JPH0359779A - Computer graphics equipment and method for displaying depth in the same - Google Patents

Abstract

PURPOSE: To speedily display depth by providing a means which supplies a width value which is indirectly relevant to depth to the edge of a line from the point of view of a user to each edge of a line to be drawn on an output display, and a means which uses the width value for deciding the vertexes of the line drawn by a means which draws the image of a quadrilateral. CONSTITUTION: A graphic unit 76 which draws a line segment by drawing a quadrilateral including vertexes for drawing a line, supplies an appropriate value to an anti-alias circuit. The output of the anti-alias circuit is transmitted to a frame buffer 78, and a line 82 is supplied from the buffer 78 to an output display 80. Vertexes 84-87 of a line 82 are supplied to the circuit without any change of luminance, and the luminance is changed by the ancharious part of the ancharious circuit. Then, according as the depth of the line is increased, the luminance of the line is reduced so that the depth can be perceived. Also, all the lines are drawn at an angle of 45 deg., and the luminance of the line is drawn by the same grey scale. Thus, a vertex calculating time can be sharply shortened, and the operating speed of this device can be sharply improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a computer graphics device.More specifically, the present invention relates to a computer graphics device. It relates to a device for displaying information to a viewer.

[Conventional technology]

In order to display a three-dimensional representation of an object on a two-dimensional output display, some means must be used to inform the viewer of the existence of the third dimension. Various methods have emerged from standard drawing techniques to achieve this result. An example of this is perspective painting, where the parallel lines that make up an object converge as the object recedes from view.

Other display techniques have been developed due to the peculiarities of computer displays. For example, in a bitmapped computer output display displayed on a cathode ray tube (CRT),
A method used to indicate or signal to the viewer the different depths of parts of an object is to vary the brightness of the bits that make up the object as the depth of the part of the object increases. Therefore, for a line extending from the viewer's position to infinity, the point closest to the line is the brightest;
The brightness at the farthest place is zero. Making the lines thinner produces the same effect that is given to images as the lines gradually extend away from the viewer. This technique enhances the feel of line depth on the output display.

Conventional methods to achieve this effect require that each pixel of a line with a depth dimension have a different brightness value from maximum to zero. In practical devices of the prior art, each individual arbitrary line with depth dimension is divided by dividing the length of the line by the number of pixels and calculating the brightness value for each neighboring pixel composing the line. is drawn. After that, I
Each individual pixel is written to the output display, n pixels at a time. In a color device where the color of the line changes from one end of the line to the other, the device's circuitry must calculate the brightness for each color, red, green, and blue, separately.

The brightness is from 0 to 1001. Conventional systems that provide this type of depth display for each pixel require separate computing devices for each color. All of the operations of those computing devices were very time consuming.

Improvements in computer equipment have focused on increasing the operating speed of the equipment. This is especially true for devices using bitmap displays where the graphics output is said to limit the operating speed of the device. Therefore, displaying depth in a three-dimensional bit mapped graphics output device has limited the operating speed of the device.

Additionally, anti-aliasing (antl-atlaslm) is used to improve the apparent depiction of lines on the display.
g) is used in computer graphics devices. In that technique, the various pixels that make up the line are rendered at different intensities in order to eliminate jagged, sharp edges along the sides of the line. Anti-aliasing is a well-known technique in this field, for example, UTEC-C8C-76-015, A
The Aliasing Problem in Computer Synthesized Images (Th
e Atlasing Probtenx In Co
mputer-8ythesizedShad@d I
It is described in a paper entitled mag@s ) J.

In that device, giving a depth indication is not a linear method of changing the brightness, since the change in line brightness is already part of the device to provide the anti-aliasing effect.

[Problem to be solved by the invention]

It is therefore an object of the present invention to increase the speed of computer graphics devices.

Another object of the invention is to provide depth display very quickly in a computer graphics device.

Another object of the present invention is to provide a new technique for displaying depth in three-dimensional graphics devices.

Yet another object of the invention is to obtain a device capable of anti-aliasing and depth display.

[Means to solve the problem]

These and other objects of the present invention provide a graphics device for drawing an image of a quadrilateral on an output display when the sides of the quadrilateral are provided, and each end of the line to be drawn on the output display. Translation means for supplying a width value that is indirectly related to the depth at the end of the line from the perspective of the viewer of the display, and a means for eliminating the image of a quadrilateral by defining the vertices of the line drawn as and means for utilizing the width value to make the determination.

Some portions of the detailed descriptions that follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by data processing professionals to most effectively convey their work to other professionals.

We define an algorithm as a self-consistent sequence of steps leading to a desired result. Those steps are physical f
requires physical processing.

Usually, but not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise processed. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, symbols, characters, terms, numbers, or the like. It should be remembered, however, that all of the terms button and similar terms should be associated with the appropriate physical quantities, and these terms are merely convenient labels applied to these quantities. .

Furthermore, the operations performed are often referred to by the terms addition or comparison. These processes are related to mental activities performed by humans. Such human capabilities are required in most cases of the processes described herein that form part of the present invention.

The operation is mechanical. Devices useful for carrying out the operations of the present invention include general purpose digital computers and other similar devices. In all cases, you should remember and write down the differences between the way a computer operates and the processing method itself. The present invention processes electrical signals and other (e.g., mechanical, chemical, and physical) signals to
The present invention relates to method steps for operating a computer to generate other desired physical signals.

The present invention also relates to devices for performing these operations. The apparatus may be specially constructed for the purpose sought, or may include a general purpose computer that is selectively activated or reconfigured by a computer program stored in the computer. The algorithms presented herein are not inherently related to any particular computer or other apparatus. In particular, it has been found that various general-purpose machines can be used with programs written in accordance with the description of this specification, or that it is even more convenient to construct more practical apparatus for carrying out the required method. are doing.

As mentioned above, in order to display a three-dimensional representation on a two-dimensional output display, some means must be used to indicate the third dimension to the viewer. One technique developed for computer output displays that are bitmapped to indicate or inform the viewer of the varying depths of portions of a line (or other object) is to It is to change the brightness of the constituent bits.

Reducing the brightness of the lines provides the same effect that is given to an image as it gradually recedes from the viewer. This effect enhances the sense of depth.

Conventional techniques implement this technique of varying the brightness of a line to give an indication of depth by applying the highest brightness to the closest part of the line and the lowest brightness to the part furthest from the eye. I was disappointed in this. Points between the beginning and end of the line were given brightness values that varied linearly between the brightness of the two points.

〔Example〕

FIG. 1 shows a line 10 within a three-dimensional cube 12 of space. A cube is provided with two axes, a Y axis and an X axis, to represent the three dimensions of space. The eye of the beholder 14 is also shown. In Figure 1, the line 10 closest to the viewer's eye 14
The end point A of is indicated as "bright". The end point B furthest from the eye 14 is designated as "dark." In fact, in most conventional devices, end point B is given a color that is mixed with the background color of the display. In this way, line 10 appears to disappear into the background. In this specification, the terms "bright" and "dark" are used to refer to the apparent brightness of the pixels that make up the point, whatever their color.

The way to achieve the effect of a button on a device using a bitmapped output display is to have each pixel forming a line between points A and B vary linearly from maximum to zero. In an actual device, a line is drawn by dividing the length of the line by the number of pixels forming the line and calculating a linearly varying brightness value for each pixel.

FIG. 2 shows the actual bits of the short line 10 as shown in FIG. 1, the brightest point A (100
At the darkest point B(0%)t, an additional multi-value is added to the bit position.

Generally, most individual lines are displayed in one color. However, for graphics displays that can depict lines that change color from one end to the other, giving depth indications is cumbersome. In a device that handles situations where the depth of the color-changing line also changes, the device's circuitry must calculate a brightness between zero and 100% for each color: red, green button, and blue. Such operations are extremely time consuming. This is one of the reasons why conventional computer graphics displays operate slowly. The prior art requires a separate computing device to determine the color for each pixel, and each line must be drawn one pixel at a time.

As computer equipment improves, at each stage
The emphasis is on increasing the operating speed of the device. This is especially true for computer systems that use bitmapped displays where graphics output is the slowest and limiting point of the system. Therefore, providing a depth indication in a three-dimensional bitmapped graphics output device has limited the operating speed of the device.

Depth cues are one of the desirable features that can be implemented in computing devices. Anti-aliasing is such a desirable feature. Figure 3a shows a highly enlarged view of a normal line segment displayed on a computer output display. Each block 24-30 represents a pixel displayed on the display. As can be seen in the enlarged view of FIG. 3a, the pixels used to approximate points on an ideal line displayed on a computer display result in jagged edges. Those burrs are visible. Figure 3b shows lines processed using anti-aliasing techniques.

In Figure 3b, m32 is represented by a larger number of pixels. In fact, each endpoint of line 32 consists of two pixels of varying gray shades. When viewed from a certain distance, this will appear as a smooth line that is close to an ideal line. As you will see, anti-aliasing is a technique that adds hidden lines to the pixels that represent an image so that the edges of the image do not have a jagged appearance. This anti-aliasing technique requires a separate complex circuit to determine the specific gray #k for each pixel to produce a display that reduces the appearance of video jaggedness on the output display. This is also a time consuming operation.

It would be desirable to provide depth instructions with a button on any type of computer device. For example, it is desirable to provide a depth indication using a device that also performs anti-aliasing of images. At times, the two techniques differ in contrast to the attempts of the prior art to utilize the varying brightness of a buttoned pixel on a computer output display to achieve the desired results.
It appears that the two technologies interfere with each other.

U.S. patent application N11L07 dated IO 14, 1988
/258.133, “Anti-Aliasing Raster
Operations (ANTI-ALIASING R
ASTEROPERATIONS incorporates anti-aliasing techniques by combining circuits used to perform other functions, making anti-aliasing much easier, faster, and cheaper. A graphics device is disclosed that includes a unique device for implementation.

In the disclosed apparatus, each addressable pixel in the frame buffer memory is logically divided into groups of 16 sub-pixels and is processed by a central processing unit (CPU) as shown in FIG. The entire screen appears to the CPU as if it had 16 times more monochromatic pixels than it actually has. Therefore, each pixel appears to have four times the number of pixels in the X and Y directions as the number of pixels actually present in the output display. This high resolution monochromatic data is provided by CP[J and is ultimately written to low resolution pixel coordinates to be stored in the frame buffer memory.

When mapping between the subpixel coordinates addressed by the CPU and the pixel coordinates stored in memory, the subpixel data (i.e., the 16 pits of information about each pixel to be displayed on the output display) is Converted to the appropriate grayscale values so that the unchased lines have appropriately shaded pixels at the edges of the lines, more or less as shown in Figure 3b. Make it.

Nine pixels of the frame buffer memory of such an anti-aliasing device are shown in FIG. Each pixel is divided into 16 subpixels.

The line 42 that intersects six of the nine pixels shown in FIG. 4 also intersects various groups of 16 subpixels representing each pixel. As shown, each subpixel intersected by line 42 is represented by a dot and is assigned a value of l. The values are summed and each pixel is assigned a number representing the total number of subpixels that line 42 intersects.

For example, #element 1 in the upper left of FIG. 4 has 13 subpixels intersected by line 42. Each of the 13 sub-pixels is assigned a value of l so that the number for pixel 1 is 13. This is the 16th value of the 13 possible total values that can be assigned to a pixel. If grayscale values are assigned based on the number of subpixels touched by the image from 0 to 16, representing white to black, then pixel number 1 is assigned a grayscale value of blackish gray. Similarly, pixel number 2, which has only 5 sub-pixels intersected by line 42, is assigned a gray scale value associated with the 16th possible value of <5 and is colored light gray. Depending on the total number of each subpixel that line 42 intersects, the remaining pixels of line 42 are shaded appropriately.

In this way, a line can be created so that the eye at a distance sees the variously shaded edges as representing a small, straight, jagged line, rather than an all-one shaded pixel. 42 jagged edges are smoothed. Therefore, this line appears to have a resolution approximately four times higher than its actual resolution. In certain graphics output devices that use this technology, the screen is 1152X
It can provide 900 actual pixel outputs and the number of sub-pixels is 46
It is 08X3600. The apparent resolution is therefore four times that of a conventional screen of approximately 126 pixels per 10 pixels (320 ICs per inch).

As can be seen from the above discussion, the application of anti-aliasing techniques to computer graphics devices as disclosed in the aforementioned patents utilizes the full grayscale capabilities of the device to overcome the tendency for jagged lines to appear in the output display. be made to do. Therefore, it is possible to display depth by changing the brightness of the image that depicts depth. Depth poses unique problems and can create interference problems between techniques.

Furthermore, graphics devices using the improved anti-aliasing technique described above display depth in the usual way in the prior art, where the luminance value of each individual pixel is calculated and plotted bit by bit. If it is,
The speed of the entire device is reduced to about one-tenth of its actual speed. The reason for this is that you first divide the video into quadrilaterals, determine the scan lines that make up those quadrilaterals, check both ends of each scan line, and then divide all scan lines without looking at the pixels in the middle. By using the technique of subtracting from the beginning to the end bt, a very high speed of rendering of the graphics output is achieved.

Such devices are described in U.S. Patent Application No. 07/297,475, dated January 13, 1989; United States Patent Application No. 07/297,604, dated January 13, 1989; /297,09
3. U.S. Patent Application No. 07/2 dated January 13, 1989
97,590 and U.S. Patent Application No. 07/287°128 dated December 20, 1989 and U.S. Patent NaQ7/2
No. 87,493, and U.S. Patent No. J [Na 07/286,997, dated December 20, 1988. All such US patent applications are assigned to the assignee of the present invention. Although the graphics display speed of these devices is very high, it is clearly argued that they use techniques to provide depth display that require determining individual pixels.

Although there appears to be an apparent conflict between anti-aliasing and depth indication in the same device, the above-described graphics devices are particularly suited to different aspects of the depth display embodiments of the present invention.

The present invention is based on the observation that the width of a constant @ appears to become narrower as the figure moves from the foreground to the background. In fact, the apparent width of an object is inversely proportional to the distance from the eye to the object. That is, the apparent width of an object of constant size is related to zt-distance from the eye as the object moves away from the eye. Thus, the lines on the computer output display can appear to recede into the background by thinning as they recede from the front of the display. The results are shown in FIG. In this figure, objects 50 are shown at three different depths from eye 14. The actual object 50(a) close to the eye 14 is either object 50(b) (see vertical dimension 51(b)1) or object 50(C) (see dimension 5).
1 (see dimension 51 (c)) also covers a sufficiently wide area of the screen (see dimension 51 (a)).

In other words, by representing an object on an output display such that the width of the object on the output display is inversely proportional to the distance from the eye to the object, it is possible to indicate depth to a computer graphics device. Ru.

Such representation, with the width of the points making up a line inversely proportional to the depth of those points, is a technique used in graphics devices such as those described above, which utilize subpixels to obtain an apparent high resolution in the output display. It can be done quickly. By mapping the line width properties in the high resolution mode provided by the CPU to determine anti-aliasing, lines can be made to have different widths. Thus, when drawing a line with varying binary or depth values, the line covers all pixels at its closest point and recedes to one subplane X width at its farthest point. The line 6o is shown in FIG. This diagram is
Figure 3 illustrates the high resolution mode of the graphics device, which is resolved into 3 pixels before being written to the frame buffer. The width of line 60 is constant and extends horizontally across the output display as it gradually recedes from the screen. The line 60 is mapped to cover approximately seven subpixels at the end 62 closest to the eye and one subpixel at the end 64 furthest from the eye. However, the width of line 60 is actually constant.

FIG. 6 shows that graphics devices that utilize sub-pixel methods of anti-aliasing are particularly suited to this depth display technique. The reason for this is that anti-aliasing effects are automatically included as the line is drawn, as shown by line 60. The anti-aliasing technique causes the object to automatically receive a brightness value that depends on the number of sub-pixels covered by the object, so that as the object recedes, less brightness is given to the width of the object.

Therefore, the edges of line 60 are filled in by the anti-aliasing technique described above. The technique varies the brightness of the individual pixels written in the seven-frame pattern according to the number of sub-pixels covered by the line 60. Therefore, line 6
The thicker end 62 of 0 appears black (thus thicker);
The narrower end S4 appears brighter (and therefore thinner).

Line 60 therefore ranges from black (the case or other foreground color) to a very light gray (or other background color) within the device.
is actually displayed on the display using the improved anti-aliasing technique one pixel width along the length of the line at progressively lower luminance.

FIG. 7 is a block diagram of a ConvTag 2 fixing device 70 that utilizes the present invention. This device 70 is a converter 7
2, a central processing unit (CPU) 74, a line plotter 76, a seven frame buffer 78, and an output display 80, such as a cathode ray tube. Although the circuitry of these individual components may be well known in the art, their construction may differ from that of the prior art and may follow the description in the aforementioned pending US patent application. for example,
Transducer 72 converts the x
, y, and z values are received as input.

Transformer T2 is conventional for transforming the original coordinates of a point by rotation, translation or 8 degree change in order to do whatever needs to be done to a particular point as it moves from output frame to output frame. Utilizing circuits well known in the art. Usually this is the new X, Y.

An output having a value of 2 is obtained.

In the device 70 of the present invention, the z value can be used directly to provide the width value used to draw the object. That is, the input z values are processed by converter 72 such that the output provides new X, Y values and a new width value. This new width value is inversely proportional to the normally generated z value.

The method used by the converter to convert to binary t-width values is an extension of the normal conversion operation. A normal transform operation applies a 4x4 transform. Translation, rotation about the desired axis results in a concatenating matrix that individually represents the R degree transformation into x, y, z values. In the present invention, by including the conversion expressed in the instruction operation, fi4X4
matrix can be realized. The conversion is based on Newman and Sprout.
Author: Principles of Interactive Computer Graphics
ofInteractiveComputerGr
aphicm) J 2nd edition.

McGraw-Hill Book Co.
Concatenation of the standard transformation matrices in Chapter 22 of Book Co., Ltd.

The transformation represents a display operation.

The display operation can be referred to as a 2-width conversion. This conversion is performed as follows using the apparatus shown in FIG.

W'= (W mlz −Wmin)☆(Z Zm
i n )/(Zmax − Zmin ) + Wm
i n Here, 2 is the binary value of the target point, Zmin is the binary value of the object closest to the screen, zm*x is the binary value of the object farthest from the screen, wrnl and Wmi. are the highest and lowest available grayscale levels.

Equation 22 for transfer from the book by Newman et al.
1, Equation 22-5 for the R-degree transformation, and the z-W conversion exchange; thus, the particular transformation that performs the movement, the R-degree transformation, and the z-W conversion is: It is. Here, Zs=(Wmax=Zmin)/(Zmax Zmi
n) Zt = (Wmln Zmin) (Wm
ax Wm1n)/(Zmax Zmin). Since binary values are the only values of interest in this conversion, only the z value is changed. Then, w'=z☆Z, +Zt.

The values of the widths of the two ends of the line segment to be represented by the transducer 72 are calculated as described above according to characteristics well known in the prior art. Those values are added to CPU 74. CP[J74 uses the widths of the two ends of the line segment to determine the location of the vertices at the two corners of each of the two ends of the line segment. The vertex values are calculated and sent to plotter 76. In a preferred embodiment of the invention, the plotter γ6 draws line segments by aligning quadrilaterals tl- containing the vertices of the line. FIG. 8 shows a line 82 with such vertices 84-8T having X and Y values.

Plotters such as plotter 76 are described in the aforementioned pending US patent application. Plotter T6 supplies appropriate values to the anti-aliasing circuit. This circuit operates as described above and sends its results to frame buffer T8, from where the results are provided to output display 80.

The vertices 84-87 of line 82 are actually fed to the anti-aliasing circuit of the device without any change in brightness.

The anti-aliasing portion of the circuit then changes the brightness in a manner similar to that described in detail in the aforementioned pending US patent application.

A second device 90 made in accordance with the present invention is shown in FIG. The device can be used in cases where the CPU does not directly access the components of the graphics device in its usual configuration. In device 90, the transformed X, Y for each end of each line segment.

A converter 72 provides a value of 2 in a manner well known in the art. Therefore, at this point, the X and Y values at the center of each line and the width of the line at each of those points are known. Those output values are sent to a 2-width converter 92. The converter provides X, Y output values and width values for each line segment.

The vertices of a line extending at an angle in two dimensions can be determined using standard trigonometry, first determining half the width of the line at each end, then to extend the line perpendicular to the center of the line.

The value of each vertex determined in this way is sent to the plotter 76, i
1, (-) is sent to the 7-frame buffer T8 and later displayed on the output display 80.

It will be appreciated that such a calculation of the exact value of the vertex applied to the end of each line can be very time consuming. In a preferred embodiment of the present invention, an apparatus has been devised which eliminates the need for the trigonometric calculations normally associated with determining the position of each vertex. With the anti-aliasing device used in the device of the present invention, any line has a starting point and an ending point drawn at an angle of 45 degrees to the horizontal, and the apex is accurately determined using various trigonometric functions. It has been found that it still has approximately the same grayscale value as above.

The two lines shown in Figures 10A and 10B illustrate this principle. For example, the apex of the line shown in FIG. 10A is drawn accurately, and the apex of the line shown in FIG. 10B makes a 45 degree angle with the horizontal. For certain anti-aliasing techniques that use subpixels, counting the number of subpixels that each line transforms shows that each line covers approximately the same deposit. Therefore, the brightness of the lines will be drawn in the same gray scale as if all lines were accurately determined, if all lines were drawn at a 45 degree angle.

Furthermore, assuming that vertices are calculated at 45 degrees for all lines, the operations are greatly reduced.

All that is required is the center point of one end of the line (line 9 in Figure 10B).
Starting from point 91) at 0, add half the width of the line at that point to the tx value, subtract half the width from the half value, and get point 92.
All you have to do is add half the width of the line to the Y value at point 91 and subtract half from the X value to get point 93. This can be obtained by pressing an angle of 45 degrees with respect to the horizontal in all four quadrants, performing almost the same method, and variously adding and subtracting half the value of the line to the X and Y values. be able to. In this way, when the button width at the end of the line is known, the calculation time of the vertices is greatly reduced, and the operating speed of the device is greatly increased.

Another great advantage of the invention is that when lines are connected to other lines, as is the case in most cases,
Two lines forming an angle of 5 degrees are to be accurately connected without overlapping each other.

In the preferred embodiment system, this means that the pixels across the connection points are drawn only once, as opposed to twice in the case of a precisely calculated line. means.

[Brief explanation of drawings]

FIG. 1 shows the viewer's perspective of a three-dimensional line; FIG. 2 shows how the prior art draws a three-dimensional line on a computer display where it is bit-mapped; and FIG. 3a shows how the line is bit-mapped. A highly enlarged enlarged view of a line displayed using conventional display techniques on a computer display, No. 3
Figure b is a greatly enlarged view of all lines drawn on a computer display being bitmapped using anti-aliasing display techniques; Figure 4 is a highly enlarged view of lines drawn on a computer display that are bitmapped using anti-aliasing display techniques; ,
Figure 5 is a diagram showing the amount of computer output display occupied by an object at three different depths; 7 is a block diagram of the computer graphics device of the present invention; FIG. 8 is a block diagram of the computer graphics device of the present invention; 9 shows a block diagram of the second computer graphics device of the present invention, and FIG. 10A shows a line whose width changes with depth. One particular method is shown for drawing the entire end, and the first OB diagram shows another method for drawing the end of a line whose width changes with depth. 12...Converter, 74...CPU, 76...
- Plotter, γ8...Frame buffer, 80...
・Display device, 92...Depth and width converter.

Claims (2)

[Claims] (1) A means for drawing an image of a quadrilateral on an output display when the vertices of the quadrilateral are supplied, and for each end of the line to be drawn on the output display, the distance from the viewer to the end of the line A computer comprising: means for supplying a width value that is indirectly related to depth; and means for utilizing the width value to determine the vertices of a line drawn by the means for drawing an image of a quadrilateral. graphics device. (2) A process of supplying a width value indirectly related to the depth from the viewer to the end of the line for each end of the line to be displayed on the output display, and a process for drawing a quadrilateral. A computer comprising: determining a width value to determine the vertices of a line to be drawn by means; and drawing an image of a quadrilateral on an output display using the vertices determined from the width value. A method of providing a representation of depth using a graphics device.