JPH05128272A - Intersection calculation method in straight line drawing processing - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to speed up the line drawing processing time and improve drawing quality. [Structure] Calculate the difference between the start and end points of the line to be drawn, set the value of the operator that calculates the drawing start dot of the line to be drawn, and set the coordinates of the temporary intersection near the boundary and outside the drawing area. Then, it is determined whether the current value of the operator exceeds the reference value, the coordinates of the temporary intersection are changed to form dummy dots until the current value of the operator is exceeded, and the current value of the operator is updated to a new value. Repeat the process with the current value of
When the current value of the operator exceeds a predetermined value, the coordinate in the direction orthogonal to the direction of 1 is changed by 1 dot in the direction of the end point to be the drawing start dot.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 5 shows an X in a general drawing processing apparatus.
It shows a drawable area that represents the position of a dot with coordinates and a Y coordinate. 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 clip0 and c in the Y-axis direction.
It is a region surrounded by lipy1. When a straight line is drawn in this drawing area, dummy dots are generated from the start point to the end point of the line drawing point, that is, dot coordinates, and when 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 to calculate the intersection. Therefore, in the conventional intersection calculation method of the straight line drawing processing, the coordinates (xp, yp) of the intersection are calculated by the mathematical formula as shown in Formula 1, and the drawing is performed by using this as the drawing start dot.

[Equation 1]

[0003]

However, in the above-described conventional intersection calculation method of the straight line drawing processing, there are dots which are in the drawing area but are not drawn. For example, as shown in FIG. 6, a boundary line cl between the line to be drawn and the drawing area A point cl
The true intersection with ipy0 is the intersection (xp,
However, there is a problem that the true intersection is not drawn and the drawing quality is deteriorated even though the dot is one before yp).

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an intersection point calculation method of an excellent straight line drawing process with high drawing quality capable of drawing a true intersection point even though the intersection point is calculated by a mathematical expression. And

[0005]

In order to achieve the above object, the present invention sets a value of an operator for calculating a difference between a starting point and an ending point of a straight line to be drawn and calculating a drawing start dot of the straight line to be drawn. Then, the coordinates of the tentative intersection near the boundary line in one direction in the X-axis direction or the Y-axis direction and outside the drawing area are set, and it is determined whether or not the current value of the operator exceeds the reference value,
Until the standard value is exceeded, the coordinate in the 1 direction of the temporary intersection is changed by 1 dot in the direction of the end point to form a dummy dot, and the current value of the operator is updated and the process of setting the new value as the current value is repeated. , When the current value of the operator exceeds the specified value 1
The coordinate in the direction orthogonal to the direction is changed by 1 dot in the direction of the end point to be the drawing start dot.

[0006]

Therefore, according to the present invention, the provisional intersection is calculated in the vicinity of the boundary line outside the drawing area which intersects the straight line to be drawn, and the dummy dot is formed after this provisional intersection to calculate the drawing start dot. The number of memory cells and the number of memory accesses can be reduced, the processing speed can be increased, and an accurate drawing start dot can be calculated by forming a dummy dot, 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 of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a flowchart of an intersection point calculation routine executed by a controller (not shown) in the drawing processing device when the drawn line intersects the boundary line clip0 in the X-axis direction, as in the case of FIG. is there.

First, in step S1 of FIG. 1, a temporary intersection (xp, y) outside the drawing area and near the boundary line clip0.
p) is calculated by the equation 2. Further, the initial value (E = − | dx |) of the operator E, which is a variable for calculating the drawing start dot of the drawing line, is set. Therefore, the initial value is smaller than the reference value 0 and E <0.

[Equation 2]

Next, in step S2, a dummy dot is formed at the coordinate (xp + 1, yp) where the X coordinate xp of the temporary intersection (xp, yp) is updated to the end point side in the X-axis direction by one dot, and the operator is formed. A new value obtained by updating the current value of E by Equation 3 is used as the current value.

## EQU00003 ## The current value of the operator E is compared with the reference value "0" in step S3. If the operator E is E≤0, the process proceeds to step S2 to form a dummy dot. And the value of the operator E is updated. And step S3
In step S3, the steps S2 and S3 are repeated until the operator E becomes E> 0. When E> 0, the process proceeds to step S4, and the dummy dot Y immediately before is processed.
A dummy dot with one dot updated on the end point side in the Y-axis direction is formed, and it is determined in step S5 whether or not the latest dummy dot is in clip0, that is, in the drawing area. For example, in step S6, the current value of the operator E is updated by the equation 4, the process proceeds to step S2, and each step up to step S5 is executed. Then, if the latest dummy dot is within the drawing area, the intersection point calculation routine ends. Then, the drawing of a straight line is started using the latest dummy dot as a drawing start dot.

[Equation 4]

In the above example, the straight line to be drawn is clipy0.
This is the intersection calculation routine when intersecting with
When intersecting with y1 or clipx0 or x1, Formula 2 becomes Formula 5 to Formula 7. That is, it is possible to set the drawing start dot by the same intersection point calculation method as in the above example, except that the update direction and the like in Formulas 1 to 4 are different.

[Equation 5]

[Equation 6]

[Equation 7]

Next, a method for calculating the angle of a straight line to be drawn and determining such an updating direction will be described with reference to FIGS. 2 and 3. FIG. 2 shows a case where the absolute value | dx | of the difference between the start point and the end point of the drawn straight line 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. The absolute value | θ | of is smaller than 45 degrees. In this case, the straight line to be drawn intersects clip0 and clip1. In this case, X from the start point to the end point
The absolute number of dots in the coordinates must be greater than or equal to the number of absolute dots in the Y coordinate.

Further, FIG. 3 shows that the absolute value | dx | of the difference in the X-axis direction between the start point and the end point of the drawn straight line is less than or equal to the absolute value | dy | of the difference in the Y-axis direction, that is, the straight line and the X-axis. The absolute value | θ | of the angle formed by and is determined to be 45 degrees or more. In this case, the line to draw is clipx
Shall intersect 0 and clipx1. Further, in this case, the absolute dot number of the Y coordinate from the start point to the end point must be equal to or more than the absolute dot number of the X coordinate.

FIG. 4 shows a straight line drawn by the intersection calculation method obtained by the intersection calculation routine of FIG. In this case, since dx = 34 and dy = 6, the absolute dot number in the X-axis direction of the drawn straight line is five times as many as the absolute dot number in the Y-axis direction. The ratio of the number of dots is determined based on the ratio of absolute values of dx and dy. The coordinates (xp, yp) of the provisional intersection calculated by the above equation 2 are (x0 + 17, clipy0-
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 temporary intersection.
8, a dummy dot is formed in the clip 0-1), and
Then, the operator E is updated to E = -22. Since E <0, the process returns to step S2 and the coordinates (x0 + 1
9. Dummy dots are formed in 9, clip 0-1) and the updated operator E = -10 is calculated. Since the operator E is still negative here, the coordinates (x0 + 20, clip0-
Dummy dots are formed in 1) and the operator E is updated to E
= 2. Here, since the operator E becomes positive for the first time, the process proceeds to step S4, and the point of the 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 a true intersection, that is, a drawing open dot.

As described above, when the 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 the provisional intersection, the drawing area is formed. Since the true intersection of the boundary line and the straight line is calculated and used as the drawing start dot, the drawing quality can be improved.

[0016]

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

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing procedure of an embodiment of an intersection point calculation method in a straight line drawing processing of the present invention.

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

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

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

FIG. 5 is a diagram showing a drawable area in which a dot position is represented by X and Y coordinates in the drawing processing apparatus.

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

## EQU1 ## xp = x0 + dx / dy * (clipy0-y0) yp = clipy0

## EQU00002 ## xp = x0 + dx / dy * {(clipy0-
y0) -1} yp = clipy0-1

[Equation 3] E = E + | 2 * dy |

[Equation 4] E = E + | 2 * dx |

## EQU00005 ## xp = x0 + dx / dy * {(clipy1-
y0) -1} yp = clipy1-1

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

## EQU00007 ## xp = clipx1-1 yp = x0 + dy / dx * {(clipx1-x0)-
1}

Claims (2)

[Claims] 1. When drawing a straight line in a drawing area surrounded by a boundary line in the X-axis and Y-axis directions in a drawable area that represents the position of a dot by the X coordinate and the Y coordinate, it is drawn with the boundary line. A method of calculating an intersection with a straight line, comprising: calculating a difference between a start point and an end point of a straight line to be drawn, setting a value of an operator for calculating a drawing start dot of the straight line to be drawn, Coordinates of a temporary intersection near the boundary line in one of the axial directions and outside the drawing area are set, and it is determined whether the current value of the operator exceeds a reference value, and the reference value is exceeded. Until the dummy dot is formed by changing the coordinate in the direction 1 of the tentative intersection to the direction of the end point, the process of updating the current value and setting the new value as the current value is repeated until the current value is reached. When exceeds the reference value How intersection calculation in the linear drawing process, characterized in that by changing one dot in the direction of the coordinate perpendicular to the first direction in the direction of the end point and the drawing start dot. 2. The direction 1 is the X-axis direction when the absolute value of the difference in the X-axis direction is larger than the absolute value in the Y-axis direction, and the absolute value in the X-axis direction is the Y-direction. The intersection point calculation method in the straight line drawing process according to claim 1, wherein when the absolute value in the axial direction is less than or equal to the absolute value, the Y-axis direction is set.