JPH0442712B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In order to improve the display speed of straight lines in an image display device, the coordinates This reduces the number of lines on which conversion is applied and improves display speed.

[Industrial Application Field] The present invention relates to an image display device, and more particularly to a preprocessing method for straight line clipping.

When performing processing such as parallel translation, rotation, or enlargement of an image on an image display device such as a graphic display device, coordinate transformation is performed on the coordinate values of both end points of a straight line, and the coordinate values after the transformation are A straight line is displayed by sending it to a straight line generator.
At this time, in order to display the straight line correctly, an operation called "clip" must be performed to delete the straight line portion that protrudes from a predetermined display area.

From the viewpoint of improving responsiveness, it is desirable that the series of processes of coordinate transformation and clipping be performed as quickly as possible.

[Prior Art] A block diagram showing the principle of the conventional clipping technique is shown in FIG. In the figure, numerals 11, 12, and 13 are registers that store coordinate values of end points of straight lines, coordinate conversion parameters, and boundary values of display areas, respectively.

4 is a coordinate transformation means, and 5 is a clip means.

The coordinate values of both end points of the straight line in register 11 are
It is sent to the coordinate conversion means 4 via the data line a.

The coordinate transformation means 4 performs coordinate transformation on the end points of the straight line according to the coordinate transformation parameters obtained from the register 12 via the data line b, and outputs the resulting coordinate values via the data line d.

The clipping means 5 compares this coordinate value with the boundary value of the display area read out from the register 13 via the data line c, and performs a so-called "pruning" process in which the portion of the straight line outside the area is deleted. and outputs the result via data line e.

[Problems to be Solved by the Invention] In the conventional clipping method, clip processing is performed after coordinate transformation processing, and therefore it is necessary to perform coordinate transformation on all straight lines.

Depending on the coordinate transformation parameters, for example, in the case of extreme enlargement processing, most of the straight lines will completely protrude from the display area, but the coordinate transformation processing must also be applied to these straight lines.

Coordinate transformation processing is a time-consuming process that involves a large number of multiplications, and is inefficient due to the large number of objects to be transformed and the inclusion of useless items.
This causes a decrease in the overall display speed.

SUMMARY OF THE INVENTION The present invention aims to provide an image display device equipped with a pre-processing section for straight line clipping which solves the above-mentioned conventional problems.

[Means for Solving the Problems] FIG. 1 shows a principle block diagram of a preprocessing section for clipping a straight line in an image display device of the present invention.

In FIG. 1, numerals 11, 12, and 13 are registers that store coordinate values of end points of straight lines, coordinate conversion parameters, and display area boundary values, respectively.

Reference numeral 2 denotes an inverse coordinate transformation means which performs inverse coordinate transformation of the display area boundary value in accordance with coordinate transformation parameters.

Reference numeral 3 denotes an unnecessary straight line eliminating means, which eliminates straight lines that are clearly located outside the display area by comparing the display area boundary value reversely transformed by the inverse coordinate transformation means 2 with the coordinate values of the end points of the straight line.

Reference numeral 4 denotes a coordinate transformation means which performs coordinate transformation of end points of straight lines other than those excluded by the unnecessary straight line elimination means 3.

Reference numeral 5 denotes a clipping means, which compares the coordinate values output from the coordinate conversion means 4 with the boundary values of the display area;
[Operation] The inverse coordinate transformation means 2 deletes the part of the straight line that is outside the area. By inversely transforming the display area boundary value using the coordinate transformation parameter,
Before executing the coordinate transformation, the unnecessary straight line eliminating means 3 can calculate a boundary value for determining an unnecessary straight line.

The unnecessary straight line elimination means 3 compares the coordinate values of the end points of the straight lines with the boundary values calculated by the inverse coordinate transformation means 2, and can eliminate straight lines that are obviously outside the area.

As a result, the number of straight lines subjected to coordinate transformation is reduced, and the overall processing speed is improved.

[Example] The present invention will be described in more detail below with reference to Examples shown in FIGS. 2 to 4.

FIG. 2 is a block diagram of a two-dimensional wireframe type (display that targets only straight lines and does not target surfaces, etc.) graphic display that is an embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes a display list buffer, which includes a register 11 for linear end point coordinate values, a register 12 for coordinate conversion parameters, a register 13 for display area boundary values, and registers for other data.

2 is an inverse coordinate conversion means, 3 is an unnecessary straight line elimination circuit, 4 is a coordinate conversion circuit, and 5 is a clip circuit, each of whose functions are the same as 2 in FIG.
- Same as 5.

6 is a straight line generator using a digital differential analyzer (DDA), which generates coordinate values of each point constituting a straight line connecting the end points from the coordinate values of the end points.

A frame buffer 7 stores the shape of a straight line generated by the straight line generator 6 as an image size memory.

8 is a CRT, which displays the contents of the frame buffer 7 on the screen.

FIG. 3 is a diagram illustrating an example of preprocessing for straight line clipping according to the present invention.

FIG. 3a is a diagram showing the arrangement of a group of straight lines reproduced from the coordinate values of the straight line end points stored in the display list buffer 1.

FIG. 5B is a diagram showing the relationship between the arrangement of straight lines and the display area boundary value when coordinate transformation is performed on these straight line groups using coordinate transformation parameters.

In FIG. 3c, the display area boundary value obtained by inverse coordinate transformation with respect to the arrangement of the straight line group shown in a is shown by a solid line frame.

From the maximum/minimum coordinate values of the vertices of this solid line frame, an unnecessary straight line exclusion boundary as shown by a broken line having a boundary parallel to the coordinate axis is obtained.

The unnecessary straight line elimination circuit 3 compares and determines the coordinate values of the end points of each straight line with the unnecessary straight line elimination boundary shown in FIG. 3c, and eliminates unnecessary straight lines based on the result.

The "Cohen &Sutherland" algorithm used in normal clip processing is applied to this comparison.

FIG. 4 is a diagram illustrating an algorithm for unnecessary straight line exclusion determination.

As shown in the figure, nine areas are set around the unnecessary straight line exclusion boundary, and a 4-bit code "0000" is assigned to the central area.

For the area to the left of the center area, ``01'' is assigned to the upper 2 bits, ``10'' is assigned to the upper 2 bits for the area to the right, and the lower 2 bits are assigned to the area above the center area. "01" is assigned to the 2 bits of the area, and "10" is assigned to the lower 2 bits of the area below the center area.

The 4-bit code assigned to each area in this way is as shown in the figure.

Elimination of unnecessary straight lines is carried out by ``in the bitwise logical product of the codes in the area where the two end points of the straight line are located,
The determination is made based on an algorithm that states that if there is a bit of "1", the straight line is clearly outside the region "0000".

For example, (1) The end points of straight line d are located in the area “0100” and the area “0000”, and their logical product is “0000”.
Therefore, since there is no "1" bit, it is not excluded.

(2) The end points of straight line e are located in area “0010” and area “1010”, and their logical product is “0010”
Since there is a "1" bit, it is subject to exclusion.

(3) The end points of the straight line f are located in the area “0001” and the area “1000”, and their logical product is “0000”.
Therefore, since there is no "1" bit, it is not excluded.

In this way, straight lines that are clearly outside the unnecessary straight line exclusion boundary, such as the straight line e shown in FIG. 3c, are excluded, and the unnecessary straight line exclusion process is completed.

For the straight lines that were not eliminated by this process, the coordinate transformation means 4 performs coordinate transformation, the clip circuit 5 performs normal clip processing, the straight line generator 6 generates the coordinates of the straight line, and the frame buffer is 7 and displayed on the CRT8.

In this embodiment, an unnecessary straight line exclusion boundary is generated from data obtained by inversely converting the display area boundary value, and a simple algorithm is used to clearly determine the exclusion of straight lines outside the display boundary. Therefore, the processing time required for eliminating unnecessary straight lines can be extremely short.

[Effects of the Invention] As explained above, according to the present invention, it is possible to eliminate to some extent straight lines that are clearly located outside the display area as a result of coordinate transformation, and to avoid coordinates that require a lot of processing time. By reducing the number of files to be converted,
Overall, the processing speed can be improved, and the practical effects thereof are extremely large.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram explaining an example of preprocessing for clipping a straight line according to the present invention, and FIG. 4 5 is a diagram illustrating an algorithm for determining whether unnecessary straight lines are eliminated, and FIG. 5 is a block diagram showing the principle of the conventional clipping technique. In the drawing, 1 is a display list buffer, 2 is an inverse coordinate transformation means (circuit), 3 is an unnecessary straight line eliminating means (circuit), 4 is a coordinate transformation means (circuit), 5 is a clipping means (circuit), and 6 is a straight line generator (DDA), 7 is a frame buffer, 8 is a CRT, 11 is a register for straight line end point coordinate values, 12 is a coordinate transformation parameter.
Registers 13 and 13 indicate display area boundary value registers, respectively.

Claims (1)

[Scope of Claims] 1. Coordinate conversion means 4 for converting coordinate values of end points of straight lines according to coordinate conversion parameters, and clipping means for pruning straight lines by comparing coordinate values after coordinate conversion with display area boundary values. 5, an inverse coordinate transformation means 2 for inverse coordinate transformation of the display area boundary value according to the coordinate transformation parameter; a boundary value coordinate-transformed by the inverse coordinate transformation means 2; An unnecessary straight line eliminating means 3 is provided which eliminates straight lines located outside the display area by comparison with end point coordinate values, and performs coordinate transformation and pruning processing only for the straight lines that are not eliminated by the elimination process. An image display device configured to display images.