JPS63289686A - Image shadowing device - Google Patents

Abstract

PURPOSE:To attain rapid processing by successively adding the brightness linear information of one optional scanning line of a polygon to the start point of each scanning line. CONSTITUTION:An inclination pattern is found out from a pattern slFH obtained by connecting a vertex F of the longest scanning line sl of a triangle with a point H on the opposite side and the brightness information of each (sl) is found out. The brightness of the point F is subtracted from the information of the slFH to obtain brightness inclination pattern linear information consisting of the information of points to be respective picture elements between F and H. The brightness information of slPQ can be obtained by successively adding the brightness information WSi of slP to the brightness information of the points to be respective picture elements from the starting point of the information SL up to the position H' corresponding to the length of PQ. The brightness information of each sl can be obtained only by adding the information SL to the brightness information of the start point of the sl successively up to the end point. Consequently, the operation capacity can be reduced and rapid processing can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Area of Application] The present invention relates to a device that performs so-called Gouraud shading, which applies a shadow with a constant slope in one direction to the inside of a polygon.

[Essentials of invention]

This invention expresses a polygon as a set of a large number of lines in a certain direction, and also provides a certain shading whose brightness changes depending on the eruption slope. By calculating and memorizing the brightness of each line and calculating it from the stored brightness gradient pattern and the information on the brightness at the beginning of each line, the calculation for calculating the brightness of each line is simplified. At the same time, it also made high-speed shading possible.

[Conventional technology]

When drawing a polygon on a display screen such as a CRT using computer graphics, the polygon is represented as a set of lines oriented in a certain direction. For example, in the case of a raster-scan type CRT, a different color or Polygons are displayed by expressing them in terms of brightness. In this case, shading is applied to express the polygon more three-dimensionally. Gouraud shading, which linearly changes luminance (for color, signal level, ie, brightness), is well known as a method for imparting shading. For example, triangle ABC as shown in Figure 6
When performing Gouraud shading, the three sides ab +
The brightness on be, aC is determined by interpolation, and then when displaying this triangle ABC on, for example, a raster scan type CRT, it is divided into horizontal scan lines and the points at both ends, for example, the 6th Position information (in this case, only the horizontal direction is sufficient) and brightness information of points indicated by P and Q in the figure are obtained. Then, a slope line of luminance between these two points PQ is determined, and from this information, luminance information for each point corresponding to each pixel on the scan line is determined by interpolation or the like.

That is, it is obtained as a result of point-by-point approximation using, for example, Bresenham's algorithm for each scan line.

[Problem that the invention seeks to solve]

Therefore, in the case of the conventional shading device, a two-dimensional amount of calculation is required, and the amount of calculation is correspondingly enormous, so the processing speed is slow and it is not suitable for high-speed processing.

Furthermore, since the brightness slope is determined from the brightness at both ends for each scan line, the brightness slope causes an error for each line. In other words, since the values of the start and end points of each scan line are approximately determined by interpolation from the values of the vertices ABC, the value of the slope straight line determined for each scan line from the approximate values has an error. will occur.

Furthermore, in the case of this conventional Gouraud shading device, it is necessary to store luminance information and position information for all pixel points within a polygon in memory, which also has the disadvantage of inefficient memory usage. .

[Means for solving problems]

In this invention, the brightness gradient straight line information of any one line among a large number of lines for representing a polygon is obtained in advance and stored in a memory, and the brightness information on each line is determined by this brightness slope straight line. The information is obtained by sequentially adding the luminance information at the starting point of each line up to the ending point.

[Effect]

The brightness information for each line is the brightness at the starting point of this line,
It can be easily found as the sum of slope straight line information.

Therefore, the amount of calculation becomes extremely small, and high-speed shading processing can be performed.

〔Example〕

In the example described below, a case will be described in which a polygon to be shaded is considered as a set of triangles, and all polygons are shaded by applying Gouraud shading to each triangle. This is because when limited to a triangle, this triangle is generally considered to be a planar shape, and Gouraud shading can be applied almost accurately to this triangle. Polygons larger than quadrangles are divided into triangles for shading, but in this case, the so-called Matsuha band effect occurs around the straight lines drawn to divide them, but in Gouraud shading of polygons larger than quadrangles, Since it is thought that the Matsuha band effect occurs more or less due to the twisting of the slope, this is not considered to be a big problem.

In this invention, Gouraud shading is performed according to the following idea.

Within a triangle, the slope of brightness on each scan line for Gouraud shading within this triangle is:
All have the same value. Therefore, in this case, the scan line H connecting the vertex F and the point H on the side eg, which is the longest scan line section in the triangle E and G in FIG.
Using, for example, Presentham's algorithm, a 1/1 diagonal pattern (brightness gradient straight line information) is obtained from the image data. Once this slope pattern is determined, since this slope pattern is the same for all scan lines regarding this triangle EFG, it is possible to use this slope pattern to obtain luminance information for each scan line.

That is, FIG. 3 is a diagram for explaining this process, in which point F (starting point) is determined from the brightness straight line information of scan line FH.
By subtracting the brightness of , brightness gradient pattern straight line information SL consisting of information about each pixel point between lines FH as shown in the figure is obtained.

For example, the luminance information regarding the scan line PQ of the triangle EFG in FIG.
It can be obtained by sequentially adding the brightness information WSi of the starting point P of the scan line PQ to the brightness information about the position of each pixel as shown in FIG.

In this case, (11
Since the diagonal line information is obtained from the scan line with the longest distance among the scan lines of this triangle EFG, the brightness information of each scan line is obtained by sequentially ending this information 11sL and the brightness information at the start point of that scan line. It can be obtained by simply adding the points that correspond to each pixel up to the position of the point.

Of course, not this scan line FH, but any one
Brightness gradient linear information can also be obtained from the scan line. However, in that case, some scan lines may be longer than the brightness gradient on-line information, so in that case, the missing portion may be replaced by a value approximated by extending the straight-line information. Therefore, the accuracy is slightly lower than when using the information SL obtained from the longest scan line.

FIG. 1 is a block diagram of an example of the apparatus of the present invention, in which the parts other than the memory are the parts where calculations are executed by the computer, and the figure shows so-called functional programs.

That is, in FIG. 1, the position coordinates (for example, C
The upper left corner of the RT screen is the zero point (origin), and the horizontal direction is
coordinates (denoting this position coordinate in the vertical direction as a Y coordinate) and brightness information are supplied to scan line conversion means (2). Here, these position coordinates and brightness information are digital information.

In this scan line converting means (2), from the position coordinates and brightness information of each vertex E, F, G of triangle EFG, each side ef, fg, e (H) is calculated as the intersection of triangle EFG with the horizontal scanning line. The starting X coordinate XSi (i = 1.2.3...) of the scan line and the ending point X coordinate Xtii (i -1, 2, 3...) are sequentially calculated, and the starting point The brightness -3i is calculated.The information about the X coordinates of these starting points and ending points, and the brightness of the starting points are stored in the frame memo (January 3) of the pointer structure. FIG. 4 shows the contents of this memory (3). That is, in Figure 4, l
(t=1.2.3...) indicates the scan line number, XSi is the X coordinate of the starting point of the i-th line,
Hi indicates the X coordinate of the end point.

Further, WSi indicates luminance information at the starting point of the first line. Further, j (j-1, 2, 3, . . . ) indicates the number of the triangle to which this scan line belongs.

Also, from the scan line conversion means (2), the triangle EF
The X coordinates and luminance information of the start point and end point of the longest one of each scan line of G are supplied to the luminance gradient straight line information calculation means (4). The longest scan line is, for example, a scan line whose start or end point is the vertex that is in the middle of the 4 points with a Y coordinate of 3y among vertices E, l-', and G, and in the example of Fig. 3, it can be easily defined as line FH. You can find it at first glance.

In the brightness gradient straight line information calculation means (4), brightness straight line information of FH is first obtained from the brightness information WF and Wo of points F and H, and from this brightness straight line information, brightness information W of the starting point F of this line FH is calculated. , is subtracted, and the brightness gradient straight line information as described above is obtained.

In other words, this information is spread over the length of 8 minutes of the line.
This is the value of the brightness of each pixel in the horizontal direction that increases sequentially from the brightness of 0 according to the vA degree slope. This brightness gradient straight line information is stored in the gradient memory (5).

Figure 5 shows the contents of this inclined memo (January 5), where:
As before, j indicates the triangle number, which means the triangle having this brightness gradient straight line information, in other words, the brightness gradient number. In the case of a polygon larger than a triangle, the same scan line conversion and brightness 4 diagonal line information as described above are obtained for each divided triangle and stored in Memo January 3) and Memo January 5), respectively.

Next, the controller (6) operates at the timing of display, and first, from the pointer-structured frame memory (3), the X coordinates of the start point and end point of the triangular scan line for the first horizontal scan line, and the start point. The brightness information and slope number j are read out and stored in this controller (6). At this time, when one horizontal scanning line intersects many triangles, all information about the scan lines for the intersecting triangles is read out. When displaying that scan line, between the positions from the start point to the end point of each scan line, the brightness slope number for the triangle is determined by the readout control signal from the controller (6). The brightness gradient linear information of is sequentially read out from the gradient memo 1/5), and the luminance of the starting point of the scan line from the memo 1/3) is sequentially added to this luminance gradient linear information in the adding means (7). . Then, the addition information is D/
The signal is returned to an analog signal by the A converter (8) and displayed on the CRT (91). By doing this for each horizontal line, shading is created on the CRT (9) with a predetermined rg degree slope. Each triangle is displayed.

In this way, according to the present invention, since the brightness gradient straight line information is calculated for only one scan line of the triangle, the amount of calculation for this is small. Further, it is possible to provide good shading without producing subtle differences in slope due to the conventional calculation of brightness slope straight line information with a finite word length for each scan line. Also,
According to this example, there is no need to calculate the brightness of all points within the triangle to be shaded and write it to memory; instead, only the position coordinates of the start and end points of each line and the brightness information of the start point are written to memory. Since the amount of information written into the memory can be compressed, it can be applied to high-definition graphic systems with a large number of display pixels.

FIG. 6 shows another example of this inventive device, and in this example,
The X coordinates of the start point and end point of each scan line and the luminance information of the start point are supplied from the scan line conversion means (2) to the controller (10).

In this example, a full frame memory (11) is provided as an image memory to store all luminance information of pixels for one screen. When horizontal scanning line information is written to this full frame memory (11), the slope between the start point and end point of the scan line for each triangle is controlled by the readout control signal from the controller (10). The brightness gradient linear information about the triangle read from the memo (January 5) and the scan line conversion means (
The brightness information of the starting point of the scan line from 2) is sequentially added in the adding means (12), and the brightness information of the point forming each pixel on the scan line is sequentially obtained from the adding means (12), This is full frame memory (1
1).

Therefore, the horizontal line luminance information is sequentially read out from this full frame memory (11), converted back to an analog signal by the 1)/A converter (13), and then transferred to the CRT.
(14), a Gouraud-shaded triangle will be displayed on CR'1' (14).

In this example, display can be performed simply by sequentially reading the luminance information from the full frame memory (11), which is convenient in that it can be displayed only when necessary. In addition, in this example, although it is not possible to compress the memory as in the example in Figure 1, the amount of calculation required to calculate information at each point on each scan line is significantly reduced compared to the conventional method. It is.

In addition, in the above example, we explained the case where Gouraud shading is performed on polygons based on triangles, but if the polygon itself has a planar structure and you want to add shading with a certain slope to it, then , it is not necessary to divide the polygon into triangles, and it is of course possible to obtain the brightness gradient straight line information from any one of the scan lines for displaying the polygon, and to obtain the brightness information of each scan line based on that information. It is.

Furthermore, in the above example, the calculation becomes very simple by obtaining the diagonal straight line information around the brightness A from the information of the longest scan line. In other words, there is no scan line that requires more @ elements than the stored brightness gradient linear information,
Luminance information for each scan line can be easily obtained by simply adding the luminances at the starting points of each scan line. However, as mentioned above, the brightness gradient straight line information does not need to be obtained by selecting the longest line in this way, and can of course be calculated using the IIi degree gradient straight line information obtained from any one line.

The above is exactly the same in the case of polygons larger than triangles.

Note that the above explanation is based on the case where polygonal shading is performed using a raster scan type display means.
The present invention is applicable even to a random scan type display device in which the inside of a polygon is represented as a set of scan lines in a fixed direction.

Further, the same processing as above is applied to the primary color signals R and G.

If this is done for each level of B, and an image is displayed using color CET using these primary color signals R, G, and H, then
This invention can also be applied to color images.

〔Effect of the invention〕

According to this invention, the brightness gradient straight line information is obtained from any one scan line for displaying a polygon, and this information is sequentially added to the starting point of each scan line. Brightness information can be obtained. Therefore, the brightness gradient straight line information only needs to be obtained for one scan line, and the amount of calculation can be extremely small.

This allows high-speed processing.

In addition, since the same brightness slope straight line information is used for each line, it is possible to perform good Gouraud shading without uneven brightness slopes, unlike the conventional case where brightness slope straight line information is obtained for each line. .

In addition, in the case of the present invention, it is not necessary to store all the luminance information at the position of each pixel within the polygon in the memory, and the positional information of the starting point and ending point of each scan line and the luminance 1 of the starting point Since only 'N'+n can be stored, there is also the advantage that a small capacity memory can be used.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of an example of this inventive device, FIGS. 2 to 5 are explanatory diagrams, FIG. 6 is a functional block diagram of another example of this inventive device, and FIG. 7 is a conventional FIG. 2 is a diagram for explaining an example of a shading device. (2) is the scan line conversion means, (4) is the brightness gradient linear information forming means, (5) is the 1st diagonal memo IJ, (7) and (12) are the addition means, (9) and (14) are the C ) is 1.

Claims (1)

[Scope of Claims] An apparatus for representing a polygon as a set of many lines in a certain direction, and for providing shading on the inside of this polygon so that the brightness changes at a certain slope in one direction, means for obtaining luminance gradient straight line information from the positional information of the starting point and ending point of any one line, and the luminance information of each of the starting point and the ending point, and a memory for storing the luminance gradient linear information. , an image in which the luminance information of each line constituting the inside of the polygon is obtained by sequentially adding the luminance of the starting point of each line to the luminance gradient straight line information read from the memory up to the position of the ending point. shading device.