JPH03139779A - Plane and line segment plotting system - Google Patents

Abstract

PURPOSE:To reduce the deterioration of picture quality due to aliasing by mixing the color of a line segment outputted from a digital differential analyzer(DDA) with that of the picture element of a corresponding plane read out from a frame buffer, and plotting the plane and the line segment as the color of the picture element of a corresponding line segment in the frame buffer. CONSTITUTION:The Z value of each picture element to which the line segment generated at the DDA approaches is compared with the Z value of a plane picture element in the neighborhood of the line segment found from a Z buffer 5 at a Z value comparison part 10, and a value in which each element of a size judging table generated based on a size-judged result by a normalization value is averaged is outputted as a mixing ratio. Then, the color of the line segment outputted from the DDA 1 is mixed with that of the picture element of the corresponding plane read out from the frame buffer 3 at a color mixing part 11, and the plane and the line segment are plotted as the color of the picture element of the corresponding line segment in the frame buffer 3. Thereby, it is possible to reduce the deterioration of the picture quality due to the aliasing.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Prior Art and Problems to be Solved by the Invention Means for Solving the Problems Actions Examples Effects of the Invention [Summary] In graphic display devices, flat Regarding the method of drawing a line segment that is mathematically tangent to the top (or included in the plane), the Z of the line segment generated by the digital differential analyzer (I] OA)
Due to a slight error between the Z value and the Z value of the plane, the line segments drawn on the plane become cut off, and the line segment cannot be drawn for each scan line, resulting in image quality due to aliasing. At least a segment buffer, a digital differential analyzer (DDA), and numerical information in the depth direction (Z(iff) used when displaying three-dimensional figures) are stored. A graphic display device that has a Z-buffer and draws line segments that are mathematically tangent to plane -1-. Using the output from a(+)D^), the hidden surface removal section performs plane drawing by hidden surface removal based on the Z value of the Z buffer written in "-", stores it in the frame buffer, and then , when drawing a line segment, the filtering unit calculates the Z value of each pixel into which the line segment is generated by the digital differential analyzer (DI) A) and - the line segment obtained from the Z buffer. The Z value of the plane pixel in the vicinity of the pixel is compared with the Z value of the plane pixel in the vicinity of the pixel, and the normalized value generated based on the result of the size determination, for example, the value obtained by averaging each element of the size determination table based on 2. is output as a mixing ratio, and based on the output mixing ratio, the color of the line segment output from the digital differential analyzer (DDA) and the color of the pixel of the corresponding plane read from the frame buffer. and are mixed in the color mixing section,
The plane and the line segment are drawn using the color of the pixel of the corresponding line segment in the frame buffer.

[Industrial application field]

The present invention provides a graphic display device that is mathematically tangent to (or included in) a plane F.
Concerning methods for drawing line segments.

In recent years, in the field of graphic displays, three
It is required to display dimensional objects. For this reason, it is necessary to use hidden surface removal technology that distinguishes and displays objects that are visible and invisible from the observer's viewpoint.

In this case, the plane is drawn by a digital differential analyzer (DD^) with respect to line segments separated by each scan line, and is mathematically tangent to the plane. Or,
When drawing a line segment included in the plane, it is drawn using digital differential analysis # (DDA) to its start and end points, so the Z value of the plane and the Z! There is a problem that the line segment becomes cut off due to a slight error with lfi.

In addition, if the pixels that make up the line segment are drawn using the color of the line segment, a so-called aliasing phenomenon will occur, resulting in a problem of loss of image quality, so a method called anti-aliasing will be used. Since this method takes a long time, there is a need for an effective plane/line segment drawing method that makes the deterioration in image quality less noticeable.

[Prior art and problems to be solved by the invention] FIG. 5 is a diagram for explaining the conventional plane/line segment drawing method.
) shows the principle configuration diagram, (bl) and (b2) show an example of drawing by a digital differential analyzer (DDA), and (c
1) to (c3) are diagrams illustrating problems of the prior art.

In Fig. 5(a), 1 expands a line segment into pixels and outputs the Z value and color of the expanded pixel.
Ital Differential Analysis
s) part (hereinafter referred to as DD8), and 6 is the said DDA
] A hidden surface removal unit 3 compares the Z value for each pixel output from the DDA 1 with the Z value accumulated in the Z buffer 5 so far, and determines whether the pixel from the DDA 1 is visible. A frame buffer 4 stores the colors of visible pixels based on the output from the hidden surface erasing unit 6, and 4 is a frame buffer 3 indicated by L.
5 is a Z buffer that holds the Z value of the pixel generated by the DDA 1.

To outline the drawing method using this Z (ii), first,
DA ] newly develops the displayed polygon or line segment into pixels, and sequentially outputs the color and Z value of the pixel.

Next, the hidden surface erasing unit 6 processes the Z value of the pixel sent from 1) I)/l and each pixel of the figure already stored in the frame buffer 3 corresponding to that pixel. The Z value stored in the Z buffer 5 is compared with the Z value stored in the Z buffer 5.

The magnitude relationship between these two Z values is examined (the magnitude relationship of Z4fi depends on the direction of the Z axis), and it is determined whether or not to update the Z value in the Z buffer 5. When updating the Z buffer 5, the hidden surface erasing unit 6 writes the color of the developed pixel to the corresponding pixel of the frame buffer 3, and at the same time changes the Z value of the Z buffer 5 to the Z value of the developed pixel. Update.

This method is a technology that displays a figure (or part of a figure) that is closer to the front than the figure (pixel) already stored in the frame buffer 3, and is This is a well-known technology that is characterized by high memory usage efficiency, as it is possible to read the graphic data one by one, process it, and then discard it by preparing and arranging a memory for this purpose.

However, according to this method, two problems arise when drawing a line segment 1 that is mathematically tangent to (or included in) a plane.

First, the first problem is that, as shown in this figure (old), the plane 55 is drawn using the above 1) l) A technique for line segments cut for each scan line. In contrast,
(h2) When drawing the line segment 56 shown in the figure, drawing is performed from the starting point to the ending point of the line segment using ODA.

This is because even if an attempt is made to increase the line segment by +108 for each scan line, it is impossible because the line segment has no thickness. Therefore, along the direction of the line segment,
When performing ODA, the Z value of a plane at a certain pixel and the Z value of a line segment often differ slightly due to calculation errors.

The figures (cl) to (c3) show this phenomenon.

Figure 5 (cl) is the Z value of the plane (this is the Z value of a figure different from Figure 5 (old)), Figure 5 (c2) is the Z value of the line segment, Figure 5 (c3) is the result of displaying both planes and line segments, with the one with the smaller Z value being displayed.

1? Pixels with a " mark indicate whether a plane or a line segment is displayed depending on the order in which the figure is displayed. "Line" indicates a line segment, and "flat" indicates a plane. .

This phenomenon of line segments being cut off is due to the fact that the number of calculation digits of existing computers is finite, and cannot be avoided. Therefore, even a slight difference in Z value causes the plane to move forward or the line segment to move forward, resulting in the line segment being cut off.

The second problem is that when displaying a line segment, the ODA identifies the pixels into which the line segment enters, but if all the pixels are filled in with the color of the line segment, as shown in Figure 5 (c2). This is a phenomenon called aliasing that causes jaggedness, which impairs image quality. Avoid this6
To do this, it is common to use a technique called unaliasing to mix the color of the line segment with the color of the surrounding figure to make the jaggedness less noticeable. However, unaliasing generally requires a lot of effort and processing time.

Therefore, when drawing a line segment that is mathematically tangent to a plane, the line segment is displayed as broken, and furthermore,
The displayed line segments were displayed with aliasing, resulting in a problem that the image quality was degraded.

In view of the above-mentioned conventional drawbacks, the present invention provides a graphic display device that uses a digital differential analyzer (DDA) when drawing a line segment that is mathematically tangent to (or included on) the plane l-. Z(li) of the line segment
Line segments drawn on the plane become cut off due to slight errors with the Z value of the plane, and the image quality deteriorates due to aliasing, which occurs when the line segments cannot be drawn for each scan line. The purpose of this invention is to provide a plane/line segment drawing method that can reduce the amount of time required.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention, in which (a) shows the basic configuration, (b) shows an example of the configuration when drawing a plane, and (c)
) shows an example of the configuration when drawing a line segment, and (d) shows an example of the internal configuration of the filtering section.

The problems described in (1)-- can be solved by a plane/line segment drawing method configured as follows.

(1) Segment buffer 200, segment management section 201, coordinate transformation section 202, and clipping section 203
, surface coating section 204, and digital differential analyzer (DD^
) 1 and a Z buffer 5 that stores numerical information (Z value) in the depth direction used when displaying a three-dimensional figure, and draws a line segment that is mathematically tangent to the plane 1-. The graph ink display device includes a hidden surface removal unit/filtering unit 2, a frame 1, a buffer 3, and a display 4, and first uses the output from the digital differential analysis @(D[)A)l. , the hidden surface erasing unit 6 performs plane drawing by hidden surface erasing based on the Z value of the Z buffer 5, and stores it in the frame buffer 3. Next, when drawing a line segment, the filtering unit 7, the digital differential analyzer (004)
The Z value of each pixel entering the line segment generated by I and the above Z
The Z value of the plane pixel near the pixel of the line segment obtained from the buffer 5 is compared with the Z value of the plane pixel in the vicinity of the pixel of the line segment, and the Z value comparing unit 10 averages each element of the binary magnitude determination table generated based on the magnitude determination result. The converted value is output as a mixing ratio, and based on the output mixing ratio, the color of the line segment output from the digital differential analyzer (+) I) A) 1 and the color read out from the frame buffer 3 are calculated. In addition, the plane and the line segment are drawn by mixing the color of the pixel of the corresponding plane using the color mixing unit 1 to obtain the color of the pixel of the corresponding line segment of the frame buffer 3. do.

(2) In the graphic display device, a buffer 20 temporarily stores only line segment data among the graphic data read from the segment buffer 200.
5 is provided, and when the figure data read from the segment buffer 200 is line segment data, it is temporarily stored in the buffer 205, and when the line segment is drawn after the drawing of the plane is completed, , buffer 2 that temporarily stores the above line segment
05, and draw the line segment by mixing two colors.

(Operation) That is, according to the present invention, in the graphic display device, when drawing a line segment that is mathematically tangent to a plane (or included on the plane), first, the switching unit 8
, 9 are changed as shown in FIG. Z (a) is compared. The magnitude relationship between these two Z values is checked (the magnitude relationship between the Z values depends on the direction of the Z axis), and it is determined whether or not to update the Z buffer 5.

When updating the Z buffer 5, the color of the pixel developed by DIIA ] is written into the corresponding pixel of the frame pan 3 4 fa 3, and the Z value of the Z buffer 5 is also updated at the same time.

This method works with figures that are closer to the front than the figures already stored in the frame buffer 3, as shown in
This is a technology that displays the eyes (or part of a figure).

Next, in the present invention, the switching units 8 and 9 are configured as shown in FIG. 1(c).
, (d), switch the input and output, and first,
A pixel (referred to as pixel A) into which the line segment enters is selected using DDA 1 for the line segment, and the Z value at that pixel A is set to the Z value comparing section 100 manually.

The Z value comparison unit 10 calculates the Z value of the line segment of pixel A (the above DD
A 1), the Z value in Z Hasinoa 3 corresponding to pixel A, and the neighborhood of that pixel, for example, 3 × 3
The Z value of the pixel in the pixel area is compared.

This is explained in figures (a) to (c) illustrating the function of the Z value comparison section in FIG. 2. FIG. 2(a) shows the Z value at the pixel 100 (indicated by a bold frame) into which the line segment has entered, and FIG. 2(b) shows the Z value at the pixel 100 into which the line segment has entered, and
This is the Z value of the plane in eight pixels (the above-mentioned 3×3 pixel area) in the vicinity.

The Z value comparison unit 10 compares the Z value of the line segment in FIG. 2 (++) with
The Z values of the pixels constituting the 3×3 pixel plane shown in FIG. 2(b) are compared, and a size discrimination table as shown in FIG. 2(c) is created based on the Z values.

Each element of this size discrimination table becomes "1" when the Z value of the line segment is smaller than or equal to the Z value of the plane, and becomes "0" when it is larger (when displaying pixels with small Z values) .

The Z value comparison unit 10 outputs a value obtained by averaging each element of this table as a mixing ratio. For example, in Figure 2 (c
), there are 6 digits for 1° and 3 digits for 0°, so the output mixing ratio is (IX6+0x3)/9.
It becomes 7%. If a line segment is completely hidden behind a plane (that is, the line segment is on another plane),
Even existing calculators can clearly determine that the distance is so far that the error can be ignored), then all the elements of this size discrimination table will be 0 degrees, and the color of this line segment will not contribute at all to the pixels on the plane. It won't, so there's no need to worry.

In the color mixing section 11, based on the mixing ratio output from the Z value comparison section 10, the color of the line segment output from the DDA 1 and the color (- plane color). In the case of the pixel shown in Figure 2, the color of the line segment from DDA 1 is set to 67%, and the color of the corresponding pixel from frame buffer 3 (-plane color).
are mixed at a ratio of 33% and output as the pixel color of the line segment after mixing.

The selector 12 in FIG. 1(d) has the function of switching between reading the color of a pixel from the frame buffer 3 and writing the mixed pixel to the frame buffer 3 in response to a request from the color mixing section 11. .

Therefore, by configuring as above, when displaying a line segment, a slight difference in the Z value due to a calculation error will cause the line segment to be completely buried in the plane or floating, and the line segment will be displayed. It is possible to reduce the phenomenon in which lines are cut off by mixing the color of the pixels that make up the line segment with the color of the surrounding pixels.Furthermore, by processing the color mixing,
This also has the effect of reducing the above aliasing that occurs when displaying line segments.

〔Example〕

The above-mentioned FIG. 1 is a diagram explaining the present invention in detail, and FIG.
The figures are diagrams for explaining the functions of the Z value comparison section, FIG. 3 is a diagram showing one embodiment of the present invention, and FIG. 4 is a diagram showing another embodiment of the present invention. , when drawing a plane, the hidden surface erasing unit 6 performs drawing by hidden surface erasing based on the Z value of each pixel, and contacts the drawn plane. Alternatively, when drawing a line segment included in the plane, the filtering unit 7 compares the Z value of the pixel of the line segment with the Z value of the surrounding pixels of the pixel of the line segment, and determines the magnitude. A method of determining a mixing ratio from the relationship and displaying the mixture of the color of the pixel of the line segment and the color of the pixel of the plane at the corresponding position as the color of the pixel of the line segment according to the determined mixing ratio. The steps are the means necessary to carry out the invention. Note that the same reference numerals indicate the same objects throughout the figures.

Hereinafter, the plane/line segment drawing method of the present invention will be explained with reference to FIGS. 3 and 4 while referring to FIGS. 1 and 2.

In this embodiment, 200 is a segment buffer which is a graphic database storing graphic elements, transformation matrices, etc., and 201 is a segment buffer for managing the segment buffer 200;
and a segment management section that controls the entire display device.
It functions to retrieve and transfer graphic data in the segment I buffer 200.

In addition, 202 uses 71-RiX operation to rotate and rotate the figure.
It is a coordinate conversion unit that performs movement, enlargement/reduction, etc. 203
is a clipping section that cuts out figures (or parts of figures) that protrude from the screen.

Furthermore, when displaying a plane, 204 is a surface painting part that expands the plane into a column (vector column) that is internal for each scan line, and when displaying a line segment, it passes through it as it is. Both are image processing functions using known techniques.

In the embodiment of FIG. 3, the segment management section 201 takes out the graphic data in the segment buffer 20o. If the extracted graphic data is a plane, the segment management section 201 If the extracted graphic data is a line segment, the extracted graphic data is discarded and the next graphic data is read.

After reading all the plane data, the segment management unit 2 old functions to select only line segment data from the beginning of the segment buffer again and send it to the next coordinate transformation unit 202. The functions of the remaining parts are as described above (see the function column).

In particular, in the hidden surface erasing unit/filtering unit 2, which is the main focus of the present invention, when drawing a plane, the hidden surface erasing unit 6 performs the Drawing is performed by surface erasure, and when drawing a line segment included in the drawn plane, the Z of the pixel of the line segment is
Compare the value with Z (i'if) of the surrounding pixels of the pixel of the line segment, and determine the mixing ratio based on the magnitude relationship. ), and according to the mixture ratio thus obtained, the color of the pixel of the line segment and the color of the pixel of the plane at the corresponding position are mixed, and the color of the pixel of the line segment is calculated. The color of the mixed line segment pixel is stored in the frame buffer 3 so as to be displayed as the color of
It works like writing to .

FIG. 4 shows another embodiment of the invention.

In FIG. 3, the segment management unit 201 sorts the graphic data taken out from the segment buffer 200 into planes and line segments, discards the line segment data when the plane data is needed, and discards the line segment data when the line segment data is needed. At times, I threw away the plane data. Therefore, in order to read the line segment data after reading all the graphic data, it is necessary to return to the beginning of the segment puffer 200 and reread the graphic data.

If the access speed of the segment tube/enfer 200 is high, you can leave it as is, but if the access speed is a problem, as shown in Figure 4, the line segment data that was discarded when plane data was needed A buffer 205 may be provided to temporarily store the .

This eliminates the need to go back to the beginning of the segment huffer 200 and reread the figure data when all the figure data has been read, and when the line segment data is needed, the line segment data can be read. The problem of access speed can be solved by reading the data from the buffer 205 that temporarily stores the data.

Thus, the present invention provides a graphical display device that is mathematically tangent to a plane.
When drawing a plane line segment (included in 2),
Based on the Z value of each pixel, the hidden surface erasing unit 6 performs drawing by hidden surface erasing, and contacts the drawn plane. Alternatively, when drawing a line segment included in the plane, the filtering unit 7 compares the Z value of the pixel of the line segment with the Z value of the pixels of the plane around the pixel of the line segment. , the mixing ratio (for example, the ratio obtained by normalizing the Z value to "0" and "1") is determined from the magnitude relationship, and according to the obtained mixing ratio, the color of the pixel of the line segment, By displaying a mixture of the color of the pixel of the plane at the corresponding position as the color of the pixel of the line segment, the phenomenon of the line segment being buried or floating in the plane, and the phenomenon of aliasing are reduced. It is distinctive in that it is made like this.

〔Effect of the invention〕

As explained above, according to the plane/line segment drawing method of the present invention, in order to draw a line segment that is mathematically tangent to a plane (or included on the plane), at least a segment buffer and It has a segment management unit, digital differential analysis a (DDA), and a Z buffer that stores numerical information in the depth direction (Z value) used when displaying three-dimensional figures. A graphic display device that draws touching line segments is equipped with a hidden surface removal unit and filtering unit, a frame buffer, and a display.
) Using the output from ), the hidden surface removal unit performs plane drawing by hidden surface removal based on the Z buffer described in (2) and stores it in the frame buffer, and then when drawing line segments. In the filtering section, the ``2nd Digital Differential Analyzer (
7 of each pixel into which the line segment generated by DDA) enters. (
iif and the Z value of a pixel on a plane near the pixel of the line segment, which is found from the Z buffer, is compared by a Z value comparison unit,
For example, a value obtained by averaging each element of a binary size judgment table generated based on the size judgment result is output as a mixing ratio, and based on the output mixing ratio, the digital differential analysis m( 1) The color of the line segment output from DA) and the color of the pixel of the corresponding plane read from the frame buffer are mixed in the color mixing section, and the color of the pixel of the corresponding line segment of the frame buffer is mixed. Since it is designed to draw planes and line segments by using colors, even when drawing line segments that are mathematically tangent to a plane, the line segments may be buried in the plane or the line segments may be This has the effect of reducing jagged display and contributes to improving the image quality of images displayed on such graphic display devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the present invention in detail, and FIG. 2 is a diagram explaining the function of a Z value comparison section. FIG. 3 is a diagram showing an embodiment of the present invention. FIG. 4 is a diagram showing another embodiment of the present invention. FIG. 5 is a diagram illustrating a conventional plane/line segment drawing method. It is. is the line segment pixel, and is the segment I buffer. is the segment management department. For example, the coordinate conversion section is the clipping section. 1 is a digital differential analyzer (DDA) 2 is a hidden surface removal unit/filtering unit 3 is a frame buffer 4 is a display (CRT) 5 is Z buffer. 7 is a filtering section. 10 is a Z value comparison section. 12 is a selector. 55 is a drawing plane 56 is a drawn line segment 6 is a hidden surface erasing section 8; 9 is a switching section 11 is a color mixing section. 5 6

Claims (2)

[Claims] (1) At least a segment buffer (200);
A segment management unit (201), a digital differential analyzer (DDA) (1), and a Z buffer (5) that stores numerical information in the depth direction (Z value) used when displaying three-dimensional figures. A graphic display device that draws line segments that are mathematically tangent on a plane, which includes a hidden surface removal unit and filtering unit (2), a frame buffer (3), and a display (4), and which first , using the output from the digital differential analyzer (DDA) (1), the hidden surface removal unit (6) processes the Z buffer (5).
Based on the Z value of , perform plane drawing by removing hidden surfaces,
Store it in the frame buffer (3). Next, when drawing a line segment, the filtering unit (7)
Then, the Z value of each pixel entering the line segment generated by the digital differential analyzer (DDA) (1), and the Z value of the plane pixel near the pixel of the line segment obtained from the Z buffer (5). A Z-value comparison unit (10) compares the values, and outputs a value obtained by averaging each element of a size determination table based on a normalized value generated based on the size determination result as a mixing ratio, and outputs the output as a mixing ratio. Based on the mixing ratio, the color of the line segment output from the digital differential analyzer (DDA) (1) and the color of the pixel of the corresponding plane read from the frame buffer (3) are mixed. A plane/line segment drawing method characterized in that a plane and a line segment are drawn by mixing the colors in a part (11) to obtain the color of a pixel of a corresponding line segment in a frame buffer (3). (2) In the graphic display device, a buffer (205) is provided that temporarily stores only line segment data among the graphic data read from the segment buffer (200), and read from the segment buffer (200). When the graphic data obtained is line segment data, the buffer (20
5), and when drawing the line segment after drawing the plane, the line segment data is retrieved from the buffer (205) that temporarily stores the line segment, and the color mixture is 2. The plane/line segment drawing method according to claim 1, wherein the line segment is drawn using the following method.