JPS60239826A - Correlation of straight line for interactive type display system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved method of correlating a straight line and a correlation window in an interactive display device.

[Prior art]

When processing a graphical image interactively, the operator typically attempts to identify a particular line in the image in accordance with the application-program with which it is interacting. and move,
A possible way to perform the operation, which may be one of various prerequisites for modifying or deleting a target shape, would be the identification of the target shape by, for example, the command ``delete line 2''. However, it is much more natural for the operator to use appropriate equipment to actually point the line. Typical devices coupled to a display screen cursor include a joystick, thumbwheel, trackball, or mouse.

By specifying the position like this, the position on the screen (x, y
) can be obtained directly. A correlation operation must then be performed to determine which lines in the picture or image actually pass through (or are sufficiently close to) the located point.

To perform the above operation, the picture or image definition (-display list) must be traversed just as one would draw an image, but instead of actually drawing the lines defined in the list, those lines Test each of them to see if they intersect (for example) a small rectangle drawn around the point in question.

It is important that the aforementioned process be carried out quickly.

The operator expects a quick system response indicating whether a particular assignment was successful.

Generally, the operator specifies only one line among many lines in the image, so how quickly each of the remaining objects can be rejected becomes an important factor in performance.

The Cohen-3Utherland clipping algorithm is designed to efficiently identify lines that can be unequivocally accepted or rejected by inspection of the region. Calculation of traversals is only required for lines that are neither accepted nor rejected. This clipping algorithm is
Things are more efficient in two extreme cases: a large window containing most of the primitives, or a relatively small window and a thick (dense, image with most of the primitives falling outside the window). and most of the lines are
You can accept or reject it tomorrow.

The algorithm is based on 9 regions or windows and creates a 4-bit outcode with bit 1 at the left end:
Begin by assigning to each endpoint of the line. The nine regions or windows are a correlation window and eight surrounding regions, four regions having edges adjacent to the edges of the correlation window, and the remaining four regions having diagonal corner regions. Each bit of the outcode is set to 1 if certain relationships between the endpoint and the window below are true.

Bit 1: End point is above the window.

Bit 2: End point is below the window.

Bit 3 = End point is on the right side of the window.

Bit 4: End point is on the left side of the window.

Otherwise, the bit is set to 0.

One way to calculate the outcode in a way that allows bit manipulation is to calculate the outcode in such a way that bit 1, bit 2, bit 3, and bit 4 are (ym□-y), (y-ym, n), (
It follows from the observation that xma

If both endpoints are within the correlation window corresponding to an outcode of (0000), then the line is clearly acceptable. If so, the line is explicitly rejected. This is true if the corresponding bits in the outcode of both endpoints are 1, and the corresponding bits are 1.
Whether or not it is determined by the conjunction of these outcodes (A
ND), and the result is carN0TO[l[]I] 〃
It can be easily determined by testing whether or not it is.

If the result of the AND is 0000, then the line cannot be explicitly rejected or accepted. this is,
This is because the line may cross the correlation window.

The algorithm has the disadvantage that it requires the calculation of at least two intersection points when clipping a line passing through a correlation window. This work must be extremely time consuming from a data processing perspective.

US Pat. No. 4,412,295 describes a circuit arrangement for eliminating line collisions in a display.

This circuit can generate curved and straight boundary parts such as those generated by a figure generation program, as well as CR
The generation of multiple clipping boundaries at different horizontal positions across the T-screen is possible.

Position information is fed into this circuit from the graphics generator, so this input information addresses the lookup table to locate between certain parts of the symbol to be displayed and the region of the symbol that is to be displayed with high priority. can determine whether a conflict will occur. If it is determined that there is a collision, this circuit will
Clip portions of symbols that would otherwise cover higher priority information.

[Problems to be solved by the invention] As mentioned above, the conventional technology for correlating straight lines in an interactive display system has the problem that it takes too much time because it requires troublesome calculations. The present invention aims to provide a technique that reduces the time required for correlation and reduces the user's waiting time.

Means for Solving Problem C] The method of correlating a straight line with a correlation window in an interactive display system provided by the present invention is as follows: (,) Defining a correlation window in a display area, and Divide the part into eight regions surrounding the correlation window; (b) calculate the outline of the region in which the end points lie, which of the lines written as coordinates in the display list buffer can be accepted or rejected unambiguously; (c) for each line not unequivocally accepted or rejected, on which side of that line one or two selected corner points of the correlation window are located; ,
Determine whether the line crosses the correlation window.

Contains steps.

An interactive display system provided as another embodiment of the present invention includes a display screen, a control device including a controller, a ROM for storing a control program, and a RAM having at least a register area and display test buffer storage. including, under the control of the control program,
a first means for defining a correlation window in the display area and dividing the remaining part of the display area into eight areas surrounding the correlation window; a second means for determining which drawn lines can be accepted or rejected unambiguously by calculating the outline of the area in which the end points are located; For each line that is not found, determine on which side of that line one or two selected corner points of the correlation window are located, and therefore whether the line crosses the correlation window. and a third means.

[Effect]

In an interactive display system, the display screen is divided into a correlated window and eight surrounding areas, and any of the lines written as coordinates in the display list are explicitly accepted. The decision is made by calculating the outline of the region in which the endpoints of those lines are located, and for valleys 2 of the lines that are not clearly accepted or rejected, one or two of the correlation windows are determined.
Correlate straight lines by determining on which side of the line the two selected corner points are located, and therefore whether the line crosses the correlation window.

〔Example〕

In FIG. 2, screen 10 is divided into nine regions consisting of correlation window (or region) 1 and surrounding regions 2-9. Each region is identified by a 5-pit outcode. The bits in each outcode are represented as follows: Bits 1 and 5 represent the bottom of the rectangular correlation window, Bit 2 represents the right side of the correlation window, Bitlo represents the top of the correlation window, and Bit 4 represents the top of the correlation window. Represents the left side of the correlation window.

Therefore, each area is represented by an outcode consisting of a combination of the following five bits.

Area 1 = 00000 (correlation window) Area 2 = 001
10. (Top left area) Area 3. = 00100 (upper middle area) Area 4 - 01100 (upper right area) Area 5 - 00010 (middle left area) Area 6 = [l 1000 (middle right area) Area 7 = 1
001'1 (lower left area) Area 8-jDDDj (lower middle area) Area 9 = 11001 (lower right area) When using this display method, by shifting the out code by one digit to the left, An outcode corresponding to the result of rotating the original outcode by 90 degrees counterclockwise is generated using 4 bits of , correlation window 1 is a rectangle of 10 or 15 pels (pixels), and the other regions take correspondingly larger areas, so the middle region has one short edge (adjacent to correlation window 1) and the other has a relatively larger edge adjacent to the area.

A preferred embodiment of the method of the invention is illustrated by the flowchart shown in FIG. 1 and the interactive display system shown in FIG. The interactive display system of FIG. 5 includes a display screen '50 and a control device 31 connected thereto.

The control device 51 includes a processor 32, a ROM 34, and a RAM.
35 and a display list-buffer 36 and a bus 33 connecting them. Input/output between the keyboard 37 or cursor control device 38 and the screen 300 is performed via the control device 31. The cursor control device 38 is
The O processor 32, which may be a light pen, mouse, tablet, or similar device, is controlled by a control program written in the ROM 54. RAM 35 has a dedicated area that serves as a temporary storage register. In a preferred implementation of the method of the invention, 10 registers A-J are used.

The control device 7+1 also has a connection point 39 with a host data processing device (not shown), and this data processing device
A display list defining the content of the images to be displayed on screen 30 is sent via the appropriate link.

The display list is stored in the display list buffer 36 in the form of the image to be displayed and the coordinates of the end points of the lines forming the image.

When a user of an interactive display system (hereinafter simply referred to as the system) wishes to indicate a line or area that requires processing, such as deletion, emphasis, or movement from the overall Move the cursor on the screen via device 38.

For complex images, the cursor does not always lie correctly on a particular line, so the system must determine which line should be selected by the cursor position. Therefore, a correlation window 1 (FIG. 2) is defined around the cursor position. The method explained below is ROM! Under the control of a control program written in 14, it is used to correlate the lines on the screen with the correlation window 1.

The area of registers A-J is defined as follows: Register C: Left edge of correlation window XL Register B:
Right edge of the correlation window χ, register C: bottom edge of the correlation window yB register D = top edge of the correlation window y
T register E: Line dot point coordinates 1y1: Result) Register J: AND (Result of AND of register F and register G) Note that register K is used as a working register.

Register F and register G are set as follows.

Outcode o of point (X+y) with respect to the correlation window
c is defined as an 8-pit byte with bits set as follows: oc(1), oc(5
): Set to 1 if y < yB, otherwise set to 0.

oc(2): Set to 1 if x>xR, otherwise OK shift left.

oc(3): Set to 1 if y>yT, otherwise set to 0.

oc(4): Set to 1 if x < xt, otherwise OK shift left.

Outcode bit 1 is set to the same value as outcode bit 55, so if the line goes from the middle to the corner, that part of the line goes clockwise around the correlation window, or counterclockwise. 0 out codes that can easily be determined to be towards are ordered counterclockwise around the correlation window ◇ SHIFT LEFT is defined as: 5HIF LEFT(oc) = oc' where: o'c'(1)=oc(2)oc' (2
)= oc(3) OC'(3) -oc(4) oc'(4)= oc(5) oc'(5)= oc(6) oc'(6)= oc(7) OC'(7 ) = 0C (8) oc” (8) −〇Register ■ is set to the result of the logical sum of register F and register G, and register J is set to the result of the logical sum of register F and register G.
is set to the result of the conjunction of .

Next, the following steps shown in the flowchart of FIG. 1 are executed. Step 1: Make the following determination.

The following conditions Contents of register F - o, o o o o o o o o o.

Contents of register G = oooooooo.

Contents of register I=oioiooo.

If any of the contents of register I -10101000 is true (T), the line is accepted to pass through the correlation window and step 2 is initiated. In other cases (F), step 3 is started.

Step 2: Set register H to 1 to indicate the hit of the line being processed, and retrieve the coordinates of the next line to be processed in the display list (the corresponding flag of sofa 3 is set). Return to step 1. Display list buffer 3
When 6 is used up, the process ends O Step 3: The following judgment is made: 0 The contents of register J = ooooooooo and the contents of register ■ = j
In the case of 111'1000 (condition A), step 5 is started. Contents of register J = o o o 'o o
o o o and contents of register I = 111110
00 (condition B), step 10 is started. If the contents of register J are \ooooooooo (condition C), step 4 is started.

Step 4: The line is rejected, register H remains set to 0, and the corresponding flag in display list buffer 36 is also set to 0. The coordinates of the next line to be processed are retrieved and the process returns to step 1. Processing ends when display list buffer 36 is exhausted.

Step 5: Compare x x and if Xl>X2, step 6 is started, otherwise step 7 is started.

Step 6: In this step, we swap the endpoints of the lines and make Xl smaller than X2. One routine that performs this function uses two working registers T, U located in RAM 35 to perform the following operations.

T = x1 Xl”X2 2-T T=yi yl=y2 2-T register be register F Register F - Register G Register G - Register U Step 7 is then initiated.

The routine consisting of steps 7.8 and 9 ensures that a line ending in region 2.9 or region 4.7 in opposite diagonal corners corresponds to the respective region of another diagonal corner of correlation window 1. Determine whether or not it intersects the line connecting the two corner points shared by .

Step 7: Compare yl and y2, and if yl<y2, start step 8; otherwise, start step 9.

Step 8: If the logical expression: %expression% ))) ))) is true (T), step 2 is initiated; otherwise (F), step 4 is initiated. However, LSID-
E and R8IDE are logical function names that will be explained later.

Step 9: If the logical expression: %expression% ))) ))) is true (T), step 2 is initiated; otherwise (F), step 4 is initiated.

(Going from the middle to the corner) Step 10. '11.12 and 13 have one endpoint in the intermediate region 3.5.6 or 8Vc, and in FIG. Determine whether a line with endpoints intersects a line connecting two corner points of the correlation window along a diagonal line passing between the two regions where the endpoints of the line are located.

Step 10: This step is the end point (x 1 , y'
1 ) and the end point ( and the result is 00oooooo
If equal to o, the end points of the line are swapped as done in step 6 above, the left shift of register F and the AND of register G are recomputed, and the result is stored in register K.
K is written.

Step 11: In this step, if either the value of the first bit or the fourth bit of register F is 1, y=yBI
Set C, and if neither of these bits is 1, set y-yT.

Step 12: In this step, if either the value of the first bit or the second bit of register F is 1, set x;

Step 13: If the logical expression: %expression%))) is true, go back to step 2; otherwise go back to step 4.

Next, the above-mentioned logical function will be explained.

Logical function LSIDE (Xp, yp, Xq, yq, Xr.

yr) is calculated by the following routine. Variables in parentheses represent formal arguments.

(xp-xr) (yq-yp)>(yp-yr
) (xq-xp), then LSIDE is true (1); otherwise, LSI'DE is false (0
).

Logical function R8I DE(Xp+ yp+ X'b yq
+ ”+Yr) is calculated by the following routine: ゛(xp-xr)(yq-yp)<(yp-yr)
(If xq-xp:1 holds true, R8IDE is true (
1), otherwise R8IDE is false (0).

The method described above can be performed by either hardware or software. In an interactive display system such as that shown in FIG.
The method is carried out under the control of a control program formed in 4. In other embodiments, the control program may reside on the disfoot and be loaded into portions of RAM 35 when necessary.

In a display control device, such as control device 31 of FIG. 3, a general purpose control program resident in ROM 34 controls cursor position on screen 50 in response to input from cursor control device 58 or keyboard 57.

Processor 2 executes the process of correlating lines and correlation windows under the control of a control program.

〔Effect of the invention〕

The method of the present invention requires less time to correlate a straight line in an interactive display system than conventional methods, thus reducing user waiting time.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the steps of a well-implemented method of the present invention; FIG. 2 is a diagram showing the display area being divided into nine regions containing correlation windows; FIG. 6 is an interactive FIG. 1 is a block diagram of a display system. 1...correlation window, 2-9...area, 10
．． 30... Screen, 31... Control device, Filter 2... Processor, 56... Bus, 34...
・ROM. 35...RAM, 36...Display list buffer, 37...Keyboard, 38...Cursor control device. Applicant International Business Machines
Corporation sub-agent Patent attorney Fumi Shinoda IGi F I 0.2 FIG, 3

Claims (1)

Claims: A method for correlating a straight line with a correlation window in an interactive display system, comprising: (a) defining a correlation window in a display area; and defining a correlation window in a display area; (b) determining which of the lines recorded as coordinates in the display list buffer can be accepted or rejected unambiguously by calculating the outline of the region in which the endpoints are located; (e) for each line not explicitly accepted or rejected, on which side of the line there are one or two selected corner points of the correlation window; A method for correlating straight lines in an interactive display system, comprising the steps of: determining whether ゛ traverses a correlation window;