JP2937587B2 - Intersection calculation method in line drawing processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of calculating an intersection of a straight line drawing process in a drawing processor such as a laser printer or a word processor.

[0002]

2. Description of the Related Art FIG. 5 shows X in a general drawing processing apparatus.
It shows a drawable area indicating the position of a dot by coordinates and Y coordinates. In FIG. 5, areas indicated by ranges A, B, C, and D are drawing areas arbitrarily set by the user, and include boundary lines clipx0 and clipx1 in the X-axis direction and boundary lines clipy0 and c in the Y-axis direction.
It is an area surrounded by lipy1. When drawing a straight line in this drawing area, a dummy dot is generated from the start point to the end point of the drawing point of the straight line, that is, the dot coordinate, and drawing is performed while calculating the coordinates of the intersection, the intersection of the straight line and the boundary line However, when the straight line is long, the number of processing steps, that is, the processing time, is longer than necessary for calculating the intersection. Therefore, in the intersection calculation method of the conventional straight line drawing processing, the coordinates (xp, yp) of the intersection are calculated by a mathematical formula as shown in Expression 1, and the drawing is performed using the calculation as a drawing start dot.

Xp = x0 + dx / dy * (clipy0−y0) yp = clipy0

[0003]

However, in the above-described conventional method of calculating the intersection point in the straight line drawing process, a dot which is in the drawing area but not drawn occurs. For example, as shown in FIG. 6, a boundary line cl between a straight line to be drawn and a drawing area A point.
The true intersection with ipy0 is the intersection (xp,
In spite of the dot just before yp), there is a problem that a true intersection is not drawn and the drawing quality is degraded.

An object of the present invention is to solve the above-mentioned conventional problem, and to provide an intersection calculation method of a straight line drawing process which can draw a true intersection and has a high drawing quality, while calculating the intersection by a mathematical formula. And

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a drawable area which represents the position of a dot by X coordinate and Y coordinate in the X axis direction and the Y axis orthogonal to the X axis direction. When drawing a straight line in a drawing area surrounded by a boundary line in a direction, an intersection calculation method for calculating an intersection between the boundary line and the straight line to be drawn, comprising: an X-axis direction of a start point and an end point of the straight line to be drawn And the difference in one direction of the Y-axis direction is compared with the difference in the other direction, and the absolute value of the angle between the one-way boundary line of the drawable area and the straight line to be drawn that intersects the boundary line is 45. When it is recognized that it is smaller than the degree, the value of the operator for calculating the drawing start dot of the straight line to be drawn is set by the difference in the one direction, and is set near the boundary line in the one direction and the drawing area. Determine coordinates of outside temporary intersection Determining whether or not the current value of the operator has exceeded a reference value, and forming a dummy dot in which the coordinates in the one direction of the temporary intersection are changed by one dot in the direction of the end point until the current value of the operator exceeds the reference value. And the process of setting the new value obtained by updating the current value as the current value is repeated, and when the current value exceeds the reference value, the coordinates in the other direction orthogonal to the one direction are changed by one dot in the direction of the end point. Then, the drawing start dot is used.

[0006]

Therefore, according to the present invention, a provisional intersection is calculated in the vicinity of a boundary line outside a drawing area which intersects a straight line to be drawn, and a dummy dot is formed after this provisional intersection to calculate a drawing start dot. It is possible to reduce the number of memory accesses and the number of memory accesses, increase the speed of processing, and calculate the accurate drawing start dot by forming dummy dots, so that high drawing quality can be obtained. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for calculating an intersection in a straight line drawing process according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart of an intersection calculation routine executed by a controller (not shown) in the drawing processing device when a straight line to be drawn intersects a boundary line clipy0 in the X-axis direction, similarly to the case of FIG. is there.

First, in step S1 of FIG. 1, a provisional intersection (xp, y) outside the drawing area and near the boundary line clipy0 is set.
p) is calculated by Equation 2. Further, an initial value (E = − | dx |) of the operator E, which is a variable for calculating a drawing start dot of a straight line to be drawn, is set. Therefore, the initial value is smaller than the reference value of 0 and E <0.

Xp = x0 + dx / dy * {(clipy0-y0) -1} yp = clipy0-1

Next, in step S2, a dummy dot is formed at the coordinate (xp + 1, yp) obtained by updating the X coordinate xp of the provisional intersection (xp, yp) by one dot toward the end point in the X-axis direction, and the operator A new value obtained by updating the current value of E by Expression 3 is set as the current value.

E = E + | 2 * dy | The current value of the operator E is compared with the reference value “0” in step S3. If the operator E satisfies E ≦ 0, the process proceeds to step S2. The process proceeds to form a dummy dot and update the value of the operator E. Steps S2 and S3 are repeated until the operator E satisfies E> 0 in step S3. When E> 0, the process proceeds to step S4, where the Y coordinate of the immediately preceding dummy dot is set to Y.
A dummy dot updated by one dot is formed on the end point side in the axial direction, and the latest dummy dot is cl in step S5.
It is determined whether or not it is within ipy0, that is, within the drawing area. If not within the drawing area, the current value of the operator E is updated by Expression 4 in step S6, and the process proceeds to step S2 to step S5. Perform the steps. Then, if the latest dummy dot is within the drawing area, the intersection calculation routine ends. Then, drawing of a straight line is started using the latest dummy dot as a drawing start dot.

E = E− | 2 * dx |

In the above example, the straight line to be drawn is clippy0.
Is an intersection calculation routine in the case of intersecting with
In the case of intersecting with y1 or clipx0 or x1, Equation 2 becomes Equation 5 to Equation 7. That is, it is possible to set the drawing start dot by the same intersection calculation method as in the above example, except that the update direction and the like in Equations 1 to 4 are different.

Xp = x0 + dx / dy * {(clipy1-y0) -1} yp = clipy1-1

Xp = clipx0-1 yp = x0 + dy / dx * {(clipx0-x0) -1}

Xp = clipx1-1 yp = x0 + dy / dx * {(clipx1-x0) -1}

Next, a method of calculating the angle of a straight line to be drawn and determining such an update direction will be described with reference to FIGS. FIG. 2 shows a case where the absolute value | dx | of the difference between the start point and the end point of the straight line to be drawn in the X-axis direction is larger than the absolute value | dy | of the difference in the Y-axis direction, that is, the angle between the straight line and the X axis. Is determined when the absolute value | θ | is smaller than 45 degrees. In this case, the straight line to be drawn intersects clipy0 and clipy1. In this case, X from the start point to the end point
The absolute dot number of the coordinate must be equal to or greater than the absolute dot number of the Y coordinate.

FIG. 3 shows a case where the absolute value | dx | of the difference in the X-axis direction between the start point and the end point of the straight line to be drawn is equal to or less than the absolute value | dy | Is to be determined when the absolute value | θ | In this case, the line to be drawn is clipx
0 and clipx1. In this case, the absolute number of dots on the Y coordinate from the start point to the end point must be equal to or greater than the absolute number of dots on the X coordinate.

FIG. 4 shows a drawing state of a straight line by the intersection calculation method obtained by the intersection calculation routine of FIG. In this case, since dx = 34 and dy = 6, the absolute number of dots in the X-axis direction of the straight line to be drawn is five times the number of absolute dots in the Y-axis direction. The ratio of the number of dots is determined based on the ratio of the absolute values of dx and dy. The coordinates (xp, yp) of the tentative intersection calculated by the above equation 2 are (x0 + 17, clippy0−
1), and the initial value of the operator E is -34.

Next, in step S2 of FIG. 1, the coordinates (x0 + 1) updated by one dot in the X-axis direction from the coordinates of the provisional intersection.
8, a dummy dot is formed on clipy0-1), and
To update E to −22. Since E <0, the process returns to step S2 and returns to the coordinates (x0 + 1) again.
9, a dummy dot is formed at (clipy 0-1), and the updated operator E = −10 is calculated. Here, since the operator E is still negative, the coordinates (x0 + 20, clipy0−
1) Dummy dots are formed and the operator E is updated to
= 2. Here, since the operator E becomes positive for the first time, the process proceeds to step S4, and a point of coordinates (xp ', yp') updated by one dot in the Y-axis direction is obtained. The coordinates of this point (x
(0 + 20, clipy0) is in clipy0, that is, in the drawing area, so this point is set as a true intersection point, that is, a drawing open dot.

As described above, when a straight line is drawn, the number of processing steps and the number of memory accesses can be reduced by calculating the provisional intersection, and by forming dummy dots from this provisional intersection, the drawing area can be reduced. Since the true intersection point between the boundary line and the straight line is calculated and used as the drawing start dot, the drawing quality can be improved.

[0016]

According to the present invention, as is apparent from the above embodiment, when a straight line is drawn in a drawing area, a provisional intersection is calculated near a boundary line outside the drawing area which intersects the straight line to be drawn. Since the dummy dot is generated after this provisional intersection and the drawing start dot is calculated, the number of processing steps and the number of memory accesses can be reduced, and the processing speed can be increased. Since an accurate drawing start dot can be calculated by generation, there is an effect that high drawing quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a processing procedure of an embodiment of an intersection calculation method in a straight line drawing process according to the present invention.

FIG. 2 is an explanatory diagram of a specific condition of an intersection of a straight line and a boundary line in the X-axis direction near a boundary of a drawing area according to the embodiment.

FIG. 3 is an explanatory diagram of a specific condition of an intersection of a straight line and a boundary line in a Y-axis direction near a boundary of a drawing area according to the embodiment.

FIG. 4 is an explanatory diagram of an intersection calculating process in which a boundary line and a straight line in the X-axis direction of a drawing area in the present embodiment are 45 degrees or less.

FIG. 5 is a diagram illustrating a drawable area indicating a position of a dot by an X coordinate and a Y coordinate in the drawing processing apparatus.

FIG. 6 shows a conventional drawing area having a boundary line and a straight line of 4 in the X-axis direction.
It is explanatory drawing of the intersection calculation processing of 5 degrees or less.

Claims (1)

(57) [Claims] When a straight line is drawn in a drawing area surrounded by a boundary in an X-axis direction and a Y-axis direction orthogonal to the X-axis direction in a drawing-possible area indicating a position of a dot by an X coordinate and a Y coordinate. An intersection calculation method for calculating an intersection between the boundary line and a straight line to be drawn, wherein an X-axis direction and a Y-axis of a start point and an end point of the straight line to be drawn
By comparing the difference in one direction of the axial direction and the difference in the other direction, the absolute value of the angle between the boundary line in one direction of the drawable area and the straight line to be drawn that intersects the boundary line is 45 degrees or more. When it is recognized that is also smaller, the value of the operator for calculating the drawing start dot of the straight line to be drawn is set by the difference in the one direction, and is set near the boundary in the one direction and outside the drawing area. Determine the coordinates of the temporary intersection, determine whether the current value of the operator has exceeded a reference value, the coordinates of the one direction of the temporary intersection in the direction of the end point by one dot until the current value of the operator exceeds the reference value The process of forming the changed dummy dot and setting the new value obtained by updating the current value as the current value is repeated, and when the current value exceeds the reference value, the coordinates in the other direction orthogonal to the one direction are calculated. 1 toward end point
An intersection calculation method in a straight line drawing process, wherein a dot is changed to the drawing start dot.