CN102819854A - Method and system for describing elliptic arc on raster display - Google Patents

Abstract

The present invention discloses a method and system for drawing an elliptical arc on a raster display. The method includes: using a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located to divide the adjacent pixels of the current pixel into two pixel groups, wherein the current pixel is a pixel that has just finished rendering during the process of drawing the elliptical arc; and Select the next pixel to be rendered from a pixel group on the direction side of the ellipse arc, and render the selected pixel. The present invention can simply realize the drawing of ellipse arcs on ellipses of various shapes.

Description

Method and system for tracing an elliptical arc on a raster display

technical field

The present invention relates to the field of computer graphics, and more particularly to a method and system for drawing an elliptical arc on a raster display.

Background technique

Simply put, the process of drawing an elliptical arc on a raster display is the process of selecting the pixels closest to the elliptical arc on the raster display and rendering these pixels. This process is usually done by tracing pixels along an elliptical arc.

There are currently two popular methods for drawing elliptical arcs on raster displays: the midpoint method and the minimum function value method. They both use gradient vectors and 8 octant quadrants to determine whether the next drawn pixel follows a square movement (Δx=±1 or Δy=±1) or a diagonal movement (Δx=±1 and Δy=±1 ). Wherein, when the ellipse arc is an ellipse arc located on an ellipse whose major axis is much larger than its minor axis (abbreviated as a very thin ellipse), the above midpoint method fails. The minimum function value method uses the intersection of the ellipse arc and the pixel square side to determine which pixel should be selected as the next pixel to be drawn among the 8 adjacent pixels around the currently drawn pixel. In the minimum function value method, there is no single definition to cover all intersection cases, so the implementation situation is not simple.

Contents of the invention

In view of the problems described above, the present invention provides a novel method and system for drawing an elliptical arc on a raster display.

The method for drawing an elliptical arc on a raster display according to an embodiment of the present invention includes: dividing the adjacent pixels of the current pixel into two pixel groups by using a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located, wherein the current A pixel is a pixel that has just been rendered during the process of drawing the elliptical arc; and a pixel to be rendered next is selected from a group of pixels on the direction side of the elliptical arc, and the selected pixel is rendered.

The system for drawing an elliptical arc on a raster display according to an embodiment of the present invention includes: a pixel grouping unit, which is used to divide the adjacent pixels of the current pixel into two groups by using a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located. In the pixel group, the current pixel is the pixel that has just finished rendering in the process of drawing the elliptical arc; the pixel rendering unit is used to select the next pixel to be rendered from a pixel group on the direction side of the elliptical arc, and Selected pixels to render.

Through the present invention, there is no need to calculate the gradient value, no need to consider various intersection situations, and no need to switch between quadrants of an octagon, and simply realize the drawing of ellipse arcs on ellipses of various shapes.

Description of drawings

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a flowchart of a method for drawing an elliptical arc on a raster display according to an embodiment of the present invention;

2 shows a block diagram of a system for drawing elliptical arcs on a raster display according to an embodiment of the present invention;

Figure 3 shows an example of a set of pixels providing the best approximation to an elliptical arc;

Figure 4 shows an example of a current pixel, an incoming pixel, and an outgoing pixel on an elliptical arc;

FIG. 5 shows an example of the process of selecting the next pixel to be rendered in the process of drawing an elliptical arc.

Detailed ways

Features and exemplary embodiments of various aspects of the invention will be described in detail below. The following description covers numerous specific details in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only to provide a clearer understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm presented below, but covers any modification, replacement and improvement of related elements, components and algorithms without departing from the spirit of the present invention.

The present invention provides a novel method and system for tracing elliptical arcs on raster displays. In the method and system for drawing an elliptical arc on a raster display according to an embodiment of the present invention, a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located is used to divide the 8 adjacent pixels around the currently drawn pixel into two plane (that is, divided into two pixel groups), and then select the next pixel to be drawn from a plane on the side of the elliptical arc. The method and system for drawing an elliptical arc on a raster display according to an embodiment of the present invention is applicable to an elliptical arc on any shape of an ellipse, and is easy to implement.

The method and system for drawing an elliptical arc on a raster display according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a flowchart of a method for drawing an elliptical arc on a raster display according to an embodiment of the present invention. Figure 2 shows a block diagram of a system for drawing an elliptical arc on a raster display according to an embodiment of the present invention.

As shown in FIG. 1, the method for drawing an elliptical arc on a raster display according to an embodiment of the present invention includes: S102, dividing the adjacent pixels of the current pixel into two parts by using a straight line connecting the center of the ellipse where the current pixel and the elliptical arc are located. pixel group, wherein the current pixel is the pixel that has just finished rendering during the process of drawing the elliptical arc; pixels to render.

As shown in FIG. 2 , the system for drawing an elliptical arc on a raster display according to an embodiment of the present invention includes a pixel grouping unit 202 and a pixel rendering unit 204 . Wherein, the pixel grouping unit 202 uses the straight line connecting the current pixel and the center of the ellipse where the ellipse arc is located to divide the adjacent pixels of the current pixel into two pixel groups (that is, step S102 is performed), and the pixel rendering unit 204 starts from the center of the ellipse arc Select the next pixel to be rendered from a pixel group on the direction side and render the selected pixel (that is, execute step S104 ).

The following describes in detail how the method and system for drawing an elliptical arc on a raster display according to an embodiment of the present invention complete the drawing of an elliptical arc with reference to an example.

Here, it is assumed that the ellipse where the elliptical arc to be drawn is located is an ellipse centered on the coordinate point (0, 0), and its implicit function is:

F(x,y)=Ax ² +Bxy+Cy ² −1=0

表示椭圆的水平半径相对于x轴的逆时针夹角。假设椭圆弧的起始点为(x₀，y₀)，终止点为(x₁，y₁)。Among them, rh represents the horizontal radius of the ellipse, rv represents the vertical radius of the ellipse,

Indicates the counterclockwise angle of the horizontal radius of the ellipse relative to the x-axis. Suppose the starting point of the elliptic arc is (x ₀ , y ₀ ), and the ending point is (x ₁ , y ₁ ).

When a pixel on the raster display is outside the ellipse where the ellipse arc to be drawn is located, the function value of the implicit function of the pixel relative to the ellipse is positive; otherwise, when a pixel on the raster display is located where the ellipse arc to be drawn is located When the pixel is within the ellipse, the function value of the implicit function of the pixel relative to the ellipse is negative.

The process of drawing an arc without thickness (that is, an arc whose width or thickness is one pixel unit) on the raster display is the process of finding the pixels closest to the arc and rendering these pixels. A direct estimate of how close a pixel is to the arc is the distance between that pixel and the arc. However, it is difficult to accurately obtain the distance between the pixel and the arc in practice, so an approximation method is needed to roughly obtain the distance between the pixel and the arc.

In the process of drawing an elliptical arc with a width of one pixel unit, the best approximation to the elliptical arc is provided by a group of pixels in which there are no three adjacent pixels to the same pixel. Figure 3 shows an example of a set of pixels that provides the best approximation to an elliptical arc. As shown in Figure 3, not all pixels (or squares of pixels) that intersect the elliptical arc should be rendered. Here, for the convenience of explanation, in the process of drawing an elliptical arc on the raster display, the current pixel (that is, the pixel that has just been drawn) is used as the reference, the previously drawn pixel is called the input pixel, and the next pixel to be drawn is called the input pixel. The pixels drawn are called out pixels.

FIG. 4 shows an example of a current pixel, a pixel-in, and a pixel-out on an elliptical arc. As shown in FIG. 4 , the pixel located to the left of the current pixel is an input pixel, and the pixel located to the upper right of the current pixel is an output pixel. It can be seen from the situations shown in FIG. 3 and FIG. 4 that, relative to the current pixel, there is only one incoming pixel and only one outgoing pixel. In some cases, the in-pixel and out-pixel may be the same pixel. In some cases, the in pixel, current pixel, and out pixel may be the same pixel.

In the example shown in Figure 4, among the adjacent pixels of the current pixel, there are two pixels intersecting the elliptical arc on the side of the elliptical arc (counterclockwise direction, that is, the direction from point A to point B) (ie , there are two candidate pixels to be rendered after the current pixel), one above and one above and to the right of the current pixel. According to the best approximation rule for the ellipse arc described above with reference to FIG. 1, it can be known that the pixel rendering unit 204 should select the pixel located on the upper right side of the current pixel as the next pixel to be drawn, and should not select the pixel located on the upper side of the current pixel. as the next pixel to be drawn.

Since the center of the ellipse where the ellipse arc is located and the current pixel are both known, it is easy to divide the 8 adjacent pixels of the current pixel into two pixel groups by using the straight line connecting the center of the ellipse where the ellipse arc is located and the current pixel. Among them, the sign of the edge equation value of the adjacent pixels in one pixel group relative to the line connecting the center of the ellipse where the ellipse arc is located and the current pixel is different from the sign of the edge equation value of the adjacent pixels in the other pixel group relative to the line symbol.

In an embodiment of the present invention, for any adjacent pixel P of the current pixel, the pixel grouping unit 202 calculates It is judged whether the adjacent pixel P belongs to a pixel group on the direction side of the ellipse arc. Specifically, if the edge equation value of the adjacent pixel P relative to the edge equation of the straight line connecting the current pixel and the center of the ellipse arc where the ellipse arc is located is greater than 0 (that is, the sign of the edge equation value is positive), then the pixel grouping unit 202 considers that the adjacent pixel P is The adjacent pixel P belongs to a pixel group on the side of the elliptical arc; otherwise, the pixel grouping unit 202 considers that the adjacent pixel P belongs to a pixel group on the opposite direction of the elliptical arc.

FIG. 5 shows an example of the process of selecting the next pixel to be rendered in the process of drawing an elliptical arc. As shown in Figure 5, the trend of the ellipse where the elliptical arc is located (that is, the trend of the elliptical arc) is counterclockwise, and in the pixel grouping unit 202, each pixel divided by the straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located In a group, there are at most 4 adjacent pixels. At this time, the pixel rendering unit 204 selects an adjacent pixel closest to the elliptical arc in a pixel group on the direction side of the elliptical arc divided by the pixel grouping unit 202 as the next pixel to be rendered. For example, in FIG. 5 , the direction of the elliptical arc is counterclockwise, so the pixel rendering unit 204 selects the sign of the side equation value of the straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located in the neighboring pixels of the current pixel One of the positive pixels is the next pixel to be drawn. If the direction of the elliptical arc is clockwise, the pixel rendering unit 204 selects one of the pixels adjacent to the current pixel with a negative side equation value relative to the line connecting the current pixel and the center of the ellipse where the elliptical arc is located as one of the pixels as The next pixel to be drawn. Specifically, the pixel rendering unit 204 uses the function value of the implicit function of the adjacent pixel in a pixel group on the direction side of the elliptical arc relative to the ellipse where the elliptical arc is located as the distance between the adjacent pixel and the elliptical arc, and selects The adjacent pixel with the smallest distance to the ellipse arc is rendered as the next pixel to be rendered.

It is assumed here that the coordinates of the center of the ellipse where the ellipse arc is located are (cx, cy), and the coordinates of the current pixel are (x _d , y _d ), then the edge equation of the line connecting the center of the ellipse where the ellipse arc is located and the current pixel is f (x, y)=ax+by+c, where a=cy- _yd , b= _xd -cx, c=cx· _yd - _xd ·cy. Since only the adjacent pixels of the current pixel need to be judged relative to the side equation value of the side equation of the straight line connecting the current pixel and the center of the ellipse where the ellipse arc is located, there are x=x _d +dx, y=y _d +dy, dx and dy is ±1 or 0. Substitute a=cy-y _d , b=x _d -cx, c=cx y _d -x _d cy, x=x _d +dx, y=y _d +dy into f(x,y)=ax+ by+c, f _d =a·dx+b·dy can be obtained through the following derivation process.

f _d = f(x _d + dx, y _d + dy)

＝a(x _d +dx)+b(y _d +dy)+c

＝(cy-y _d )(x _d +dx)+(x _d -cx)(y _d +dy)+cx y _d -x _d cy

＝cy x _d +cy dx-y _d x _d -y _d dx+x _{d y d +} x d dy-y _d cx-cx dy+cx y _d -x _d cy

＝x _d cy-x _d cy+y _d cx-y _d cx+x _d y _d -x _d y _d +(cy dx-y _d dx)+(x _d dy-cx dy)

＝(cy-y _d )dx+(x _d -cx)dy

= a·dx+b·dy

The side equation values of the eight adjacent pixels of the current pixel relative to the side equations of the straight line connecting the center of the ellipse where the ellipse arc is located and the current pixel are:

f _d0 = -ab, (dx = -1, dy = -1);

f _d1 = -b, (dx = 0, dy = -1);

f _d2 = ab, (dx = 1, dy = -1);

f _d3 = a, (dx = 1, dy = 0);

f _d4 = a+b, (dx=1, dy=1);

f _d5 = b, (dx = 0, dy = 1);

f _d6 =-a+b, (dx=-1, dy=1);

f _d7 = -a, (dx = -1, dy = 0);

When the current pixel moves to the next pixel to be rendered, there will be x _d =x _d +dx, y _d =y _d +dy, where dx and dy are ±1. Only by updating a and b can the edge equation value of each adjacent pixel of the current pixel relative to the straight line connecting the current pixel and the center of the ellipse be obtained.

In order to calculate the function value of the implicit function of the adjacent pixels of the current pixel relative to the ellipse where the ellipse arc is located, the forward difference method can be used in one embodiment of the present invention. For example, for an ellipse centered at (0,0), its implicit function is F(x,y)=Ax ² +Bxy+Cy ² −1=0.

The first-order difference of the implicit function of the ellipse where the elliptic arc is located is:

${\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; By</span>}<span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; Bx</span>}<span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; \&Delta;F</span>}}_{\mathrm{<span\; class="notranslate">\; xy</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>$

The second-order difference of the implicit function of the ellipse where the elliptic arc is located is:

Δ ² F _x =ΔF _x (x±1,y)-ΔF _x (x,y)=±2A,

Δ ² F _y = Δ F _y (x, y ± 1) - Δ F _y (x, y) = ± 2C,

Δ ² F _xy = ΔF _xy (x±1, y±1)-ΔF _xy (x, y)=±2(A+B+C)

Here it is assumed that the coordinates of the pixel closest to the starting point of the elliptical arc are (x _s , y _s ), the function value of this pixel relative to the implicit function of the ellipse where the elliptical arc is located is F(x _s , y _s ), and the pixel is at The first-order difference values of are ΔF _x (x _s , y _s ), ΔF _y (x _s , y _s ), ΔF _xy (x _s , y _s ). If the pixel whose coordinates are (x _s +1, y _s ) is selected as the next pixel to be judged, then the function value of the implicit function of this pixel relative to the ellipse where the ellipse arc is located can be obtained by combining F(x _s , y _s ) with ΔF _x (x _s , y _s ) is added together. By analogy, only based on the initial value of (x _s , y _s ), the function value of the implicit function of all the pixels to be judged relative to the ellipse where the ellipse arc is located can be obtained through addition calculation.

As can be seen from the above description, the present invention does not need to calculate the gradient value, does not need to consider various intersection situations, and does not need to switch between quadrants of the 8-point circle, but simply realizes the ellipse arc on the ellipse of various shapes of the drawing.

The present invention has been described above with reference to the specific embodiments of the present invention, but those skilled in the art will understand that various modifications, combinations and changes can be made to these specific embodiments without departing from the requirements set by the appended claims or their equivalents. The spirit and scope of the present invention defined by the material.

The steps can be performed by hardware or software as desired. Note that steps may be added to, removed from, or modified in the flowcharts presented in this specification without departing from the scope of the present invention. In general, a flowchart is only used to indicate one possible sequence of basic operations for implementing a function.

Embodiments of the present invention may utilize programmed general purpose digital computers, utilize application specific integrated circuits, programmable logic devices, field programmable gate arrays, optical, chemical, biological, quantum or nanoengineered systems, components and mechanisms accomplish. Generally speaking, the functions of the present invention can be realized by any means known in the art. Distributed or networked systems, components and circuits can be used. Communication or transfer of data may be wired, wireless or by any other means.

It will also be appreciated that one or more of the elements shown in the figures may be implemented in a more separate or integrated manner, or even removed or disabled in some cases, depending on the needs of a particular application. It is also within the spirit and scope of the present invention to implement a program or code storable in a machine-readable medium to allow a computer to perform any of the methods described above.

Furthermore, any signal arrows in the figures should be considered as illustrative only, and not restrictive, unless specifically indicated otherwise. Combinations of components or steps are also considered to have been recited when terms are foreseen to obscure the ability to separate or combine.

Claims (10)

1. A method for drawing an elliptical arc on a raster display, comprising: Divide the adjacent pixels of the current pixel into two pixel groups by using a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located, wherein the current pixel is a pixel that has just been rendered during the process of drawing the elliptical arc ;as well as Select a pixel to be rendered next from a pixel group on the direction side of the ellipse arc, and render the selected pixel. 2. The method according to claim 1, wherein, for any adjacent pixel P of the current pixel, according to the relative position of the adjacent pixel P relative to the ellipse connecting the current pixel and the elliptical arc, The edge equation value of the edge equation of the straight line in the center is used to determine whether the adjacent pixel P belongs to a pixel group on the direction side of the ellipse arc. 3. The method according to claim 1, characterized in that, selecting an adjacent pixel closest to the elliptical arc in a pixel group on the direction side of the elliptical arc as the pixel to be rendered next . 4. method according to claim 3, it is characterized in that, take the function value of each adjacent pixel in a group of pixels on the direction side of the elliptic arc relative to the implicit function of the ellipse where the elliptic arc is located as the said elliptical arc The distance between each adjacent pixel and the ellipse arc. 5. The method according to claim 4, characterized in that, the forward difference method is used to calculate the hidden value of each adjacent pixel in a pixel group on the direction side of the elliptic arc relative to the ellipse where the elliptical arc is located. The function value of the function. 6. A system for tracing an elliptical arc on a raster display, comprising: A pixel grouping unit, configured to divide the adjacent pixels of the current pixel into two pixel groups by using a straight line connecting the current pixel and the center of the ellipse where the elliptical arc is located, wherein the current pixel is in the process of drawing the elliptical arc The pixel that has just finished rendering in The pixel rendering unit is configured to select a pixel to be rendered next from a pixel group on the direction side of the ellipse arc, and render the selected pixel. 7. The system according to claim 6, wherein, for any adjacent pixel P of the current pixel, the pixel grouping unit connects the current pixel and the Determine whether the adjacent pixel P belongs to a pixel group on the direction side of the ellipse arc by using the side equation value of the side equation of the straight line at the center of the ellipse where the ellipse arc is located. 8. The system according to claim 6, wherein the pixel rendering unit selects an adjacent pixel closest to the elliptical arc in a pixel group on the direction side of the elliptical arc as the lower pixel. A pixel to render. 9. The system according to claim 8, wherein the pixel rendering unit converts each adjacent pixel in a pixel group on the direction side of the elliptical arc to the implicit function of the ellipse where the elliptical arc is located The function value of is taken as the distance between each adjacent pixel and the ellipse arc. 10. The system according to claim 9, wherein the pixel rendering unit uses forward difference method to calculate the relationship between each adjacent pixel in a pixel group on the direction side of the ellipse arc relative to the ellipse The function value of the implicit function of the ellipse in which the arc lies.

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