JP3496381B2 - Line drawing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention draws a line segment using a printer device, a plotter device, or the like, and CAD (C
The present invention relates to a line segment drawing device that draws a line segment in an computer aided design) system, computer graphics, and the like, and particularly to a line segment drawing device that is suitable for drawing thick lines.

[0002]

2. Description of the Related Art FIG. 23 is an explanatory diagram of an example of a conventional line segment drawing method. First, according to the line segment drawing method shown in FIG. 23A, a circular pixel pattern having a diameter of a target line width is used as a known DDA (Digital D) from the start point to the end point of the line segment.
The image is overlaid and drawn based on an differential analyzer (digital differential analyzer) algorithm. Further, for example, as described in Japanese Patent Application Laid-Open No. 4-23179, after the circular pixel pattern is drawn at the starting point, the number of pixels to be accessed multiple times using a rectangular pattern based on the circular pixel pattern is set. A method of reducing the amount is also proposed. Next, in the line segment drawing method shown in FIG. 23 (B), a straight line having a line width of 1 pixel can be generated at high speed by a known DDA algorithm. Draw a line segment. This method is described, for example, in JP-A-5-233821. Further, in the line segment drawing method shown in FIG. 23C, the outline of the thick line to be drawn is drawn in advance, and then the line segment is drawn by using a general filling process. This method is disclosed in, for example, JP-A-4-205575, JP-A-5-67215, and JP-A-4-779.
No. 77, etc. Also, Japanese Patent Application No. 7-82
As described in No. 432, a method has also been developed in which a line segment for a line width is generated in the normal direction and the line segment is drawn by overlapping the line segments.

By the way, for example, when the frame memory has a byte structure or a word structure and a plurality of pixels are assigned to one byte and one word, when writing data for one pixel into the frame memory, word boundaries and Byte boundary alignment processing is required, and the writing speed decreases. Further, even if a plurality of generated drawing pixels are present in the same word or byte, access is generated each time because of sequential writing, and the processing speed is further reduced. Therefore, when drawing a straight line, a method of writing in a buffer once and then transferring to a frame memory is generally adopted, instead of directly writing in the frame memory. Further, it is desired to reduce the time required for drawing a straight line in the frame memory by efficiently performing the transfer from the buffer to the frame memory.

However, in order to temporarily store the entire straight line generated with an arbitrary line width in an arbitrary direction in a buffer,
There is a problem that a huge memory capacity is required as a buffer. In particular, in the method of performing the filling process as shown in FIG. 23C, the filling process cannot be performed until all the coordinates of the contour line are held, and thus a large capacity buffer is essential. For example, the above-mentioned JP-A-5-6
In Japanese Patent No. 7215, a straight line image storage unit is provided, and a straight line generated in this straight line image storage unit is temporarily stored and transferred to the binary image storage unit. However, the straight line image storage unit must have a large capacity. Absent.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a line segment drawing apparatus which uses a small number of buffers, efficiently transfers the data to a frame memory, and improves the drawing processing speed. The purpose is to do.

[0006]

According to a first aspect of the present invention, in a line segment drawing device, an initial value for outputting a start point and an end point of a line segment drawn from input information and a line width of the line segment. Setting means, reference line generating means for generating coordinates on a straight line connecting the start point and the end point output from the initial value setting means, and a distance between the coordinates generated by the reference line generating means and the starting point Based on the calculation result of the distance calculation means and the coordinates generated by the reference line generation means, and is orthogonal to a straight line connecting the start point and the end point and is output from the initial value setting means. And a normal vector generation means for generating a pixel row having a length equal to the line width of the line segment, and a pixel row generated by the normal vector generation means for each coordinate generated by the reference line generation means. And a drawing means for Data holding means having a plurality of holding portions for temporarily holding the formed pixel row, a frame memory for storing the drawn image, and a holding portion coordinate calculation for calculating the corresponding position on the frame memory by the holding portion. Means, holding section control means for setting or selecting the holding section from coordinates of the pixel column obtained by the drawing section and position information of the holding section by the holding section coordinate calculation means,
It is characterized by further comprising data transfer means for sequentially transferring the data from the holding unit after storing the data to the frame memory, and data holding unit initialization means for clearing the holding unit after the data is transferred by the data transferring unit. It is a thing.

According to a second aspect of the present invention, in the line segment drawing apparatus according to the first aspect, the frame memory is configured to store a plurality of pixels in one word, and the holding unit is the frame memory. The position is set on the basis of the word boundary of, and the data transfer means performs the transfer for each word.

According to a third aspect of the present invention, in the line segment drawing device, an initial value setting means for outputting a start point and an end point of the line segment to be drawn from the input information and a line width of the line segment, and the initial value setting means. Reference line generating means for generating coordinates on a straight line connecting the start point and the end point output from the value setting means, and distance calculating means for calculating the distance between the coordinates generated by the reference line generating means and the start point. And a line width of a line segment that is orthogonal to a straight line connecting the start point and the end point based on the calculation result of the distance calculation means and the coordinates generated by the reference line generation means and that is output from the initial value setting means. A normal vector generating means for generating a pixel row having a length equal to, a drawing means for generating a pixel row generated by the normal vector generating means for each coordinate generated by the reference line generating means, The pixel row generated by the drawing means A data holding means for storing, a frame memory for storing the drawn image, a holding unit coordinate calculating means for calculating a position on the frame memory corresponding to the data holding means, and a pixel row to be newly drawn. On the basis of the drawing pixel correction means for comparing and correcting the coordinates and the coordinates of the pixel row already stored in the data holding means to make it equal to the pixel row to be newly drawn, and the pixel row generated by the drawing means. A holding unit control unit that determines whether to end the storage of the data in the data holding unit or the correction of the stored data, and a data transfer unit that transfers the data stored or modified in the data holding unit to the frame memory. It is characterized by.

[0009]

1 is a block diagram showing a first embodiment of a line segment drawing apparatus of the present invention. In the figure, 1 is an initial value recognition unit, 2 is a reference line scanning unit, 3 is a distance calculation unit, 4
Is a normal vector generation unit, 5 is a line segment drawing unit, 6 is a calculation data transfer unit, 7 is a frame memory, 11 is a holding unit control unit,
Reference numeral 12 is a data holding unit, 13 is a holding unit coordinate calculation unit, 14 is a data transfer unit, and 15 is a data holding unit initialization unit.

The initial value recognition unit 1 recognizes the starting point and the ending point of a line segment to be drawn and the line width of this line segment from the input information. The reference line scanning unit 2 generates coordinates on the straight line connecting the start point and the end point recognized by the initial value recognition unit 1. The distance calculation unit 3 calculates the distance between the coordinates generated by the reference line scanning unit 2 and the start point. The normal vector generation unit 4 is orthogonal to the straight line connecting the start point and the end point based on the calculation result of the distance calculation unit 3 and the coordinates generated by the reference line scanning unit 2, and the initial value recognition unit 1 A pixel column having a length equal to the line width of the recognized line segment is generated. The line segment drawing unit 5 causes the pixel array generated by the normal vector generation unit 4 to be generated for each coordinate generated by the reference line scanning unit 2. The drawing data transfer unit 6 temporarily holds the drawing data from the line segment drawing unit 5 and efficiently transfers it to the frame memory 7. The drawn image is developed in the frame memory 7.

The drawing data transfer unit 6 includes a holding unit control unit 1.
1, a data holding unit 12, a holding unit coordinate calculation unit 13, a data transfer unit 14, and a data holding unit initialization unit 15.
The holding unit control unit 11 sets the holding unit inside the data holding unit 12 to an area on the frame memory 7 that includes the drawing coordinates calculated by the line segment drawing unit 5, and instead of drawing in the frame memory 7, this data is stored. When it is determined that the data is to be drawn in the holding unit 12 and no more is drawn in the set holding unit, the data in the holding unit and the offset value indicating the coordinates on the frame memory 7 are passed to the data transfer unit 14.

The data holding unit 12 has a plurality of holding units for holding data in a small area having a size corresponding to a transfer unit to the frame memory 7. For example, the frame memory 7
In the case of a so-called word-structured or byte-structured memory in which 1 word or 1 byte of data corresponding to one address is read and written, several registers each having an integer multiple of this word length and byte length are collected to form one block as one block. It is possible to configure one holding unit and collect four or more holding units. In FIG. 1, four holding parts are shown.

The holding unit coordinate calculation unit 13 is a data holding unit 1.
Make sure that one of the holding parts in 2 always includes drawing coordinates,
Further, the position of the holding unit on the frame memory 7 is calculated so as not to overlap each other. For example, when the frame memory 7 is a memory having a word structure or a byte structure, the position of the holding unit is set in accordance with a 1-word unit delimiter (word boundary) or a 1-byte unit delimiter (byte boundary).

The data transfer unit 14 offsets the data drawn in the holding unit inside the data holding unit 12 specified by the holding unit control unit 11 from the holding unit passed from the holding unit control unit 11 on the frame memory 7. Transfer to the frame memory 7 based on the value.

The data holding unit initialization unit 15 initializes the inside of the holding unit after all the drawn data is transferred to the holding unit inside the data holding unit 12.

FIG. 2 shows a concrete example of the reference line scanning unit 2, the distance calculation unit 3, the normal vector generation unit 4, and the line segment drawing unit 5 in the first embodiment of the line segment drawing apparatus of the present invention. It is a block diagram. In the figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals. Reference numeral 21 is a coordinate generation unit, 22 is a scanning coordinate storage unit, 23 is a movement distance calculation unit, 24 is a line width scanning determination unit, 2
5 is a 90 ° rotation unit, 26 is a normal vector storage unit, 27 is a reference line movement processing unit, 28 is a pixel omission determination unit, 29 is a drawing unit, and 30 is an end condition determination unit.

The reference line scanning section 2 has a coordinate generating section 21 and a scanning coordinate storing section 22. The coordinate generator 21 generates the coordinates of a point on the straight line from the start point to the end point based on the initial value set by the initial value recognition unit 1. The coordinate generation unit 21 can be configured by DDA, for example. The generated coordinates are stored in the scanning coordinate storage unit 22 and passed to the movement distance calculation unit 23. The line formed by the coordinates stored in the scanning coordinate storage unit 22 will be referred to as a reference line below.

The distance calculating section 3 has a moving distance calculating section 23 and a line width scanning determining section 24. The movement distance calculation unit 23 calculates the movement distance from the start point to the pixel generated in the coordinate generation unit 21, and the calculation result is passed to the line width scanning determination unit 24. The line width scanning determination unit 24 determines whether the movement distance calculated by the movement distance calculation unit 23 exceeds the line width recognized by the initial value recognition unit 1 or both are equal, and the coordinates generated by the coordinate generation unit 21 are coordinated. Interrupt the occurrence of. As a result, the process is interrupted when the line width coordinates are generated.

The normal vector generating unit 4 includes a 90 ° rotating unit 2
5. It has a normal vector storage unit 26. The 90 ° rotation unit 25 creates coordinates that are rotated 90 ° clockwise around the start point based on the coordinates stored in the scanning coordinate storage unit 22, and uses them as normal vector information to store the normal vector storage unit 26. Store to. However, the 90 ° rotating part 25
Rotates only the coordinates between the coordinates determined by the line width scanning determination unit 24 and the start point to generate a line segment in the normal direction of the line width (hereinafter referred to as a normal vector).

The line segment drawing section 5 includes a reference line movement processing section 27,
Pixel missing determination unit 28, drawing unit 29, end condition determination unit 30
Have. When the drawing unit 29 generates a normal vector at the coordinates on the reference line, the reference line movement processing unit 27 sets a position at which the normal vector is generated with respect to the coordinates on the reference line. That is, the reference line movement processing unit 27
For example, it is set whether the normal vector stored in the normal vector storage unit 26 is generated on the right side, the left side, or both sides of the reference line with respect to the direction from the starting point to the ending point of the reference line. It is also possible to draw a wavy line or a sawtooth line by appropriately changing the distribution amount at each point of the reference line. Further, it is possible to draw an n-fold line such as a double line or an outline line by appropriately extracting pixels of the normal vector.

The pixel omission determination unit 28 determines the presence or absence of pixel omission and notifies the drawing unit 29 of the position of pixel omission. Pixel omission occurs in a portion where adjacent pixels forming a normal vector are at a licked position when the y coordinate of the pixel on the reference line changes. The pixel omission determination unit 28 may detect this and determine the pixel omission.

The drawing unit 29 determines the normal direction for each coordinate in the scanning coordinate storage unit 22 based on the normal vector stored in the normal vector storage unit 26 according to the movement amount by the reference line movement processing unit 27. Draw on. Further, when the pixel omission determination unit 28 determines pixel omission, the missing pixel is also repaired.

The end condition judging unit 30 judges the condition that the coordinate generated by the coordinate generating unit 21 becomes the end point, and terminates the process.

Next, an example of the operation of the above-described line segment drawing apparatus in the first embodiment will be described. FIG. 3 is an explanatory diagram of a basic line segment drawing operation in the first embodiment of the line segment drawing apparatus of the present invention. When drawing a line segment, the initial value recognition unit 1 first recognizes the start point and end point of the line segment to be drawn and the line width thereof. Subsequently, the reference line scanning unit 2 sequentially generates coordinates on the straight line connecting the starting point and the ending point recognized by the initial value recognizing unit 1 from the starting point. For example, the coordinates of points indicated by black circles in FIG. 3A are sequentially generated. At this time, the distance calculation unit 3 calculates the distance between the coordinates generated by the reference line scanning unit 2 and the starting point.

Then, the calculation result by the distance calculation unit 3 and
When the reference line scanning unit 2 generates the coordinates up to the coordinates at which the line width recognized by the initial value recognition unit 1 becomes equal, the normal vector generation unit 4 calculates all the coordinates generated between the coordinates and the start point. The coordinate of is rotated by 90 °, and pixels in the line width direction necessary for drawing the line segment are generated on the rotated coordinate. That is,
In the normal vector generation unit 4, as shown in FIG.
A pixel row that is orthogonal to the straight line connecting the start point and the end point recognized by the initial value recognition unit 1 and has a length equal to the line width of the line segment is generated.

When the normal vector generation unit 4 generates a pixel row, the line segment drawing unit 5 starts this pixel row from the starting point recognized by the initial value recognition unit 1 as shown in FIG. Up to the end point, it is generated for each coordinate generated by the reference line scanning unit 2.
The drawing data transfer unit 6 temporarily holds the generated data of the pixel column in a certain section and efficiently transfers the data to the frame memory. As a result, a line segment having a desired line width is drawn from the start point to the end point.

The above line segment drawing operation will be described more specifically. FIG. 4 is an explanatory diagram of an example of an operation up to normal vector generation. The initial value recognition unit 1 recognizes the coordinates and line widths of the start point and end point of the line segment to be drawn. Here, it is assumed that a line segment represented by a quadrangle determined from the start point p0 and the end point pe and the line width is drawn on the image in which the intersection of the grid shown in FIG. 4A is the center position of the pixel.

The coordinate generation unit 21 determines the start point p0 to the end point p based on the initial value set by the initial value recognition unit 1 by DDA.
Coordinates p1, p2, p3 ,. ． ． And the generated coordinates are passed to the scanning coordinate storage unit 22 and the moving distance calculation unit 23. The moving distance calculation unit 23 constantly calculates the moving distance from the starting point p0 to the generated coordinates,
The calculation result is passed to the line width scanning determination unit 24.

FIG. 5 is an explanatory diagram of an example of the operation of the moving distance calculating section. In this example, in order to reduce the calculation error of the moving distance, the moving distance calculating unit 23 traces back to the coordinates of two pixels generated in the past and performs the calculation using the distance between these two coordinates. As shown in FIG. 5, when a pixel (next pixel to be referred to below) Pn + 1 which is newly generated from a pixel (next pixel to be referred to below) Pn generated last at the present time is generated, the movement distance calculation unit 23 First, the provisional movement distances Pn to Pn + 1 to the next pixel are calculated. At this time, if the unit distance between adjacent coordinates is 1 in both the x-axis direction and the y-axis method, the provisional movement distance is either 1.0 or √2 because the image has pixels in a grid pattern. Further, based on the moving distances Pn-1 to Pn from the pixel generated before the current pixel (hereinafter referred to as the previous pixel) held by the moving distance calculation unit 23 and the previous provisional moving distances Pn to Pn + 1, The moving distances Pn to Pn + 1 to the pixels are calculated. That is, the moving distance values of consecutive pixels are 1.0 and √2.
Alternatively, only in the case of √2 and 1.0, these are collectively set to √5 by the Pythagorean theorem.

In the example shown in FIG. 5, Pn-1 to Pn = 1.
0, Pn to Pn + 1 = √2, and Pn-1 to Pn + 1 = √2
5 so that Pn to Pn + 1 = (√5-1.
0) is output as the movement distance. After calculating the moving distance, P
The values of n to Pn + 1 (√5-1.0) are from Pn + 1 to P
It is held in the moving distance calculation unit 23 for calculating the moving distance up to n + 2.

FIG. 6 is a flow chart showing an example of the operation of the moving distance calculating section. In S51, the provisional movement distance to the next pixel generated by the coordinate generation unit 21 is input.
Hereinafter, the value of this provisional movement distance is Dn. Further, the movement distance from the previous pixel held in the movement distance calculation unit 23 is input. Hereinafter, the value of this moving distance is defined as Dp.

In S52, it is determined whether or not the provisional movement distance Dn is 1. When the provisional movement distance Dn is 1, it is further determined in S53 whether the movement distance Dp is √2. If the moving distance Dp is not √2, S
At 54, the addition distance from the current coordinate Pn to the next coordinate Pn + 1 is set to 1 and added to the cumulative distance. When the moving distance Dp is √2, in S55, the added distance from the current coordinate Pn to the next coordinate Pn + 1 is set to √5-√2 and added to the cumulative distance.

When it is determined in S52 that the provisional movement distance Dn is not 1, it is further determined in S56 whether the movement distance Dp is 1. Moving distance Dp is 1
If so, in S57, the current coordinate Pn to the next coordinate Pn
The addition distance up to +1 is set to √5-1 and added to the cumulative distance. If the movement distance Dp is not 1, S58
In, the addition distance from the current coordinate Pn to the next coordinate Pn + 1 is set to √2 and added to the cumulative distance.

On the other hand, the 90 ° rotation unit 25 stores the coordinates p1, p2 and the coordinates p1, p2 in FIG.
p3 ,. ． ． From the start point p0 in the clockwise direction 9
Coordinates p1 ′, p2 ′, p3 ′ ,. ． ． Are stored in the normal vector storage unit 26 as normal vector information. At the same time, the line width scanning determination unit 2
4 determines whether the moving distance exceeds the line width recognized by the initial value recognizing unit 1 or both are equal. When the moving distance is equal to or exceeds the line width, the coordinate generation of the coordinate generating unit 21 is stopped. As a result, the normal vector storage unit 26 stores the normal vector for the line width. Since the straight line p0p3 is closest to the line width in FIG. 4A, the coordinate generation of the coordinate generation unit 21 is temporarily stopped at the time when the coordinate p3 is generated. Coordinates p1, p2 generated so far
p3 is rotated by the 90 ° rotation unit 25, and coordinates p1 ′, p
2 ', p3'. As a result, normal vectors v0 to v3 as shown in FIG. 4 (B) are obtained.

Next, after it is determined from the normal vector generation unit 4 that a normal vector has been created, line segment drawing is performed based on the normal vector. FIG. 7 is an explanatory diagram of an example of operation from normal vector generation to line segment drawing. As shown in FIG. 7, the coordinate generation unit 21 uses the start point a0 to the end point f0.
Up to the above, coordinates are sequentially generated and stored in the scanning coordinate storage unit 22. Each time the pixels a0 to f0 on the reference line are generated, the reference line movement processing unit 27 moves the reference line in parallel, and the area in which the line segment is drawn is located on the right or left side or the center of the line in the direction from the start point to the end point. Set the normal vector to. Next, the drawing unit 29 causes the normal vectors v0 to v3 shown in FIG.
Based on the above, each line is drawn in the normal direction as shown in FIG. That is, when the pixel a0 is generated, the pixels a1, a2, and a3 are formed as lines in the normal direction from the pixel a0.
To generate. Similarly, when the pixel b0 is generated, the pixels b1, b2, and b3 are generated, and when the pixel c0 is generated, the pixel c is generated.
1, c2, c3, when pixel d0 is generated, pixel d1,
When the pixel e0 is generated, the pixels d1 and d2
2, e3, when pixel f0 is generated, pixels f1, f2,
f3 is generated respectively. The pixels generated in this way are passed to the data holding unit 12 of the drawing data transfer unit 6 and held in any one of the data holding units 12.

When the y-coordinates of the pixels on the reference line change like the pixels c0 and d0 in FIG. 7, when the adjacent pixels forming the normal vector are at the licked position, that is, in this example, the normal vectors v0 to v0. A pixel omission occurs between v2 and v3 in v3. Therefore, the pixel omission determination unit 28 determines whether there is a pixel omission, and the pixel omission position is determined by the drawing unit 29.
Then, the pixel is inserted at the position where the pixel is missing and the pixel is removed.

Then, the end condition judging unit 30 judges the condition that the coordinate generated by the coordinate generating unit 21 becomes the end point, and the process is ended. By such processing, it is possible to draw a line segment having an arbitrary line width at an arbitrary drawing angle at a high speed with an image quality that is almost ideal.

When a line segment such as a broken line, a dotted line, or a chain line that is interrupted in the middle is drawn, pixels on the reference line are generated according to the line type, or pixels on the reference line for a predetermined length at a predetermined interval are drawn. It is possible to draw a broken line, a dotted line, or the like having an arbitrary line width by not drawing the normal vector with respect to. For example, in the example shown in FIG. 7, it is possible to draw a dotted line with a 2-dot interval by controlling the pixels c0 and d0 as pixels on the reference line so as not to form a line in the normal direction. In this way, various line types can be easily accommodated.

Further, in the above-described line segment drawing process, only pixels for one line in the normal direction are generated as normal vectors, but for example, a plurality of adjacent normal vectors are generated and a plurality of generated normal vectors are generated. You may draw using the data of a line vector.

Next, the transfer operation of the drawn line segment in the first embodiment of the line segment drawing apparatus of the present invention will be described. FIG. 8 is an explanatory diagram of a specific example of the line segment to be drawn.
In the following description, as a specific example, a case where a thick line shown by hatching in the upper right direction in FIG. 8 is drawn will be described. As described above, the line segment drawing section 5 generates a line segment by generating a normal vector orthogonal to the reference line connecting the start point and the end point for each pixel forming the reference line. In FIG. 8, normal vectors are intermittently shown by arrows.

For example, consider a case where the frame memory 7 has a word structure. Vertical lines in FIG. 8 are word boundaries. When a line segment is drawn in the frame memory 7 having such a word structure, the pixel of each normal vector corresponds to a certain bit of each word. When a pixel is directly drawn in such a frame memory 7, the address and bit position of the word of the frame memory 7 are calculated based on the pixel position, the word is read out by the calculated address, and the calculated bit is further calculated. It is necessary to change the value of the bit in the word based on the position and write the word back. Such processing takes time and the drawing speed decreases. Further, even when a plurality of pixels are written in the same word, since the frame memory 7 is accessed for each pixel, the number of accesses increases and the drawing speed decreases.

In the first embodiment, the data holding unit 12 which can be accessed at a relatively high speed is provided, and the alignment process is eliminated by transferring data to the frame memory 7 in units of words, and the number of accesses is reduced to perform drawing. It is improving the speed. Further, by effectively using the holding unit in the data holding unit 12, it is possible to configure with a small memory capacity. Therefore, the area of the holding unit in the data holding unit 12 is allocated along the word boundary of the frame memory 7. For example, in the example shown in FIG. 8B, the holding unit has an area of 1 word × 1 word. Generally, the start point and the end point of a line segment to be drawn are shown in FIG.
Since it does not always exist on the word boundary as shown in FIG. 3, the area of the holding unit is set not on the drawing line segment but on the word boundary of the frame memory 7 so that the data transfer unit 14 sets the frame memory 7 Can be transferred at high speed. The position of the holding unit on the frame memory 7 is calculated by the holding unit coordinate calculation unit 13. For example, the coordinates of the upper left position of the holding unit can be calculated and set as shown in FIG.

FIG. 9 is a flow chart showing an example of the storage and transfer processing of the drawn pixels in the first embodiment of the present invention. When pixels are generated in the line segment drawing unit 5, the process proceeds from S61 to S62, and the drawing coordinates of the pixels generated in S62 are received. In S63, the holding unit control unit 11 determines whether or not the received drawing coordinates fall within the already set holding unit among the four holding units.
If it can be held in any of the holding units, in S64, the holding unit is selected and a pixel is drawn in the holding unit based on the drawing coordinates. If it does not fit into any of the set holding units, in S65, a free holding unit is selected, the holding unit coordinate calculation unit 13 calculates the coordinates on the frame memory 7 corresponding to the holding unit, and the setting is performed. To do. Then, a pixel is drawn in the holding unit.

In S66, the holding unit control unit 11 determines whether or not there is a holding unit for which drawing has been completed. If there is no holding unit for which drawing has been completed, the process returns to S61. If there is a holding unit for which drawing has been completed, the setting position of the holding unit for which drawing has been completed is given to the data transfer unit 14 in S67, and the internal data is transferred to the set position on the frame memory 7. When transferring the data in the holding unit to the frame memory 7, the data transfer unit 14 transfers only the drawn data while looking at the holding unit to the frame memory 7 word by word. After the transfer is completed, in S68, the data holding unit initialization unit 15 initializes only the drawn data of the transferred holding unit in units of words, or initializes the entire area of the transferred holding unit. The initialized holding unit is S6
It is reset when a new holding unit is required in 5.
After the initialization is completed, the process returns to S61.

Such processing is performed every time a pixel is generated in the line segment drawing section 5, and when it is determined in S61 that the drawing is completed, the contents of the holding section set at that time in S69 are transferred to the data transfer section. 14 by the frame memory 7
To end the process.

FIGS. 10 to 17 are explanatory diagrams of a specific process of storing and transferring the drawn pixels in the first embodiment of the present invention. In the following description, it is assumed that the data holding unit 12 is provided with four holding units, which are a first holding unit, a second holding unit, a third holding unit, and a fourth holding unit, respectively. In the figure, only the number of each holding unit is shown. The frame memory 7 has a word structure, and each holding unit has a capacity of 1 word × 1 word corresponding to the word of the frame memory 7.

First, the line drawing unit 5 sends the drawing coordinates of the pixel corresponding to the starting point to the drawing data transfer unit 6. At this point, the holding unit has not been set, so
Set the holding unit. In FIG. 10 to FIG. 17, the set area of the holding portion is shown by hatching to the lower right. In FIG. 10, the first holding unit is assigned so as to be along the word boundary on the frame memory 7 and to enter the starting point of the normal vector generated by the line segment drawing unit 5.
Then, the holding unit coordinate calculation unit 13 calculates the coordinates assigned to the upper left pixel of the first holding unit on the frame memory. Then, the pixel at the starting point of the line segment is drawn in the first holding unit.

Then, the line segment drawing section 5 sequentially generates drawing coordinates of each pixel of the normal vector corresponding to the starting point pixel. Since these drawing coordinates are included in the first holding unit,
Drawing on the first holding unit. Further, the pixel generated along the reference line and each pixel of the normal vector corresponding to the pixel are sequentially drawn in the first holding unit while the drawing coordinates are included in the first holding unit. .

Depending on the positional relationship between the start point of the normal vector and the word boundary, the end point of the normal vector may not be in the same holding section. However, if the line width is large enough to fit in one holding unit, that is, one word or less in this example, drawing can be performed by newly allocating a holding unit as described below.

The holding unit control unit 11 always determines to which holding unit currently used the drawing coordinates calculated based on the reference line and the normal vector belong. As shown in FIG. 11, when the normal vector reaches the position of b, the drawing coordinates of the pixel at the starting point of the normal vector b cannot be stored in the first holding unit. At this time, the holding unit control unit 11 determines that the starting point of the normal vector b is outside the range of the holding unit. Therefore, the holding unit control unit 11 newly allocates the second holding unit along the word boundary of the frame memory 7 so that the coordinates of the pixels that are out of the range are included, and the pixel at the starting point of the normal vector b is set to the first pixel. Draw to the second holding unit. At this time, even if the normal vector spans the drawing areas assigned to the two holding units, the holding unit control unit 11
Can determine the holding unit for each pixel, and thus can be drawn without any problem.

When the drawing further proceeds and the normal vector reaches the position of c as shown in FIG. 12, the pixel drawn according to the normal vector is not written in the first holding unit. When a straight line is drawn, the data is not drawn in the first holding unit even if drawing is further progressed.
Drawing of the first holding unit in the drawing is completed. Holding unit control unit 11
Requests the data transfer unit 14 to transfer the contents of the first holding unit to the frame memory 7, and sends the coordinates indicating the position of the first holding unit.

As shown in FIG. 13, when the normal vector reaches the position of d, the end point of the normal vector d protrudes from the second holding unit. Therefore, the third holding unit is newly added to the second holding unit.
The pixel at the end point of the normal vector d is drawn by allocating it to a position below the holding part of the. Of course, since the first holding unit has already transferred the contents, it is possible to assign the first holding unit at this point. After the allocation of the third holding unit, the second holding unit and the third holding unit are used as shown in FIG.

When the drawing further progresses and the normal vector reaches the position of e as shown in FIG. 14, the drawing coordinates of the pixel at the starting point of the normal vector e are used by the second holding unit. Or it is outside the range of the third holding unit. Therefore, the fourth holding unit is newly set so that the coordinates of the pixels that are out of the range are included, and the pixel at the starting point of the normal vector e is drawn.

In FIG. 15, when the normal vector reaches the position of f, a pixel appears outside the range of the second, third, and fourth holding units during drawing along the normal vector. Therefore, the contents of the first holding unit which is not currently used are cleared by the data holding unit initializing unit 15 so that the coordinates of this pixel can be entered, and new allocation is performed. The clearing of the holding unit by the data holding unit initializing unit 15 may be performed after the contents of the holding unit are transferred and before newly allocated and drawn.

At this time, no more pixels are drawn in the second holding unit. Therefore, the data transfer unit 14 is requested to transfer the contents of the second holding unit, and at the same time, on the frame memory 7. The coordinates indicating the position of the second holding unit of the are sent. After transferring the contents of the second holding unit, the first, third and fourth contents are transferred.
Drawing will be performed using the holding unit.

As shown in FIG. 16, when the normal vector reaches the position of g, the pixels to be drawn along the normal vector are no longer written in the third holding unit, so the third holding unit draws. It will be completed. The holding unit control unit 11 is the data transfer unit 1.
4 is requested to transfer the contents of the third holding unit, and the coordinates indicating the position of the third holding unit on the frame memory 7 are sent.

As shown in FIG. 17, when the normal vector reaches the position of h, that is, when the drawing is completed up to the end point, the holding unit control unit 11 instructs the data transfer unit 14 to use all the currently used data. A request is made to transfer the contents of the holding unit to the frame memory 7, and the coordinates indicating the position on the frame memory of each holding unit for transferring the contents are sent. Since the first and fourth holding units are used in FIG. 17, the contents of these holding units are transferred. This allows
The drawing data of the line segment shown in FIG.
Stored on top.

As described above, when the line width of the line segment is less than the number of pixels corresponding to one word, the line segment can be drawn by sequentially using the four holding units. Further, since the drawing data is transferred to the frame memory 7 in units of words, the number of accesses to the frame memory 7 is reduced and the drawing processing time can be further shortened.

In the above example, the x-coordinates of the holding units set adjacent to each other on the left and right are set to be the same, and the coordinates of the holding units are set. The x-coordinates of the parts need not be aligned. For example, in FIG.
When assigning the second holding unit in, the area may be set such that the upper side of the second holding unit is aligned with the x coordinate of the starting point of the normal vector b. Further, in this example, the size of the holding unit is set to 1 word × 1 word, but the size is not limited to this, and any size may be used as long as the width is 1 word or more. At this time, the memory can be efficiently used by making the width of the holding unit an integral multiple of 1 word.

FIG. 18 and FIG. 19 are explanatory views of an example of the drawing and transfer processing when the line width does not fit into one holding unit in the first embodiment of the present invention. As shown in FIG. 18, when the line width of the line segment to be drawn does not fit into one holding portion, the holding portions are insufficient with only four holding portions as described above. As one method of solving this, there is a method of drawing the line segment in several times. That is, the normal vector of the line segment is divided so as to fit into one holding unit, and drawing is performed toward the end point based on the divided normal vector. Then, subsequently, drawing is performed based on the normal vector divided next from the start point to the end point. The above process is repeated until the line width becomes thick. By processing in this way, drawing data can be efficiently transferred to the frame memory 7 using at least four holding units as described above.

Specific drawing processing and transfer processing are shown in FIG.
This will be described using 9. Here, consider a case where a line segment having a line width of 2 words or more is drawn, as shown by hatching in FIG. When a line segment having a line width that does not fit in one holding unit is drawn in this way, if a normal vector for the line width is prepared and drawn as it is as described above,
The four holding units in the data holding unit 12 are insufficient. Therefore, as shown in FIG. 19, the line width is divided for each drawing area, and the normal vector is divided into sub-normal vectors to. In FIG. 19, each area in which drawing is divided and shown is shown with different hatching.

When the sub-normal vector is created, the normal vector is clipped by the starting point of the normal vector and the area of the holding unit allocated along the word boundary. In FIG. 19, the holding unit control unit 11 creates a sub-normal vector from the normal vector, and sequentially holds the sub-normal vectors in the same manner as in the case where the above-mentioned line width enters one holding unit based on the sub-normal vector. And draw. FIG. 19 also shows the process of assigning the holding units, and the numbers of the assigned holding units are indicated by numbers.

After drawing to the end point of the straight line by the sub-normal vector, the sub-normal vector,
Draw while creating each sub-normal vector. As described above, when the line width does not fit into one holding unit, the normal vector is clipped to the size of the holding unit and used to draw the line segment using the four holding units. You can

In the above-mentioned example, an example in which at least four holding units are effectively used to draw a line segment having a line width that does not fit in one holding unit has been shown. However, for example, the number of holding units is five. When it is possible to secure one or more, it is possible to make the length of the sub-normal vector to be divided more than the length that can fit into one holding unit. As a result, the number of sub-normal vector divisions can be reduced, and high-speed drawing can be performed. Further, when the required number of holding units can be secured, it is possible to draw the normal vector as it is without dividing it into sub-normal vectors.

In the first embodiment described above, a method of drawing a line segment by overlapping normal vectors as described in Japanese Patent Application No. 7-82432 is used.
The configuration has been shown in which drawing data is transferred to the frame memory via the data holding means. However, the method of transferring the drawing data shown in the first embodiment is not limited to this, and can be applied to, for example, a method of drawing a line segment by overlapping line segments connecting a start point and an end point. It is possible. In this case, since the length of the line segment is generally longer than the size of the holding portion, it is possible to use a method of dividing and drawing as shown in FIG.

FIG. 20 is a block diagram showing a second embodiment of the line segment drawing apparatus of the present invention. In the figure, the same parts as those in FIG. 41 is a drawing pixel correction unit, 42 is a holding unit coordinate calculation unit, 43 is a holding unit control unit, 44 is a data holding unit, and 45 is a data transfer unit. In this embodiment, the drawing pixel transfer unit 6 is provided with a drawing pixel correction unit 41, a holding unit coordinate calculation unit 42, a holding unit control unit 43, a data holding unit 44, and a data transfer unit 45. ing. The drawing pixel correction unit 41 compares the coordinates of the reference line calculated in the reference line scanning unit 2 with the coordinates of the reference line already drawn in the data holding unit, and if a different pixel is found, the drawing pixel correction unit 41 sets the normal vector. The data in the data holding unit is changed based on the above.

The holding unit coordinate calculation unit 42 uses the data holding unit 4 so that the data holding unit can hold as many line segment drawing pixels as possible based on the coordinates of the reference line and the normal vector.
The setting coordinates of 4 are calculated.

When the line drawing unit 5 draws a line segment in the data holding unit 44 for the first time, or when the drawing pixel correction unit 41 corrects the data held in the data holding unit 44, the holding unit control unit 43 corrects the data. , DDA is determined based on the operation result of DDA, and the data transfer unit 45 is controlled to transfer the data after either processing is completed.

The data holding unit 44 holds drawing data of a rectangular area of n × m pixels. At this time, efficient transfer can be performed by setting the size according to the transfer unit. As a specific example, a rectangular area of 8 × 8 pixels can be used, and in the case of 1 bit / pixel, it can be configured by 8 bits × 8 bytes.

The data transfer unit 45 calculates the data drawn in the data holding unit 44 by the holding unit coordinate calculation unit 42 after the holding unit control unit 43 determines that the access to the data holding unit 44 is completed. Transfer to the position on the frame memory.

FIG. 21 and FIG. 22 are explanatory views of an example of a concrete operation in the second embodiment of the line segment drawing apparatus of the present invention. 21 shows the transition of the contents of the data holding unit 44, and FIG. 22 shows the contents of the frame memory 7. Also in the second embodiment, similarly to the first embodiment described above, after generating the normal vector (corresponding to v0 to v3 in FIG. 4), this is used as a starting point for each pixel on the reference line. The line segment drawing unit 5 calculates the drawing coordinates of the line segment. At this time, the data is not directly drawn on the frame memory 7, but is drawn on the data holding unit 44 or the already drawn data is corrected and used.

When drawing in the data holding unit 44 for the first time, based on the drawing coordinates calculated in the line segment drawing unit 5, the holding unit coordinate calculation is performed so that the data holding unit 43 can hold as many line segment drawing pixels as possible. The unit 42 calculates and sets the set coordinates of the data holding unit 44. For example, the start point and the end point of the normal vector may be set so as to come to the edge portion of the data holding unit 44. The area of the data holding unit 44 is set corresponding to the area on the frame memory 7 as shown by the thick line in FIG.

As shown in FIG. 21A, pixels on the reference line of the line segment are sequentially generated from the pixel A ', and a normal vector is drawn in the data holding unit 44 starting from the pixel. At this time, the pixel missing portion is also corrected based on the determination result by the pixel missing determination unit 28 in FIG. The holding unit control unit 43 keeps the data holding unit 44 until the residuals at the start point of the reference line in the data holding unit 44 (pixel A'in FIG.
Draw within the range. In FIG. 21A, the pixel A'is closest to the residual of the pixel A '. As a result, the drawing pattern from the next pixel on the reference line is changed to the data holding unit 44.
It does not change much from the current pattern drawn in. Pixels a'on the reference line are generated, pixels are drawn in the data holding unit 44 based on the normal vector, and then transferred to the position set in the frame memory 7 by the data transfer unit 45. As a result, the line segment of the portion from the pixel A to the pixel B on the reference line in FIG. 22 is drawn in the frame memory 7.

Next, the drawing pixel correction unit 41 is operated by the drawing pixel correction unit 41 shown in FIG.
As shown in (B), the holding unit coordinate calculation unit 42 calculates the position of the data holding unit 44 so that the reference line in the data holding unit 44 is well connected to the drawing portion of FIG. 21 (A). The pixels on the reference line are sequentially compared with the pixels on the reference line and the coordinates of the previously drawn reference line in the data holding unit 44. If a different pixel is found, that part is modified. That is, if the pixel on the reference line is shifted by one pixel,
Since the normal vector also shifts by one pixel, the two pixels at the start point and the end point of the normal vector are corrected. In the example shown in FIG. 21B, two pixels of pixel o'and pixel power 'are corrected. Such processing is performed for the pixels on the reference line up to the pixel d having a residual close to that of the pixel c. Then, the contents of the corrected data holding unit 44 are transferred to the set position on the frame memory 7 by the data transfer unit 45. As a result, FIG.
In FIG. 2, the line segment of the portion from the pixel C to the pixel D on the reference line is drawn in the frame memory 7.

Similarly, also in FIG. 21C, first, the reference line in the data holding unit 44 corrected and used by the holding unit coordinate calculation unit 42 in FIG. 21B is well connected to that in FIG. 21C. Then, the position of the data holding unit 44 is calculated, the drawing pixel correction unit 41 corrects the pixel K ′ and the pixel K ′, and the data transfer unit 45 transfers the data to the frame memory 7. As a result, the line segment of the portion from the pixel K to the pixel K on the reference line in FIG. 22 is drawn in the frame memory 7. In this way, the entire line segment is drawn in the frame memory 7.

By using the data thus drawn in the data holding unit 44 while correcting it, the drawing process can be speeded up. In addition, the data holding unit 44
High-speed transfer can be performed by using the byte unit or the word unit. When the frame memory 7 has a word structure or a byte structure, even if the frame memory 7 is transferred in units of words or bytes from the data holding unit 44, it may not match the word boundaries or the byte boundaries. However, it is sufficient to access the frame memory 7 twice for each word or byte transferred from the data holding unit 44, and the access frequency can be significantly reduced as compared with the case where the frame memory 7 is accessed for each pixel. . Therefore, the time required for transfer can be reduced, and high-speed drawing processing can be realized.

In the above-mentioned examples shown in FIGS. 21 and 22, for example, continuous line segments are drawn, but this embodiment is not limited to this and may be dotted lines, broken lines, or other line types. However, it can be drawn similarly. If the line width is equal to or larger than the size of the data holding unit 44, it may be divided into several parts and drawn as described above with reference to FIG.

[0078]

As is apparent from the above description, according to the present invention, the drawing data is temporarily held in the small-capacity data holding means in accordance with the transfer unit and is transferred to the frame memory. The number of accesses to the memory can be reduced. Thereby, there is an effect that the transfer time can be shortened and the drawing processing can be speeded up.

In particular, according to the invention described in claim 1, by providing four or more holding units each having a small capacity and allocating the holding units as needed, the drawing data can be efficiently used by using the memory having a small capacity. It can be transferred to the frame memory, and high-speed drawing processing can be performed with a small capacity memory. According to the second aspect of the present invention, by allocating the area to the holding unit at the word boundary, word-by-word transfer becomes possible and high-speed drawing data transfer can be performed.

According to the third aspect of the invention, the drawing data previously drawn in the data holding means is used, and the drawing data is drawn into the data holding means by appropriately modifying and transferring to the frame memory. By improving the speed and transferring the drawing data from the data holding unit to the frame memory for each transfer unit, the number of accesses can be markedly reduced as compared with the case of accessing the frame memory for each pixel. Drawing processing can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a line segment drawing apparatus of the present invention.

FIG. 2 is a block diagram showing a specific example of a reference line scanning unit 2, a distance calculation unit 3, a normal vector generation unit 4, and a line segment drawing unit 5 in the first embodiment of the line drawing apparatus of the present invention. is there.

FIG. 3 is an explanatory diagram of a basic line segment drawing operation in the first embodiment of the line segment drawing apparatus of the present invention.

FIG. 4 is an explanatory diagram of an example of an operation up to generation of a normal vector.

FIG. 5 is an explanatory diagram of an example of an operation of a movement distance calculation unit.

FIG. 6 is a flowchart showing an example of the operation of a moving distance calculation unit.

FIG. 7 is an explanatory diagram of an example of an operation from normal vector generation to line segment drawing.

FIG. 8 is an explanatory diagram of a specific example of a line segment to be drawn.

FIG. 9 is a flowchart showing an example of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 10 is an explanatory diagram of a specific process of storing and transferring drawn pixels according to the first embodiment of the present invention.

FIG. 11 is an explanatory diagram (continuation) of a specific process of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 12 is an explanatory diagram (continuation) of a specific process of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 13 is an explanatory diagram (continuation) of a specific process of storing and transferring a drawn pixel in the first embodiment of the present invention.

FIG. 14 is an explanatory diagram (continuation) of a specific process of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 15 is an explanatory diagram (continuation) of a specific process of storing and transferring a drawn pixel in the first embodiment of the present invention.

FIG. 16 is an explanatory diagram (continuation) of a specific process of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 17 is an explanatory diagram (continuation) of a specific process of storage and transfer processing of drawn pixels according to the first embodiment of the present invention.

FIG. 18 is an explanatory diagram of an example of a line segment when the line width does not fit into one holding unit according to the first embodiment of the present invention.

FIG. 19 is an explanatory diagram of an example of drawing and transfer processing when the line width does not fit into one holding unit according to the first embodiment of the present invention.

FIG. 20 is a block diagram showing a second embodiment of a line segment drawing device of the present invention.

FIG. 21 is an explanatory diagram of an example of a specific operation in the second embodiment of the line segment drawing device of the present invention.

FIG. 22 is an explanatory diagram (continuation) of an example of a specific operation in the second embodiment of the line segment drawing device of the present invention.

FIG. 23 is an explanatory diagram of an example of a conventional line segment drawing method.

[Explanation of symbols]

1 ... Initial value recognition unit, 2 ... Reference line scanning unit, 3 ... Distance calculation unit, 4 ... Normal vector generation unit, 5 ... Line segment drawing unit, 6 ... Calculation data transfer unit, 7 ... Frame memory, 11 ... Hold Control unit, 12 ... data holding unit, 13 ... holding unit coordinate calculation unit,
14 ... Data transfer unit, 15 ... Data holding unit initialization unit, 2
DESCRIPTION OF SYMBOLS 1 ... Coordinate generation unit, 22 ... Scanning coordinate storage unit, 23 ... Moving distance calculation unit, 24 ... Line width scanning determination unit, 25 ... 90 ° rotation unit, 26 ... Normal vector storage unit, 27 ... Reference line movement processing unit , 28 ... Pixel missing determination unit, 29 ... Drawing unit, 30 ... End condition determination unit, 41 ... Drawing pixel correction unit, 42 ... Holding unit coordinate calculation unit, 43 ... Holding unit control unit, 44 ... Data holding unit, 4
5 ... Data transfer unit.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-163677 (JP, A) JP-A-2-208694 (JP, A) JP-A-4-117583 (JP, A) JP-A-57- 159389 (JP, A) JP-A 1-166177 (JP, A) JP-A 63-195696 (JP, A) JP-A 60-227292 (JP, A) JP-A 4-117582 (JP, A) Actual Kaihei 1-111358 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G06T 11/20 G09G 5/36

Claims (3)

(57) [Claims] 1. An initial value setting means for outputting a start point and an end point of a line segment drawn from the input information and a line width of the line segment, and a start point and an end point output from the initial value setting means. Reference line generating means for generating coordinates on a straight line, distance calculating means for calculating a distance between the coordinates generated by the reference line generating means and the starting point, a calculation result by the distance calculating means and the reference A normal line that is orthogonal to a straight line connecting the start point and the end point based on the coordinates generated by the line generation means and that generates a pixel column having a length equal to the line width of the line segment output from the initial value setting means Vector generation means, drawing means for generating the pixel row generated by the normal vector generation means for each coordinate generated by the reference line generation means, and temporarily holding the pixel row generated by the drawing means Data holding with multiple holding units Means, a frame memory for storing the drawn image, a holding portion coordinate calculating means for calculating the corresponding position on the frame memory by the holding portion, the coordinates of the pixel row obtained by the drawing means, and the holding A holding unit control unit that sets or selects the holding unit based on positional information of the holding unit by the partial coordinate calculation unit, a data transfer unit that sequentially transfers data from the holding unit that has stored data to the frame memory, and the data. A line segment drawing apparatus having a data holding unit initialization unit that clears the holding unit that has been transferred by the transfer unit. 2. The frame memory is configured to store a plurality of pixels in one word, the holding unit has its position set based on a word boundary of the frame memory, and the data transfer unit sets each word. The line segment drawing device according to claim 1, wherein the line segment drawing device transfers the data to the line segment. 3. An initial value setting means for outputting a start point and an end point of a line segment drawn from the input information and a line width of the line segment, and a start point and an end point output from the initial value setting means. Reference line generating means for generating coordinates on a straight line, distance calculating means for calculating a distance between the coordinates generated by the reference line generating means and the starting point, a calculation result by the distance calculating means and the reference A normal line that is orthogonal to a straight line connecting the start point and the end point based on the coordinates generated by the line generation means and that generates a pixel column having a length equal to the line width of the line segment output from the initial value setting means Vector generation means, drawing means for generating the pixel row generated by the normal vector generation means for each coordinate generated by the reference line generation means, and data holding for temporarily storing the pixel row generated by the drawing means Means and
A frame memory that stores a drawn image, a holding unit coordinate calculation unit that calculates a position on the frame memory corresponding to the data holding unit, a coordinate of a pixel row to be newly drawn, and the data holding unit. Drawing pixel correction means for comparing and correcting the coordinates of the pixel row stored in the pixel row to be newly drawn and data to the data holding means based on the pixel row generated by the drawing means Holding section control means for determining the end of storage or correction of stored data, and data transfer means for transferring data stored or modified in the data holding means to the frame memory. apparatus.