JPH0719198B2 - Display control method in multi-window display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A display control method in a multi-window display device capable of displaying several partial screens on a display screen while allowing them to overlap each other. A screen control method that manages the entire window display screen as the sum of several partial rectangles is used to control the placement of windows and the priority of duplication in order to display line segments without missing dots. , If the line segment to be drawn is outside the partial rectangle, find the intersection of the boundary and the line segment of the rectangular area, then find the point 1 dot away from the boundary, and find the point 1 dot before that point. Displayed as dots,
When the line segment to be drawn falls within the partial rectangle, an intersection is obtained on a line one dot before the boundary of the rectangular area, a point on the boundary is then obtained, and the point is displayed as an intersection dot.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display control method in a multi-window display device capable of displaying several partial screens on a display screen while allowing them to overlap with each other. The present invention relates to a display control method that uses DDA to perform clipping without missing dots in a partial rectangular area in screen control that manages the entire screen as the sum of several partial rectangles.

[Prior Art] FIG. 15 is an explanatory view of a multi-window screen, and FIG. 16 is a conceptual diagram showing a state of area division on a memory for displaying the entire multi-window display screen as a sum of partial rectangular areas. .

When the entire screen of a display device such as a CRT is used as a display screen, the multi-window display device has a plurality of independent small display areas (windows) in the display screen as shown in FIG. It is a multi-window display as C. Here, if the multi-windows partially overlap,
It is necessary to control the display of which one is on top (the one above is displayed, but the one below is hidden and not displayed).

As such a display control method, as shown in FIG.
The displayable area (area not shaded by other partial screens) of the partial screen is divided into some partial rectangular areas (for example, B1 and B2) according to a certain rule, and the entire display screen is Some are managed as the sum of partial rectangular areas (Japanese Patent Laid-Open No. 59-102284).

Such a display control method has a feature that it is easy to set and change the partial screen, and these can be performed in pixel units.

[Problems to be Solved by the Invention] However, for example, in the case of displaying a line segment extending over two partial rectangular areas B1 and B2 in FIG. 16, a line segment outside the two partial rectangular areas is displayed on the screen. There was a problem that it was not displayed and there was a gap in the middle of the line segment, resulting in an unnatural display.

FIG. 17 is a display explanatory diagram showing a boundary portion between the partial rectangular areas B1 and B2 in FIG. 16 in an enlarged manner. When displaying a line segment l that spans two partial rectangular areas B1 and B2, the actual screen display is as shown in the figure, the x-axis coordinate closest to the line segment l and y.
Done on the intersection of the axis coordinates. Here, the rectangular areas B1 and B2 adjacent to each other are not separated by one boundary line, but are separated by each boundary line. For this reason, the intersection of the boundary line of the rectangular area B1 and the line segment l and the intersection point of the boundary line of the rectangular area B2 and the line segment l are x1 and x2, respectively, and the points of the part of x1 to x2 (marked with a circle). The indicated dot) is not displayed, and a gap is created in the middle of the line segment. In addition,
In each rectangular area B1, B2, display the line segment in each area,
A process (clipping) of giving points on the X and Y coordinates to be excluded outside the region is performed.

The present invention has been made in view of the above circumstances, and provides a display control method in a multi-window display device capable of displaying a line segment without a dot drop between boundaries of respective rectangular areas. The purpose is to

[Means for Solving Problems] FIG. 1 is a flowchart showing the principle of the present invention. The present invention is a multi-window display device capable of overlappingly setting a plurality of windows on a display screen. In order to control the arrangement of windows and the priority order of overlapping, the entire window display screen is divided into several partial rectangles. When the line segment to be drawn goes out of the partial rectangle using the screen control method of managing as a sum, the intersection of the boundary line of the rectangular region and the line segment is obtained (step). Next, a point 1 dot away from the boundary line is obtained, and a point 1 dot before the point is obtained and displayed as an intersection dot (step). Also,
When the line segment to be drawn falls within the partial rectangle, an intersection is obtained in a line one dot before the boundary of the rectangular area (step). Next, a point on the boundary line is obtained and the point is displayed as an intersection dot (step).

[Operation] For the line segment from the intersection on one partial rectangular area to the intersection on the other partial rectangular area, a new intersection is obtained by the method of the present invention using the DDA algorithm, and the point is displayed. Therefore, there is no dot dropout at the boundary of the partial rectangular area.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a conceptual diagram of the display control method of the present invention. In the figure, B1 and B2 are partial rectangular areas on the display screen. l ₁ is a line segment drawn out from the partial rectangular area B1 as shown by an arrow (a), and l ₂ is a line segment drawn so as to enter the partial rectangular area B1 as shown by an arrow (b).

In the case of the line segment l ₁ , first, the boundary line of the partial rectangular area B1 and the line segment l ₁
After obtaining the intersection point P1 of P1, the point P2 that is one dot away from the boundary line is obtained, and the point P3 that is one dot before the point P2 is the intersection point to be obtained.

Further, in the case of the line segment l ₂ , after obtaining the intersection point Q1 in the line one dot before the boundary of the partial rectangular area B2, the point Q2 on the boundary line is obtained, and that point is set as the intersection point to be obtained. As a result, it is possible to display the dots on the boundary line of the partial rectangular area B2 that have been missing until now. Here, the points P3 and Q2 obtained on the above-mentioned boundary line are known
It uses the DDA algorithm, and its schematic concept is shown in FIG.

This DDA algorithm is a line segment drawing algorithm, and when drawing the line segment l in the figure, the x coordinate of the starting point x =
When the x coordinate is increased by 1 from x1, whether the y coordinate is equal to the current y coordinate or is increased by 1 is sequentially performed from the start point to the end point according to the y-axis direction distance from the line segment l. While making the determination, the display point on the intersection point is obtained as indicated by a dot. By using such a DDA algorithm to obtain dots on the boundary line of a partial rectangular area, it is possible to display a continuous line segment between the partial rectangular areas.

FIG. 4 is a conceptual diagram of the configuration of an apparatus that realizes the display control method of the present invention. In the figure, 1 is a display such as a CRT, 2 is a frame memory that stores image data to be displayed on the display 1, and 3 is a display control unit.
By using a DDA to draw a line segment in each of the divided partial rectangular areas (windows) and perform clipping processing to eliminate the outside of the applicable area, and dots on the boundary line of each partial rectangular area. It has a correction means 32 for obtaining. Reference numeral 4 is a memory for storing display data, and vector data for line segment approximation is stored therein. 5 is a main control unit,
The memory 4, the display controller 3, and the frame memory 2 are coupled to each other via a data bus BS. This main control unit 5
Uses a CPU that operates according to a program, multi-window control for display 1,
Coordinate conversion for converting the data in the memory 4 into the coordinate values on the display 1 is performed.

The operation of the apparatus thus configured will be described below.

FIG. 5 is a flowchart showing the outline of the entire operation. First, the main control unit 5 reads the data of the line segment to be drawn (all the figures to be drawn on the display 1 are stored as the information of the line segment) from the memory 4, and this line segment is outside the partial rectangle. It is determined whether or not it is within the partial rectangle (steps 1 and 2). By this determination, it is determined whether or not the line segment to be drawn is to be clipped.

FIG. 6 is a diagram showing the relationship between the line segment l to be drawn and the partial rectangular area B. Here, as shown in (a), the line segment 1 is not a target of clipping because the line segment l is a partial rectangular area B.
The case where the line segment 1 is on the outer side is the case where the line segment 1 is on the inner side of the partial rectangular area B as shown in FIG. In these cases, the process branches from step 1 to step 11 or from step 2 to step 21, respectively, and the process is performed without the drawing region or the process of drawing the entire line segment is performed. In cases other than the above, clipping is performed and clipping processing is performed (step 3). Here, as a case to be the object of clipping, as shown in (c), when both the start point and the end point of the line segment l are outside the partial rectangular area B,
As shown in (d), the starting point is in the partial rectangular area B,
When the end point is outside, as shown in (e), there are three cases where the start point is outside the partial rectangular area B and the end point is inside.

Of these, in the case of (c), the clipping of the start point and the clipping of the end point are necessary, and in the case of (d),
The end point needs to be clipped, and in the case of (e), the start point needs to be clipped. The clipping of the starting point is
In FIG. 2, the line segment l ₁ is drawn in the direction of arrow a, and the clipping of the end point is the case where the line segment l ₂ is drawn in the direction of arrow b in FIG.

FIG. 7 is a flowchart showing the flow of clipping processing. The clipping process consists of start point clipping and end point clipping, and a schematic flow of each clipping is shown in FIGS. 8 and 9.

Here, the starting point clipping is the intersection of the line segment l ₁ shown in FIG. 10 and the virtual area boundary BO that is 1 dot wider than the partial rectangular boundary.
O1 is obtained (step 31), and then the determination is continued by the DDA algorithm (step 32), and the point O2 on the actual partial rectangular area boundary B1 is adopted as the intersection (step 3).
3,34).

In the end point clipping, after obtaining the intersection O1 of the line segment l ₂ shown in FIG. 11 and the partial rectangular area boundary B1 (step 35), the point is placed on the virtual area boundary BO which is one dot wider than the partial rectangular area. The determination is continued by the DDA algorithm until then (steps 36 and 37), and the point O2 immediately before riding is adopted as the intersection (step 38).

A line segment extending from the starting point to the ending point is drawn with respect to the starting point and the ending point thus obtained (FIG. 5, step 4).

With the above-described operation, it becomes possible to interpolate the dot omission on the multi-window boundary.

FIG. 12 is a flow chart showing the details of the start point clip shown in FIG. 8, and FIG. 13 is a flow chart showing the details of the end point clip shown in FIG.

In these flow charts, dinit at intersection X, Y
, Which assumes the Bresenham DDA algorithm, and the value of d may be calculated sequentially from d1 according to the algorithm, but it is calculated by calculation because it takes time. d is defined by the equation (1).

d = dx (S−t) (1) Here, s and t are distances (1) in the y-axis direction as shown in FIG.
(Smaller than dot).

From the equation (1), d = dx (S−t) = dx {S− (1−S)} = dx (2S−1) (2) where s is S = y ₀ + from FIG. (Dy / dx) (x−x ₀ ) −Y (3)

By substituting the equation (3) into the equation (2), the equation (4) is obtained, which is the value of d at the point (X, Y).

_{d = dx [2 {y 0} + (dy / dx) (x-x 0) -Y} -1] = 2 {dy (x-x 0) + dx (y 0 -Y)} -d × ... (4 [Effects of the Invention] As described above in detail, according to the present invention, a new intersection is obtained from the intersection at the boundary of the partial rectangular area by using the DDA algorithm, and the intersection is drawn as a part of the line segment. By doing so, it is possible to provide a display control method capable of displaying a line segment having no missing dots between the boundaries of the respective partial rectangular areas.

[Brief description of drawings]

FIG. 1 is a flow chart showing the principle of the present invention, FIG. 2 is a conceptual diagram of a display control method of the present invention, FIG. 3 is a schematic explanatory diagram of a DDA algorithm, and FIG. 4 is a display control method of the present invention. FIG. 5 is a conceptual diagram of the configuration of the apparatus, FIG. 5 is a flowchart showing the outline of the overall operation, FIG. 6 is a diagram showing the relationship between the line segment to be drawn and the partial rectangular area, and FIG. 7 is a flowchart showing the flow of clipping processing. 8 and 9 are flowcharts showing the outline of the start point and end point clipping, FIG. 10 is an explanatory view of the start point clipping, FIG. 11 is an explanatory view of the end point clipping, and FIGS. 12 and 13 are the start point and end point clipping. Fig. 14 is an explanatory diagram for obtaining the value of d in the DDA algorithm, Fig. 15 is an explanatory diagram of multi-window, and Fig. 16 is a schematic diagram showing how areas are divided on the memory. Fig, 17 Fig. Is a display diagram showing an enlarged boundary of the partial rectangular region B1, B2 in FIG. 16. In FIG. 4, 1 is a display, 2 is a frame memory, 3 is a display controller, 4 is a memory, 5 is a main controller, 31 is clipping means, and 32 is correction means.

Claims (1)

[Claims] 1. In a multi-window display device capable of overlappingly setting a plurality of windows on a display screen, several partial rectangles are formed on the entire window display screen to control the arrangement of windows and the priority of overlapping. When the line segment to be drawn goes out of the partial rectangle using the screen control method that manages it as the sum of the two, the intersection point of the rectangle area and the line segment is obtained (step), and then the point 1 dot away from the border line Then, the point one dot before that point is calculated and displayed as an intersection dot (step), and if the line segment to be drawn falls within the partial rectangle, the intersection point is calculated on the line one dot before the boundary of the rectangular area (step). ), Next, a point on the boundary line is found and the point is displayed as an intersection dot (step) Display on a multi-window display device characterized by the following: Control method.