JP2902799B2 - How to clip shapes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a clipping how the graphics to be drawn cut out in the image processing from the drawing path only partially included in the clipping path.

[0002]

Clipping how BACKGROUND OF THE INVENTION graphic creates an edge data list with the list structure relative shapes as shown in FIGS. 12 and 13, the address of the head of the edge data has been set to the bucket. That is, the address of the memory that stores the side data is stored in the bucket, and the side data can be obtained by this. In addition, NULL is assigned to a portion where the address of the side data is not stored. An entry is made in the bucket with the minimum value of y of the side, and if the side already exists, the data is linked by link information.

As shown in FIG. 11, the edge data has a slope m,
Start point coordinates xS, ys, end point coordinates xE, yE, direction flag "+
1 ", a clip flag" -1 ", and a pointer to linked side information.

In Japanese Patent Application Laid-Open No. 1-154293, a bucket is searched in order, edge data is extracted from the bucket, edges are intersected, and if they intersect, the edge is divided at the intersection to form a new edge. In the side data list, and this intersection processing is repeated until the end of the bucket. Next, the bucket is searched again from the beginning, and the edge data linked to the bucket of interest is put into the active table. The sides entered in this active table are sequentially set as a noticed side, and whether the noticed side is a drawing path or a clipping path, a control rule method is determined and processed, and whether or not the noticed side is valid as a side to be actually drawn is determined. Are sequentially performed. Then, again, the sides entered in the active table are sequentially set as the noticed sides, and the start or end of the effective side is determined, and the sides to be actually drawn are obtained, and the trapezoid is cut out and drawn.

[0005]

However, when the sides intersect as described above, a new side is set at the intersection, so that there is a problem that the side data creation processing is wasted. In addition, duplication of bucket search and active table search occurred,
Unnecessary processing such as determination and processing of the control rule method for the drawing path deviating from the clipping path, determination of validity, determination of the start or end of the valid side occurs, and as a result, there is a problem that the clipping processing takes time. Was.

Accordingly, the present invention eliminates the need to perform a new edge creation process even when edges intersect, and provides a control method for a drawing route that overlaps a search of a bucket, a search of an active table, and a drawing route that deviates from a clipping route. determining a treatment effective for determining whether or not, clipping how <br/> of figures useless processing such as determining whether start Rika end of active edges can increase the speed of the clipping process without generating It is something to offer.

[0007]

Means for Solving the Problems and effects of the present invention is put to the side coming out of each vertex of the drawing path and the clipping path
That the starting point, first an endpoint, create an edge data list the edge data storing decide the order of the edges, such as tilt, entry to a bucket for indexing the <br/> edge data of the edge data list
Walking vertices of each side of the steps of, attention sides from the bucket and attention sides of search perilla drawing path and the clipping path
Indicates the side data for each Y coordinate scan line passing through the intersection.
A second step for performing intersection processing with sides in the active table stored in a fixed order and creating intersection information if there is an intersection, and two adjacent vertices passing through the vertices or intersections of the side .
A third step of sequentially retrieving a set of sides of the clipping region as a clipping side attention sides among the sides included between the Y coordinate scan lines, extracting this third stearyl <br/>-up A fourth step of taking out a set of sides constituting the drawing area from the active table between the set of sides thus determined, and determining an effective side; and forming a trapezoid with the effective side determined by the fourth step. A fifth step of painting,
Intersection exists between two adjacent Y coordinate scan lines
5th step, the trapezoidal fill
When this is done, it is included between these two Y coordinate scan lines.
This step comprises a sixth step of changing the order of the sides of the active table cut out at the sides to be inserted .

That is, as shown in FIG. 1, first, a side data list is created from drawing path data and clipping path data, and the list is entered into a bucket. Subsequently, intersection processing of sides in the active table is performed. Then, the right side and the left side of the clipping trapezoid are determined with the clipping path side in the active table as the target side. Subsequently, the left side and the right side of the trapezoid to be actually drawn are determined based on the control rule using the side of the drawing path located between the left side and the right side of the clipping trapezoid as the attention side. Thus, the valid side is determined and the trapezoid is painted.

As a result, the control process for the drawing path when the side of the clipping path does not exist in the active table and the control rule processing for the drawing path located on the right side of the right side of the clipping trapezoid are omitted.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

In the route control rules, non-zero number rules and odd-even rule rules are defined. In the non-zero number rule, the initial value is set to "0" on each Y coordinate scan line,
When the Y coordinate scan line intersects the route, the value is incremented by +1 when the Y increasing direction of the route is positive, and is decreased by -1 when the Y increasing direction of the route is negative.
to add. The section having the value “0” is defined as the outside, and the section other than the value “0” is defined as the inside. And the inside becomes an effective area.

In the odd-even rule, the initial value is set to "0" on each scan line, and the value is incremented by one every time the Y coordinate scan line crosses the path. When the value is an odd value, it is determined as internal, and when the value is even, it is determined as external. And the inside becomes an effective area.

Both the clipping path and the drawing path comply with one of the rules described above, and the inside is a filled area in the case of a drawing path, and the inside is a clipping area in the case of a clipping path.

As shown in FIG. 3, when the polygon consisting of the clipping paths of C0, C1, and C2 and the polygon consisting of the drawing paths of l0, l1, and l2 are overlaid and painted, both the clipping path and the drawing path are used. Follow non-zero numbering rules. The active table 1 stores side data for each scan line based on a predetermined order (order appearing from the left side in the figure).

The basic flow chart of this series of processing is as shown in FIG. 5. First, in step S1, a side data list 2 is created from the sides of the clipping path and the sides of the drawing path, and is entered in the bucket 3. (First Step) Thus, the side data list 2 and the bucket 3 shown in FIG. 4 are created. NULL is stored in the bucket 3 having no side data. ("/" Part in the figure) Then, in step S2, it is searched whether there is edge data in the bucket of interest. If there is edge data, edge data is extracted in step S3.

Subsequently, it is checked whether or not there is an intersection between the side data extracted in step S4 and the side in the active table 1. If there is an intersection, the intersection is stored in the intersection information area in step S5. That is, as shown in FIG. 2, the value of the scan line passing through the intersection and the address of the intersecting side data are stored in the intersection information area 4, and the address of the intersection information area 4 is designated by the intersection information stack 5. I have. If there is no intersection, the intersection processing is not performed. Subsequently, the sides extracted in step S6 are stored in the active table 1 and sorted.

Then, in step S7, it is checked whether or not the edge data is linked. If the link has been made, the process returns to step S3. If there is no link, the bucket 3 of interest is searched in step S8. Steps S2 to S7 correspond to the second step.
Has formed.

Next, in step S9, the interval between the bucket 3 of interest and the scan line of the bucket 3 of interest is
The trapezoid cut out by the effective side in the active table 1 is painted.

Subsequently, in step S10, the side in the active table 1 in which the maximum value of the y coordinate of the side is smaller than the scan line of the bucket 3 of interest next is deleted from the active table 1 and the active table 1 is sorted. I do. Then, the process returns to step S2 to search for the next side of interest, and repeats a series of processing. When there is finally no side data in the bucket 3 of interest, the processing is terminated. FIG. 6 shows the details of the processing in step S9.

First, the bucket 3 of interest in step S11
It is checked whether there is an intersection between the scan line of the bucket 3 and the scan line of the bucket 3 of interest next. If there is no intersection, a trapezoid is cut out and painted between the scan line of the bucket 3 of interest and the scan line of the bucket 3 of interest in step S12.

If there is an intersection, a trapezoid is cut out and painted in step 13 between the scan line of the bucket 3 of interest and the scan line passing through the intersection. Then, in step 14, the order of the sides of the active table 1 is changed. (Sixth
Step) Subsequently, in Step 15, it is checked whether another intersection exists, and if there is, in Step 16, a trapezoid is cut out and painted between scan lines passing through the intersection. And step 17
The order of the sides of the active table 1 is changed.
(Sixth Step) This process is repeated until another intersection does not exist. Step 18 if another intersection does not exist
A trapezoid is cut out and painted between the scan line passing through the intersection and the scan line of the bucket 3 of interest next. FIG. 7 shows the details of the processes in steps S12, S13, S16, and S18.

First, at step S21, a drawing path counter,
The clipping path counter, the clipping trapezoid left side number CL, the clipping trapezoid right side number CR, the painted trapezoid left side number PL, and the painted trapezoid right side number PR are each set to "0".

Then, in step S22, a set of clipping sides constituting the clipping area is searched from the active table 1 after the clipping trapezoid right side number CR, and the smaller number is searched for the clipping trapezoid left side number CL.
, And the larger number is set to the right side number CR of the clipping trapezoid. (Third Step) Subsequently, in step S23, it is checked whether or not a clipping side exists, and if not, the process ends.

If there is, the right side number PR of the trapezoid after the painted trapezoid right side number PR in step S24.
1 that constitutes a drawing area from the active table 1 up to
The drawing side of the set is searched, and the smaller number is set as the painted trapezoid left side number PL, and the larger number is set as the painted trapezoid right side number PR.

Subsequently, in step S25, it is checked whether or not there is a pair of sides of the painted trapezoid left side number PL and the painted trapezoid right side number PR. If not, the process proceeds to the processing in FIG. . If it exists, then in step S26, the painted trapezoid right side number PR is replaced with the clipping trapezoid left side number C
Check if it is less than L. If it is smaller, the process returns to step S24. If it is larger, then in step S27, it is checked whether the painted trapezoid left side number PL is smaller than the clipping trapezoid left side number CL.

If it is smaller, the clipping trapezoid left side number CL is set to the left side of the mapping trapezoid, and the painted trapezoid right side number PR is set to the right side of the mapping trapezoid in step S28. If it is larger, in step S29, the left side number PL of the filled trapezoid is set to the left side of the mapping trapezoid, and the right side number PR of the filled trapezoid is set to the right side of the mapping trapezoid. Steps S24 to S29 are performed in the fourth step.
Forming a step. Subsequently, a trapezoid is mapped in step S30. (Fifth step) When this mapping is completed, the process returns to step S24. In the process of FIG. 8, it is checked in step S31 whether both sides PL and PR of the paint do not exist. If not, the process returns to the process of step S22 in FIG. If there is, then in step S32, it is checked whether or not the painted trapezoid left side number PL is smaller than the clipping trapezoid left side number CL.

If it is smaller, in step S33, the clipping trapezoid left side number CL is set to the left side of the mapping trapezoid, and the clipping trapezoid right side number CR is set to the right side of the mapping trapezoid. If it is larger, step S34
, The left side number PL of the filled trapezoid is set on the left side of the mapping trapezoid, and the right side number CR of the clipping trapezoid is set on the right side of the mapping trapezoid. And step S in FIG.
Perform step 30. FIG. 9 shows details of the processing of steps S22 and S24 in FIG.

First, in step S41, the designated type of path counter is set in the internal counter. Subsequently, in step S42, it is determined whether a path of the specified type exists in the active table 1 and, if so, whether to pay attention to the side. Then, when there is no route of the specified type, and when the route is present and attention is not paid to that side, the process returns to the beginning.

If a route of the specified type exists and attention is paid to its side, it is checked in step S43 whether the control rule is a non-zero number rule. If the control rule is a non-zero number rule, the value of the direction flag is added to the internal counter in step S44. Then, in a step S45, it is checked whether or not the internal counter is "0". If the internal counter is not "0", then it is checked in step S46 whether the internal counter of the previous side is "0". If the internal counter of the previous side is "0", the process proceeds to the process of FIG. 10E, and if the internal counter of the previous side is not "0", the process returns to the step S42.

In step S45, the internal counter "0" is set.
Is determined, it is checked in step S47 whether the internal counter of the previous side is "0". If the internal counter of the previous side is not “0”, the process shifts to the process of F in FIG. 10. If the internal counter of the previous side is “0”, the process returns to step S42.

If the control rule is not the non-zero number rule in step S43, it is checked in step S48 whether the internal counter is an even number. If the internal counter is an odd number, the internal counter is incremented in a step S49, and in a step S50, it is checked whether or not the internal counter of the previous side is an even number. If the internal counter of the previous side is an even number, the process shifts to the processing of E in FIG. 10, and if the internal counter of the previous side is an odd number, the process returns to step S42.

If it is determined in step S48 that the internal counter is even, the internal counter is incremented in step S51, and in step S52 it is checked whether the internal counter of the previous side is even. If the internal counter of the previous side is an odd number, the process shifts to the process of F in FIG. 10. If the internal counter of the previous side is an even number, the process returns to step S42.

In the process of FIG. 10E, first, at step S53, it is checked whether or not the path is a clipping path. If it is a clipping path, the active table number is set to the clipping trapezoid left side number CL in step S54. Subsequently, in step S55, the internal counter is set to the clipping path counter, and the process returns to step S42 in FIG. If it is not the clipping path, the active table number is painted in step S56 and the trapezoid left side number PL
Set to. Subsequently, in step S57, the internal counter is set to the drawing path counter, and the process returns to step S42 in FIG.

The processing of F in FIG. 10 is performed first in step S58.
Check whether it is a clipping route or not. If it is a clipping path, the active table number is set to the clipping trapezoid right side number CR in step S59. Subsequently, in step S55, the internal counter is set to the clipping path counter, and the process returns to step S42 in FIG. If it is not a clipping path, the active table number is set to the painted right side number PR in step S60. Subsequently, in step S57, the internal counter is set to the drawing path counter, and the process returns to step S42 in FIG.

In this embodiment which performs the above-described processing, the polygon consisting of the clipping paths of C0, C1, and C2 shown in FIG. 3 and the polygon consisting of the drawing paths of l0, l1, and l2 are overlaid and painted. Considering the case, first, step S
At step 1, the side data 2 of the route of the sides C0, C1, C2, l0, l1, l2 is created. The side data 2 has the same configuration as that of FIG.

Then, the address of the memory storing the side data 2 is entered in the bucket 3 of the corresponding Y coordinate. At this time, NULL is entered in the bucket 3 having no side data. FIG.
The part of "/" in the middle.

Next, the bucket Y of interest in step S3
Search for 0 and extract the side data of side C0. Since there is nothing in the active table in the check in step S4, no intersection processing is performed. And step S
Insert the side C0 taken out in step 6 into the active table. Subsequently, since the side data C0 is linked to the side data C2, the side C0 is taken out in step S3 and the intersection processing is performed with the side C0 in the active table 1.

Since there is no intersection between the sides C0 and C2, the side C2 taken out in step S6 is put into the active table 1. Since the side data C2 is not linked, the next bucket Y1 of interest is searched in step S8. I do.

In step S9, the trapezoid cut out by the effective side in the active table 1 is filled between the scan line of the bucket Y0 of interest and the scan line of the next bucket Y1 of interest.

Since there is no intersection between the scan lines of the buckets Y0 and Y1, the trapezoid cut out by the side in the active table 1 is filled with Y1 as the upper base and Y0 as the lower base in step S12.

In this process, the value "0" of the crib path counter is set in the internal counter. Then, the side C0 of the clip path in the active table is set as the target side. Since the control rule is a non-zero number rule, in step S44, the Y direction flag +1 of side C0 is added to the value of the internal counter, and
The internal counter is set to “1”. Since the previous internal counter is "0", the active table number of this side C0 is set to the clipping trapezoid left side number CL in step S54.

Then, the process returns to step S42, and the side C2 of interest is taken out. In step S44, the direction flag "-1" is added to the internal counter, and the internal counter is set to "0".
Since the previous internal counter is not "0", the active table number of the side C2 is set to the clipping trapezoid left side number CR in step S59. Then search for a set of drawing sides from the active table 1 from the fill trapezoid right side number PR until clipping trapezoidal right sides number CR at step S24.

Since the designated drawing side does not exist in the active table 1, no painting is performed. Side C0, C2
Are larger than the scan line Y1, the sides C0 and C2 are kept in the active table 1.

Let Y 1 be the bucket of interest and the edge data l
Take out 1. Then, the intersection processing is performed between the side data l1 and the side in the active table 1. Since the side l1 intersects with the side C0, the value of the scan line SC1 passing through the intersection in the intersection information area 4 and the small value on the scan line Y1 in step S5. The address of the side data l1 having the x coordinate is entered. The address of the intersection information area 4 is put in the intersection information stack 5. The extracted edge l0 is placed in the active table 1 and sorted. Next, in step S8, the bucket Y2 of interest is searched. The trapezoid cut out by the effective side in the active table 1 is filled between the scan line of the bucket of interest Y1 and the next bucket of interest Y2.

Since there is a scan line SC0 passing through the intersection between the scan line of the bucket Y1 and the scan line of the bucket Y2, the target scan line Y1 is set to the lower bottom in step S13, and the scan line SC0 passing the intersection is set to the upper side. Fill the bottom with a trapezoid cut out by the active side of the active table 1.

Specifically, in step S21, the counters and the trapezoid left and right side numbers are initialized to "0". Step S
At 22, a search is made from the active table 1 for a set of clipping sides that make up the clip area. That is, in step S41, the clipping path counter is set to the internal counter. In step S42, the clipping path side in the active table 1 is searched, and the side C0 is set as the target side.

Since the control rule is a non-zero number rule, the direction flag "+1" of the side data C0 is added to the internal counter to make it "1". Since the internal counter of the previous side is "0" and is a clipping path, the side C is determined in step S54.
The active table number "2" of 0 is set to the left side number CL of the clipping trapezoid. In step S55, the internal counter "1" is set to the clipping path counter.

In the active table 1, the noted side C0
The side of the subsequent clipping path is searched, and the side C2 is set as the target side. The control rule is a non-zero number rule, and the internal counter is "1". The direction flag "-1" of the side data C2 is added to the internal counter to make it "0". Since the internal counter of the previous side is "1" and is a clipping path, the active table number "3" of the side C2 is set to the clipping trapezoid right side number CR in step S59. In step S55, the internal counter is set to the clipping path counter. Then, since there is no clipping side in the active table 1, the search ends.

Next, a set of drawing sides constituting a drawing path is searched from the active table 1 from the right side number PR = 0 of the filled trapezoid to the right side number CR = 3 of the clipping trapezoid, and PL = 0, PR = 1. Get. PR = 1 is trapezoidal fill is not performed is smaller than the clipping trapezoidal left sides number CL.

Since one set of drawing sides does not exist in the active table 1 following the filled trapezoid right side number PR and one set of clipping sides does not exist in the active table 1 following the clipping trapezoid right side number CR. The search for 1 ends. In step S14, a search is made in the active table 1 from the side l0 intersecting and the position of the next side C0 in the active table 1 is switched.

Scan line SC0 and scan line Y
2, there is a scan line SC1 passing through the intersection, so that the scan line SC0 is located below the scan line SC1.
Is filled with a trapezoid cut out by the effective side of the active table 1 with.

More specifically, in step S21, each path counter and the trapezoid left and right side numbers are initialized to "0". Searching a set of clipping sides of the clipping region from the clipping trapezoid right side number CR subsequent side in step S22, the active table number "1" of the clipping trapezoid left sides number CL is side C0, and the clipping trapezoidal right The side number CR obtains the active table number "3" of the side C2.

Then, in step S24, the right side number of the painted trapezoid right side PR = 0 and the right side number of the clipped trapezoid right side CR = 3
From the sides in the active table 1 up to a set of drawing sides constituting the drawing area, and a filled trapezoid left side number P
The active table number "0" of the side l1 is set to L, and the active table number "2" of the side l0 is set to the right side number PR of the painted trapezoid.

Since the filled trapezoid right side number PR is larger than the clipped trapezoid left side number CL and the filled trapezoid left side number PL is smaller than the clipped trapezoid left side number CL, the side C0 of the clipped trapezoid left side number CL is Set on the left side of the mapping trapezoid. The trapezoid is painted out by setting the side l0 of the painted trapezoid right side number PR to the right side.

Since one set of drawing sides does not exist in the active table 1 from PR = 2 to CR = 3, one set of clipping forming a clipping region from the sides in the active table 1 after the right side number CR of the clipping trapezoid. Search for an edge. Since there is no clipping side, the extraction of the trapezoid from the side in the active table 1 ends.

The intersecting side l1 is searched from the active table 1 and the order of the side l1 and the next side C0 is exchanged. Scan line Y2 and scan line SC
Since there is no scan line passing through the intersection between 1, the trapezoid cut out by the effective side of the active table 1 is painted with the scan line SC1 at the bottom and the scan line Y2 at the top.

More specifically, at step S21, the path counters and the trapezoid left and right side numbers are initialized to "0". In step S22, a set of clipping sides constituting the clipping region is searched from the sides subsequent to the clipping trapezoid right side number CR. The clipping trapezoid right side number CL becomes the active table number "0" of the side C0, and the clipping trapezoid right side. The number CR obtains the active table number "3".

Then, a set of drawing sides constituting the drawing area is searched from the sides of the active table 1 from the right side number PR = 0 of the filled trapezoid to the right side number CR = 3 of the clipped trapezoid, and the left side number of the filled trapezoid is searched. The active table number "1" of the side l1 is set in PL, and the active table number "2" of the side l0 is set in the right side number PR of the filled trapezoid.
Is set.

Since the filled trapezoid right side number PR is larger than the clipping trapezoid left side number CL and the filled trapezoid left side number PL is smaller than the clipped trapezoid left side number CL, the side l1 of the filled trapezoid left side number PL is larger. Is set on the left side of the mapping trapezoid. Filled trapezoid right side number PR
Is set to the right side, and the trapezoid is painted.

Since one set of drawing sides does not exist in the active table 1 from PR = 2 to CR = 3, one set of clipping forming a clipping area from the sides in the active table 1 after the right side number CR of the clipping trapezoid. Search for an edge. Since there is no clipping side, the extraction of the trapezoid from the side in the active table 1 ends.

In the side of the active table 1, the maximum Y coordinate value of the side C0 is equal to or less than the bucket scan line Y2 of interest next. Therefore, the side C0 is removed from the active table 1 in step S10, and the active table 1 is sorted. Next, the side of interest is searched, and the above-described series of processing is repeated. By performing such a process, the figure shown by the hatched portion in FIG. 3 is cut out and drawn.

As described above, the region having a complicated shape is divided into simple trapezoids, and the process of determining the effective side of the drawing side outside the clipping region can be omitted. Further, even when the sides intersect, there is no need to perform a new side creation process, and the sorting of the active table 1 at the intersection can be omitted. Further search for bucket 3 and active table 1
Does not occur in the search for. Therefore, the drawing and drawing processing of the figure can be performed at high speed.

[0063]

As described above in detail, according to the present invention, it is not necessary to perform a new edge creation process even when edges intersect, and it is also necessary to search for a bucket, overlap an active table search, or perform a clipping path. A graphic that can speed up the clipping process without unnecessary processing such as determination and processing of the control rule method of the drawing path deviating from, determination of validity, determination of the start or end of the valid side, etc. clipping how of those that can offer.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining basic processing of the present invention.

FIG. 2 is a diagram showing an intersection information area and an intersection information stack in the embodiment of the present invention.

FIG. 3 is a diagram showing a drawing path, a clipping path, and an active table in the embodiment of the present invention.

FIG. 4 is a diagram showing bucket and side data according to the embodiment of the present invention.

FIG. 5 is a flowchart showing clipping processing according to the embodiment of the present invention.

FIG. 6 is a flowchart showing in detail a process of painting a trapezoid cut out by an effective side in the active table in FIG. 5;

FIG. 7 is a flowchart showing in detail a process of filling a trapezoid between two scan lines in FIG. 6;

FIG. 8 is a flowchart showing in detail a process of filling a trapezoid between two scan lines in FIG. 6;

9 is a flowchart showing in detail a process of searching for a set of sides constituting a clip area or a drawing area in FIG. 7;

FIG. 10 is a flowchart showing in detail a process of searching for a set of sides constituting a clip area or a drawing area in FIG. 7;

FIG. 11 is a diagram showing a configuration example of edge data.

FIG. 12 is a view for explaining the relationship among figures, buckets, and side data.

FIG. 13 is a view for explaining the relationship among figures, buckets, and side data.

[Explanation of symbols]

1 active table, 2 side data list, 3 bucket, 4 intersection information area, 5 intersection information stack.

Claims (1)

(57) [Claims] 1. A created starting at the edges emanating from each vertex of the drawing path and the clipping path, ending, the edge data list storing edge data such as inclination determine the order of the edges,
A first step of entering this edge data list into a bucket for indexing edge data; searching for a target edge from the bucket, searching for the target edge, drawing path, and clipping;
Scan each Y vertex or vertex of each side of the
A second step of performing intersection processing with the side in the active table storing the side data for each line in a predetermined order and creating intersection information if there is an intersection; Between two adjacent Y coordinate scan lines
A third step for sequentially extracting a set of sides forming a clipping region with the target side as a clipping side among the included sides, and a third step for extracting a set of sides extracted in the third step. A fourth step of extracting a set of sides constituting the drawing area from the active table and determining an effective side, and filling a trapezoid with the effective side determined by the fourth step Fifth step and two adjacent Y coordinate
When there is an intersection between the scan lines,
When the trapezoidal painting is performed in step 5, this two
Is cut out on the side included between two Y coordinate scan lines
Sixth switching the order of the edges of the active tables
Clipping how shapes, characterized in that it consists of steps.