JPH08138064A - Device and method for graphic processing - Google Patents

Abstract

PURPOSE: To output a curve after correcting and adjusting it by adding an intersection nearer to the intersection part of the curve than the vertex of an approximate straight line as the vertex of the approximate straight line and deleting the vertex of the approximate straight line judged as disuse. CONSTITUTION: A tangent vector at the intersection of a designated curve is found by a CPU 1. Thence, when it is judged that the tangent vector differs from a short vector at a curve intersection, a comparison vector v0 is set on the short vector adjacent to the short vector at the curve intersection. The intersection between the short vector v0 and the extension line in a direction opposite to the tangent vector of the curve is found. Moreover, the coordinate of vertex of the intersection is compared with that of the vertex of the short vector v0. Consequently, when it is judged that the intersection is located nearest to the curve intersection, the data of the vertex in a deletion candidate buffer is excluded from an approximate point list. The intersection is added to the approximate point list newly as the vertex of the short vector. Moreover, the vertex of the short vector v0 is set on the deletion candidate buffer. The curve concerned is outputted to an output means 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphic processing apparatus and method capable of generating a curve.

[0002]

2. Description of the Related Art Conventionally, in this type of graphic processing apparatus,
When a curve is drawn, a set of short vectors that approximate the curve is generated and the set of short vectors is drawn.

[0003]

However, in the conventional graphic drawing apparatus, if this processing is performed by integer arithmetic in order to maintain the calculation processing speed for obtaining the short vector from the input control point data of the curve, the calculation will be performed. The above rounding error occurs, and it becomes impossible to properly process the acute angle portion at the intersection of the curves having a width exceeding one drawing unit.
This will be described with reference to FIGS. 7 and 8.

FIG. 7 shows an example of the case where the vertices of the short vector adjacent to the intersection of the curves are located outside the actual curve, and FIG. 8 is the case where the vertices of the short vector are located inside the actual curve. Here is an example. FIGS. 7 and 8 show that a designated curve of dark gray is approximated by vertices p1 to p9, and in order to draw a curve having a width exceeding one drawing unit, it is finally converted into a light gray polygon. It means inflating and drawing.

At the intersection of the curves, the noise generated by the rounding error is the short vector p5-p6 of FIG.
Alternatively, it appears as short vectors p5-p6 in FIG. When a curve with an arbitrary width is to be drawn using this short vector, the sharp-angled portion that should originally be output sharply is a light gray color consisting of the intersections of the extended lines of the straight line AB and the straight line CD in FIGS. It is output like a polygon (in the normal acute angle processing, a rule that a remarkably long vertex is not drawn, so in FIG. 8, the intersection of the straight line AB and the straight line CD is replaced by the straight line BC).

Further, if floating point arithmetic is performed to prevent rounding errors, there is a problem that the processing speed is significantly deteriorated.

The present invention is intended to solve the above-mentioned problems in the prior art, and it is possible to correct a calculation error of a curve having a width exceeding one drawing unit, shape it, and output it. A processing apparatus and method are provided.

[0008]

In order to achieve the above object, the graphic processing apparatus of the present invention has the following configuration.

That is, deriving means for deriving an intersection of a tangent line at an intersection of the curve and an approximate straight line approximating the curve, and the derived intersection is closer to the intersection of the curve than the apex of the approximate straight line. If it is determined by the determination means that determines whether or not there is a proximity, the intersection point is added as the vertex of the approximate straight line as data for representing a curve, and as a result, it is unnecessary. Correction means for deleting the vertices of the approximate straight line.

The graphic processing method of the present invention has the following configuration.

That is, a deriving step of deriving an intersection of a tangent line at an intersection of the curve and an approximate straight line that approximates the curve, and the derived intersection is closer to the intersection of the curve than the apex of the approximate straight line. If it is determined in the determination step that determines whether or not the two are close to each other, as data for representing a curve,
A correction step of adding the intersection points as vertices of the approximate straight line and deleting unnecessary vertices of the approximate straight line.

[0012]

With the above configuration, it is possible to correct a calculation error in a curve having a width exceeding one drawing unit, shape it, and output it.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. It should be noted that as long as the functions of the present invention can be executed, the present invention can be applied to a single device, a system including a plurality of devices, or a system that performs processing via a network such as a LAN. Needless to say, can be applied.

FIG. 1 is a system block diagram of a curve drawing apparatus according to an embodiment of the present invention. 1 is a CPU (Central) for processing data regarding a curve
Processing Unit). Reference numeral 2 is an input device for inputting the start point, the end point of the curve, and the position of the control point. As the input device, for example, a control point may be input by a keyboard or a pointing device (not shown), or a device that inputs a control point previously stored in a storage device such as an FD or HD. Reference numeral 3 denotes a storage device including ROM, RAM, HD, FD, etc. for storing data received from the input device 2, temporary data handled by the CPU, and a program according to a flowchart described later. 4 is an output means for outputting a curve,
It may be a display device such as a CRT display device or a liquid crystal display device, or a printer such as a laser beam printer, an inkjet printer or a thermal printer. For the start point, end point, control point and vector,
In the present invention, the expression method in input or output is not particularly limited.

FIG. 2 shows an example of the structure of graphic information and its constituent coordinate information stored in the RAM or HD used for drawing, which is used in this embodiment. FIG. 2 shows the structure of graphic drawing information. Reference numeral 21 is a figure identification number, and one figure uniquely corresponds to one figure identification number in this system. Reference numeral 22 is surface type information indicating information such as a surface pattern type and its color when the surface is filled in the figure, 23 is a line shape (solid line, dotted line, etc.) and its thickness,
Line type information indicating information such as color. Reference numeral 24 is data of a coordinate data group forming the figure, and the structure of each coordinate data is shown in FIG.

FIG. 3 shows individual structures of the configuration coordinate information stored in the RAM or HD and how they are configured. Reference numeral 31 is coordinate data of the point, 32 is information about the attribute of the point, and information indicating whether the end point of the straight line or the middle point of the curve data is set together with the identification information of the start point and the end point. There is. Reference numeral 33 is a pointer for pointing the coordinate next to the coordinate, and 34 is a pointer for pointing the previous coordinate similarly. This constituent coordinate information is realized by a bidirectional list as shown in the figure, and unnecessary coordinate points can be deleted or newly generated coordinate points can be inserted by updating 33 and 34 in the figure. Become. Here, an example in which the data enclosed by the dotted line is being inserted into the list is shown. As indicated by the dotted line, the pointers of the elements before and after the position to be inserted are changed to point to the new elements, and the new elements are pointed to the elements before and after the position to be inserted.

4 and 5, according to the present invention, at the intersection of two curves having a width exceeding one drawing unit,
An example of processing of an acute angle portion will be described.

First, referring to FIG. 4, a method of obtaining the Miter vertices drawn by the present invention will be described.

In the figure, curve1 and curve2
Is a designated curve to be generated, and q is the intersection of both curves. cv1 and cv2 are curve at intersection q
1 and curve2 are tangent vectors, and these can be geometrically obtained by using the equations of both curves. p ₁ and p ₂ are the other vertices that form a short vector that approximates this curve at the intersection point q, and their direction vectors are the same as the corresponding tangent vectors (p ₁ q = cv ₁ , p ₂ q = cv2). R
1 and R2 are rectangles generated based on the above short vector in order to approximate both curves near the intersection in consideration of the line width of the curves. r ₁ and r ₂ are the miter-side vertices of the outer sides of R1 and R2, respectively.

The Miter vertex m of the original curve exists on the vector obtained by combining the tangent vectors of both designated curves. Considering the line width of the curves, the above-mentioned rectangles R1 and R2 are considered.
Is equal to the intersection of the extended outer sides of. Therefore, the acute angle portion to be drawn in consideration of the line width is the portion of the polygon r ₁ mr ₂ q in FIG.

Next, an example of a short vector changing method for obtaining the miter vertices will be described with reference to FIG. Here, in order to simplify the description, only one of the curves (curve2 in the figure) will be focused. In the present embodiment, the intersection of the curves can be obtained by a known method, and for example, a cubic Bezier curve can be represented by a start point, an end point, and two control points.
Therefore, if a point that doubles as a start point and an end point is found, then that point is the intersection of the curves. Therefore, in this embodiment, it is assumed that p5 and p6 are recognized as intersections. In addition, the slope of the straight line connecting the end point of the curved portion a and the control point one before and the straight line connecting the start point of the curved portion b and the control point one after (or of the curved portions a and b If the slopes are substantially the same (smaller than a predetermined value), they may not be recognized as the intersections of the curves (to shorten the processing time).

In the figure, cu at the intersection point p ₅ of the two curves
and anti-straight line that the tangent vector of rve2 was extended in the opposite direction, the intersection of each short vector to approximate the curve2, slide into calculated in order from those close to the intersection p _5. Since the intersection point p _{5 of the} short vector p ₅ p ₆ is one of the vertices of the short vector, if it is excluded, the intersection points with p ₆ p ₇ are p _n0 , p
The intersection with ₇ p ₈ does not exist, and the intersection with p ₈ p ₉ is p _n1 . Among these intersections, the one that becomes the vertex of the newly generated short vector must satisfy the condition that it is closer to the intersection of the curves than both vertices of the short vector.

Therefore, among the above intersections, the point to be obtained is the point p _n1 , and as a result, the unnecessary short vector is
_{p 5 p 6, p 6 p} 7, p 7 p 8, it is. Also, p ₈ can be replaced with p _n1 .

[0024] That is, from the list that is stored at the intersection p ₅ in the RAM or HD approximating the curve2 by the process, together with the point p ₅ ~p ₈ is removed, a new point p _n1 is added.

FIG. 6 shows the graphic drawing apparatus of the present invention.
6 is a flowchart showing an example of the processing procedure of FIG. 5. The programs according to the flowchart of FIG. 5 are ROM, FD,
It is stored in the HD or the like and controlled by the CPU 1.

First, in step S601, the tangent vector at the intersection of the designated curves is obtained. Then in step S60
In step 2, it is checked whether the tangent vector and the short vector at the curve intersection are the same.
If it is determined that they are the same, it is not necessary to change the approximate point list, and this processing ends. If it is determined that the two vectors are different, step S603.
Then, the process for changing the approximate point list is performed. In step S603, the short vector adjacent to the short vector at the curve intersection is set as the comparison vector v0.
In step S604, the intersection of v0 and the extension of the tangent vector of the curve in the opposite direction is obtained. Step S60
In step 5, the coordinates of the intersection and the vertices of v0 are compared. If it is determined in step S606 that the intersection is the closest to the curve intersection as a result of the comparison processing in step S605, the process branches to step S607. In step S607, the vertex data in the removal candidate buffer set in step S609 is removed from the approximate point list. In step S608, the intersection is newly added to the approximate point list as a vertex of the short vector. Step S609
Then, the vertex of v0 is set in the removal candidate buffer. In step S610, a short vector adjacent to v0 is newly set as the comparison vector v0, and then in step S60.
Return to 4.

Incidentally, one drawing unit in this embodiment is
It is a pixel unit in the display and a dot unit in the printer.

[0028]

As described above, according to the present invention, 1
There is an effect that a curve having a width exceeding the drawing unit can be corrected, the shaping error corrected, and output.

[Brief description of drawings]

FIG. 1 is a system block diagram of an apparatus according to an embodiment.

FIG. 2 is a diagram showing a data structure of line information and point information in the apparatus of the embodiment.

FIG. 3 is a diagram showing pointer change in the device of the embodiment.

FIG. 4 is a diagram showing an example of calculating miter points at intersections of curves having a width exceeding one drawing unit.

FIG. 5 is a diagram showing an example of correcting a short vector at an intersection of curves.

6 is a diagram showing a flowchart showing an example of the processing procedure of FIG. 5 in the graphic drawing apparatus of the present invention.

FIG. 7 is a diagram showing an example in which a connection point of a short vector is shifted outward.

FIG. 8 is a diagram showing an example in which the connection points of short vectors are inward.

[Explanation of symbols]

p1 to p9 Short vector vertices approximating the curve A to E 1 Contour points when approximating a curve having a width exceeding the drawing unit cv1, cv2 Tangent vector r1, r2, q, M1 at the intersection of the curves Joint part of curve having width exceeding 1 1 Input device 2 CPU 3 Storage device 4 Output device 21 Graphic identification number 22 Identifier indicating surface type 23 Identifier indicating line type 24 Constitutional coordinate data 31 Coordinates of 32 points Attribute information 33 Pointer pointing to the next point 34 Pointer pointing to the previous point

Claims (12)

[Claims] 1. A deriving means for deriving an intersection between a tangent line at an intersection of a curve and an approximate straight line approximating the curve, the derived intersection being closer to the intersection of the curve than the apex of the approximate straight line. When it is determined by the determining means that the distance is close, the intersection is added as an apex of the approximate straight line as data for expressing a curve, and as a result, it is unnecessary. A graphic processing device, comprising: a correction unit that deletes a vertex of an approximate straight line. 2. An input means for inputting control point information including a start point and an end point for expressing a curve, and a deriving means for deriving an approximate straight line that approximates the curve based on the input control points. The graphic processing device according to claim 1, wherein: 3. The graphic processing apparatus according to claim 1, further comprising: deriving means for deriving an intersection part of the curve, and deriving means for deriving a tangent line at the derived intersection part. 4. The graphic processing apparatus according to claim 1, further comprising output means for outputting a curve based on the data for representing the curve modified by the modifying means. 5. The graphic processing according to claim 1, further comprising a determination unit that determines whether or not a tangent line at an intersection of the curves and an approximate straight line that approximates the curves are the same. apparatus. 6. A deriving step of deriving an intersection of a tangent line at an intersection of a curve and an approximate straight line approximating the curve, wherein the derived intersection is closer to the intersection of the curve than the apex of the approximate straight line. If it is determined that they are close to each other, the intersection point is added as a vertex of the approximate straight line as data for representing a curve, and as a result, it is unnecessary. And a correction step for deleting the vertices of the approximate straight line. 7. An input step of inputting control point information comprising a start point and an end point for expressing a curve, and a deriving step of deriving an approximate straight line that approximates the curve based on the input control points. The graphic processing method according to claim 6, wherein: 8. The graphic processing method according to claim 6, further comprising a deriving step of deriving an intersection point portion of a curve and a deriving step of deriving a tangent line at the derived intersection point portion. 9. The graphic processing method according to claim 6, further comprising an output step of outputting the curve to the output means based on the data for representing the curve modified by the modifying means. 10. The graphic processing according to claim 6, further comprising a determination step of determining whether or not a tangent line at an intersection of the curves and an approximate straight line that approximates the curves are the same. Method. 11. The graphic processing apparatus according to claim 3, wherein the deriving unit derives the intersection point portion in accordance with a slope of a curve forming the intersection point portion. 12. The graphic processing method according to claim 8, wherein the deriving step derives the intersection point portion in accordance with a slope of a curve forming the intersection point portion.