JPS62237584A - Scissoring processing system - Google Patents

Abstract

PURPOSE:To improve the efficiency of graphic processing by executing scissoring processing in the graphic processing of a computer system based on simple decision logic. CONSTITUTION:In a processing step 33, plural decision points are set up on a display line 2 in a section between a start point 5 and the succeeding intersecting point 3. For instance, the decision points are equally dispersed into the decision point section by a method for distributing the decision points equally on the (x) or (y) coordinate in the section. In a processing step 34, whether each decision point in all the decision points exists on the inside or outside of a frame is discriminated and the number of points on the inside of the frame in case the decision points exist inside the frame or the number of points on the outside of the frame in case of the outside of the frame is counted up. In a processing step 35, the number of inside points and the number of outside points to be the discriminated result in the preceding step are compared with each other, and in case the number of inside points is larger than the number of outside points, the program is advanced to a processing step 36 and a curve in the section between the two intersecting points practically processed determined as a display part. In case the number of inside points is smaller than the number of outside points, the section processed at present is determined as a cut-off part by a processing step 37.

Description

[Detailed Description of the Invention] [Summary] A scissoring processing method for displaying only the portion of a quadratic curve figure included within a predetermined frame. Find all the intersections between the display line of the display target and the frame line, take a plurality of points on the display line between adjacent intersections, and identify whether those points are within the frame. If a majority of the points are identified as being within the frame, that part of the display line is set as the display part; otherwise, it is set as the truncated part. This method simplifies and speeds up processing.

[Industrial application field]

The present invention relates to a scissoring processing method for displaying a portion within a predetermined frame of a quadratic curve figure in graphic processing of a computer system.

When displaying a figure on a display device, etc., it is necessary to display a part of a large figure, or to divide the display surface into multiple frame areas and display a different part of the figure in each frame area. Become.

In this case, the process of cutting out a portion limited by a predetermined frame from the original figure is called scissoring, and the scissoring process is often used in figure display processing.

[Conventional technology]

FIG. 2 is a diagram showing an example of a display surface. Further, FIG. 3 is a process flowchart showing an example of scissoring process.

In Figure 2, when scissoring display line 2 so that it fits into designated frame 1 on the display screen, the equation of the quadratic curve representing display line 2 and the straight line representing each side of frame 1 are used. From each equation, calculate the points that satisfy both conditions (processing step 20 in Figure 3),
A point on the side is set as the intersection point 3.4, and its coordinate values are obtained (processing step 22).

Further, the coordinates of both ends of the display line are separately determined as a starting point 5 and an ending point 6.

In order to determine the display portion of the display line 2, for example, the intersection point 3.
4. The starting point 5 and the ending point 6 are arranged according to the size of their coordinate values (processing step 23), and first, it is determined whether the starting point 5 is inside or outside the frame (processing step 24).

This can be easily determined, for example, by comparing the coordinate values of the four corner vertices of the frame 1 with the coordinate values of the starting point 5.

According to the example shown in the figure, when it is identified that the starting point 5 is outside the frame, in processing step 25, the intersection point 3 next to the starting point 5 is
The part up to this point is discarded, and the process proceeds to process step 27 via process step 26.

In processing step 27, curve 2 enters the frame from intersection point 3,
It is determined that the image goes outside the frame at the next intersection point 4, and this area is set as the display area.

Similarly, if there is another intersection next to intersection 4, the process returns from processing step 28 to processing step 25, and the area from intersection 4 to the next intersection is cut off.

In this way, processing steps 25 and 27 are carried out alternately, and finally, in processing step 26 or 28, it is determined that processing has been completed up to the end point 6, and the part within the frame of one curve, that is, the display part is identified. I can do it.

In the example shown in the figure, there is no other intersection after intersection 4 and the end point is 6, so it is determined that curve 2 ends outside the frame at intersection 4, and only the part from intersection 3 to intersection 4 is displayed. It is determined that

The display part on the curve can be determined by the logic illustrated above, but as a special case, for example, the display "
As in the case of MA 7, if the display line is a quadratic curve that touches frame 1, the intersection point is one point of contact 8, and judging by the above logic, the point of contact 8 is the boundary, ζ, and curve 7 is the frame. It is determined that it straddles the inside and outside of 1, and half of it is considered to be within the frame.

In order to prevent this, in the process of calculating the intersection point, it is identified that the solution is a root, and in that case, for example, it is assumed that there is no intersection point (processing step 21), so as not to cause a contradiction in the identification based on the above logic. must be done.

As is well known, errors generally occur when solving intersection points by a computer, so in the above case, as a result of the error, it is not necessarily detected as a square root, and there may be no real root at all, or there may be a double root (
In other words, there may be cases where the result is that there are no intersections or there are two intersections, but in that case, the discrimination based on the logic described above can provide a result that does not pose any practical problem in terms of display control.

As another special case, when the display line passes through only one corner vertex lO of the frame 1, as shown as the display line 9,
Assuming there is no error, vertex 10 is side 1 of frame 1
It must be the intersection of both sides 1 and 12, i.e. a total of 2
intersection points are obtained.

However, in reality, due to errors, two different points are generally obtained as a solution, and the point may not be on sides 11 or 12, but may be a point outside the frame on the extension thereof. As a result, the number of intersections between the display line 9 and the frame 1 may be 0, 1, or 2.

In this case, when the number of intersections is O and two, it is possible to obtain a result with no practical problems, as in the case of the contacts described above. However, if there is only one intersection, it will obviously be erroneously determined that half of the display line 9 is within the frame.

To avoid this, for example, it is determined whether the point obtained as a solution to the equation is an intersection with the frame (processing step 22
), a method is adopted to cover deviations due to errors by widening the range of the intersection judgment conditions for determining that the point is on the line of the frame.

[Problem that the invention seeks to solve]

According to the conventional scissoring processing method, the basic processing is relatively simple, but in consideration of special cases such as the two cases mentioned above, it is always necessary to perform imperial ancestor determination/removal processing, and calculation errors may occur. It is necessary to appropriately relax and set the intersection determination conditions in consideration of the above.

In particular, if the intersection point judgment conditions are not appropriate, results such as displaying incorrect parts may occur. However, depending on the shape of the displayed curve, the coefficients of the curve equation may vary over a relatively wide range, so the error range is It is often difficult to determine the conditions appropriately, and there are problems such as the need to set judgment conditions in consideration of the figures being handled.

[Means for solving problems]

FIG. 1 is a process flowchart showing the configuration of the present invention.

In the figure, 30 to 32 are processing steps for finding intersection points;
33 to 38 are processing steps for determining whether a display portion or a truncated portion is to be displayed between each two intersection points.

[For production]

Through processing steps 30 to 32, intersection points are determined and arranged along with the end point and start point.

The processing from processing step 33 is performed for each two adjacent intersection points (or starting point, end point) starting from the starting point, and in processing step 33, a determination point is provided on the display line so as to appropriately divide the two intersection points. .

In processing step 34, it is determined whether all determination points are within the frame or outside the frame, and the number of points within the frame or the number of points outside the frame is counted according to the result.

In processing step 35, the number of points inside the frame and the number of points outside the frame as a result of the previous step are compared, and if the number of points inside the frame is greater than the number of points outside the frame, the process proceeds to step 36, and the curve of the currently processed two-intersection section is determined as the display part. .

If the number of points within the frame is less than the number of points outside the frame, in processing step 37, the portion of the current processing section is determined to be the portion to be discarded.

Until it is determined in processing step 38 that the process has reached the end point, the processing from processing step 33 is sequentially executed for the section with the next intersection point.

With the above processing method, there is no need to specifically detect the imperial ancestor when solving the equation, and the intersection judgment condition that takes the error range into consideration does not directly affect the identification of the display part.
The display portion can always be selected correctly.

〔Example〕

In the following, the explanation will be given again with reference to the example shown in FIG.

In processing step 30 in FIG. 1, points that satisfy both equations are determined by calculation from the equation of the quadratic curve representing the display line 2 and the equations of the straight lines representing each side of the frame 1, as in the conventional method. However, there is no need to specifically detect that the person is a royal ancestor.

In the next processing step 31, it is determined whether the obtained point is on frame 1, and intersection points 3, 4, etc. are determined. This determination is performed in the same manner as the conventional processing step 22, but for the reasons described below,
In the present invention, there is no need to particularly relax the intersection point determination conditions in consideration of erroneous determination of intersection points of curves passing through the vertices of the frame.

In processing step 32, the determined intersection point is determined as before,
Arrange the starting point 5 and ending point 6 in the order of their coordinate values.

In processing step 33, a plurality of determination points are first set on the display line 2 in the section starting from the starting point 5 and with the next intersection point 3.

It is desirable to set this so that the judgment points are evenly distributed within the section, for example by dividing the section into equal parts on the X or y coordinates, and the number of judgment points is, for example, about 7. It is better to set it to an odd number for ease of judgment.

In processing step 34, it is determined whether each judgment point is inside or outside the frame, and if the judgment point is inside the frame, the number of points inside the frame is counted, and if it is outside the frame, the number of points outside the frame is counted.

In processing step 35, the number of points inside the frame and the number of points outside the frame as a result of the previous step are compared, and if the number of points inside the frame is greater than the number of points outside the frame, that is, the number of judgment points determined to be within the frame in this section is greater than the number of judgment points outside the frame. If there are many, the process proceeds to step 36, and the curve of the currently processed two-intersection section is determined as the display portion.

If the number of points within the frame is less than the number of points outside the frame, in processing step 37, the portion of the current processing section is determined to be the portion to be discarded.

In processing step 38, the processing from processing step 33 is sequentially executed for the section with the next intersection point until it is determined that the end point has been processed.

In the above processing, in many cases where the arrangement of frames and display lines is normal, such as display line 2 in Fig. 2, in each section,
Only one of the points within the frame or the number of points outside the frame is counted, and the other is O, and correct identification is performed.

In a case like the display "IrfA7", if there is one intersection (point of contact 8), two sections are created: the section from the start point 40 of the display line 7 to the contact point 8, and the section from the contact point 8 to the end point 41. However, in the processing of steps 33 to 37, since there are many determination points outside the frame in both sections, both sections are determined to be truncated sections, and no erroneous determination occurs.

In the case of the example of display line 9, even if there is only one intersection,
Processing is performed for two sections with the intersection near the vertex 10 as the boundary, and as a result of the overwhelmingly large number of out-of-frame determination points being counted in each section, both sections become truncated sections.

In other words, the display portion and the truncated portion can always be identified without error by the regular processing that does not require consideration of special cases.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the scissoring process in the graphic processing of a computer system is executed using a simple judgment logic, and erroneous identification does not occur, thereby improving the efficiency of the graphic processing. This has a significant industrial effect.

[Brief explanation of drawings]

FIG. 1 is a flowchart of processing showing the configuration of the present invention, FIG. 2 is an explanatory diagram of an example of a graphic display screen, and FIG. 3 is a flowchart of conventional processing. In the figure, 1 is the frame, 2.7.9 is the display line, 3.4 is the intersection, 5.4o is the starting point, 6.41 is the ending point,
8 is the contact point, 10 is the vertex, 11.12 is the edge, 20 to 28
．． Days 30-3 represent processing steps. Figure 1

Claims (1)

[Scope of Claims] When displaying a quadratic curve figure that is cut out only within a frame surrounded by a predetermined frame line, means for calculating all the intersection points between the frame line and the display line of the figure ( 30, 31, 32), and for each two adjacent intersection points among the calculated intersection points, each point is selected from the part sandwiched between the two intersection points on the display line, and each point is within the frame. means (33) for identifying whether the points are within the frame or outside the frame; and when a majority of the points are identified as being within the frame, the part of the display line is determined as the part that requires display (34,
35, 36) A scissoring processing method characterized by being configured as follows.