JPS62127972A - Clipping system in line segment drawing - Google Patents

Abstract

PURPOSE:To make line segment patterns coincident with each other completely by setting a value to be given to a cross point integer coordinate while supposing that an error and an offset of a line style register especially as the initial condition to a digital differentiation analyzer (DDA) are used to draw a line segment from a start point coordinate to an end point coordinate. CONSTITUTION:A line segment from a start point PS to an end point PE is clipped by a line through an optional midpoint of the line segment in parallel with the X or Y coordinate, and a line segment from a cross point integer coordinate PC nearest the cross point between the clipping line and the line segment (from the PS to the PE) to the point PE is drawn. As the initial condition given to the DDA, each axis difference and main axis designation are calculated from the coordinates of the points PS, PE and as the error and the offset of the line style register, values to be given at the point PC are set when a line segment is drawn from the point PS to the point PE as assumption, and as the main axis length, the main axis length from the point PC to the point PE is set to start the DDA. Thus, the line segment drawn completely and the clipping line segment generate a dot string of the equivalent line style.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to windowing required for displaying multiple windows on a display screen in a workstation that executes graphic processing. This relates to a clipping function method that extracts only the minutes.

In particular, the present invention relates to a clipping method for drawing a line segment having a line style such as a solid line, a dotted line, or a chain line in a bitmap memory. Conventionally, in this type of clipping method, a line segment was drawn according to a new line pattern register from the coordinates determined by clipping, so it had the disadvantage that the results were different depending on whether it was clipped or not. Was.

The present invention uses a digital differential analyzer that generates line segments on a memory that can be accessed with two-dimensional integer coordinates, and when a line segment from arbitrary start point coordinates to end point coordinates is clipped by a vertical or horizontal straight line, the clipping line Initial conditions are determined to be given to the digital differential analyzer when drawing a line segment leading to the end point from the intersection integer coordinates closest to the intersection of the line segment and the line segment. That is, each axis direction difference value and principal axis specification are set to values calculated from the coordinate values of the start point and end point, and the error amount and line style register offset are assumed to have drawn a line segment from the start point coordinates to the end point coordinates. When this happens, set the value that the intersection integer coordinate should have, set the length in the principal axis direction from the intersection integer coordinate to the end point coordinate, and start the digital differential analyzer. There is. In this way, even when drawing a line segment with a line style, the line segment patterns of the drawn portions with and without clipping will completely match.

[Industrial application field]

The present invention relates to windowing required for displaying multiple windows on a display screen in a workstation that performs graphic processing, and particularly to a clipping method for extracting only necessary line segments from a display file.

More particularly, the present invention relates to a clipping method for drawing line segments in a bitmap memory with a line style.

[Traditional technique]

With the development of integrated technology, the importance of technology that realizes graphic processing on workstations by effectively using dedicated processors dedicated to graphic processing, which is the basic technology of man-machine interfaces, has increased. This workstation mainly has a multi-window function that displays multiple windows on the display screen using a bitmap display device that associates one bit in memory with one dot on the screen, and each window is displayed in an overlamp manner. You can also split the screen and display it. An important technology in this multi-window method is the windowing function that extracts interesting parts from figures defined in a wide coordinate system and converts them to the window coordinate system. In order to perform this windowing, not only functions such as parallel translation, rotation, enlargement, and reduction are required for the figure, but also a function that allows the faces and lines of a partial figure to be hidden by the faces of other partial figures, and reproduces them from the hidden state. Is required. For this windowing, a clipping function that extracts only necessary line segment data from the display file is important. In a display file, each partial figure is formed as a set, and when each figure undergoes figure transformation to become a window, a window is first set in a wide coordinate system on the display file, and then a display corresponding to the display screen is set. Viewing conversion is performed so that it can be displayed in a desired location on the screen as a multi-window. When performing viewing transformation, transformations such as enlargement, reduction, translation, rotation, etc. of a specific partial figure are so-called mapping transformations, which are performed by matrix multiplication operations, but in the clipping function, line segments are cut out. It needs to be done efficiently. In particular, this clipping divides the window on the display file into the part that is actually visible on the display and the part that is not.
Line segments will be drawn only in the visible areas.

Line segment drawing having such a ripping function is performed using a digital differential analyzer (DDA) that generates line segments on a memory that can be accessed using two-dimensional integer coordinates. Further, when generating a dot sequence of line segments on a bitmap display using the DDA, it is sometimes possible to specify a line style such as a dotted line, a solid line, a one-dot chain line, or a two-dot chain line as the type of the line segment. Conventionally, as a clipping method when drawing a line segment having such a line style, a line segment is newly drawn according to a line pattern register from the coordinates obtained by clipping. Therefore, when drawing a line segment with a line style, there is a problem in that the line segment patterns drawn with and without clipping do not completely match.

[Problem that the invention seeks to solve]

The present invention eliminates such conventional drawbacks and uses a clipping method when drawing a line segment with a line style in a bitmap memory. When clipping occurs on a horizontal straight line, the initial condition given to the digital differential analyzer DDA is to draw a line segment that perfectly matches what would have been done without clipping by appropriately specifying the offset to the line style register. Provides a clipping method for line segment drawing that allows

[Means for solving problems]

In order to achieve the above object, the present invention uses a digital differential analyzer that generates line segments on a memory that can be accessed by two-dimensional integer coordinates to generate line segments from arbitrary start point coordinates to end point coordinates in a vertical or horizontal direction. As an initial setting value given to the digital differential analyzer when clipping is performed using a clipping line and a line segment is drawn from the intersection of the line segment and the clipping line to the end point, each axis direction difference value and principal axis designation are set to the coordinates of the start point and Set the value calculated from the coordinate value of the end point coordinate, and the error amount and line register offset are the intersection integer coordinates closest to the intersection coordinate found from the root of the equation when assuming that the error amount and line register offset are drawn from the start point coordinate to the end point coordinate. The digital differential analyzer is started by setting the value that should be at , and setting the length in the principal axis direction from the integer coordinates of the intersection point to the end point coordinates.

[For production]

Clip a line segment from an arbitrary starting point PS to PH with a straight line parallel to the intermediate X or Y coordinate, and draw a line segment from the intersection integer coordinate PC closest to the intersection of the clipping line and the line segment to PE. In that case, as the initial conditions given to DDA, each axis direction difference value and principal axis specification are PS,
Calculated from the PE coordinate values, the error amount and line style register offset are set to the values that should be in the PC when drawing from PS to PE, and the length in the principal axis direction is the length in the principal axis direction from pc to PE. is set to start DDA.

〔Example〕

Next, a clipping method for line segment drawing according to the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a graphic processing device showing an embodiment of the present invention.

The main control unit 100 is a part that performs overall control to perform graphic processing, and includes a central processing unit therein. The main control unit 100 mainly executes parameter setting and startup for the digital differential analyzer (DDA) 200. DDA2
00 is enlargement, reduction, translation, rotation of a specific partial figure,
Alternatively, it is hardware for processing line segments dot by dot, especially in the part that processes line segments in drawing processing for executing windowing in a multi-window. In the windowing function for extracting and displaying the necessary parts from the entire target figure defined in a very large coordinate system, the DDA 200 uses clipping to write only the necessary line segment data to the bitmap memory 301, 302, and 303. Generate or cut out line segments for features. This DDA200 is
For example, the Bresenh (Bresenh) shown in FIG.
am ) includes a function to draw line segments according to the algorithm. The DDA 200 is the main control unit 10
Parameters such as the coordinates X and Y from 0, the absolute values DX and DY of the differences between X and Y, the length LEN in the principal axis direction DIR1, and the error ff1E are input, and a line segment is drawn. FIG. 4 shows a flowchart when the main axis is in the X direction. D.D.A.
First, subtract DX from DY, double it to get DD, and then Y
Let D be the difference in direction DY multiplied by two. Next, the initial value of E is determined based on the sign of the error amount E. That is, if E is positive, DD is added to E to create E; if it is not positive, D is added to E to create a new E. After that, a routine that generates a point sequence is entered. First, a point of the color indicated by the color designation register 410 is set at the coordinates X, Y. If the error amount E is positive, add DD to it and update E,
Decrement Y by 1. If E is not positive, D is added to E and E is updated. That is, Y is decremented only if E is positive. After that, X is always incremented. This is the case where X is the main axis, and X is always incremented by 1. Then the length LEN is decremented and the above routine becomes LE
Line segments are drawn repeatedly until N=0, and the line segments are drawn as a series of dots.

The X and Y coordinates indicating each point sequence are stored in each RGB bitmap memory 301.3 as shown in the block diagram of FIG.
Given on 02.303. And color specification register 4
10, a line is sent to the CRT 600 via the CRT control unit 500, which is a bitmap display device that makes each bit in the memory correspond to one dot on the screen. A series of dots will be displayed. That is, when a line segment, which is a basic drawing unit, is formed on the bitmap memory, the vector of the line segment is generated as a discrete pixel string by the Rask-type display devices 500 and 600. In this case, discrete line segments are drawn as an integer sequence of points at each intersection on the grid. In addition, in clipping in the multi-window method, the main control unit 100
Of the contents of the display file held within the display file, only necessary line segment data is extracted and displayed on the bitmap display 600, and this clipping process is executed by the main control unit 100. In other words, in a multi-window system, the figure is moved in parallel, scaled, etc. in order to establish a correspondence between the window and the viewport, but if there are generally multiple windows, the view for that window is Boats can be prioritized and displayed overlapping, and the priority order can be changed dynamically. As the window is converted, line segment clipping will be performed at the border of the window. For example, if a line segment is drawn in a certain window, and that window's priority is lowered and half of the line is hidden by another window, clipping of the line segment will occur at the border of the window. Therefore, special ripping processing must be performed to display only the line segments inside the window.

In the configuration of such a graphic processing device, in the present invention, the type of line, ie, dotted line, solid line, single point I\ A line style such as a line or a two-dot chain line can be specified in the line style register 420.

When providing logic for generating a dot sequence of the color specified by the color specification register 410 to the bitmap memory, the dot sequence is appropriately masked via the mask circuit 430 using the contents of the line style register 420. I am trying to generate line segments that correspond to the line style.

When generating clipped line segments according to the present invention,
It follows the method of finding the intersection. As shown in Figure 3,
For example, if you clip with a straight line parallel to the Y coordinate x = XC in the middle of a line segment from arbitrary starting point coordinates PS to end point coordinate PE, the most The closest integer coordinate value PC is found, and the line segment from pc to PE is generated on the line specified by the line style register. In this way, by finding the intersection between the clipping line and the line segment and drawing the line segment between the intersection and the end point PE, you can draw the clipped line segment without generating a sequence of points from the starting point PS to PC. It will be faster because it can be done. However, if a line segment is newly drawn according to the contents of the line pattern register 420 from the intersection point PC obtained by clipping, there is a problem that the result will be different depending on whether the intersection point PC is clipped or not. The present invention sets the value that the offset of the line style register 420 should have at the integer intersection point coordinate PC when assuming that a line segment from the start point PS to the end point PJE is drawn, with or without clipping. The line segment patterns of the parts that are displayed are made to match completely. Therefore, the line style register 420 will be briefly explained next. As shown in FIG. 2 (al), the line style register 420 is composed of an N-bit register, and each of the N bits corresponds one-to-one to the position of a point on a line segment to be drawn. If the content is logically 1, the point of the color specified by the color specification register 410 is set to 1 at the position of the line segment corresponding to it.
You will be hit with a dot. Therefore, the N-bit pattern of the line style register 420 is synchronized with the pointer that marks a series of dots on the screen. That is, bit information is output one after another in synchronization with the synchronization signal when outputting the X and Y coordinate points of the DDA 200, and the information is sent to the mask circuit 4.
It is determined whether the contents of the color designation register 410 are to be written to the bitmap memories 301, 302, and 303 via the bitmap memories 301, 302, and 303. For example, FIG. 2 (bl, (C)) is an explanatory diagram for explaining how a line segment is drawn, and shows how a line segment point sequence is generated according to the bit pattern of the line style register 420. What is important here is that when drawing a line segment, the dot sequence of the line segment is drawn from the position specified by the offset value of the line style register.

That is, in the line style register 4 in FIG.
The contents of 20 are 111001110 from the beginning...
The offset position is the 2nd position of the third bit from the beginning. Therefore, the line segment drawn is offset ↑
A line segment will be drawn according to the bit pattern starting from the third bit where the determination is made. In Figure 2(b), the bit pattern from the specified offset position is 1.
001110 ..., so Figure 2 (C
As shown in 1, the line segment is P, and the point 2 is the offset specified.
Since it corresponds to the position of P2. P, is not hit, P4゜Ps, Pb is hit, but P7 is not hit. In this way, a line segment is drawn in the line style corresponding to the bit pattern specified by the offset in the line style register 420. That is, bit information is read out one after another from the position specified by the offset value from the beginning of the line style register 420, and a dot is placed at the position where the bit value is logical 1, but not at the position where the bit value is logical 0. , In this way, a line segment with a line style will be drawn.

Next, the flow of processing showing the operation of the present invention will be explained using FIG. Figure 5 (al is an explanatory diagram of clipping,
Arbitrary starting point coordinates PS = (XS, YS) to ending point coordinates P
E= In the middle of the line segment leading to (XE, YE), that is, X=X
When clipping in a straight line parallel to the COY axis, PS,
Consider the case where a line segment leading to the end point coordinate PE is drawn from the integer coordinates PC=(XC, YC) closest to the intersection of the line segment between PEs and the clipping line X=XC. FIG. 5(b) is a flowchart. In this embodiment, a case will be described in which the X-axis is the main axis, but the same applies to cases where clipping is performed on a straight line parallel to the X-axis or when the Y-axis is the main axis. When the operation starts, first, the integer coordinates PC of the intersection of the line segment PS - PE and the clipping line of x=XC are determined.

Next, initial conditions for the DDA 200 are set as follows. In other words, for each axis direction difference value and principal axis specification, set the value calculated from the coordinate values of PS and PE, and for the error amount and offset, set the value that should be in the PC when it is assumed that drawing is done from PS to PE, The length in the main axis direction is set from PC to PE. Then, the DDA is activated. When drawing the line segment PC-PE, the starting point coordinates are X=XC, Y=YC. Difference value D in the X direction
X is the absolute value of XE-XS, and the difference value DY in the Y direction is YE-
It is the absolute value of YS. The direction DIR is an identification value indicating each direction given when 360 degrees is divided into 8 equal parts, and in this case indicates the direction of the PC-PE vector. The length LEN is the absolute value of XE minus XC plus 1, which corresponds to the number of points in the point sequence. The intersection point between the line segment between PS and PE and the clear pin line is actually a value determined as a real value, but in a bitmap display, the intersection point is also given in an integer coordinate system, so an error occurs, and the amount of error is P
Set the value that the PC should have when it is assumed that drawing is done from S to PE. In this way, the initial parameters for the DDA 200 are set, and then the color specification register 420
Set the logic that represents the color at each coordinate of the line segment to be drawn.

Next, the line style pattern and offset are set in the line style register 420. In this case, the offset value a is given as the remainder when the absolute value obtained by subtracting XS from XC is divided by N. That is, a=lxc-XSI(modN
). This offset value is clearly from PS to PE
It is important that it is set as the value that should be held in the integer coordinate PC when it is assumed that the drawing is done up to the point. Using each parameter determined as above, DDA200
By activating , line segments can be drawn correctly in a line style that follows the contents of the line style register 420 regardless of whether or not there is clipping.

In this way, by using the value that the error amount or the offset for the line style register should have in the PC when drawing from PS to PE, for example, in a multi-window method, once the PC is Even when the line segment between PE is erased and the priority is changed again and the line segment between PC and PE is reproduced, it will be reproduced in the correct line style.

〔Effect of the invention〕

In this way, when drawing a line segment with a line style, the present invention clips a line segment from arbitrary starting point coordinates to end point coordinates with a vertical or horizontal straight line, and draws a line segment from the intersection point to the end point. , as an initial condition for DDA, in particular, by setting the error amount and the offset value for the line style register to the value that should be at the intersection integer coordinate when it is assumed that the drawing is done from the start point coordinate to the end point coordinate, regardless of the presence or absence of clipping. This has the effect that a point sequence with an equivalent line style can be generated between a completely drawn line segment and a clipped line segment, and the two can be made to perfectly match each other.

[Brief Description of the Drawings] Fig. 1 is a block diagram of a device according to the clipping method of the present invention, Fig. 2 is an explanatory diagram of drawing a line segment with a line style using the line style register of the present invention, and Fig. 3 is a block diagram of a device according to the clipping method of the present invention. FIG. 4 is a flowchart showing the control operation of the DDA, and FIG. 5 is a flowchart of the main control section according to the clipping method in line segment drawing of the present invention. 100... Main control unit, 200... DDA. 301, 302, 303...RGB bitmap memory, 500...CRT control unit, 600...CRT. 420...Line style l/Desta, 430...
Mask circuit, 410...Color specification register, N°C Go Soto N bit nomatashi '2 #ni' + smell! sL&u(a
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Claims (1)

[Claims] In a digital differential analyzer that generates line segments on a memory that can be accessed using two-dimensional integer coordinates, a line segment from arbitrary start point coordinates to end point coordinates is clipped by vertical or horizontal clipping lines. , as the initial setting values given to the digital differential analyzer when drawing a line segment from the intersection of the line segment and the clipping line to the end point, each axis direction difference value and principal axis designation are the coordinates of the start point coordinates and the end point coordinates. Set the value calculated from the value, and set the value that the error amount and line register offset should have at the intersection integer coordinate closest to the intersection coordinate found from the root of the equation when it is assumed that the line is drawn from the start point coordinate to the end point coordinate. a clipping method for line segment drawing, characterized in that the digital differential analyzer is activated by setting the length in the principal axis direction from the integer coordinates of the intersection point to the coordinates of the end point.