JPH0452881A - Segment plotting parameter setting-up circuit - Google Patents

Abstract

PURPOSE:To reduce the size of hardware and to rapidly set up parameters by providing the segment plotting parameter setting-up circuit with a means for finding out a difference function value relating to the X and Y coordinate values of a segment to be plotted, a storage means and a means for finding out a parameter. CONSTITUTION:A differentiator 210 finds out a difference between the X coordinate X2 of a start point and the X coordinate X6 of an end point and an absolute value circuit 212 outputs an absolute value X=¦Xe - Xc¦. A 1-bit code bO is outputted from the differentiator 210 and the code b0 is '0' when X3>=Xs or '1' when Xe<=Xs. The pattern of a segment to be plotted is sorted to eight areas around the start point of plotting. Out of three bit codes outputted from an area code calculating circuit 120, the bits b1, b0 are outputs from an X differential absolute value circuit 212 and a Y differential absolute value circuit 213 and the bit b2 is obtained by comparing the outputs X, Y of differential absolute circuits 100, 110 and goes '0' when X>= Y or '1' when X< Y. When a segment plotting parameter is set up by using the area codes of segments, the hardware size can be reduced and the setting up speed can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to setting up parameters in line segment drawing processing.

[Prior Art] The basis of graphic drawing processing is the drawing of line segments, and various methods have been used for this line segment drawing. Among these methods, Bresenham's method is particularly suitable for hardware implementation because of its simple algorithm, and it is very widely used today.
``Graphic Vector Generator Setup Device'' filed by IBM in 1986
280).

[Problem to be solved by the invention] "Graphic vector generator setup device"
(Japanese Unexamined Patent Publication No. 62-165280) is a device that takes into account the symmetry of one figure, so depending on nine conditions, parameters related to the X coordinate value and parameters related to the Y coordinate value must be exchanged. For this reason, a "swap circuit" is required, resulting in problems such as an increase in hardware scale and slow parameter setup.

[Means for Solving the Problems] The present invention includes means for determining a difference function value regarding the X-coordinate displacement value and Y-coordinate displacement value of the line segment to be drawn, in order to set up the drawing parameters for #i.

and storage means for storing the difference function value.

means for determining parameters according to the difference function values recorded in the storage means;

It is characterized by having the following.

[Operation] According to the line segment drawing parameter/setup circuit according to the present invention, a swap circuit, which is essential in the conventional method, becomes unnecessary. Therefore, the hardware scale can be reduced and parameters can be set up quickly.

[Embodiments] FIG. 1 is a diagram showing an overall outline of two embodiments of the present invention. Input the coordinate values of both end points of the line segment to be drawn and set the X and Y coordinates.
Difference value calculation means (11) for calculating the difference function value of the coordinates and difference value storage means (2) for storing the output of the difference value calculation means (1) are provided, and the value storage means (2) for the difference function is provided. Based on the output, Bresenha
It is composed of a parameter calculation means (3) for determining parameters in the m algorithm.

FIG. 2 is a conceptual diagram of a line segment drawing parameter/setup circuit showing an embodiment of the present invention.

In Figure 2, 100 is X from both end points of the line segment.
X difference absolute value circuit for calculating the difference in coordinates and its absolute value;
110 is a Y difference absolute value circuit for calculating the difference in Y coordinates and its absolute value from both end points constituting a line segment; 120 is the X difference absolute value circuit 100 and the Y difference absolute value circuit 1;
A region code calculation circuit 130 calculates the region code of a line segment based on the signal output from the region code calculation circuit 120.
An initial value calculation circuit for calculating an initial value of an error in the am algorithm; 140 is also the area code calculation circuit 1;
150 is a positive addition value calculation circuit that calculates a value to be added to the error when the error in the Bresenham algorithm is positive based on the signal output from the region code calculation circuit 120; A negative addition value calculation circuit 160 calculates a value to be added to the error when the error in the Bresenham algorithm is negative; This is a circuit for calculating the number of drawing points.

FIG. 3 is a flowchart explaining the parameter calculation process in correspondence with FIG.

In Figure 3, 5TEPI is the process of reading the X and Y coordinate values, 5TEP2 is the process of calculating the absolute value of the X difference,
5TEP3 is a Y difference absolute value calculation process, 5TEP4 is an area code calculation process, and 5TEP5 is an initial value calculation process.

5TEP6 is a positive addition value calculation process, 5TEP7 is a negative addition value calculation process, and 5TEP8 is a drawing point number calculation process.

The operation will be explained based on FIG. First of all.

The X difference absolute value circuit 100 in FIG. 2 will be explained.

210 is a circuit that calculates the difference between two human forces, and the X coordinate of the starting point and the X coordinate of the ending point x0 of both end points constituting the line segment.
Find the difference. Reference numeral 212 denotes a circuit for determining the absolute value of the input signal, which receives the output -x8 of the circuit 210 and outputs the absolute value Δx = 1 x, -x, 1. That is, the calculation of 5TEP2 in FIG. 3 is performed, and the absolute difference ΔX between the X coordinates of both end points constituting the line segment can be determined.

Further, the circuit 210 outputs a 1-bit code bO. This 1-bit code bO is 0 if X,>X.
Conversely, if X, ,<X, then it is 1.

The operation of the Y difference absolute value circuit 110 in FIG.
The operation is similar to that of the absolute difference circuit 100, and X,.

The calculation of 5TEP3 in Figure 3 is performed by replacing Ys with Y and
The absolute difference value ΔY of coordinates can be determined.

Further, the code output from the Y difference absolute value circuit 110 is
It becomes bl.

Next, the operation of the area code calculation circuit 120 in FIG. 2 will be explained. If the line segment patterns to be drawn are classified around the starting point of drawing, they can be classified into line segment patterns belonging to eight areas as shown in FIG. Moreover, the conditions of the area to which each pattern belongs are shown in FIG. FIG. 5 shows a 3-bit code in the area to which each line segment pattern belongs, and this 3-bit code is used by the area code calculation circuit 12.
The output will be 0. As can be seen from FIG. 6, the lower two bits blbO of this 3-bit code are the outputs of the X difference absolute value circuit 100 and the Y difference absolute value circuit 110. The remaining 1 bit b2 is obtained by comparing ΔX and ΔY, which are the outputs of the X difference absolute value circuit 100 and the Y difference absolute value circuit 110. 0 if △X≧ΔY. Conversely, if ΔX<ΔY, it is 1.

In this way, the calculation of 5TEP4 in Figure 3 is performed,
A 3-bit area code is output from area code calculation circuit 120.

Next, the initial value calculation circuit 130 in FIG. Positive addition value calculation circuit 140. Next, the negative addition value calculation circuit 150 will be explained. These circuits are connected to the area code calculation circuit 120.
It operates according to the output b2.

In other words, as can be seen from Figure 5, if b2 is O, the line segment will be drawn along the X axis, and the initial value in the Bresenham algorithm is 2ΔY−ΔX, plus the calculated value ΔY−
2ΔX, and the negative addition value becomes 2ΔY. vice versa.

If b2 is 1, the line segment will be drawn along the Y axis and Brese
The initial value of the nham algorithm is 2ΔX-ΔY, the positive addition value is ΔX-2ΔY, and the negative addition value is 2ΔX. In FIG. 4, sign inverters 214 and 215 calculate the reciprocal of the input value. 216 to 219 are shifters that double the value input by one person.

Adders 220 to 223 calculate the sum of the power of two people.

Further, 224 to 226 are selectors, and when b2 is 1, the upper row is selected, and conversely, when b2 is O, the lower row is selected. The output ΔX of the X difference absolute value circuit 100 passes through a sign inverter 214 and then becomes -2ΔX by passing through a 1ΔX footer 218.

Similarly, from the output ΔY of the Y difference absolute value circuit 110,
2ΔY, -ΔY, and -2ΔY are obtained.

By passing these values through adders 220 to 223, 2△X - △Y, 2△X - 2△Y, 2△Y - △X, and 2
ΔY−2ΔX is obtained. In addition, shifters 216 and 21
There are 2ΔX and 2ΔY as outputs of 7. By selecting these values by the selectors 224 to 226, calculations of 5TEP5 to 5TEP7 in FIG. 3 are performed, and Brese
Initial value in nham algorithm.

A positive addition value and a negative addition value are obtained.

Finally, the operation of the drawing point number calculation circuit 160 in FIG. 2 will be explained. This circuit also has the initial value calculation circuit 13.
0. Like the positive addition value calculation circuit 140 and the negative addition value calculation circuit 150, it operates according to b2, which is the output from the area code calculation circuit 120. That is, as described above, when b2 is 0, the line segment is drawn along the X axis, so the number of points to be drawn is 8X+1. Conversely, b2 is 1
In the case of , the number of points to be drawn is ΔY+1 since the drawing is performed along the line segment Y-axis. In FIG. 4, 227 is a selector and 228 is an adder. The selector 227 selects ΔX when b2 is 0, and ΔY when b2 is 1.
is selected, and the adder 2
By adding 1 to 28, the calculation of 5TEP8 in FIG. 3 is performed, and the number of drawing points can be calculated.

FIG. 7 shows a correspondence table between the initial value, pressure added value, negative added value, number of drawing points, and area code in the Brese Ham algorithm obtained as described above.

[Effects of the Invention] As described above, according to the present invention, the line segment drawing parameters are set up by using the area code of the line segment, so the swap circuit that is necessary in the conventional method becomes unnecessary. As a result.

The hardware scale is smaller and parameters can be set up faster.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an overall outline of an embodiment of the present invention. Fig. 2 is a conceptual diagram of a line segment drawing parameter/setup circuit showing an embodiment of the present invention, Fig. 3 is a flowchart showing a parameter calculation process, and Fig. 4 is a detailed parameter/setup circuit showing Fig. 2 in detail. 5 is a diagram showing a line segment pattern and its area code, FIG. 6 is a diagram showing conditions of the area code, and FIG. 7 is a diagram showing the correspondence between the area code and each parameter. In the figure, 100 is an X difference absolute value circuit, 110 is a Y difference absolute value circuit, and 120 is an area code calculation circuit. 130 is an initial value calculation circuit, 140 is a positive addition value calculation circuit,
150 is a negative addition value calculation circuit, and 160 is a drawing point number calculation circuit. In addition. In the figure. Same symbols are the same. or a corresponding portion.

Claims (1)

[Scope of Claims] Means for determining a difference function value regarding an X-coordinate displacement value and a Y-coordinate displacement value of a line segment to be drawn; a storage means for storing the difference function value; and a difference function stored in the storage means. A line segment drawing parameter setup circuit comprising: means for determining parameters according to values; and a line segment drawing parameter setup circuit.