JP2748787B2 - Curve generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphics-related apparatus for outputting characters and graphics to a display or a printer, and to a curve generator for generating a free curve from a given control point sequence.

[0002]

2. Description of the Related Art In recent years, Japanese word processors and DTRs (Des
With the practical use of k top publishing, there is an increasing demand for print quality of characters.
In the DTP field in particular, it goes without saying that there is a high demand for character quality, but there are also many demands for character sizes and typefaces. Therefore, outline fonts have been attracting attention instead of bit map fonts. Also, in the field of personal computers, WYSIWYG (What You See See) allows the characters displayed / printed on the display and the printer to match and the printed image to be confirmed on the screen as it is.
Outline font technology is also attracting attention for realizing Is What You Get.

[0003] An outline font is also called an "outline vector font", which means that the outline of a character pattern is expressed by a mathematical expression, and characters are generated by painting between outlines (or in a closed loop). A mathematical expression used to express a curved portion with a character outline generally employs a curve called a Bezier curve.

The Bezier curve is a curve that can be interpolated between control points by a smooth curve when several control points are given, and a cubic Bezier curve is most frequently used. For a cubic Bezier curve, if any four points are given as control points, curve interpolation between the control points can be performed. Thus, the free curve has the advantage that the amount of information defining its shape is very small, and the character quality does not deteriorate even if the character is enlarged or reduced.

Next, a conventional Bezier curve algorithm will be described. Generally, an algorithm for obtaining a curve from a starting point is well known.However, since division and multiplication need to be performed frequently, an algorithm based on geometric processing is often used to achieve high speed. .

FIG. 3 is a block diagram of a conventional curve generator which has been implemented as dedicated hardware, and FIG. 4 is a geometric coordinate diagram for generating a cubic Bezier curve. In FIG.
1 and 2 are RAMs for storing coordinate points, 3 is a pointer for storing the address of the RAM, and 4 is the R set by the pointer 3.
An arithmetic unit for adding the two data of AM and an arithmetic unit 5
Shifter for shifting the result of the addition by 1 bit, 9 for a sequencer for controlling a RAM, a pointer, an arithmetic unit and a shifter, 6 for a distance register for storing a distance value, 7 for an output value of the shifter and four controls This is a comparator that compares the distance between the point and the start point with the value stored in the distance register 6. The given four control points A to D are respectively stored in RAM
Is stored in

First, midpoints E, F, and G of line segments AB, BC, and CD composed of four points in FIG. 4 are obtained. As for the middle point, the coordinate points stored in the RAMs 1 and 2 are transferred to the arithmetic unit 4 by operating the pointer 3, and the arithmetic unit 4 adds the coordinate values of the two control points. The result of this operation is
And then halving it. This calculation result is stored in the RAMs 1 and 2 according to the sequencer 9.

Similarly, the midpoints H and I of the line segments EF and FG are obtained, and the midpoint J of the line segments H and I is obtained. This point J is 3
This is a point on the next Bezier curve. Next, when the above-described processing is similarly performed using the points A, E, H, and J as control points, a point Q on the next curve is obtained. After the points on the curve are obtained in this manner, the points on the Bezier curve can be obtained by repeatedly performing recursive processing on four new control points.

Another consideration in the generation of the Bezier curve is replacement of control points. By repeating the above processing, the obtained point on the Bezier curve approaches the point A without limit. Therefore, it is necessary to terminate the processing when a certain distance from the point A is approached, and to change the processing to the calculation of a point at another location. That is, the distance value serving as this criterion is stored in the distance register 6, and the distance between the output value from the shifter 5 and the point A is compared with the value stored in the distance register 6. When the distance between the point A in FIG. 4 and the obtained point Q on the curve is smaller than the value of the distance register 6 set in advance, the next four control points are designated as points J, I,
The same processing is repeatedly executed for G and D.

[0010]

As described above, the generation of a free curve by the conventional dedicated hardware is performed every time a point on the cubic Bezier curve obtained from four control points is determined.
The distance between this point and the start point of the four control points is compared with the value stored in the distance register 6. As a result of the comparison, if the distance is larger than the distance register value, a point on the cubic Bezier curve is recursively obtained from four control points given next. That is, in order to obtain a point on the cubic Bezier curve, recursive processing is repeatedly performed until the distance between the obtained point on the cubic Bezier curve and the start point becomes smaller than the value of the distance register 6. While the value of the distance register is being compared with the calculated distance between the point on the curve and the start point, the adder (4) is in a state of waiting for determination of the comparison result. That is, the comparison operation is performed until the point on the curve converges to a certain value. Therefore, the more the comparison operation is, the longer the waiting time of the arithmetic unit 4 is.

An object of the present invention is to solve these problems,
An object of the present invention is to provide a curve generating device in which arithmetic processing is speeded up.

[0012]

According to the structure of the present invention, the coordinates of the midpoint between these control points are calculated from the coordinate values of a plurality of designated control points, thereby performing curve interpolation around the control points. A plurality of storage means for storing the plurality of control points and the plurality of midpoints in a number of groups, a pointer for storing addresses of these storage means, An arithmetic unit for adding the coordinate values of two predetermined points stored in the means, a shifter for shifting the output value of the arithmetic unit by one bit and storing it in any of the storage means, and a predetermined distance value , A comparator for comparing the value of the register with the output value of the shifter, a pointer control circuit for controlling the operation of the pointer based on the comparison result of the comparator, and an output of the comparator. Characterized in that it comprises a sequencer for controlling the comparator and the shifter and the operation unit in accordance with the signal.

[0013]

The curve generator according to the present invention is mainly concerned with the operation of the arithmetic unit during the period in which the distance between the calculated point on the curve and the start point of the four control points is compared with the value of the distance register. There is a difference. That is, at the same time as the comparison is performed by the comparator, the calculator starts the calculation of the next four control points given as forward processing. The algorithm of the geometric cubic Bezier curve divides a trapezoid given by four control points at the beginning, each time a point on the curve is calculated, divides the trapezoid into two around that point, and Repeat recursive processing for trapezoid. The above processing is repeated until the calculated point on the curve approaches a certain distance from the start point of the first four control points. Therefore, the pointers of the four control points are not largely changed until the value of the distance register becomes larger in the comparison result, and the comparison operation and the operation of the arithmetic unit can be performed in parallel, and high-speed processing can be performed.

[0014]

FIG. 1 is a block diagram of a first embodiment of the present invention. In this embodiment, a pointer control circuit 8 is added to the conventional example shown in FIG. As in FIG. 3, the addresses of the two RAMs 1 and 2 for storing a plurality of control points and a plurality of middle points in two groups are stored in the pointer 3. The arithmetic unit 4 adds the coordinate values of two predetermined points stored in the two RAMs 1 and 2. The output value of the arithmetic unit 4 is shifted by one bit by the shifter and stored in one of the two RAMs 1 and 2. The distance register 6 stores a preset distance value, and compares the output value of the shifter 5 with the value of the register 6 by the comparator 7. The pointer control circuit 8 controls the pointer operation based on the comparison result of the comparator 7. In accordance with the output signal of the comparator 7, the arithmetic unit 5, the shifter 6, and the comparator 7
Are controlled by the sequencer 9.

In the present embodiment, four coordinate values are input and points on a cubic Bezier curve are generated from a point closer to the start point. Sampling of a straight line is performed until the distance between adjacent points becomes smaller than the predetermined distance in both the X coordinate and the Y coordinate. The coordinate value expression is a 16-bit fixed point, and the hardware configuration of FIG. 1 is provided for each of the X coordinate value and the Y coordinate value. However, since the processing sequence is the same, the sequencer 9, the pointer control circuit 8, and the pointer 3 can be shared.

First, as shown in FIG. 4, each midpoint of line segments AB, BC and CD composed of four control points A, B, C and D stored in the RAM is obtained. The pointer 3 points to a coordinate point A and a coordinate point B in accordance with a pointer control circuit 8, reads the coordinate points from the RAMs 1 and 2 and transfers them to the arithmetic unit 4, and adds two coordinates according to a control signal from the sequencer 9. Next, according to the control signal from the sequencer 9, the shifter 5 performs a 1-bit shift operation on the result of the arithmetic unit 4, and the pointer 3 points to the coordinate points B and C according to the pointer control circuit 8, and the like. Then, the coordinates are read from the RAM and transferred to the arithmetic unit 4, and the two coordinates are added by the control signal from the sequencer 9.

By repeating such processing, the midpoints E, F, and G of the line segments AB, BC, and CD are obtained, the end points H and I of the line segments EF and FG are obtained, and the line segment HI is further obtained. Middle point J
Is obtained, and this point J becomes a point on the cubic curve. When the point J is calculated, the output of the shifter 5 is stored in the RAM, and the output point J of the shifter 5 is controlled by the control signal of the sequencer 9.
Is stored in the comparator 7.

In parallel with this operation, the first four control points A, B, C, and D are transformed into two trapezoids of points A, E, H, J and points J, I, G, and D around the point J. Divide the four control points A, E, H, and J to find the middle point in the same manner, and start the calculation process for finding the point Q shown in FIG. Calculate points).

The comparator 7 compares the distance between the points A and J with the value of the distance register 6 set in advance. In this case, since the distance between the points A and J is still larger than the value of the distance register 6, a control signal is sent to the pointer control circuit 8 so as to repeat the recursive processing as it is. Also, the comparator 7
Is sent to the sequencer 9 to control the recursive processing to be repeated.

During this time, the arithmetic unit 4 and the shifter 5 simultaneously determine the midpoint of the line segment AE. When the point Q on the cubic Bezier curve is obtained from the trapezoids A, E, H, and J, a comparison is performed by the comparator 7 in the same manner as the point J, and the following four control points A,
A recursive process for finding a middle point for K, O, and Q is performed by the arithmetic unit 4.
Start with. In the comparator 7, if the value is smaller than the preset value of the distance register 6, the control points A, K, O, Q
It is not necessary to find a middle point for the four control points J, I, G, and D.

Therefore, the arithmetic unit 4 and the shifter 5
Is sent to the sequencer 9 and a control signal is sent to the pointer control circuit 8 so that the pointer 3 points to the coordinate values of four new control points J, I, G, and D. By repeating the above operation, it is possible to interpolate between the points A and D at the first four control points A, B, C and D according to the cubic Bezier curve.

FIG. 2 is a block diagram of a second embodiment of the present invention. In the present embodiment, four RAMs, two arithmetic units, and two shifters are prepared for the first embodiment to further increase the speed, and the RAMs 10 and 11 and the arithmetic units are compared to FIG. 12 and a shifter 13 are added. In order to find one point on the cubic Bezier curve from four control points and perform interpolation processing, it is necessary to find the middle point seven times, and with one arithmetic unit and one shifter, the waiting time of the arithmetic unit is reduced. Speed up. Other processes are the same as in the first embodiment.

Four RAMs 1, 2, 10, 1 for storing a plurality of control points and a plurality of middle points in four groups
One address is stored in the pointer 3. These four R
The coordinate values of two predetermined points stored in the AM are calculated by the arithmetic units 4 and 12.
, And after shifting the output values of these arithmetic units 4 and 12 by 1 bit with shifters 5 and 13, the four RAMs 1, 2, 1
0 or 11 is stored. The comparator 7 compares the output values of the shifters 5 and 13 with the register 6 and the value, and the pointer control circuit 8 controls the pointer operation based on the comparison result of the comparator 7.

[0024]

As described above, according to the present invention, 4
From the three control points, a point on the cubic Bezier curve is obtained and compared with the value of the distance register.
By starting the calculation of the points on the next Bezier curve in parallel, the waiting time in the arithmetic unit is reduced and the speed can be made higher than in the conventional example. Further, by increasing the number of arithmetic units and shifters, it is possible to further increase the speed. Further, in the present invention, since the distance between the four control points increases when a character is enlarged, the number of recursive processes for finding a point on a cubic Bezier curve increases. High-speed processing can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional curve generator.

FIG. 4 is a coordinate diagram illustrating a geometric algorithm of a cubic Bezier curve.

[Explanation of symbols]

 1, 2, 10, 11 RAM storing coordinates and midpoint 3 Pointer indicating RAM address 4, 12 Operator 5, 13 Shifter 6 Register storing value to be compared 7 Comparator 8 Pointer control circuit 9 Sequencer

Claims (1)

(57) [Claims] 1. A curve generating apparatus for calculating a coordinate of a midpoint between control points from a plurality of designated control point coordinate values to interpolate a curve in the vicinity of the control points to generate a curve. A plurality of storage means for storing the control points and the plurality of midpoints divided into several groups,
A pointer for storing the addresses of these storage means, an arithmetic unit for adding the coordinate values of two predetermined points stored in each of the storage means, and some of the storage means after shifting the output value of this arithmetic unit by 1 bit , A register for storing a predetermined distance value, a comparator for comparing the value of this register with the output value of the shifter, and operating the pointer based on a comparison result of the comparator. And a sequencer for controlling the operation unit, the shifter, and the comparator in accordance with an output signal of the comparator.