Display control method for multi-window system

Abstract: In a multi-window system for setting a plurality of win­ dows (W₁, W₂, W₃, W₄) on the screen for independent display in each window, a novel display control method is disclosed in which a visible region of a given window is determined from the positions and overlapped relations between the windows on the display screen (30), and display data is selectively applied to the visible region. The visible region is checked for crossing between an object window and another window making up a reference window on the screen, and if they cross each other, the object window is divided into subregions, while the subre­ gion not overlapped with the reference window is regarded as a new object region, which is collated with another reference window and subdivided. This process of collation and division is repeated. A display output is thus applied sequentially to the subregions which are found to be a visible region.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a method of controlling a display screen of a terminal unit of a data processing system, or more in particular, to a display control method for a multi-window system in which a plurality of rectangular display regions called windows are set in a display screen for independent data display in each window. DESCRIPTION OF THE PRIOR ART In a data processing terminal having a display unit, a retangular region called a "window" is set on the display screen, and data representing such as a document and read-out from a data file unit is displayed in this window. By key input operation while referring to this window another document is displayed in another region on the display screen. In what is called a multi-window system with a plurality of windows set on a single display screen, the windows are set in partially overlapped relationship with each other. By shifting the window display position or changing the order in preference of display, the display in a given window which has been initially hidden in part behind another window can be made wholely visible. In the multi-window system, the respective windows set on the display screen correspond to logical or virtual display screens set on a memory which is referred to by a data processing system. Data stored in a part of this virtual screen is extracted, and developed as a bit map in a predetermined region on a frame memory corresponding to an actual display screen so as to be read-out as the contents to be displayed in the window. Data representing the position and size of each window on the actual screen and the correspondence between the window and an extraction region on the virtual screen are registered in a specific area alloted to that window on a window control table, so that the operator can, by inputting a screen operation command into the data processing system, change and control the contents of the display in any desired window on the display screen by reference to the window control table. Assume, for example, that the operator designates a specific one window by cursor and gives a command to shift this window to another position on the screen designated by cursor. On the window control table, the positional data of the particular window is rewritten and the contents of the frame memory are changed, thereby shifting the window position on the display screen. When a window is specified and a command to change the size thereof is given, on the other hand, the window size data on the window control table is rewritten, and the contents of the frame memory are changed so that a window of a different size appears on the display screen. Further, if a command is given to scroll the contents of display in a window, the position of a partial region on the virtual screen from which the data to be displayed is extracted is shifted so that an image corresponding to the shifted region is displayed in the window. In a conventional multi-window system disclosed in US-A- 4 785 296, the position of a window is changed in such a manner that after the original window is cancelled from the screen, data is again extracted from a partial region on the virtual memory corresponding to the new window, and developed as a bit map at the new window position on the frame memory. In changing the window size, too, data is extracted from a partial region on the virtual memory corresponding to a new window size and developed as a bit map on the frame memory. This is also the case with the scrolling process, in which all the data required for display after scrolling are extracted from the virtual screen and developed as a bit map on the frame memory. The process of developing display data into a bit map such as converting data stored in the form of character code on the virtual screen into the form of character font, however, takes considerable time, and therefore a conventional method in which all the contents to be newly displayed must be developed into a bit map has a problem that it cannot rapidly replace the contents on the display screen. In a multi-window system where a plurality of windows are set in a partially overlapped relationship with each other on the display screen, on the other hand, the data for a window lower in display order extracted from the virtual screen and supplied to the frame memory must exclude those data corresponding to the invisible part thereof overlapped with another window higher in display order. For the purpose of such partial display or non-display in each window as mentioned above, Japanese Patent Publication JP-A-59-102284 (1984) discloses a control system in which each window is divided into a plurality of rectangular subregions along the sides of other windows overlapped therewith as dividing lines, the data representing the position and size of each subregion together with the data discriminating each subregion "visual" (displayable) or "non-visual" (non-displayable) are stored in a visible region control table, and display data are applied only to the displayable subregions. In the conventional multi-window systems, the above-mentioned data set on the display screen for visible and non-visible subregions on each of all the windows are always registered in the visible region control table, and in the case of a change in the display order or positional relationship of the windows or addition of another window on the screen, the data in the visible region control table are updated in accordance with the new arrangement in display of the display screen, thus making it possible to change the display of any selected window immediately by referring to the control table. With the complication of superimposition of windows on the display screen, however, windows are much divided into smaller subregions, resulting in that the conventional methods in which the data for visible subregions of all the windows must be always stored require a large memory capacity of the visible region control table, as well as a problem of an increased processing time for updating the data of the table. WO-A-8 401 655 discloses a display control method, wherein the entire bit map of a window (layer) includes visible areas and obsured areas and the bit map (display area) of the obscured areas is stored in a memory. Further, the display data of the visible area, which is preliminarily stored in the bit map memory, is transferred to a second bit map memory. This document gives no considerations as to how the positions and the sizes of the obscured or visible portions of an objection layer (window) are to be determined. EP-A-0 147 542 discloses a display control system comprising a first memory means for storing display data, a second memory means for storing display data of virtual screens and a third memory means for storing window definition data. SUMMARY OF THE INVENTION An object of the present invention is to provide a display control method for a multi-window system which allows to use a reduced memory capacity for the control data necessary for discriminating visible and non-visible regions in each of the windows set on the display screen. Another object of the present invention is to provide a display control method for a multi-window system in which the display arrangement of the display screen can be changed at high speed. In order to achieve the above-mentioned objects, there is provided according to the present invention a display control method in which the visible region of an object window of which the content of display are required to be changed, is calculated on the basis of current relative positions of the windows on the display screen, and display data is applied to the visible region thus determined. For calculation of the visible region, the object window is collated with other windows (reference windows) sequentially, and if the object window is overlapped with one of the reference windows, it is divided into a plurality of rectangular subregions, of which those subregions which are not overlapped with the one reference window are selected as new rectangular regions to be divided, and each of the new regions is collated with other reference windows, sequentially, and repeating such sequential subdivision of the rectangular regions. Specifically, the present invention provides a display control method for a multi-window system comprising a display screen in which a plurality of rectangular windows are set, first memory means for storing display data correspondingly to positions to be displayed on the display screen, second memory means for storing a plurality of display data for virtual screens corresponding to the windows, respectively, each window displaying data contained in a partial region of the corresponding virtual screen, third memory means for storing definition data representing the correspondency between position data of each window on the display screen and the virtual screen, and control means for rewriting a part of the display data stored in the first memory means, the display control method comprising the first step of collating an object window designated as an object of display control with a plurality of other windows selected sequentially as reference windows on the display screen, on the basis of the positional data stored in the third memory means, and if the object window crosses one of the reference windows, dividing the object window into subregions overlapped with the reference window and at least one rectangular non-overlapped subregion along the boundaries with the overlapped subregions as dividing lines; the second step of collating the non-overlapped subregion thus obtained as a dividing object rectangle region with another reference window and if the object rectangle region crosses the reference window, dividing the object rectangle region into subregions overlapped with the another reference window and at least one rectangular non-overlapped subregion, and repeatedly applying the collation and the division into subregions to a newly obtained non-overlapped subregion, as a new dividing object rectangular region, until no reference window to be collated with remains, and the third step of rewriting a part of the display data in the first memory means in accordance with the result of division of the object rectangular region, thereby changing the contents of display in the visible region included in the object window on the display screen. In the display control method according to the present invention in which a visible region in a window is calculated as required, the capacity of memory area in the visible region control table is greatly reduced as compared with the conventional system. Assume that a window on the display screen is designated, and an operator takes care of data input and output with respect to this window. The definition data for the visible region determined by sequential division of a rectangular region is stored in the visible region control table and utilized for subsequent display control. When the control object is changed from one to another window, this definition data is kept stored if the visible region control table has a sufficient storage capacity. If no area remains for storing new definition data for a visible region determined for another window, however, the old definition data is delated and the delated definition data will be again calculated when required. In the present invention, the definition data for a visible region are not always stored in the control table, but may be used provisionally for the purpose of change of the display order or deletion of a given window. The foregoing and other objects, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the configuration of a multi-window system embodying the present invention. Fig. 2 is a diagram for explaining the relationship between a window set on the display screen and a partial region of the virtual screen displayed on the window. Fig. 3 is a diagram for explaining the visible region in a window overlapped with another window. Figs. 4A and 4B are diagrams for explaining a method of sequential division of the display region for calculating the visible region according to the present invention. Fig. 5A shows a configuration of a window control table. Fig. 5B shows a configuration of a visible region control table. Fig. 5C shows a detailed view of data blocks of the visible region control table. Fig. 6 is a program flowchart for executing the sequential division of a display region. Fig. 7 is a flowchart showing an embodiment of a subroutine constructing the program of Fig. 6. Figs. 8A and 8B are diagrams for explaining the display screen from which a window is deleted according to a second embodiment of the present invention. Fig. 9 is a flowchart of a program for realizing the second embodiment. Figs. 10A and 10B are diagrams for explaining the display screen in which the order in display of window is changed according to a third embodiment of the present invention. Fig. 11 is a flowchart of a program for realizing the third embodiment of the present invention. Figs. 12A and 12B are diagrams for explaining the display screen in which the size of a window is changed according to a fourth embodiment of the present invention. Fig. 13 is a flowchart for a program for realizing the fourth embodiment. Fig. 14 is a diagram for explaining the display screen in which the position of a window is shifted according to a fifth embodiment of the present invention. Fig. 15 is a flowchart of a program for realizing the fifth embodiment. Fig. 16 is a diagram for explaining the display screen of which the display is scrolled according to a sixth embodiment of the present invention. Fig. 17 is a diagram for explaining a virtual screen used in the sixth embodiment. Fig. 18 is a diagram for explaining a redisplay region for data on the display screen according to the sixth embodiment. Fig. 19 is a flowchart of a program for realizing the sixth embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a block diagram showing a general configuration of terminal device for a multi-window system according to the present invention. In Fig. 1, reference numeral 11 designates a data processing unit (CPU) for controlling the general operation of the terminal device, numeral 12 a memory for storing a program executed by the CPU, numeral 13 a work memory for temporarily storing the data generated in the process of execution of the program, numeral 14 a memory for storing the table data for window control, numeral 15 a memory for storing the table data for controlling the visible subregion in a window, numeral 16 an auxiliary memory for storing file data such as document data, and numeral 17 a memory for storing the data of a virtual screen corresponding to each window, which are read out of the auxiliary memory 16. Numeral 18 designates a character font memory for storing a character font corresponding to a character code, numeral 19 a keyboard for entering the data and various commands, numeral 20 a bit map processor (BMP) for developing the display data as a bit map on a bit map memory 22 (frame memory), numeral 21 a memory for storing various commands for operating the BMP 20 and numeral 23 a CRT controller for reading the contents of the frame memory 22 sequentially and applying the same to CRT 30. Fig. 2 shows the relationship between a virtual screen 60 provided in the memory 17 and a window 31 set on a display screen (actual screen) 30. In this example, the position and size of the window is expressed by the X-Y coordinate (X₁, Y₁) of the starting point (upper left corner) and the X-Y coordinate (X₁′, Y₁′) of ending point (lower right corner) of the window rectangle. The values of X and Y coordinates increase in downward and rightward directions, respectively. The virtual screen 60 has the same size as the actual screen 30, and the data positioned in a region S occupying a part thereof is displayed on the window 31. The virtual screen 60, however, may be larger than the actual screen 30. The position and size of the partial region S, like the window 31, is expressed by the X-Y coordinate (x₁, y₁) and (x₁′, y₁′) of the starting and ending points respectively. The correspondency between the window 31 and the partial region S is stored in the window control table 140 described later with reference to Fig. 5A. Fig. 3 shows a display screen of a multi-window system in which a plurality of windows W₁, W₂, W₃, W₄ are displayed overlapped on the display screen 30. In the illustrated positional relationship, the display order of the window W₁ is highest, the display order of the window W₄ is lowest and the display order of the window W₂ is lower than that of the window W₁ but higher than that of the window W₃. Assume that the order in display of the windows is determined such that the window W₃ is positioned under the windows W₁ and W₂, and only a part thereof including subregions w₃₁, w₃₂ and w₃₃ are visible as shown in Fig. 3. According to the present invention, these visible subregions w₃₁ to w₃₃ in the window w₃ are determined for display control in the manner mentioned below. First, the object window w₃ to be checked for division is collated with the window W₁ (reference window) having the highest display order to see whether these two windows cross each other. In the case where the coordinates of the starting and ending points of the object window W₃ are given as (X₃, Y₃), (X₃′, Y₃′) and those of the reference window W₁ as (X₁, Y₁), (X₁′, Y₁′) respectively, the following relationship holds if the windows W₁ and W₃ cross and are overlapped with each other. (X₃ < X₁′) and (Y₃ < Y₁′), and (X₁ < X₃′) and (Y₁ < Y₃′) In the case where there is any overlapped portion, the window W₃ is divided into a plurality of subregions by a dividing line along any of the upper, lower, left and right sides of the window W₁ located within the window W₃. In an example shown in Fig. 4A, the window W₃ is divided into two parts by the lower side (coordinate Y₁′) of the window W₁, and the upper part is further halved by the right side (coordinate X₁′) of the window W₁, thus obtaining three subregions a , b and c . Of these subregions, the subregion a is completely covered by the window W₁ and therefore becomes an invisible region, while the subregions b and c remain as visible regions (if the window W₂ is cancelled). According to the present invention, the subregions b and c which have remained as invisible regions (non-overlapped regions) are taken as object subregions, and checked with respect to the window W₂ having the second highest display order within the windows whose display orders are higher than the window W₃ as a reference window by repeating a similar dividing process to that applied to the window 3 by using the window W₁ as a reference window. As a result, as shown in Fig. 4B, the subregion b is further divided into b₁ and b₂, and the subregion c into c₁, c₂ and c₃, so that the three subregions b₁, c₁ and c₂ except for b₂ and c₂, which are completely covered by the window w₂, remain as visible subregions. If there is any other window having higher display order than the window W₃, the subregions b₁, c₁ and c₃ are further checked with respect to the windows W₃ and divided into visible and non-visible subregions. In the case under consideration, the subregions b₁, c₁ and c₃ make up the final visible subregions corresponding to the visible subregions w₃₁, w₃₂ and w₃₃ respectively in Fig. 3. Fig. 5A shows a construction of the window control table 140 formed in the memory 14. Such window control tables 140 are prepared in correspondence with the windows W₁ to W₄ set on the display screen respectively. Each table includes a display order 141 of that window, assuming that each window is identified by its display order, an identification number 142 of the virtual screen corresponding to the window, a pointer 143 for the visible region table described below, the number 144 of visible subregions, X-Y coordinate 145 of the starting point of the window, the X-Y coordinate 146 of the ending point of the window, the X-Y coordinate of the starting point of a partial region extracted from the virtual screen, and the X-Y coordinate 148 of the ending point of the same partial region. Fig. 5B shows the construcution of a visible region table 150 formed on the memory 15, This table includes a number N of blocks 152-1 to 152-N and an area 151 indicating the occupied blocks in the table. The above-mentioned pointer 143 points to the leading position P of continued m blocks whose number m is stored in the area 144 in Fig. 5A. Each block, as shown in Fig. 5C, includes the X-Y coordinates 153 and 154 of the starting and ending points respectively of a visible subregion on the display screen and the X-Y coordinates 155 and 156 of the starting and ending points of the subregion on the virtual screen corresponding to the visible subregion. In the conventional multi-window systems, the visible region table 150 is provided with a sufficient number of blocks to store all the definition data of the visible subregions of each window even in the case where an allowable maximum number of windows are set on the display screen. According to the present invention, in comparison, the number N of the blocks of the visible region table 150 is greatly reduced. Once visible subregions are determined by the steps mentioned in Figs. 4A and 4B for display control, the definition data for these visible subregions are registered in the table 150. In the case where the table 150 already has much definition data registered therewith and has no sufficient remaining blocks for registering all the definition data of the newly-calculated visible subregions, a part or whole of the already-registered data is deleted, and definition data of the new visible subregions are registered in its place. At the same time, the pointer 143 and the number 144 are cleared from the control table 140 for the window corresponding to the visible subregions deleted from the table 150. As to the window for which the pointer 143 is cleared, its visible subregion will be determined by the sequential region-dividing process as mentioned-above on the basis of positional relationship with other windows, when it is required to again take up that window as an object window to be subjected to display control and then registered with the table 150 followed by the updating of the frame memory 22 with reference to this table 150. As to a window which is not an object to be subjected to display control, on the other hand, the contents of the corresponding region on the frame memory remain unchanged, and therefore the absence of the definition data of the visible subregions in the table 150 poses no problem. Assume that a window W₀ on the display screen is designated as an object window, and the display for this window is to be changed. If the pointer 143 is recorded on the window control table 140, the visible region table 150 is referred to according to this pointer, and on the basis of the definition data of the visible subregion registered therein, the frame memory 22 is partially rewritten. If the pointer 143 fails to point to the table 150, by contrast, the program shown in the flowchart of Fig. 6 is executed in such a manner that step 201 thereof set the initial value "0" at the first parameter designating the reference window generally represented by the display order thereof, step 202 sets a second parameter as the display order of the object window W₀, step 203 sets the values of the X-Y coordinates 145, 146 of the window W₀ as third parameters defining the object rectangle, and step 204 calls the subroutine (SUB1) for calculating the visible region with these parameters as arguments. In the subroutine SUB1, as shown in Fig. 7, step 210 sets the value of the first parameter to parameter RW, the second parameter to parameter OW, and the third parameter to the coordinate data of the object rectangle which may be an object window or subregion. Step 212 increments the value of RW by one, and step 214 compares the value of RW with OW. If RW is smaller than OW, that is, if the display order of the reference window is higher than that of the object rectangle window, the process proceeds to step 218 to decide whether the reference window crosses the object rectangle. Assume that the coordinates of the starting and ending points of the object rectangle are given as (X01, X02), (X02, Y02), and those of the reference window as (XR1, YR1), (XR2, YR2), then if the relations hold that (X01 < XR2) and (Y01 < YR2), and (XR1 < X02) and (YR1 < Y02) the object rectangle crosses the reference window. In this case, process is passed to step 220, and the object rectangle is subdivided into a plurality of subregions in the manner mentioned with reference to Figs. 4A and 4B. If the object rectangle does not cross the reference window, on the other hand, the process is returned to the step 212 where the reference window is replaced by the one having the next higher display order followed by the checking whether it crosses the object rectangle. If RW is found equal to OW at step 214, it is decided that there is no other window overlapped with the object rectangle, and step 216 registers the definition data of the whole rectangle as a display region in the visible region table 150, followed by the returning to the original program. When the step for dividing into subregions ends at step 220, step 222 checks whether they include any visible subregion. If they include any one, step 224 checks to see whether the reference window just used is located immediately above the object rectangle. If so, the visible subregion currently determined is considered to be true, and step 226 registers the visible subregion in the visible region table 150. In the event that the reference window is not located immediately above the object rectangle, on the other hand, any visible subregion currently determined is required to be checked to see whether it crosses another window of higher display order. Such uncertain visible subregions are stored in a work table provided to the memory 13 at step 230, and they are selected, sequentially one by one, as an object rectangle to be subjected to collation with the remaining reference windows as mentioned below. First, step 232 sets the initial value "1" at the parameter k which designates one subregion to be taken up from the work table, and sets the number of the subregions at the parameter n . Step 234 sets the present value of at the first parameter by which the reference window is designated, followed by step 236 where the definition data of the k-th subregion on the work table is set at the third parameter. The second parameter set by step 202 is used as it is. With these first to third parameters as arguments, the subroutine SUB1 is called. As a result, the k-th subregion on the work table is collated with the (RW + 1)th and subsequent windows, sequestially. After step 238, step 240 increases the value of the parameter k by one, and steps 236 to 249 are repeated until the value k exceeds n . When the subroutine SUB1 is executed repeatedly in this way, the subregion estimated as a display region in view of the positional relationship with the reference window of the highest display order is sequentially divided into smaller subregions on the basis of its positional relationship with other reference windows having higher display order than the object window, so that the definition data of finally determined visible subregion is registered in the visible region table 150. Figs. 8A to 10 show a second embodiment of the present invention. In this embodiment, four windows W₁, W₂, W₃ and W₄ are initially overlapped on the display screen 30 as shown in Fig. 8A. If the second window W₂ is deleted from the screen, the display of the part that has initially been an non-visible region overlapped by the window W₂ must be restored. In this case, according to the invention, the window W₂ to be deleted is used as an object rectangle, and the sequential collation process with other windows (reference windows) is applied to the window W₂ so as to sequentially divide it into subregions. If a reference window is higher in display order than the object window (rectangle), any subregion thus obtained which is not overlapped with the reference window is stored in the work table, and used as the next object rectangle, which is sequentially divided in the same manner as in the first embodiment. In this second embodiment, all the windows having lower display order than the object window are also used as reference windows. Display is restored in succession in the subregions which are initially overlapped completely with the reference windows of lower display order. Any subregion which is not overlapped with any of the reference windows of lower display order is deleted from the screen, and a blank is left there without any display. According to this control method, the second window W₂ in Fig. 8A is subdivided into a, b₁, b₂, c₁, c₂, c₃₋₁, and c₃₋₂, as shown in Fig. 8B, and the contents of the window W₃ are displayed in the subregions b₂ and c₂, and those of the window W₄ in the subregions c₁ and c₃₋₁. The subregions b₁ and c₃₋₂ that are not overlapped with any other windows are cleared. Fig. 9 shows a flowchart for the subroutine SUB2 for realizing the second embodiment mentioned above. This subroutine has the number of windows on the display screen as the fourth parameter in addition to the first to third parameters described above, and is called with these parameters as arguments. At the first step 310, the values of the above-mentioned arguments are set at the respective parameters in the subroutine, followed by step 312 for incrementing the value of display order RW by +1 by which the reference window to be used is designated. Step 314 compares the value RW with the number MAX of the windows. If RW does not exceed MAX, step 318 decides whether the object rectangle crosses the RW-th reference window, and if not, the process is returned to step 312. The decision on the crossing is made in the same manner as in step 218 of SUB1. If RW is found larger than MAX at step 314, by contrast, it means that the object rectangle does not cross any window, and therefore step 316 clears the contents of display of the object region on the display screen, thus terminating this subroutine. If step 318 decides that the object rectangle crosses the reference window, step 320 divides the object rectangle into a plurality of subregions. Step 322 compares the display order RW of the reference window with the display order OW of the object window, and if RW is found equal to or lower than OW, then the contents of the reference window are displayed in the subregion overlapped with the reference window (step 324). If RW is higher, on the other hand, there is no need to display. In the case where the subregions currently divided include a subregion not overlapped with the reference window, the process is passed to step 328, while if there is no subregion not overlapped with the reference window, the subroutine is ended. If step 328 finds that the display order RW of the reference window is equal to MAX as a result of comparison, step 329 clears these non-overlapped subregions on the display screen, thus ending this subroutine. If RW is not equal to MAX, by contrast, these non-overlapped subregions are required to be collated with other windows. Step 330 thus stores these subregions in the work table, followed by execution of steps 332 to 342. Steps 332 to 342 are the same as steps 232 to 242 in Fig. 7 except that the subroutine called at step 338 is SUB2. A third embodiment of the present invention is shown in Figs. 10A to 11. Assume that three windows W₁, W₂ and W₃ are initially displayed on the display screen as shown in Fig. 10A, and the display order of the window W₁ is to be changed from the lowest one as shown in Fig. 10A to a higher one as shown in Fig. 10B. The data of the window W₁ is required to be displayed in the subregions w₁₁ and w₁₂ that have so far been hidden behind the windows w₂ and w₃. Even in the case of change in display order such as this example, the processes for collation and division are performed by taking the window W₁ as an object rectangle and the windows W₂ and W₃ as reference windows, thereby to calculate the subregions w₁₁ and w₁₂ and change the display in these subregions. Fig. 11 shows a flowchart of subroutine SUB3 for changing the display order mentioned above. In this subroutine, the initial value "0" is set at a first parameter indicating a reference window, and the new display order of the object window is called as a second parameter, the coordinate data of the object window or object rectangle as a third parameter, and the original display order of the object window as a fourth parameter. The first step 410 of the subroutine SUB3 sets the value of the first parameter to the display order RW of the reference window, the second parameter to the display order OW of the object rectangle, the third parameter to the coordinate value of the rectangle to be divided, and the fourth parameter to the last reference value MAX. Step 412 increments the value RW by 1, and step 418 checks whether the object rectangle crosses the RW-th window (reference window) until RW exceeds MAX. When the value RW exceeds MAX, this subroutine ends. If the object rectangle crosses the reference window, step 420 divides the object rectangle into a plurality of subregions. Step 422 compares RW with OW, and if the former is larger (that is, lower in display order), the contents of the subregion overlapped with the reference window are replaced by the contents of the object window at step 424. Step 426 decides whether the subregions currently obtained include subregions not overlapped with the reference window, and if there is no non-overlapped region, this routine ends. If there is any non-overlapped region, by contrast, step 428 compares the display order RW of the reference window with MAX, and if they are equal to each other, this routine is ended. If RW is not equal to MAX, the process proceeds to step 430. Step 430 stores the subregions not overlapped with the reference window in the work table. Steps 432 to 442 divide these subregions based on positional relationship with the other window in the same manner as in the first and second embodiments. In the case of Fig. 11, the display order of the object window is changed higher. If the display order is to be changed lower, the second parameter is used as the original display order of the object window, and the fourth parameter as a new display order of the object window. In this case, step 424 in Fig. 11 is adapted to display the contents of the reference window in the overlapped subregions. A fourth embodiment of the present invention is shown in Figs. 12A to 13. In this embodiment, as in Fig. 12A, for example, the second window W₂ among the three windows W₁, W₂ and W₃ displayed in overlapped relations is used as an object window, whereby the partial region a on the lower side thereof is deleted, while the right side is expanded by the region b . In such a screen size change as this, according to the invention, the size data before and after the change of the object window are compared as shown in Fig. 13, thereby determining by calculation the deleted partial region a and the expanded partial region b (Step 510). As to the partial region b to be expanded, on the other hand, it is regarded as an object rectangle and sequentially divided into subregions in the manner shown with reference to the first embodiment, with the result that the display change is made by developing a bit map only for the visible subregions thereof (Step 520). Also, as for the region a to be deleted, it is regarded as an object rectangle, and sequentially divided in the manner shown in the second embodiment, whereby a partial screen is restored for the windows of lower display order (Step 530). As a result, as shown in Fig. 12B, the contents of the windows W₂ and W₃ are additionally displayed in the visible subregions w₁₂ and w₁₃ respectively. Now, a fifth embodiment of the invention will be described below. Fig. 14 shows the manner in which the window W₃ that has so far been located under the window W₁ among the three windows W₁, W₂ and W₃ displayed on the display screen is relocated to the position of W₃′ indicated by one-dot chain. In the window W₃′ after relocation, w₃₃′ indicates the parts hidden behind the window W₂ and w₃₁′ the part that has so far been hidden behind the window W₁. According to the present invention, the display control with this window shift is effected by the steps shown in Fig. 15. First, step 610 checks whether the window W₃′ after relocation (shift) as an object rectangle crosses another window, and if it does, determines a visible subregion R′ (= Subregion a′ + Subregion b′). After that, step 620 determines the subregion R (= Subregion a + Subregion b ) within the window (W₃) after relocation corresponding to the visible subregion R′. Step 630 checks whether the subregion R as an object rectangle crosses any other windows, and if so, determines the overlapped region w₃₁ and the redisplay region r (hatched region). Step 640 determines the region r′ after relocation corresponding to the redisplay region r . Step 650 relocates the image data of the region r to the region r′ on the frame memory. Step 660 determines the subregion w₃₁′ in the window W₃′ corresponding to the overlapped region w₃₁, and by developing a bit map from the virtual screen, displays on the subregion w₃₁′. Further, step 670 sequentially divides the screen region occupied by the window W₃ before relocation by taking it as an object rectangle and applying thereto the process as mentioned in the second embodiment thereby to restore the screen. If another window is located under the window W₃ in Fig. 14, a part hidden comes to appear on the screen at step 670. As explained above, the display of the visible region of the window after relocation is effected by a combination of data shift from the old window on the frame memory and the bit map development on the virtual screen, so that the amount of data developed as a bit map is reduced thereby to increase the speed of display change. A sixth embodiment of the present invention is shown in Figs. 16 to 19. According to the embodiment under consideration, in what is called the scroll operation for shifting the visual field in a window, the overlapped relations of a visible region on a virtual screen before and after scroll are used to determine those display regions before scroll which become redisplay regions on the screen after scroll, and these redisplay subregions are displayed by shifting data on the frame memory, so that the data from the virtual screen are developed as a bit map only for the regions newly covered by the visual field, thus reducing the amount of data to be developed as a bit map. Now, assume that the contents of display of the window W₂ overlapped with the window W₁ on the display screen 30 are scrolled as shown in Fig. 16. The window W₂ divided into three subregions w₂₁, w₂₂ and w₂₃, of which w₂₂ and w₂₃ make up visible regions. Fig. 17 shows a virtual screen 60 corresponding to the window W₂. Numeral 70 designates a region corresponding to the window before scroll, and numeral 80 after scroll. In this example, the partial regions S1 and S2 in the virtual screen region 71 corresponding to the subregion w₂₂ remain at the left end of the subregion w₂₂ and the upper left corner of the subregion w₂₃ after scroll respectively. In similar manner, the partial region S3 of the virtual screen region 72 corresponding to the subregion w₂₃ is left at the lower left corner of the subregion w₂₃ after scroll. If these display regions S1, S2 and S3 are capable of being specified, therefore, a scroll screen may be obtained by shifting the contents of the redisplay regions S1′, S2′ and S3′ to S₁″, S₂″ and S₃″ respectively on the frame memory as shown in Fig. 18 and by developing the data from the virtual screen as a bit map only for the other visible regions. Fig. 19 is a flowchart showing the steps of display control for scroll operation. First, step 710 determines the visible subregions w₂₂ and w₂₃ from the subroutine SUB1 shown in the first embodiment with the window (W₂) to be scrolled as a target window. Step 720 determines the visible subregions 71 and 72 on the virtual screen before scroll corresponding to the visible subregions mentioned above, followed by step 730 for determining the visible subregions 81 and 82 on the virtual screen after scroll. Step 740 checks the manner in which the visual subregions before and after scroll are overlapped, and determines the overlapped regions S1, S2 and S3. If there is no overlapped region, the process is passed to step 780 to determine all the visible subregions w₂₂ and w₂₃ after scroll by bit map development of the data from the corresponding regions 81 and 82 on the virtual screen. If there is any overlapped region, on the other hand, step 750 determines the redisplay subregions S1′, S2′ and S3′ on the display screen before scroll corresponding to the overlapped regions S1, S2 and S3, followed by step 760 for determining the subregions S1″, S2″ and S3″ on the display screne after scroll corresponding to the overlapped regions mentioned above. Step 770 transfers the contents of the redisplay subregions before scroll to the corresponding subregions after scroll on the frame memory. If the image transfer is executed for each overlapped region, the operation of the steps 750 to 770 is repeated for all the overlapped regions as shown by the dashed line. Upon completion of these processes, the process is passed to step 780, where a bit map of the data from the virtual screen is developed in the visible regions except for the redisplay regions.

Claims: A method of display control for a multi-window system provided with a display screen (30) in which a plurality of rectangular windows (31: W1, W2, W3, W4) are set, first memory means (22) for storing display data in positions corresponding to those on the display screen, second memory means (17) for storing a plurality of display data of a virtual screen (60) corresponding to each of said windows which displays data included in the partial region of the virtual screen corresponding thereto, third memory means (14) for storing definition data representing the positional data on the display screen for each window and the correspondence thereof with the virtual screen, and control means (11, 20) for partially rewriting the display data stored in said first memory means (22), the method comprising: a first step (203) of designating one of the windows on the display screen as an object window (OW), the display status of which is to be changed; a second step (212, 214, 218) of sequentially selecting another one of the windows on the display screen as a reference window (RW) and comparing said object window with said reference window on the basis of the definition data stored in the third memory means (14), to check whether said object window crosses said reference window; a third step (220) of dividing said object window (OW) into a subregion overlapped with said reference window and at least one rectangular non-overlapped subregion defined by at least one of the boundaries of said reference window extended into the object window if said object and reference windows cross each other; a fourth step (238) of comparing said non-overlapped subregion selected as an object rectangle with still another window selected sequentially as a new reference window among the rest of said windows on the screen and, if said object rectangle and said new reference window cross each other, subdividing said object rectangle into a new subregion overlapped with said new reference window and at least one new rectangular non-overlapped subregion with the boundary of said new overlapped subregion as a dividing line, said comparing and subdividing being repeated by substituting said obtained non-overlapped subregion for a new object rectangular region until no more windows remain to be selected as said reference window; and a fifth step of transferring the display data of at least one partial area in said second memory means (17) to a corresponding partial area in said first memory means (22), said partial area being determined in accordance with the definition data stored in said third memory means (14) as to the object window (OW) designated in the first step and definition data of the resultant overlapped or non-overlapped subregions, thereby changing the contents of display in the visible region occupied by the object window on the display screen. A method of display control according to Claim 1, wherein said reference windows are selected among only those windows having higher display priority than the object window, said windows being selected as a reference window in descending display priority, said display data being rewritten in the fifth step about the partial region of the first memory means corresponding to the non-overlapped subregion that remains finally. A method of display control according to Claim 2, wherein a window of which the size is to be increased is designated as said object window in said first step, and a rectangular region corresponding to the expanded part, in place of the object window of said second step, is compared with the reference window. A method of display control according to Claim 1, wherein a window to be deleted from the display screen is designated as said object window in said first step, said reference window being selected sequentially in descending display priority, said fifth step being executed to display the contents of the virtual screen corresponding to the reference window on the part of the display screen corresponding to said overlapped subregion each time an overlapped subregion is obtained, and the part of the display screen corresponding to the last non-overlapped subregion is cleared. A method of display control according to Claim 1, wherein a window to be reduced in size is designated as said object window in said first step, and a partial rectangular region of the object window which disappears as the result of size reduction is compared with the reference window in place of the object window in the second step. A method of display control according to Claim 1, wherein a window for which the upgrading of the display priority is commanded is designated as said object window in said first step, the windows higher in display priority than the original display priority of said object window are selected as said reference windows in the descending display priority, and the contents of the virtual screen corresponding to said object window are sequentially displayed at the part of the display screen corresponding to the overlapped subregion. A method of display control according to Claim 1, wherein a window for which the display position on the display screen is to be shifted from a first position (W3) to a second position (W3′) is designated as said object window in said first step, said second to fourth steps being executed for the object window at said second position, said method further comprising a sixth step (610, 620) of determining a rectangular region (a, W31, b) in said object window at said first position corresponding to at least one non-overlapped subregion (a′, W31′) obtained for the object window at said second position, and a seventh step (630) of comparing the rectangular region obtained in said sixth step with another window (W1) selected as a reference window among the rest of the windows on the display screen, and when said rectangular region crosses said reference window, dividing said rectangular region into a subregion (W31) overlapped with said reference window and at least one rectangular non-overlapped subregion (a, b) with the boundary of said overlapped subregion as a dividing line, the comparing with other reference windows being repeated with the non-overlapped subregion as a new object rectangle, said fifth step further comprising an eighth step (650) of shifting the display data of the final non-overlapped subregion (a, b) obtained in said seventh step from the first position to the second position within said first memory means (22), a ninth step (660) of applying the contents of the virtual screen of said object window corresponding to the overlapped subregion obtained in said seventh step to the non-display region in the window at said second position, and a tenth step (670) of clearing the display data in the object window at the first position except for the overlapped subregion obtained in said seventh step. A method of display control according to Claim 1, wherein a window for which the contents of display are to be scrolled is designated as said object window in said first step, said method further comprising a sixth step (720) of determining a first visible region before scroll on the virtual screen corresponding to said object window, corresponding to the non-overlapped subregion obtained through said second to fourth steps, a seventh step (730) of determining a second visible region after scroll on the virtual screen corresponding to said object window, corresponding to said non-overlapped subregion obtained through said second to fourth steps, and an eighth step (740) of comparing said first and second visible regions with each other to determine a mutually overlapped region as a redisplay region, said fifth step further including a ninth step (770) of transferring the display data corresponding to said redisplay region on said first memory means to the display position after scroll, and a tenth step (780) of applying the display data of the partial region in said second visible region except for said redisplay region to a corresponding partial region on said first memory means (22) from said second memory means (17).

Inventors: IWAMI HIDEFUMI, KOJIMA TOMIHIKO, MURATA FUMIYA, NAKAMURA SHOUJI, IWAMI, HIDEFUMI, KOJIMA, TOMIHIKO, MURATA, FUMIYA, NAKAMURA, SHOUJI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1986
Main classification: G09G1
IPC codes: G09G5