordinate data (Ex) of the end point register 12 and the clip frame X=Xmin data of the clip frame register 13, and compares the two data. If the comparison result is Ex ≧ Xmin, the comparator 145 outputs "0" to the output line 165, and Ex
<Xmin, comparator 145 connects output line 16
Output “1” to 5. Comparator 146 is end point register 1
The X coordinate data (Ex) of 2 and the clip frame X=Xmax data of the clip frame register 13 are input, and the
Compare two data. The comparison result is Ex ≦ Xma
If Ex > Xmax, the comparator 146 outputs a “0” on the output line 166, and if Ex > Xmax, the comparator 146 outputs a “1” on the output line 166. The comparator 147 receives the Y coordinate data (Ey) of the end point register 12 and the clip frame Y=Ymin data of the clip frame register 13, and compares the two data. The comparison result is Ey
When ≧Ymin, the comparator 147 outputs “0” to the output line 167, and when Ey<Ymin, the comparator 147 outputs “1” to the output line 167. Comparator 1
Reference numeral 48 inputs the Y coordinate data (Ey) of the end point register 12 and the clip frame Y=Ymax data of the clip frame register 13, and compares the above two data. If the comparison result is Ey≦Ymax, the comparator 148 outputs “0” to the output line 168, and if Ey>Ymax, the comparator 148 outputs “0” to the output line 168.

Four output lines 161, 162, 163, 1
64 indicates a clip code (Scode) at the starting point of the straight line, 161 corresponds to the 0th bit, 162 corresponds to the first bit, 163 corresponds to the second bit, and 164 corresponds to the third bit, respectively. In addition, four output lines 165, 166
, 167, 168 are the clip codes (Ec
ode ), 165 corresponds to the 0th bit, 166 corresponds to the first bit, 167 corresponds to the second bit, and 168 corresponds to the third bit, respectively.

Next, the operation of the logic synthesis circuit 15 will be explained. Output lines 161, 162, 1 of comparison circuit 14
The clip code of the starting point of the straight line indicated by 63 and 164 (
Code ) and the output lines 165 and 166 of the comparison circuit 14
, 167, and 168, data indicating the relationship between the straight line and the clipping frame is generated from the clip codes (Ecode) at the end points of the straight line.

The clip-in determination circuit 21 has one NOR
It consists of gates, Scode and Ecode.
is input. The clip-in discrimination circuit 21 has Scode and Ecocode.
When both are "0000", that is, in the case of clip-in, "1" is output, and when at least one of Scode and Ecode is not "0000", that is, when it is not clip-in, "0" is output.

The clip-out determination circuit 22 has four ANs.
It consists of a D gate and one OR gate, and Sc
ode and Ecode are input, and Scode and E
Determine whether the logical product of code is "0000". When the logical product is not "0000", that is, in the case of clip-out, the clip-out determination circuit 22 outputs "1", and when it is "0000", that is, in the case that it is not clip-out, it outputs "0". When neither clip-in nor clip-out occurs, the actual clip frame determination circuit 23 is enabled.

The actual clip frame determination circuit 23 has four XOR
It consists of a gate, and Code and Ecode are input, and if the straight line and the clip frame intersect, the bit corresponding to that clip frame is “1”, and if it does not intersect, the bit is “0”.
” The calculation result of Code XOR Ecode is output.

Next, a specific example will be explained using FIG. First, the Scode and E of straight line 31, straight line 32, and straight line 33
Generate code. The starting point coordinates and ending point coordinates of each straight line are set in the starting point register 11 and ending point register 12, and the coordinates of the clipping frame are set in the clipping frame register 13. Comparators 141, 142, 143, and 144 compare the data in the starting point register 11 and the data in the clipping frame register 13 to generate a Code. Comparators 145, 14
At steps 6, 147, and 148, the data in the end point register 12 and the data in the clip frame register 13 are compared, and the Eco
is generated. The code of straight line 31 is “0000”
”, Ecode is “0000”, Scod of straight line 32
e is "0100", Ecode is "0110", Scode of the straight line 33 is "0001", and Ecode is "1000".

These clip codes are used by the logic synthesis circuit 1
5, and is converted into data indicating the relationship between the straight line and the clipping frame. In the clip-in discrimination circuit 21, the code
The OR Ecocode operation is executed. The calculation result is "0000" for straight line 31, "0110" for straight line 32,
In the straight line 33, it is "1001". The clip-in determination circuit 21 determines whether the clip-in condition (the calculation result is "0000")
If the straight line 31 satisfies the above condition, "1" is output, and if the straight line 32 or 33 satisfies the non-clip-in condition (the calculation result is not "0000"), "0" is output.

In the clip-out determination circuit 22, the Sco
The operation de AND Ecode is executed. The calculation result is "0000" for straight line 31 and "01" for straight line 32.
00", and "0000" for the straight line 33. The clip-out determination circuit 22 outputs "1" for the straight line 32 that satisfies the clip-out condition (the calculation result is not "0000").
, if the condition is not clip out (the calculation result is "0000")
"0" for straight line 31 and straight line 33 that satisfy
Output.

As described above, the logic synthesis circuit 15 indicates that the straight line 31 is clip-in and the straight line 32 is clip-out. Since the straight line 33 is neither clip-in nor clip-out, it is regarded as a real clip, and the real clip frame determination circuit 23 becomes effective.

In the real clip frame discrimination circuit 23, Scod
The operation e XOR Ecode is performed. The calculation result is "0000" for straight line 31 and "001" for straight line 32.
0", the straight line 33 is "1001". Since the straight line 32 intersects the clip frame Xmax, the first bit is "1",
Since the straight line 33 intersects the clip frames Xmin and Ymax, an arithmetic result in which the 0th bit and the 3rd bit are "1" is obtained. The actual clip frame determination circuit 23 outputs this calculation result data.

As described above, in this embodiment, in a graphic display device that displays a straight line or the like on the screen, a start point register that holds the starting point coordinates of the straight line, an end point register that holds the end point coordinates of the straight line, and a clip frame register that holds the coordinate values of the clip frame that indicates the boundary of the display area; a plurality of comparators that compare data in the start point register and end point register with data in the clip frame register; and a plurality of comparators described above. The clip tester circuit is characterized in that it is equipped with a logic synthesis circuit that generates data representing the relationship between a straight line and a clip frame from data representing the coordinates of the start point and end point and the positional relationship of the display area output from the clip tester circuit.

Furthermore, in this embodiment, the logic synthesis circuit is
A logic circuit generates data indicating that the straight line is inside the display area from input data, a logic circuit generates data indicating that the straight line is outside the display area, and a logic circuit generates data indicating that the straight line is outside the display area. The clip tester circuit is characterized in that it is comprised of a logic circuit that generates data indicating the type of clip frame that intersects with a straight line.

Example 2. In the above embodiment, a start point register that holds the starting point coordinates of a straight line, an end point register that holds the end point coordinates of the straight line, and a clip frame register that holds the coordinate values of the clip frame that indicates the boundary of the display area on the screen are Although the case where these registers exist separately is shown, these registers may exist in the same register.

[0034]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

Since the data of the clipping frame and the starting point coordinate data and the ending point coordinate data of the straight line are compared by a comparison circuit (or a comparison process) composed of a plurality of comparators, clip codes can be generated at high speed.

Data indicating the relationship between the straight line and the display area is generated by the logic synthesis circuit (or logic synthesis process) from the clip code indicating the relationship between the start and end points of the straight line output from the comparison circuit (or comparison process) and the display area; Data indicating the relationship between straight lines and clip frames can be generated, and frames to be clipped during clip-in, clip-out, and actual clipping can be quickly and easily determined.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a clip tester circuit showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a logic synthesis circuit showing a first embodiment of the present invention.

FIG. 3 is a diagram showing a specific example of the embodiment of the invention.

FIG. 4 is a diagram showing clip codes determined by clip frames.

FIG. 5 is a flowchart diagram of clip code generation.

FIG. 6 is a flowchart diagram of a clip test.

[Explanation of symbols]

11 Start point register 12 End point register 13 Clip frame register 14 Comparison circuit (comparison process) 141-148 Comparator 15 Logic synthesis circuit (logic synthesis process) 161-168
Output line 21 Clip-in discrimination circuit 22 Clip-out discrimination circuit 23 Actual clip frame discrimination circuit

Claims (2)

[Claims] Claim 1: A clip tester circuit having the following elements: (a) a starting point register that holds starting point coordinates of a straight line;
(b) An end point register that holds the end point coordinates of the straight line, and (c
) A clip frame register that holds the coordinates of the clip frame that indicates the boundary of the display area; (d) Compare the data in the start point register and end point register with the data in the clip frame register, and calculate the coordinates of the start point and end point and the coordinates of the display area. a comparison circuit that outputs data indicating the positional relationship; (e) generating data representing the relationship between the straight line and the clip frame from the data indicating the positional relationship between the coordinates of the start point and the end point and the display area output from the comparison circuit; Logic synthesis circuit. 2. A clip test method comprising the following steps: (a) simultaneously comparing the coordinates of the starting point of the straight line, the coordinates of the ending point of the straight line, and the coordinates of a clipping frame indicating the boundary of the display area on the screen using a plurality of comparators; (b) a process of generating data indicating that the straight line is within the display area from data indicating the positional relationship between the coordinates of the start point and the end point and the display area output from the above comparison process; A logical synthesis process that simultaneously performs processing for generating data indicating that the line is outside the display area, and processing for generating data indicating the type of clipping frame that intersects the straight line when the line intersects the display area.