JPH0241790B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] The present invention relates to windowing required for multi-window display in which multiple windows are displayed on a display screen in a workstation that executes graphic processing. This invention relates to a clipping function method for extracting only the material.

In particular, the present invention relates to a clipping method for drawing a line segment having a line style such as a solid line, dotted line, or one-dot chain line in a bitmap memory. Conventionally, in this type of clipping method, line segments were newly drawn according to the line pattern register from the coordinates obtained by clipping, so the drawback was that the results were different depending on whether clipping was performed or not. had.

The present invention is a digital differential analyzer that generates line segments on a memory that can be accessed using two-dimensional integer coordinates. Initial conditions are determined to be given to the digital differential analyzer when drawing a line segment that reaches the end point from the intersection integer coordinates closest to the intersection of the line 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 offset of the line style register 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. This has the effect that even when drawing a line segment with a line style, the line segment patterns of the drawn portions with and without clipping completely match.

[Industrial application field]

The present invention relates to windowing necessary 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 a line segment in a bitmap memory with a line style.

[Prior art]

With the development of integrated technology, the importance of technology that realizes graphic processing at workstations by effectively using a dedicated processor 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 makes each bit of memory correspond to one dot on the screen, and each window is displayed in an overlapping manner. It also allows you to split the screen and display it. An important technology in this multi-window method is a windowing function that extracts interesting parts from figures defined in a wide coordinate system and converts them to the window's coordinate system. In order to perform this windowing, in addition to functions such as parallel translation, rotation, enlargement, and reduction of the figure, the faces and lines of the partial figure are hidden by the faces of other partial figures, and the hidden state is reproduced. A function to do this is required. For this windowing, a clipping function that extracts only necessary line segment data from the display file is important. In the 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 created. Viewing conversion is performed so that it can be displayed in a desired location on the screen as a multi-window. When performing a viewing transformation, transformations such as enlarging or reducing a specific partial figure, or translating or rotating it are so-called mapping transformations, which are performed by matrix multiplication operations, but the clipping function can efficiently cut out line segments. You need to do it well. In particular, this clipping divides the window on the display file into the visible part and the non-visible part of the display, and draws line segments only in the visible part.

Line segment drawing with this kind of clipping function uses a digital differential analyzer (DDA) that generates line segments in memory that can be accessed using two-dimensional integer coordinates.
This is done using Furthermore, when generating a dot sequence of line segments on a bitmap display using the DDA, there are cases where you can specify the style of the line, such as a dotted line, solid line, one-dot chain line, or two-dot chain line. be. Conventionally, as a clipping method for 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 these conventional drawbacks and provides a clipping method for drawing line segments with a line style in a bitmap memory.
When a line segment from arbitrary start point coordinates to end point coordinates is clipped with a vertical or horizontal straight line, as an initial condition given to the digital differential analyzer DDA,
To provide a clipping method for drawing a line segment that can draw a line segment that completely matches the state when no clipping is performed by appropriately specifying an offset to a line style register.

[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 using two-dimensional integer coordinates. As the initial setting values 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, the difference value in each axis direction and the principal axis specification are as follows. Set the value calculated from the coordinate values of the starting point coordinates and the ending point coordinates, and the error amount and the offset of the line register are the ones that are the closest to the intersection coordinates found from the roots of the equation when it is assumed that the drawing is from the starting point coordinates to the ending point coordinates. The digital differential analyzer is started by setting a value to be held at the near intersection integer coordinates, and setting the length in the principal axis direction from the intersection integer coordinates to the end point coordinate. .

[Effect]

Clip a line segment from an arbitrary starting point PS to PE with a straight line parallel to the intermediate X or Y coordinate, and select a line segment from the intersection integer coordinate PC closest to the intersection of the clipping line and the line segment to PE. As an initial condition for drawing and giving to DDA in that case, each axis direction difference value and principal axis specification are calculated from the coordinate values of PS and PE, and the error amount and line style register offset are assumed to be drawn from PS to PE. When I did
Set the value that the PC should have, and set the length in the main axis direction from the PC to the PE.
I am trying 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 apparatus 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. DDA200 processes line segments in units of dots, especially in the drawing process to enlarge, reduce, translate, rotate, or perform windowing in multi-windows of specific partial figures. This is the hardware to do so. In the windowing function for inserting and displaying a necessary part from the entire target figure defined in a very large coordinate system, the DDA 200 uses the bit map memory
302 and 303 generate or cut out line segments for a clipping function that writes only necessary line segment data. This DDA200 is, for example, a Bresenham model shown in FIG.
It includes a function to draw line segments according to the algorithm. Then, the DDA 200 is the main control unit 10
Input parameters such as the coordinates X and Y from 0, the absolute values DX and DY of the differences between X and Y, the main axis direction DIR, the length LEN in the main axis direction, and the error amount E.
Draw a line segment. FIG. 4 shows a flowchart when the main axis is in the X direction. In DDA, first subtract DX from DY and double it to obtain DD, and double the difference DY in the Y direction to obtain D. Next, the initial value of E is determined based on the sign of the error amount E. That is, if E is positive, add DD to E to make E, and if not positive, E
Add D to create a new E. After that, a routine that generates a point sequence is entered. First, the color point indicated by the color specification register 410 is set to the coordinates X, Y.
Hit Y. If the error value E is positive, add DD to E.
is added to update E, and Y is decremented by 1. If E is not positive, D is added to E and E is updated. That is, Y only if E is positive
is decremented. After that, X is always incremented. This is the case where X is the main axis, and X is always incremented by 1.
The length LEN is then decremented, and the above routine is repeated until LEN=0, a line segment is drawn and the line segment is printed as a series of dots.

The X and Y coordinates indicating each point sequence are given to RGB bitmap memories 301, 302, and 303, as shown in the block diagram of FIG. Then, when logic indicating a dot of a specific color is written into memory according to the contents of the color specification register 410,
A bit map display device in which each bit in memory corresponds to one dot on the screen, i.e.
A line segment dot sequence is displayed on the CRT 600 via the CRT control unit 500. That is, when a line segment, which is a basic drawing unit, is formed on the bitmap memory, the raster type display devices 500 and 60
0 means that the line segment vector is generated as a discrete pixel string. 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 in 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 section 100. In other words, in multi-window type windowing, figures are moved in parallel, enlarged and reduced, etc. in order to associate windows and viewports, but if there are generally multiple windows, the corresponding viewports are It allows you to set priorities and display them one on top of the other, and to dynamically change the priority order. As the window is converted, line segments will be clipped at the window boundaries. For example, if you are drawing a line segment in a certain window, and that window's priority is lowered and it becomes half hidden by another window, clipping of the line segment will occur at the window border. Therefore, special clipping processing must be performed to display only the line segments inside the window.

In the configuration of such a graphic processing device, the present invention determines the type of line, ie, dotted line, solid line, single point, according to the output of the DDA 200, which generates line segments on a memory that can be accessed with two-dimensional integer coordinates. A line style such as a chain 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. By doing this, line segments corresponding to the line style are generated.

When generating clipped line segments according to the present invention, a method of finding intersection points is followed. As shown in Figure 3, from the arbitrary starting point coordinate PS to the ending point coordinate
For example, in the middle of the line segment leading to PE,
When clipping with a straight line parallel to the coordinates, x
= Find the integer coordinate value PC closest to the intersection of the line segment between XC, PS, and PE, and make the line segment from PC to PE occur 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 becomes faster because it can be done. However, if a new line segment is drawn according to the contents of the line pattern register 420 from the intersection point PC determined by clipping, there is a problem that the result will be different depending on whether clipping is performed or not. The present invention allows drawing with and without clipping by setting the value that the offset in the line style register 420 should have at the integer intersection point coordinate PC when assuming that a line segment from the starting point PS to the ending point PE is drawn. The line segment patterns of the parts are made to match completely. Therefore, the line style register 420 will be briefly explained next. Line style register 420
As shown in FIG. 2a, it 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, one dot of the color specified by the color specification register 410 is placed at the position of the corresponding line segment. Therefore, the N-bit pattern in the line style register 420 is synchronized with the pointer that marks a series of dots on the screen. That is, bit information is read out 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 43.
It is determined whether the contents of the color designation register 410 are written to the bitmap memories 301, 302, and 303 via 0. For example, FIGS. 2b and 2c are explanatory diagrams for explaining how a line segment is drawn, and show how a line segment dot 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, a sequence of dots for the line segment is drawn from the position specified by the offset value of the line style register. That is, the second
In FIG. b, the contents of the line style register 420 are 111001110... from the beginning, and the offset position is the third bit 2 from the beginning. Therefore, the line segment to be drawn will be drawn according to the bit pattern starting from the third bit for which the offset is specified. In Figure 2b, the bit pattern from the offset specified position is 1001110..., so as shown in Figure 2c, the line segment is such that the point _P1 is at the offset specified position.
, P ₂ and P ₃ are not hit, P ₄ , P ₅ , and P ₆ are hit, and P ₇ is not hit.
In this way, a line segment is drawn in a 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 5a is an explanatory diagram of clipping, and is located in the middle of a line segment from arbitrary starting point coordinates PS = (XS, YS) to end point coordinates PE = (XE, YE), that is, parallel to the Y axis of x = XC. When clipping is performed with a straight line, the integer coordinate PC = closest to the intersection of the line segment between PS and PE and the clipping line x = XC
Consider the case of drawing a line segment from (XC, YC) to the end point coordinate PE. FIG. 5b 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 find the integer coordinates PC of the intersection of the line segment PS·PE------→ and the clipping line of x=XC. Then DDA
The initial conditions for 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 it is drawn from PS to PE, The length in the main axis direction is set from PC to PE. Then, I try to start DDA. When drawing the line segment PC/PE――――――→, the starting point coordinates are X
=XC,
Y=YC. The difference value DX in the X direction is XE−XS
The absolute value of Y-direction difference value DY is the absolute value of YE-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 vector of PC/PE ------>. length
LEN is the absolute value of XE minus XC plus 1, which corresponds to the number of points in the point sequence. PS,
The intersection point between the line segment between PEs and the clipping line is actually a value determined as a real value, but in the bit map display, the intersection point is also given in an integer coordinate system, so an error occurs, and the amount of error is calculated from PS to PE.
Set the value that should be held on the PC when it is assumed that it has been drawn up to. In this way, the initial parameters for the DDA 200 are set, and then the logic representing the color at each coordinate of the line segment to be drawn is set in the color specification register 420. Next, the line style pattern and offset are set in the line style register 420. In this case, the offset value a is
Give the absolute value of XC minus XS as the remainder when divided by N. That is, a=|XC−XS|(modN). It is important that this offset value is clearly set as the value that the integer coordinate PC should have when it is assumed that drawing is done from PS to PE. By activating the DDA 200 using each parameter determined as described above, line segments can be drawn correctly in a line style according to the contents of the line style register 420, regardless of whether or not clipping is performed. In this way, the amount of error or the offset for the line style register can be changed from PS to PE.
For example, in a multi-window method, the line segment between the PC and PE is erased by the upper window, and the priority is changed again. Even if the line segment between PC and PE is reproduced due to a change in , it will be reproduced with 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 vertical or horizontal straight line in the middle of the line segment from arbitrary starting point coordinates to end point coordinates, and draws a line segment from the intersection point to the ending point. As an initial condition for DDA, in particular, by setting the error amount and the offset value for the line style register as 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, it is possible to set the value that should be held at the intersection integer 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 perfectly matched.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of an apparatus 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 an explanatory diagram of clipping of the present invention. , Figure 4 is a flowchart showing the control operation of DDA,
FIG. 5 shows a flowchart of the main control section according to the clipping method in drawing line segments according to the present invention. 100...Main control unit, 200...DDA, 30
1,302,303...RGB bit map memory, 500...CRT control unit, 600...CRT,
420... Line style register, 430...
Mask circuit, 410...color specification register.

Claims (1)

[Claims] 1. 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 can be converted into a vertical or horizontal clipping line. Therefore, as an initial setting value to be given to the digital differential analyzer when clipping and drawing a line segment from the intersection of the line segment and the clipping line to the end point, each axial difference value and principal axis designation are set to the coordinates of the starting point. Set the value calculated from the coordinate value of the end point coordinate, and set the error amount and line register offset to the intersection integer coordinate closest to the intersection coordinate found from the root of the equation when assuming that the line is drawn from the start point coordinate to the end point coordinate. clipping in line segment drawing, characterized in that the digital differential analyzer is started by setting a value that should be at the axis, and setting a length from the intersection integer coordinates to the end point coordinates as the length in the principal axis direction. method.