JPS628275A - Vector drawing system - Google Patents

Abstract

PURPOSE:To prevent a remainder for erasing and the generation of the abnormal color of the boundary of a color graphic form due to a harmful hysteresis appearing during the development of vector by developing the vector by a specific algorithm when a segment is developed to a two dimensional memory through the vector development by the algorithm of a digital differential analyzer (DDA). CONSTITUTION:A comparison circuit 15 consists of an OR gate 17, a selector 18 and a comparator 16. A picture drawing direction by writing a segment AB to a two dimensional memory, namely the direction of a vector development can be judged including the operation of a parallel moving conversion of a coordinate system to an origin coordinate system, since before the start of an algorithm of a DDA, the parallel movement conversion of the coordinate system to the origin coordinate system is previously carried out. As the origin, a point A or B can be optionally selected and by taking the selected origin for an origin of the origin coordinate system, the direction from the origin directed to other point, namely an end point is the direction of the vector development in the origin coordinate system O.

Description

[Detailed Description of the Invention] [Summary] When a line segment is drawn by vector expansion on memory using an algorithm using a digital differential analyzer (DDA) method (hereinafter abbreviated as DDA algorithm), the expansion of the same line segment is However, the writing coordinates (addresses) may not match depending on the direction of expansion, but the present invention is a method to prevent this mismatch from occurring.

[Industrial application field]

A vector drawing device equipped with a two-dimensional memory having an X-axis and a Y-axis is widely used in printers, display devices, etc. In particular, color printers and color display devices have a plurality of two-dimensional memories.

As an example, FIG. 2(a) shows a block diagram of the configuration of a color vector drawing device including three two-dimensional memories each having an X axis and a Y axis. In the figure, 1 is a vector that receives instructions such as the coordinates of both ends of a line segment, designation of a write memory, etc. from an external device (for example, a central processing unit) and generates an address for drawing the line segment in each memory. 2 is a generation circuit (hereinafter abbreviated as VG); 2 is a read/write circuit (hereinafter abbreviated as R/W); 3.
4. 5 are red, green, and blue two-dimensional memories (hereinafter referred to as MB).
, MG, MR).

The DDA algorithm is used in the vector generation circuit VC to perform vector expansion (drawing) of line segments of each color component. The present invention provides a vector generation circuit V as shown in this example.
This relates to the DDA algorithm used in GI.

Since the ODA algorithm is capable of high-speed vector expansion with a simple circuit, it is widely used not only for the above example but also for general line segment generation.

[Conventional technology]

Traditionally used DDA for vector expansion of line segments
A flow diagram of an example of the algorithm and a block diagram of the main part of the vector generation circuit VC,1 (part related to the DDA algorithm) for realizing the algorithm are shown in FIGS. 3 and 4, respectively. This is explained by: The line segment AB to be drawn is
As shown in Figure 5 (al), by giving the coordinates of point A and point B (each as an integer) in the two-dimensional memory coordinate system (origin Om, hereinafter abbreviated as memory coordinate system Om), The vector generation circuit VG is instructed.

Direct the vector expansion (drawing) from point A to point B, that is,
When drawing the starting point as point A, vector expansion is performed using a coordinate system (origin Oa, hereinafter abbreviated as origin coordinate system Oa) obtained by converting the coordinate system Om to point A by parallel movement, as shown in Figure 5(b). conduct. This parallel movement is performed by the vector generation circuit VC
The correction by parallel movement transformation is performed by correcting the output of vector expansion, which is performed in advance prior to execution of the DDA algorithm.

The coordinates of point A in the origin coordinate system Oa are 0.0, and the coordinates of point B
If the coordinates of the points are △X and △Y, then the following relationship exists: Xb - Xa = △ These are the coordinates of points A and B in the coordinate system Om.

As shown in FIG. 5(b), point B is in the first quadrant of the origin coordinate system Oa, and therefore Δx>0. A case in which ΔY>0 and ΔX≧ΔY, that is, in the first 178 quadrants, will be described as a basic case.

In FIG. 4, 6 and 7 are registers (hereinafter abbreviated as YR and XR) that hold ΔX and ΔY, respectively, 8 is an inverter (hereinafter abbreviated as IN), and 9 is a clock (n will be described later). This is a counter (hereinafter abbreviated as CNT) that has the function of counting by ΔX and comparing the counted number with ΔX. 1
0 is the output of inverter IN8 (
A multiplexer (hereinafter abbreviated as MPX) that alternately selects and outputs the inverted output of register XR6) and the output of register YR7, and 11 is an accumulation register (hereinafter abbreviated as AR).

12 is an adder (hereinafter abbreviated as AD) that adds the output of the multiplexer MPXIO and the content A of the accumulation register ARII.
, 13 is a multiplier (
(hereinafter abbreviated as MU), and 14 is an accumulation register ARII
A comparator (
(hereinafter abbreviated as CM). In the figure, clock-related circuits are omitted.

The output of MU13 is C=(1/2 ”)△X, and the output condition of the comparator is A>C. Integers n and m are the X and Y coordinates from the origin Oa in the origin coordinate system Oa. (in units of one step of the two-dimensional memory address).

As an initial setting, △X and △Y are set to registers XR6゜YR7.
and n=0. m=0. Let A=O (because the starting point is the origin Oa).

It is assumed that the clock alternately repeats the period A and the period B, and the pair of A and B constitutes one period of the clock and is repeated.

In period A, multiplexer MPXIO registers YR
7 is selected, and the first stage of the DDA algorithm flow in FIG.
This is carried out by performing Y and setting the content A of the accumulation register AR11 to A+ΔY→A.

In period B, multiplexer MPXIO connects inverter I
The output of N8 is selected, and the comparator C in the second stage of the flow
A and C are compared by M14, and if A>C, an output is output instructing one step of the value of m, which is the third stage of the flow, and an instruction is given to the adder AD to start the third step of the flow. Perform A-△X which is 4 stages, and the content A of the accumulation register AD
Let be A-ΔX-A. When A>C is not satisfied, the operations in the third and fourth stages of the flow are passed. On the other hand, the counter CNT9 counts the clock at this period, and in the fifth stage of the flow, the count number is set to n-1-n-)-1. 6th flow
In the second stage, writing into the two-dimensional memory is performed using this n and m, which is the accumulation result of the output instructing the increment of m obtained in the third stage (the accumulation circuit is not shown).

Next, in the seventh stage of the flow, counter CNT9 indicates that n=n=
A comparison is made to see if ΔX has been reached, and if not, the loop operation repeating from the first stage of the flow is continued, but when n=ΔX is reached, the counter CNT9 issues a completion signal E and ends the process. The above 7-stage flow is expressed as n 7')<
By repeating until n = △X, line segment AB
is expanded into a vector from point A to point B and drawn in a two-dimensional memory.

Figure 6 shows △X=6. In the case of △Y=3, D in the above example
This is the result of calculation using the DA algorithm,
In the same figure (al is a numerical example for each loop operation, ○ and × marks are YES, respectively in the judgment result column of the second stage of the flow)
Indicates NO, and m is the sum of m step signals. In the same figure (bl shows the line segment AB drawn by vector expansion in the origin coordinate system Oa with the origin as the point A, the coordinate points are indicated by O marks, and move in the order shown by the solid line for each loop operation. It is drawn while

In addition, FIG. 7 shows the determination condition of the second stage of the flow in the above example, that is, the output condition of the comparator CM, such that A≧C−(1/2
) ΔX, and each label and symbol in the figure is the same as in Figure 6.

In the above, as shown in FIG. 5(b), point B is in the first quadrant of the origin coordinate system Oa, and therefore, △X〉0゜ΔY〉0
and ΔX≧ΔY, that is, the first 1/8
The case in the quadrant was explained as the basic case. The reason why this case is basic is well known, but will be explained below to facilitate the subsequent explanation.

First, in the origin coordinate system O, if ΔY≧△X, that is, the second
If it is in the 1/8 quadrant of , then ΔY.

This problem can be solved by exchanging ΔX and correcting the writing to the two-dimensional memory and executing the above-mentioned DDA algorithm.

Therefore, in the case of the first quadrant, all vectors can be expanded using the same algorithm.

In the origin coordinate system O, if there is a line segment outside the first quadrant, △X
, △Y are as shown in Fig. 8(a), but in the case of the second quadrant, the sign of △
It is possible to move to the first quadrant by inverting the signs of both X and △Y, and in the case of the fourth quadrant, by inverting the sign of △Y. Perform these processes in advance and write to the two-dimensional memory. By performing the correction, vector expansion can be substantially performed using the above-mentioned DDA algorithm.

Figure 5 (C1 shows the case where the line segment AB in the above example is drawn by vector expansion in the direction from B to A with point B as the starting point, and as shown in the figure, the starting point coordinate system ob is The origin is set at point B. Since point A is in the third quadrant, vector expansion can be performed by inverting the signs of both ΔX and ΔY and performing the procedure described above.The result of this execution is shown below. Corresponding to the case of vector expansion from point A to point B, respectively, in FIGS. 6(b) and 7), the vectors are expanded as indicated by the 9 dotted lines marked with an x, and written into the memory. Depicted by

[Problem to be solved by the invention] In the example shown in FIGS. 6(b) and 7), the same line segment A
Even though B is vector-expanded using the same DDA algorithm, some points do not match due to the difference in the expansion direction.

In other words, there is a discrepancy between the 0 points and the x points.

This discrepancy is because the coordinates of points A and B are given as integers, and the calculated value of the Y coordinate for the integer value of the X coordinate regarding a point on the line segment connecting them is, when q is an arbitrary integer. q
When the value is +0.5, this occurs by rounding up or rounding down regarding 0.5, and corresponds to the selection of equal signs in the second step of the judgment in the flow shown in FIG. Generally, it appears only when ΔY is an odd number and ΔX is an even number, and FIGS. 6 and 7 are examples of this. In the DDA algorithm that performs approximate calculations, this selection cannot be avoided because only one of them is selected.

This shows that hysteresis will occur if line segment AB is drawn from point A to point B and then vector expanded from point 8 to point A. This means that when the output of the vector generating circuit VG1 is erased and writing is performed in the reverse direction, there are points that cannot be erased and remain. Therefore, for erasing, there is a drawback that considerations such as always remembering the direction of past writing are required.

Further, as an example, color figures as shown in FIG. 2(b), that is, red ΔEAC, green ΔABC, and blue ΔDBA, are separated by color, and as shown in FIG. 2(a), Red, green, memory for ex-wife (primary colors in this case) MR3, MG
4. It is written to MB#, but for boundary lines such as sides AB and BC, the direction of expansion is the vector expansion direction of the line segments forming the sides of each figure that sandwich these boundaries, as shown in Figure 2 (a). When they are different, the points will be shifted, so all the shapes of each color are
When composite display or printing is performed at the same time, bordering side AB
.

There is a drawback that an unintended color may be displayed in the vicinity of AC (particularly in a filled figure), which is extremely inconvenient.

It is an object of the present invention to provide a simple and effective method for eliminating harmful hysteresis and the occurrence of abnormal colors at figure boundaries in the case of color, as described above.

[Means for solving problems]

In order to achieve the above object, the vector generation circuit VG1 is provided with a drawing direction determination function, and the determination condition in the comparator CM14 of the conventional circuit shown in FIG. 4 can be changed based on the result. The algorithm is switched depending on the direction of vector expansion.

[Effect]

In this way, when the judgment conditions are changed and the vector expansion is performed, the results are shown in the examples of FIGS. 6 and 7 mentioned above.
In the case of point B from
In the case of point A from , it can be seen that the x points in FIG. 7(b), which are obtained by switching the judgment condition to A≧(ΔX/2) and performing vector expansion, match. In addition, in the case of direction from point A to point B, the 0 point in Figure 7 in which vector expansion was performed with the judgment condition A≧(△X/2) (=C), and conversely, the direction from point B to point A
In the case of the direction, it can be seen that the x points in FIG. 6 (in which vector expansion was performed by switching the judgment condition to A>(ΔX/2) (=C)) match.

As shown above, how to expand the equal sign in the judgment condition
By making a selection based on the direction, it is possible to eliminate inconsistencies in the vector expansion results due to the direction of expansion.

〔Example〕

FIG. 1 shows a block diagram of essential parts of an example of a vector generation circuit embodying the present invention as an example. In this figure, the same parts as in the above-mentioned figure 4 are indicated by the same symbols, and only 15 is different from the case in figure 4, which compares A and (△X/2)(-C''). This is a comparator (hereinafter abbreviated as CMS) whose judgment conditions can be switched by a selection signal S, which will be described later.Comparator C
The contents of the MS 15 are shown in FIG. 8(b) as an example, where 16 is a comparison circuit (hereinafter abbreviated as COM), 17 is an OR gate (hereinafter abbreviated as OR), and 18 is an input with a selection signal S. This is a selector (hereinafter abbreviated as SEL) for selecting.

The drawing direction of the line segment AB by writing it into the two-dimensional memory, that is, the direction of vector expansion, must be determined before initial settings are made in order to start the operation of the main parts of the vector generation circuit shown in FIG. However, as mentioned above, before the start of the DDA algorithm, a translation transformation of the coordinate system to the origin coordinate system is performed in advance, so the direction of vector expansion can be determined by including it in the operation. .

As the starting point, point A or point B can be arbitrarily selected,
By setting the origin of the origin coordinate system at the selected origin point, the direction from the origin to another point, that is, the end point, is the vector expansion direction in the origin coordinate system 0 (the line segment becomes a vector starting from the origin O). ).

As explained in Fig. 5, by taking △X and △Y in the origin coordinate system 0 and checking their signs, it is possible to know the quadrant in which the line segment exists, and the correspondence is 8
As shown in Figure (a).

The direction of vector expansion, that is, the direction of drawing, is opposite to each other, which means that the first quadrant is the third quadrant, and the second quadrant is the fourth quadrant.
The quadrants are opposite quadrants, and the method of giving them in which the selection of the equal sign in the second stage judgment condition of the flow in Figure 3 is reversed is 0MS in Figure 8 (a). Four types, a, b, c, and d shown in the control column are possible. As described above, this circuit for determining the selection of equal signs can be easily realized by being included in the conversion to the origin coordinate system.

Choose one of these and always use that combination.
By making it correspond to the selection signal S, the judgment condition of the comparator CMS can be switched depending on the direction of vector expansion.

Comparator CMS 15 is a comparison circuit C0M that compares A and C.
16 A>C output and OR gate 0R17
The output obtained by ORing the outputs of c and A=C is the selection signal S.
The choice is made based on the following.

As explained above, by switching the judgment condition of the second stage in the flow of the DDA algorithm shown in FIG. can be excluded.

In addition, in the example of FIGS. 6 and 7 mentioned above, from point A to point B
In the case of direction, the judgment condition is A>(△ Figure 7 shows vector expansion performed by switching to X/2) (I explained that the X points of bl match, but this case is the case where b is selected as the judgment condition based on the direction. Also, the point In the case of going from A to point B, the judgment condition is A≧(△X/2) (=C) (in Figure 7) where vector expansion was performed), and vice versa, in the case of going from point B to point A, The judgment condition is A>(ΔX/2)(=C
) and vector expansion was performed, and it was shown that the X points in ) in FIG.

〔Effect of the invention〕

As explained above, the vector drawing method of the present invention is based on the D
When a line segment is expanded into a two-dimensional memory using vector expansion using the DA algorithm, it is necessary to prevent deletion residue due to harmful hysteresis that appears depending on the direction of vector expansion, and occurrence of abnormal colors at figure boundaries in the case of color. , has the effect of eliminating with simple operation and circuit.

[Brief explanation of drawings]

Figure 1 is a block diagram of the main part of an example of a vector generation circuit that implements the present invention, Figure 2 is an explanatory diagram of vector expansion from the vector generation circuit to memory, and Figure 3 is an example of vector expansion algorithm 1. Figure 4 is a block diagram of the main parts of the vector generation circuit,
FIG. 5 is an explanatory diagram of the drawing direction, FIGS. 6 and 7 are examples of rendering by the conventional algorithm, and FIG. 8 is an explanatory diagram of algorithm change control according to the vector rendering direction of the present invention. 1, 2, 4, and 8, 1 is a vector generation circuit VC, 2 is a read/write circuit R/W, and 3.4.5 is a two-dimensional memory MR opener for red, green, and blue, respectively. or
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Claims (1)

[Claims] In a vector drawing device equipped with at least one two-dimensional memory having an Vector drawing method.