JP2008257456A - Unit and method for antialias image rendering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antialias image rendering unit which carries out antialias image rendering at high speed. <P>SOLUTION: In the case of rendering a line, a distance between the line to be rendered and a pixel is obtained by adding differences from an initial value along a horizontal scan line. From the obtained distance and a line width to be rendered, an appropriate transmittance is calculated, and the pixel is rendered using the obtained transmittance. In the case of a polygon, by dividing it into trapezoids on the basis of each horizontal scan line, a processing is performed while obtaining the distance between the left or the right edges of each trapezoid and the pixel by adding the differences along the horizontal scan line. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an anti-aliasing drawing apparatus and an anti-aliasing drawing method for performing anti-aliasing drawing.

  In general, a bitmap display system is employed when displaying graphics or the like with computer graphics. In this bitmap display system, a raster scan type display device and a display memory (frame buffer) for supplying bit pattern data corresponding to a display figure to the display device are used.

  In such a bitmap display system, when diagonal lines and curves are drawn, jaggy occurs due to display by pixels, and aliasing appears. In order to eliminate such aliasing, it is known that the interval between the lattices of the display pixels may be narrowed.

  Although the aliasing is improved by narrowing the lattice spacing, it is necessary to increase the horizontal scanning frequency of the raster scan of the bitmap display system. However, since there is a limit to increasing the horizontal scanning frequency, in a raster scan type display system, it is necessary to improve aliasing by a method other than narrowing the grid interval. Here, a general term for such processing for improving aliasing is called anti-aliasing.

  In general, anti-aliasing is performed by calculating a contribution area of a drawing figure for each pixel and expressing a halftone by a pixel value according to the ratio of the areas. Such processing is generally heavy, and the drawing speed is reduced to about 1/10 to 1/100 as compared with the case where anti-aliasing is not performed. Therefore, this anti-aliasing is not suitable for real-time processing.

  In order to improve this point, a technique for anti-aliasing is known by extracting only the edge part of a figure and expressing it with semi-transparent composite (alpha blending) drawing that considers the contribution area only for that part. (See Patent Document 1).

JP-A-7-282274

  However, in the anti-aliasing drawing apparatus described above, an increase in processing time can be suppressed as compared with the case where anti-aliasing is not performed, but processing such as edge extraction becomes procedurally complicated. In addition, the drawing of the edge portion takes time with respect to the drawing area. This is because, as a characteristic of the memory, when random access is performed, the performance is extremely lowered as compared with burst access. In particular, since the edge portion of the figure is linear, access to the memory is close to random access, and the use efficiency of the memory is greatly reduced as compared to burst access when performing general rectangular drawing.

  An object of the present invention is to provide an anti-aliasing drawing apparatus and an anti-aliasing drawing method capable of performing high-speed anti-aliasing drawing.

  The present invention provides a distance generation unit that obtains a distance between a straight line to be drawn and a pixel by adding a difference from an initial value along a horizontal scan line, a distance obtained by the distance generation unit, and a distance between the straight line to be drawn Provided is an anti-alias drawing apparatus including a transmittance generation unit for obtaining a transmittance from a line width, and a drawing unit for drawing the pixel with the transmittance obtained by the transmittance generation unit. As a result, when drawing a straight line, high-speed antialiasing drawing can be performed by performing processing along the horizontal scan line without reprocessing the edge portion.

  The present invention also provides a distance generation unit that obtains the distance between two oblique sides of a trapezoid to be drawn and a pixel by adding a difference from an initial value along a horizontal scan line, and the distance generation unit. Provided is an anti-alias drawing apparatus including a transmittance generation unit that obtains transmittance from two distances, and a drawing unit that draws the pixels with the transmittance obtained by the transmittance generation unit. Thus, when drawing a trapezoid, high-speed antialiasing drawing can be performed by performing processing along the horizontal scan line without reprocessing the edge portion.

  The anti-alias drawing apparatus includes an edge update unit that maintains an optimal scan line along each hypotenuse at the time of vertical difference update of the trapezoid, and an error of a distance generated by processing performed by the edge update unit is detected in the hypotenuse Correct according to the inclination of the. Thereby, an anti-alias trapezoid can be processed at high speed. In addition, it is possible to suppress scanning of useless areas.

  In the anti-aliasing drawing apparatus, the presence or absence of an anti-aliasing effect on each edge is controlled by forcibly changing the transmittance with respect to the left and right edges.

  In the anti-aliasing drawing apparatus, a polygon to be drawn is divided into trapezoids along a horizontal line, and drawing is performed on the divided trapezoids. As a result, even when drawing an arbitrary polygon, high-speed antialiased graphics can be drawn.

  The anti-alias drawing apparatus has a frame buffer for storing bit pattern data corresponding to a display graphic, determines a transmittance when a drawing point is drawn as it is, and controls data reading from the frame buffer. . By determining the transmittance in this way, access control with the frame buffer can be performed, and the operation speed can be improved.

  The anti-aliasing drawing apparatus determines the transmittance when the data already stored in the frame buffer remains at the coordinates of the drawing point, and controls data reading from the frame buffer and data writing to the frame buffer. To do. Thereby, the data transfer time with the frame buffer is reduced, and the operation speed can be improved.

  In the anti-alias drawing apparatus, a threshold value of the transmittance is set, it is determined whether or not the transmittance of a drawing point is larger than the threshold value, and it is determined whether or not drawing is performed according to the determination result. And Further, two threshold values of the transmittance are set, it is determined whether or not the transmittance of the point to be drawn is larger than each of the threshold values, and it is determined whether or not drawing is performed according to the determination result.

  The present invention is also an anti-aliasing drawing method in which an anti-aliasing drawing device performs drawing, and a distance generation step for obtaining a distance between a straight line to be drawn and a pixel by adding a difference from an initial value along a horizontal scan line; A transmittance generation step for obtaining a transmittance from the distance obtained in the distance generation step and a line width of the straight line to be drawn, and a drawing step for drawing the pixel at the transmittance obtained in the transmittance generation step; An antialiased drawing method is provided.

  Furthermore, the present invention is an anti-aliasing drawing method in which an anti-aliasing drawing apparatus performs drawing by adding a difference between two hypotenuses of a trapezoid to be drawn and a pixel from an initial value along a horizontal scan line. A distance generating step, a transmittance generating step for obtaining a transmittance from the two distances obtained in the distance generating step, and a drawing step for drawing the pixel with the transmittance obtained in the transmittance generating step. An antialiasing drawing method is provided.

  According to the anti-aliasing drawing apparatus and the anti-aliasing drawing method according to the present invention, high-speed anti-aliasing drawing can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating an anti-aliasing drawing apparatus according to an embodiment. As shown in FIG. 1, the anti-alias drawing device of the present embodiment includes a drawing processor 2, a frame buffer 4, a display output device 5, and a display 6.

  The frame buffer 4 is a display memory that supplies data of a bit pattern corresponding to a display figure to the display 6, and has a two-dimensional array having a width of the display screen × the height. Each array stores a color code corresponding to each pixel. The drawing processor 2 writes a display graphic to the frame buffer 4. The display graphics written in the frame buffer 4 are sequentially read out by the display output device 5 and sent to the display 6.

  Dot drawing is realized by storing a desired color code at a specific coordinate position in the frame buffer 4. In the present embodiment, the following procedure considering alpha blending is used. As DOT (X, Y, α), data is stored at the coordinate position (X, Y) of the frame buffer 4 with the transmittance α. At this time, the transmittance α is a value in the range of 0 to 1, and an α blend operation represented by the following formula is performed on each of the red, green, and blue components of the color code.

FR (X, Y) = α · R + (1−α) · FR (X, Y)
FG (X, Y) = α · G + (1−α) · FG (X, Y)
FB (X, Y) = α · B + (1−α) · FB (X, Y)

  Here, R, G, and B are the red, green, and blue color intensities of the color code of the drawing point. FR (X, Y), FG (X, Y), and FB (X, Y) are the red, green, and blue colors of the color code already stored at the coordinate position (X, Y) of the frame buffer 4. Indicates strength.

  When the transmittance α = 1, that is, when the point to be drawn is drawn as it is, there is no need to perform the α blending operation, so when it is determined that the transmittance α = 1, reading of data from the frame buffer 4 is stopped. As a result, the data transfer time is reduced and the operation speed is improved.

  If the transmittance α = 0, that is, FR (X, Y), FG (X, Y), and FB (X, Y) remain as they are, it is not necessary to perform α blending, and drawing is performed. Since it is not necessary, if it is determined that the transmittance α = 0, the data transfer time is reduced and the operation speed is improved by stopping the data reading from the frame buffer 4 and the data writing to the frame buffer 4. .

  Further, by setting a threshold value for the transmittance α and determining whether or not drawing is performed by determining whether the transmittance α of the drawing point is larger or smaller than the threshold value, for example, the transmittance α is a value. When the drawing point close to 0 is hardly noticeable, the operation speed is improved by stopping the drawing when the transmittance α is smaller than the threshold value.

  Further, two threshold values (threshold value A and threshold value B) are provided for the transmittance α, and the transmittance α is smaller than the threshold value A when the transmittance α is close to the value 0 and the point to be drawn is hardly noticeable. In this case, when the transmittance α is close to the value 1 and FR (X, Y), FG (X, Y), and FB (X, Y) are hardly visible, the transmittance α is a threshold value. If it is larger than B, α blending is not performed, and reading of data from the frame buffer 4 is stopped, so that the operation speed is improved.

  In a general memory configuration, the addresses (X, Y) and (X + 1, Y) of the frame buffer are arranged consecutively. In this embodiment, for simplification, it is described that the memory is accessed one by one. However, in the actual configuration, data access on the same horizontal line should be performed collectively.

(Anti-alias straight line drawing)
The operation of the anti-alias drawing apparatus of this embodiment will be described. FIG. 2 is a flowchart showing an anti-alias straight line drawing processing procedure. The example shown in FIG. 2 shows a case where LINE “(X1, Y1) − (X2−Y2)” having a width W is drawn as antialiased straight line drawing. The coordinates (X1, Y1) and (X2, Y2) of the both ends of the straight line and the line width W are given as arguments in advance. As parameters used in this processing, (X, Y) represents the coordinates of the pixel currently being processed. L represents the distance between the point (X, Y) and the straight line to be drawn. XS, XE, YS, and YE represent the X and Y coordinate values of the four corners of the circumscribed rectangle of the figure to be processed. A represents the calculated transmittance. D * D * represents the update amount of each parameter and corresponds to the differential symbol d * / d *.

  First, the initial setting unit calculates various parameters (S1). Various parameters are expressed by the following equations.

D = √ ((X2-X1) * (X2-X1) + (Y2-Y1) * (Y2-Y1))
DLDX = (Y2-Y1) / D
DLDY = (X1-X2) / D
W2 = (W + 1) / 2
XS = min (X1, X2) −W2
Y = min (Y1, Y2) −W2
LS = DLDX * XS + DLDY * Y + (X2 * Y1-X1 * Y2) / D
XE = max (X1, X2) + W2
YE = max (Y1, Y2) + W2

  At this time, each value of DLDX, DLDY, W2, and LS is assumed to have a decimal part with appropriate accuracy. Other parameters may be integer values. Also, min and max shall return the minimum value and maximum value of the argument, respectively.

The setting unit sets the initial setting part of the X-direction repetition loop (S2). In the drawing unit, the value of the parameter L is converted into the transmittance A according to the following expression, and data that becomes DOT (X, Y, A) with the transmittance A is stored in the position (X, Y) of the frame buffer 4. Actual point drawing is performed (S3).
A = min (max (0, W2-abs (L)), 1)

  However, abs returns an absolute value. Further, min (max (0, x), 1) represents processing for saturating the value of x with a value of 0 to 1.

The determination unit compares the number of repetitions in the X direction (whether X ≦ XE) (S4). When iterating with X ≦ XE, the updating unit performs parameter updating according to the following equation (S5).
X = X + 1
L = L + DLDX

On the other hand, when the number of repetitions in the X direction is satisfied (X> XE), the determination unit further compares the number of repetitions in the Y direction (whether Y ≦ YE). When iterating with Y ≦ YE, the updating unit performs parameter updating according to the following formula, and returns to the processing of the setting unit (S2).
Y = Y + 1
LS = LS + DLDY

  On the other hand, when the number of repetitions in the Y direction is satisfied (Y> YE), this process ends.

  The above parameters are derived from the formula of the straight line ax + by + c = 0 and the distance L = | aX + bY + c | / √ (a * a + b * b) between the point (X, Y). The distance is used as an approximate value of the area contribution ratio in each pixel.

(Anti-alias trapezoid drawing)
FIG. 3 is a flowchart showing an anti-alias trapezoid drawing process procedure. In the example shown in FIG. 3, as anti-aliased trapezoidal drawing, the area between the left side LINE “(XL1, Y1)-(XL2, Y2)” and the right side LINE “(XR1, Y1)-(XR2, Y2)” is shown. . As parameters other than the parameters described above used in this process, LR and LL represent the distance between the point (X, Y) and the left and right edges to be drawn. AL and AR represent the calculated transmittance.

  As arguments, left side coordinates (XL1, Y1), (XL2, Y2) and right side coordinates (XR1, Y1), (XR2, Y2) are given in advance. At this time, Y1 ≦ Y2, and the left side and the right side do not intersect within the range of Y1 <Y <Y2. The anti-alias trapezoid drawing process itself is very similar to the anti-alias straight line drawing process described above, but differs in that the update parameters are increased to two on the left side and the right side.

  First, the initial setting unit calculates various parameters (S10). Various parameters are expressed by the following equations.

DL = √ ((XL2-XL1) * (XL2-XL1) + (Y2-Y1) * (Y2-Y1))
DR = √ ((XR2-XR1) * (XR2-XR1) + (Y2-Y1) * (Y2-Y1))
DLDXL = (Y2-Y1) / DL
DLDXR = (Y1-Y2) / DR
DLDYL = (XL1-XL2) / DL
DLDYR = (XR2-XR1) / DR
XS = min (XL1, XL2)
Y = Y1
LSL = (XS−XL1) * DLDXL + 0.5
LSR = (XS−XR1) * DLDXR + 0.5
XE = max (XR1, XR2)

The setting unit sets an initial setting part of the X-direction repetition loop (S11). In the drawing unit, the values of the parameters LL and LR are converted into transmittances AL and AR, respectively, according to the following formulas, and DOT (X, Y, AL) with the transmittances AL and AR at the position (X, Y) of the frame buffer 4 * AR) is stored, and actual point drawing is performed (S12).
AL = min (max (0, LL), 1)
AR = min (max (0, LR), 1)

The determination unit compares the number of repetitions in the X direction (whether X ≦ XE) (S13). When iterating with X ≦ XE, the updating unit performs parameter updating according to the following equation (S14).
X = X + 1
LL = LL + DLDXL
LR = LR + DLDXR

On the other hand, when the number of repetitions in the X direction is satisfied (X> XE), the determination unit compares the number of repetitions in the Y direction (whether Y ≦ Y2 or not) (S15). When iterating with Y ≦ Y2, the updating unit performs parameter updating according to the following formula (S16), and returns to the processing of the setting unit (S2).
Y = Y + 1
LSL = LSL + DLDYL
LSR = LSR + DLDYR

  On the other hand, when the number of repetitions in the Y direction is satisfied (Y> Y2), this process ends.

  As described above, the transmittance calculation portion in the drawing unit (S12) changes so as to be reflected in the update result of the two parameters. When it is not desired to apply the anti-aliasing effect to a specific side, it may be changed to 1 (or 0) when the AL and AR parameters of the drawing unit (S12) corresponding to the side are 0 to 1. .

  In the antialiased trapezoidal drawing process of this embodiment, only trapezoidal drawing can be performed. However, even a polygon having a complicated shape can be drawn by the antialias trapezoid drawing process by dividing the polygon having a complicated shape by a horizontal line as shown in FIG.

(Improved anti-aliased trapezoidal drawing)
In the anti-alias straight line drawing and anti-alias trapezoid drawing described above, since the entire circumscribed rectangle surrounding the figure is scanned, many unnecessary parameter updates that are not actually drawn occur.

  In order to improve this, for the trapezoid drawing, the right and left edges are generated by a DDA (Digital Differential Analyzer) algorithm, and only the space between both sides is filled. At this time, it is necessary to apply an error correction algorithm similar to the correction of the (u, v) value shown in Japanese Patent No. 3068007.

  FIG. 5 is a flowchart showing an anti-aliased trapezoid drawing process procedure when DDA is performed on both edges. In the example illustrated in FIG. 5, as anti-aliased trapezoidal drawing, the area between the left side LINE “(XL1, Y1)-(XL2, Y2)” and the right side LINE “(XR1, Y1)-(XR2, Y2)” is illustrated. . As parameters other than the parameters described above used in this process, XSL and XSR represent the X coordinate values of the left and right edges of the trapezoid to be processed. E represents a DDA error correction parameter. floor shall return the largest integer that does not exceed the argument. In this case, since some parameters relating to L have a value of 0, an operation relating to that parameter can be omitted.

  As arguments, left side coordinates (XL1, Y1), (XL2, Y2) and right side coordinates (XR1, Y1), (XR2, Y2) are given in advance. First, the initial setting unit calculates various parameters (S20). Various parameters are expressed by the following equations.

DL = √ ((XL2-XL1) * (XL2-XL1) + (Y2-Y1) * (Y2-Y1))
DR = √ ((XR2-XR1) * (XR2-XR1) + (Y2-Y1) * (Y2-Y1))
DLDXL = (Y2-Y1) / DL
DLDXR = (Y1-Y2) / DR
DLDYL = 0
DLDYR = (XR2-XR1)-(XL2-XL1) / DR
XSL = XL1 + 0.5
XSR = XR1 + 0.5
Y = Y1
DXDYL = (XL2-XL1) / (Y2-Y1)
DXDYR = (XR2-XR1) / (Y2-Y1)
LSL = 0.5
LSR = (XL1-XR1) * DLDXR + 0.5
E = XSL-floor (XSL)
DEDY = DXDYL-floor (DXDYL)
DLDXR = DLDXR-DEDY * DLDYR

The setting unit sets an initial setting part of the X-direction repetition loop (S21). In the drawing unit, the values of the parameters LL and LR are converted into transmittances AL and AR, respectively, according to the following formulas, and DOT (X, Y, AL) with the transmittances AL and AR at the position (X, Y) of the frame buffer 4 * AR) is stored, and actual point drawing is performed (S22).
AL = min (max (0, LL), 1)
AR = min (max (0, LR), 1)

The determination unit compares the number of repetitions in the X direction (whether X ≦ XSR) (S23). When iterating with X ≦ XSR, the updating unit performs parameter updating according to the following equation (S24).
X = X + 1
LL = LL + DLDXL
LR = LR + DLDXR

On the other hand, when the number of repetitions in the X direction is satisfied (X> XSR), the determination unit compares the number of repetitions in the Y direction (whether Y ≦ Y2 or not) (S25). When iterating with Y ≦ Y2, the updating unit performs parameter updating according to the following equation (S26).
XSL = XSL + DXDYL
XSR = XSR + DXDYR
Y = Y + 1
E = E + DEDY
LSR = LSR + DLDYR

Then, the DDA error correction parameter E is compared (whether E ≧ 1) (S27), and if E <1, the process returns to the setting unit (S21). On the other hand, if E ≧ 1, the parameter is updated according to the following equation (S28), and the process returns to the setting unit (S21).
E = E-1
LSL = LSL + DLDXL
LSR = LSR + DLDXR

  On the other hand, if the number of repetitions in the Y direction is satisfied in S25 (Y> Y2), this process ends.

  Note that the same expansion process as described above can be performed for anti-aliased line drawing.

  As described above, according to the anti-aliasing drawing apparatus of the present embodiment, high-speed anti-aliasing drawing can be performed by performing processing along the horizontal scan line without reprocessing the edge portion. Also, high-speed antialiased graphics such as straight lines, trapezoids, and arbitrary polygons can be drawn. It is also possible to control the presence or absence of the anti-aliasing effect for any side of the figure. Further, by determining the transmittance, access control with the frame buffer can be performed, and the operation speed can be improved within a range that does not affect the appearance of the drawn figure. In addition, it is possible to suppress scanning of useless areas. In addition, the data transfer time with the frame buffer is reduced, and the operation speed can be improved.

  The anti-aliasing drawing apparatus according to the present invention is useful as a drawing apparatus that realizes high-quality graphics at low cost.

1 is a block diagram illustrating an anti-aliasing drawing apparatus according to an embodiment; Flow chart showing anti-alias straight line drawing processing procedure Flow chart showing the anti-alias trapezoid drawing processing procedure Figure showing a polygon divided by a horizontal line Flowchart showing an anti-aliased trapezoid drawing process procedure when DDA is performed on both edges

Explanation of symbols

2 Drawing processor 4 Frame buffer 5 Display output device 6 Display

Claims (11)

A distance generator that obtains the distance between a straight line to be drawn and a pixel by adding a difference from an initial value along a horizontal scan line;
A transmittance generation unit for obtaining a transmittance from the distance obtained by the distance generation unit and the line width of the straight line to be drawn;
A drawing unit for drawing the pixel with the transmittance determined by the transmittance generation unit;
An anti-aliasing drawing apparatus comprising: A distance generator that obtains the distance between the two hypotenuses of the trapezoid to be drawn and the pixel by adding a difference from the initial value along each horizontal scan line;
A transmittance generation unit for determining the transmittance from the two distances obtained by the distance generation unit;
A drawing unit for drawing the pixel with the transmittance determined by the transmittance generation unit;
An anti-aliasing drawing apparatus comprising: The anti-aliasing drawing apparatus according to claim 2,
An edge update unit that maintains an optimal scan line along each hypotenuse during the vertical difference update of the trapezoid,
An anti-aliasing drawing apparatus, wherein an error of a distance generated in processing performed by the edge update unit is corrected according to a slope of the hypotenuse. The anti-aliasing drawing apparatus according to claim 2,
An anti-aliasing drawing apparatus that controls the presence or absence of an anti-aliasing effect on each edge by forcibly changing the transmittance with respect to the left and right edges. The anti-aliasing drawing apparatus according to claim 2,
An anti-aliasing drawing apparatus, wherein a polygon to be drawn is divided into trapezoids along horizontal lines, and drawing is performed on the divided trapezoids. The anti-aliasing drawing device according to claim 1 or 2,
It has a frame buffer that stores bit pattern data corresponding to the display figure,
An anti-aliasing drawing apparatus characterized by determining a transmittance when a drawing point is drawn as it is, and controlling reading of data from the frame buffer. The anti-aliasing drawing apparatus according to claim 6,
The transmittance is determined when the data already stored in the frame buffer remains at the coordinates of the point to be drawn, and the data reading from the frame buffer and the data writing to the frame buffer are controlled. Anti-alias drawing device. The anti-aliasing drawing device according to claim 1 or 2,
An anti-alias drawing apparatus that sets a threshold value of the transmittance, determines whether or not the transmittance of a drawing point is larger than the threshold value, and determines whether or not to perform drawing according to the determination result. The anti-aliasing drawing apparatus according to claim 8,
Two threshold values of the transmittance are set, it is determined whether or not the transmittance of a point to be drawn is larger than each of the threshold values, and it is determined whether or not drawing is performed according to the determination result. Anti-alias drawing device. An anti-aliasing drawing method in which an anti-aliasing drawing device performs drawing,
A distance generation step for obtaining a distance between a straight line to be drawn and a pixel by adding a difference from an initial value along a horizontal scan line;
A transmittance generation step for obtaining a transmittance from the distance obtained in the distance generation step and the line width of the straight line to be drawn;
A drawing step of drawing the pixel with the transmittance determined in the transmittance generation step;
An antialiased drawing method characterized by comprising: An anti-aliasing drawing method in which an anti-aliasing drawing device performs drawing,
A distance generation step for obtaining the distance between the two hypotenuses of the trapezoid to be drawn and the pixel by adding a difference from an initial value along each horizontal scan line;
A transmittance generation step of obtaining a transmittance from the two distances obtained in the distance generation step;
A drawing step of drawing the pixel with the transmittance determined in the transmittance generation step;
An antialiased drawing method characterized by comprising:

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