Patent Publication Number: US-9406283-B2

Title: Display control device, display control method, and control system

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a display control device, a display control method, and a control system. 
     2. Description of Related Art 
     In the related art, a display system, such as the one described in Patent Literature 1, in which a shared display server (display control device) that controls the display on a shared display device and a plurality of participant terminals (input operation devices) are connected via a communication line, thus allowing display operations performed at the individual participant terminals to be reflected on the display at the shared display server has been disclosed. However, with the display system described in Patent Literature 1, for each shared display server, only one terminal is granted the right to operate cursor, etc. displayed on the shared display server. 
     On the other hand, known processing methods for sharing a single display control device among a plurality of input operation devices include, for example, time-sharing processing, serial processing, and so on. 
     Time-sharing processing is a processing method in which a display control device allocates an operable period to each of the input operation devices, thereby sequentially executing processing for the individual input operation devices. 
     Serial processing is a method in which a display control device successively processes the contents of individual operations performed at the input operation devices, and display processing, etc. is performed in order on the basis of instructions received from the individual operation devices by updating display content indicated by drawing request information every time the drawing request information is received from the individual input operation devices. 
     CITATION LIST 
     Patent Literature 
     {PTL 1} Japanese Unexamined Patent Application, Publication No. 2004-21595 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, with the time-sharing processing described above, because the processing time allocated to the individual input operation devices is determined in accordance with the number of input operation devices, there is a problem in that the time allocated to the individual input operation devices decreases when the number of the input operation devices is increased, which impairs the operational performance. 
     As described above, with the serial processing, because operation events received from the individual input operation devices are analyzed at the display control device to successively execute processing for the individual input operation devices, there is a problem in that a processing unit (CPU: Central Processing Unit) of the display control device is subjected to a large processing load. In addition, if operation events are simultaneously sent from the plurality of input operation devices, because the subsequent processing is not executed until the preceding processing is completed, real-time responsiveness is lost at the input operation device that has sent the subsequent operation event, which causes a user to experience the poor operational performance. 
     The present invention has been conceived in light of the above-described circumstances, and an object thereof is to provide a display control device, a display control method, and a control system that make it possible to maintain real-time responsiveness in updating display contents on a shared display device without impairing the operational performance for users, even if a large amount of drawing request information is output from a plurality of input operation devices. 
     Solution to Problem 
     In order to solve the above-described problems, a display control device of the present invention employs the following solutions. 
     Specifically, a display control device according to a first aspect of the present invention is a display control device that is connected to a plurality of input operation devices via a communication line and that updates display contents on a shared display device on the basis of drawing request information sent from the input operation devices, the display control device including a storage unit that stores multiple pieces of the drawing request information sent from the input operation devices; and a control unit that controls the shared display device so that the display contents based on the drawing request information stored in the storage unit are displayed by being updated in order of priority level, which is predetermined for each type of the drawing request information. 
     With the first aspect of the present invention, the display control device is connected to the plurality of input operation devices via the communication line and updates the display contents at the shared display device on the basis of the drawing request information sent from the input operation devices. Then the display control device displays the display contents based on the drawing request information been sent from the input operation devices and stored in the storage unit, by updating them in order of priority level, which is predetermined for each type of the drawing request information. 
     The display control device is connected to the plurality of input operation devices via the communication line. Because of this, the drawing request information is sometimes sent to the display control device in a large amount per unit time. In such a case, it may become impossible to maintain real-time responsiveness in updating the display contents at the shared display device. However, because the display contents based on the drawing request information stored in the storage unit are displayed by being updated in the order of priority level, which is predetermined for each type of drawing request information, by increasing the priority level of the drawing request information indicating display content of importance for a user, as with the present invention, it is possible to maintain real-time responsiveness in updating the display contents on the shared display device without impairing the operational performance for users, even if a large amount of drawing request information is output from the plurality of input operation devices. 
     With the display control device according to the first aspect of the present invention, in the case in which real-time responsiveness would be lost in updating the display contents in the shared display device if the display contents are updated based on the multiple pieces of the drawing request information stored in the storage unit, the control unit may control the shared display device so that the display contents based on the drawing request information stored in the storage unit are displayed by being updated in the order of priority level, which is predetermined for each type of the drawing request information. 
     With the first aspect of the present invention, instead of constantly controlling the shared display device so as to display the drawing request information stored in the storage unit, updated in the order of the priority level, the control unit performs this control only when real-time responsiveness will be lost in updating display contents at a shared display device if the display contents based on the multiple pieces of the drawing request information stored in the storage unit are updated. By doing so, the present invention can reduce the processing load on the display control device. 
     The display control device according to the first aspect of the present invention may be provided with a sorting unit that sorts the multiple pieces of the drawing request information stored in the storage unit in the order of priority level, which is predetermined for each type of the drawing request information, wherein the control unit may read out the multiple pieces of the drawing request information that have been sorted by the sorting unit and stored in the storage unit, in the sorted order, and may control the shared display device so as to display the display contents based on the read-out drawing request information. 
     With the first aspect of the present invention, the multiple pieces of drawing request information stored in the storage unit are sorted by the sorting unit into the order of priority level, which is predetermined for each type of drawing request information. Then, the control unit reads out the multiple pieces of drawing request information sorted and stored in the storage unit, in the sorted order, and controls the shared display device so that the display contents based on the read-out drawing request information are displayed. 
     By doing so, with the first aspect of the present invention, it is possible to maintain real-time responsiveness in updating the display contents on the shared display device, with a simple configuration and without impairing the operational performance for users, even if a large amount of drawing request information is output from the plurality of input operation devices. As an example of a storage unit according to the first aspect of the present invention, a FIFO (First In First Out) buffer is employed. 
     In the display control device according to the first aspect of the present invention, a predetermined type of the drawing request information stored in the storage unit may be deleted from the storage unit, excluding the most recent drawing request information. 
     With the first aspect of the present invention, because the predetermined type of drawing request information stored in the storage unit is deleted from the storage unit, excluding the most recent drawing request information, the processing load on the display control device can be reduced, and it is possible to better maintain real-time responsiveness in updating the display contents on the shared display device without impairing the operational performance for the users. 
     With the display control device according to the first aspect of the present invention, the drawing request information may include cursor movement information that indicates a cursor destination displayed on the shared display device, wherein the cursor movement information may specify the cursor destination by means of an absolute position with reference to a predetermined position on a screen indicated by the shared display device. 
     With the first aspect of the present invention, because the cursor movement information included in the drawing request information specifies the cursor destination by means of an absolute position with reference to the predetermined position on the screen indicated by the shared display device, the display control device does not need to compute the cursor destination, which reduces the processing load on the display control device. In addition, the cursor movement information can be designated as the drawing request information to be deleted from the storage unit. 
     With the display control device according to the first aspect of the present invention, the display control device may be switched either to a first mode, in which first cursor movement information that specifies the cursor destination by means of absolute position with reference to a predetermined position on the screen of the shared display device, is used as the cursor movement information, or to a second mode, in which second cursor movement information that specifies a next cursor destination at the shared display device on the basis of an amount of cursor movement per unit time at the input operation devices with reference to a previous cursor destination, is used as the cursor movement information. 
     With the first aspect of the present invention, when the processing load on the display control device needs to be reduced, the first mode is employed, which uses the first cursor movement information that specifies the cursor destination by means of the absolute position with reference to the predetermined position on the screen indicated by the shared display device. On the other hand, when the cursor displayed in the shared display device needs to be more finely moved, the second mode is employed, which uses the second cursor movement information that specifies the next cursor destination at the shared display device on the basis of the amount of cursor movement per unit time in the input operation devices with reference to the previous cursor destination serve. 
     The cursor movements displayed on monitor devices provided in the input operation devices are reflected in the display at the shared display device. 
     Because of this, in the case in which the resolution of the monitor device described above is lower than that of the shared display device, in the first mode, the first cursor movement information in which absolute values for the cursor destination in the monitor devices are corrected on the basis of the resolution difference with respect to the shared display device is sent from the input operation devices to the display control device. Accordingly, in the first mode, because the display control device does not need to compute the cursor destination, the processing load on the display control device can be reduced; however, the cursor cannot be finely moved in accordance with the resolution of the shared display device. 
     On the other hand, in the second mode, because the second cursor movement information indicates the amount of change in relative positions with respect to the previous cursor destination on the screens of the monitor device in the input operation devices, the display control device needs to determine the amount of cursor movement in the shared display device by computing the amount of cursor movement per unit time on the monitor devices described above on the basis of the second cursor movement information. Because of this, in the second mode, the processing load on the display control device is increased. However, in the second mode, because the amount of cursor movement can also be made smaller in the shared display device by making the amount of relative cursor movement per unit time smaller on the screens in the monitor devices described above, the cursor can be moved at the resolution of the shared display device. 
     In order to solve the above-described problems, a display control method of the present invention employs the following solutions. 
     Specifically, a display control method according to a second aspect of the present invention is a display control method, in which a plurality of input operation devices are connected via a communication line and display contents in a shared display device are updated on the basis of drawing request information sent from the input operation devices, the display control method including controlling the shared display device so that the display contents based on the drawing request information sent from the input operation devices and stored in a storage unit are displayed by being updated in order of priority level, which is predetermined for each type of the drawing request information. 
     In order to solve the above-described problems, a control system of the present invention employs the following solutions. 
     Specifically, a control system according to a third aspect of the present invention is a control system including a plurality of input operation devices that send drawing request information for updating display contents at a shared display device; a display control device that is connected to the input operation devices via a communication line, that stores the drawing request information sent from the input operation devices in a storage unit, and that updates the display contents at the shared display device on the basis of the drawing request information stored in the storage unit, wherein the display control device controls the shared display device so that the display contents based on the drawing request information stored in the storage unit are displayed by being updated in order of priority level, which is predetermined for each type of the drawing request information. 
     Advantageous Effects of Invention 
     The present invention affords an excellent advantage in that it is possible to maintain real-time responsiveness in updating display contents on a shared display device without impairing the operational performance for users, even if a large amount of drawing request information is output from a plurality of input operation devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the overall configuration of a control system according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram showing the electrical configuration of an input operation device according to the first embodiment of the present invention. 
         FIG. 3  is a block diagram showing the electrical configuration of a display control device according to the first embodiment of the present invention. 
         FIG. 4  is a flowchart showing the processing flow of a sorting program according to the first embodiment of the present invention. 
         FIG. 5  is a schematic diagram required for explaining sorting processing according to the first embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of a display control device, a display control method, and a control system according to the present invention will be described below with reference to the drawings. 
     First Embodiment 
     An embodiment of the control system according to the present invention will be described below with reference to the drawings. 
       FIG. 1  is a block diagram showing, in outline, the configuration of a control system  10  according to a first embodiment. 
     As shown in  FIG. 1 , the control system  10  according to the first embodiment is provided with, for example, a plurality of input operation devices  12 , which are information processing terminals, a display control device  16  that is connected to the plurality of input operation devices  12  via a communication line  14 , and a shared display device  18  that displays an image on the basis of an image signal output from the display control device  16 . 
     The input operation devices  12  are operation terminals with which individual operators manipulate a cursor and perform operations in windows, which are displayed on a large-screen display at the shared display device  18 , and the number provided is, for example, the same as the number of operators. Then, the input operation devices  12  send drawing request information, which indicates contents to be displayed on the shared display device  18 , to the display control device  16  via the communication line  14 . 
     The above-described drawing request information includes, for example, cursor movement information, which indicates a cursor destination to be displayed on the shared display device  18 , image drawing information for drawing images (diagrams such as line, circle, rectangle, and so forth, as well as image data) generated at the input operation devices  12  on the shared display device  18 , click information for executing an application by clicking a button or the like over which the cursor is placed on the shared display device  18 , emergency-message display information, created at the input operation devices  12 , for causing an emergency message to be displayed on the shared display device  18 , and so on. 
     The communication line  14  is a wide-area communication line provided by electrical services companies, an internal communication network, such as a LAN (Local Area Network), and so forth, and they may be wired or wireless. 
     The display control device  16  controls the shared display device  18  so that the display contents thereof are updated on the basis of the operation information input from the individual input operation devices  12 . 
     The shared display device  18  is a display device having a liquid-crystal screen, a plasma screen, or the like, and may be a single-screen display device or a display device in which a single large screen is formed by combining a plurality of display devices. 
       FIG. 2  shows the electrical configuration of the input operation devices  12 . 
     The input operation devices  12  are provided with a CPU  20  that governs the overall operation of the input operation devices  12 , a ROM (Read Only Memory)  22  in which various programs, various parameters, and so forth are stored in advance, a RAM (Random Access Memory)  24  that serves as a work area or the like when the CPU  20  executes various programs, and an HDD (Hard Disk Drive)  26  that serves as storage means (storage unit) for storing various programs and various information. 
     Furthermore, the input operation devices  12  are provided with an input device  28  that is formed of, for example, a keyboard, a mouse, and so forth, and receives inputs for various operations, a local monitor device  30  for displaying various images, and an external interface  32  that is connected with the display control device  16  via the communication line  14  and that sends and receives various information to and from the display control device  16 . 
     The CPU  20 , the ROM  22 , the RAM  24 , the HDD  26 , the input device  28 , the local monitor device  30 , and the external interface  32  are electrically connected with each other via a system bus  34 . Therefore, it is possible for the CPU  20  to individually access the ROM  22 , the RAM  24 , and the HDD  26 , to ascertain the operating states of the input device  28 , to display various images on the local monitor device  30 , to send and receive various information to and from the display control device  16  via the external interface  32 , and so on. 
     Individual screen resolutions of the local monitor device  30  and the shared display device  18  may be the same or may be different. The local monitor device  30  displays the same image as an image displayed at the shared display device  18 , and the local monitor device  30  displays images based on the information input by means of the input device  28  and a cursor reflecting the movements thereof caused by means of the input device  28 . 
     In addition, the information, cursor movement, and so forth input by means of the input device  28  are sent to the display control device  16  as drawing request information via the external interface  32 . Specifically, the operator who operates the input operation device  12  displays images, cursor movements, and so forth that they want to display on the shared display device  18  on the local monitor devices  30 , and the input operation device  12  sends drawing request information in accordance with the images, cursor movements, and so forth to the display control device  16  so that the images, cursor movements, and so forth displayed on the local monitor device  30  is reflected at the shared display device  18 . 
     In the first embodiment, there is a set priority level, which is predetermined for each type of drawing request information. Table 1 shows examples of the priority levels corresponding to the types of drawing request information, where drawing request information whose priority level is shown with a smaller value has a higher priority level. 
     The priority levels shown in Table 1 are set so as to be higher for drawing request information indicating display content of greater importance for users. For example, the emergency-message display information is set to the highest priority level because it is drawing request information for displaying an emergency message on the shared display device  18 . On the other hand, the click information is set to a lower priority level than the cursor movement information because it is information for clicking a button or the like over which the cursor is placed, where it is assumed that the cursor has been moved to the position of a button or the like according to the cursor movement information. 
     The input operation device  12  according to the first embodiment adds priority-level information, which indicates the priority level described above, to each piece of drawing request information and sends it to the display control device  16 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 TYPE OF DRAWING REQUEST 
                   
               
               
                   
                 INFORMATION 
                 PRIORITY LEVEL 
               
               
                   
                   
               
             
            
               
                   
                 EMERGENCY-MESSAGE DISPLAY 
                 1 
               
               
                   
                 INFORMATION 
               
               
                   
                 IMAGE DRAWING INFORMATION 
                 2 
               
               
                   
                 CURSOR MOVEMENT INFORMATION 
                 3 
               
               
                   
                 CLICK INFORMATION 
                 4 
               
               
                   
                   
               
            
           
         
       
     
     The input operation device  12  according to the first embodiment specifies the absolute position of a cursor destination on the screen of the local monitor device  30  and sends the absolute positions to the display control device  16  as cursor movement information so that the cursor destination can be specified by means of the absolute position on the screen of the shared display device  18 . 
     For the cursor absolute position, for example, predetermined positions on the screens of the shared display device  18  and the local monitor device  30  serve as reference positions. In this embodiment, the lower left portion of the screen with the coordinate origin at (x, y)=(0, 0) is used as an example of the reference position. In this case, the horizontal direction from the lower left portion is defined as the x-axis and the vertical direction therefrom is defined as the y-axis, and the x-coordinate value increases rightward with reference to the lower left portion of the screen and the y-coordinate value increases upward with reference to the lower left portion of the screen. 
     In addition, in the case in which resolutions differ between the shared display device  18  and the local monitor device  30 , because the CPU  20  corrects the cursor movement information on the basis of the resolution difference between the shared display device  18  and the local monitor device  30  and sends it to the display control device  16 , the display control device  16  does not need to compute the cursor destination, which reduces the processing load on the display control device  16 . 
     For example, when the resolution of the shared display device  18  is 4096 pixels by 768 pixels, and the resolution of the local monitor device  30  is 1024 pixels by 768 pixels, the CPU  20  sets the cursor destination specified on the screen of the local monitor device  30  to be four times greater in the x-axis direction and sends this information to the display control device  16  as the cursor movement information. 
       FIG. 3  shows the electrical configuration of the display control device  16 . 
     The display control device  16  is provided with a CPU  30  that governs the overall operation of the display control device  16 , a ROM  42  in which various programs, various parameters, and so forth are stored in advance, a RAM  44  that serves as a work area or the like when the CPU  40  executes various programs, and an HDD  46  that serves as storage means (storage unit) for storing various programs and various information. 
     Furthermore, the display control device  16  is provided with a video card  48  that is connected to the shared display device  18  and that outputs to the shared display device  18  an image signal that indicates an image to be displayed on the shared display device  18 , an external interface  50  that is connected to the individual input operation devices  12  via the communication line  14  and that sends and receives various information to and from the input operation devices  12 , and a buffer  52  that stores the drawing request information sent from the input operation devices  12 . 
     The CPU  40 , the ROM  42 , the RAM  44 , the HDD  46 , the video card  48 , the external interfaces  50 , and the buffer  52  are electrically connected with each other via a system bus  54 . Therefore, it is possible for the CPU  40  to individually access the ROM  42 , the RAM  44 , the HDD  46 , and the buffer  52 , to give instructions to the video card  48  with regard to image signal output, to send and receive various information to and from the input operation devices  12  via the external interface  50 , and so on. 
     The buffer  52  according to the first embodiment is a FIFO buffer and stores the drawing request information sent from the individual input operation devices  12  in the order in which the drawing request information is sent thereto. 
     Then, the display control device  16  according to the first embodiment controls the shared display device  18  so that display contents based on the multiple pieces of drawing request information stored in the buffer  52  are displayed by being updated in the order of the priority level, which is predetermined for each type of drawing request information. Then, in order to control the shared display device  18  in this way, the display control device  16  performs sorting processing in which the multiple pieces of drawing request information stored in the buffer  52  are sorted in the order of the priority level, which is predetermined for each type of drawing request information, reads out the multiple pieces of drawing request information that have been sorted by the sorting processing and stored in the buffer  52 , in the sorted order, and controls the shared display device  18  so that the display contents are displayed on the basis of the read-out drawing request information. 
     Next, the operation of the display control device  16  according to the first embodiment will be described. 
       FIG. 4  is a flow chart showing the processing flow of a sorting program executed by the CPU  40  when performing the sorting processing, and the sorting program is stored in a predetermined region of the HDD  46  in advance. This program is started when the operation of the shared display device  18  is started. 
     First, in Step  100 , the external interfaces  32  are in a standby state until the drawing request information is received from one of the plurality of input operation devices  12 , and the process advances to Step  102  when the drawing request information is received. 
     In Step  102  that follows, the received drawing request information is stored in the buffer  52 . 
     In Step  104  that follows, it is judged whether or not real-time responsiveness in updating the display contents in the shared display device  18  will be lost or not, and the process advances to Step  106  in the case of an affirmative judgment, whereas the process advances to Step  108  in the case of a negative judgment. 
     A situation in which real-time responsiveness will be lost is a situation in which updating of the display contents based on any drawing request information among the multiple pieces of drawing request information stored in the buffer  52  is performed after a predetermined amount of time (for example, one second) or more has passed after the drawing request information has been sent to the display control device  16 . In other words, a situation in which real-time responsiveness will be lost is a situation in which a large amount of drawing request information is sent to the display control device  16  per unit time, which makes the processing load on the CPU  40  a high load. 
     Because the processing time for displaying contents based on the drawing request information can be predicted in advance for each type of drawing request information, the CPU  40  can judge whether or not real-time responsiveness will be lost by accumulating the processing time of the drawing request information stored in the buffer  52 . 
     In Step  106 , the drawing request information stored in the buffer  52  is sorted. 
     The processing executed in Step  106  will be described with reference to  FIG. 5 . 
       FIG. 5(A)  shows a case in which a large amount of drawing request information is stored in the buffer  52 , making the processing load on the CPU  40  a high load, and, as an example, cursor movement information  1 , image drawing information, cursor movement information  2 , cursor movement information  3 , emergency-message display information, and click information are stored in the buffer  52 . It is assumed that various types of drawing request information described above have been sent to the display control device  16  from the plurality of input operation devices  12  in this order. Specifically, when the sorting processing is not performed, the cursor movement information  1 , the image drawing information, the cursor movement information  2 , the cursor movement information  3 , the emergency-message display information, and the click information are read out in this order, image signals are generated on the basis of the read-out drawing request information, and the display contents at the shared display device  18  are updated. 
     Then, as shown in  FIG. 5(B) , the multiple pieces of drawing request information stored in the buffer  52  are sorted in the order of the priority levels of each type of drawing request information. Specifically, the priority level information added to the drawing request information is read out and the individual pieces of drawing request information are sorted on the basis of the priority level information. Because the same types of drawing request information have the same priority level, the same types of drawing request information are sorted so as to be placed in order of the time at which the drawing request information is sent to the display control device  16 . 
     In the example in  FIG. 5(B) , the emergency-message display information, the image drawing information, the cursor movement information  1 , the cursor movement information  2 , the cursor movement information  3 , and the click information are sorted into this order. 
     Furthermore, in the sorting processing according to the first embodiment, a predetermined type of drawing request information stored in the buffer  52  is deleted from the buffer  52 , excluding the most recent drawing request information. 
     In the first embodiment, the above-described predetermined type of the drawing request information is, as an example, assumed to be the cursor movement information. Accordingly, as shown in  FIG. 5(C) , the cursor movement information (the cursor movement information  1  and the cursor movement information  2 ), excluding the cursor movement information  3 , which is the most recent cursor movement information, are deleted from the buffer  52 . 
     As shown in Table 2, the possibility of deletion from the buffer  52  is predetermined for each piece of the drawing request information, and, in the first embodiment, deletion possibility information, which indicates the possibility of deletion, is added to the drawing request information together with the priority level information, and the CPU  40  deletes the drawing request information on the basis of the deletion possibility information. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 TYPE OF DRAWING 
                   
                 DELETION 
               
               
                 REQUEST INFORMATION 
                 PRIORITY LEVEL 
                 POSSIBILITY 
               
               
                   
               
             
            
               
                 EMERGENCY-MESSAGE 
                 1 
                 NOT POSSIBLE 
               
               
                 DISPLAY INFORMATION 
               
               
                 IMAGE DRAWING 
                 2 
                 NOT POSSIBLE 
               
               
                 INFORMATION 
               
               
                 CURSOR MOVEMENT 
                 3 
                 POSSIBLE 
               
               
                 INFORMATION 
               
               
                 CLICK INFORMATION 
                 4 
                 NOT POSSIBLE 
               
               
                   
               
            
           
         
       
     
     Then, once the sorting of the drawing request information, performed in Step  106 , is performed, the display control device  16  reads out the drawing request information stored in the buffer  52  in the sorted order, in other words, in order starting from higher priority levels, generates image signals based on the read-out drawing request information, and updates the display contents at the shared display device  18 . 
     In Step  108  that follows, it is judged whether or not an instruction for ending the operation of the shared display device  18  has been input, and this program is ended in the case of an affirmative judgment, whereas the process returns to Step  100  in the case of a negative judgment. The instruction for ending the operation of the shared display device  18  is input through, for example, a predetermined input operation device  12  assigned to manage the control system  10  or an input device (not shown) provided in the display control device  16 . 
     As has been described above, the display control device  16  according to the first embodiment is connected to the plurality of input operation devices  12  via the communication line  14  and updates the display contents at the shared display device  18  on the basis of the drawing request information sent thereto from the input operation devices  12 . In addition, because the display control device  16  is provided with the buffer  52  that stores the multiple pieces of drawing request information sent from the input operation devices  12  and controls the shared display device  18  so that the display contents based on the multiple pieces of drawing request information stored in the buffer  52  are displayed by being updated in the order of the priority level, which is predetermined for each type of drawing request information, it is possible to maintain real-time responsiveness in updating the display contents on the shared display device  18  without impairing the operational performance for the users, even if a large amount of drawing request information is output from the plurality of input operation devices. 
     Because the buffer  52  according to the first embodiment is a FIFO buffer, by sorting the drawing request information in the order starting from higher priority levels, it is possible to maintain real-time responsiveness in updating the display contents on the shared display device, with a simple configuration and without impairing the operational performance for the users, even if a large amount of drawing request information is output from the plurality of input operation devices  12 . 
     Second Embodiment 
     A second embodiment of the present invention will be described below. 
     The configuration of a control system  10  according to the second embodiment is the same as the configuration of the control system  10  according to the first embodiment shown in  FIG. 1 ; the electrical configuration of input operation devices  12  according to the second embodiment is the same as the electrical configuration of the input operation devices  12  according to the first embodiment shown in  FIG. 2 ; the electrical configuration of a display control device  16  according to the second embodiment is the same as the electrical configuration of the display control device  16  according to the first embodiment shown in  FIG. 3 ; and therefore, descriptions thereof will be omitted. 
     The display control device  16  according to the second embodiment can be switched to either an absolute position mode that uses first cursor movement information, which specifies a cursor destination by means of an absolute position with reference to a predetermined position on the screen of the shared display device  18 , or a relative position mode that uses second cursor movement information, which specifies a next cursor destination at the shared display device  18  on the basis of an amount of cursor movement per unit time in the input operation devices  12  with reference to previous cursor destination. 
     The processing load on the display control device  16  can be reduced in the absolute position mode, whereas the cursor displayed on the shared display device  18  can be moved more finely in the relative position mode. 
     To give a more specific description, as described in the first embodiment, the display at the shared display device  18  reflects cursor movements displayed on the local monitor devices  30  provided in the input operation devices  12 . 
     Because of this, in the absolute position mode, if the resolution of the local monitor device  30  is lower than that of the shared display device  18 , first cursor movement information in which absolute values of the cursor destination in the local monitor device  30  are corrected based on the resolution difference with respect to the shared display device  18  is sent to the display control device  16  from the input operation device  12 , as described in the first embodiment. Accordingly, in the absolute position mode, because the display control device  16  does not need to compute the cursor destination, the processing load on the display control device  16  can be reduced; however, it is not possible to finely move the cursor in accordance with the resolution of the shared display device  18 . 
     On the other hand, in the relative position mode, because the second cursor movement information indicates the amounts of change in the relative position between the previous cursor destination and the next cursor destination on the screen of the local monitor device  30 , the display control device  16  needs to determine the amount of cursor movement on the shared display device  18  by computing the amount of cursor movement per unit time on the local monitor device  30  based on the second cursor movement information. Because of this, in the relative position mode, the processing load on the display control device  16  is increased. However, in the relative position mode, because the amount of cursor movement can also be made smaller at the shared display device  18  by making the amount of relative cursor movement per unit time on the screen of the local monitor device  30  smaller, the cursor can be moved at the resolution of the shared display device  18 . 
     For example, in the case in which the resolution of the shared display device  18  is 4096 pixels by 768 pixels and the resolution of the local monitor device  30  is 1024 pixels by 768 pixels, in the absolute position mode, the CPU  20  generates the first cursor movement information to be sent to the display control device  16  by setting the cursor destination specified on the screen of the local monitor device  30  to be four times greater in the x-axis direction. Because of this, for the cursor on the screen of the shared display device  18 , the cursor cannot be finely moved in the x-axis direction. 
     On the other hand, in the relative position mode, by making the amount of relative cursor movement per unit time on the screen of the local monitor device  30  smaller, the cursor on the screen of the shared display device  18  can be finely moved pixel-by-pixel in the x-axis direction. 
     A user may arbitrarily switch between the absolute position mode and the relative position mode. Because the user inevitably moves the cursor on the screen of the local monitor device  30  slowly when the user attempts to finely move the cursor on the screen of the shared display device  18 , switching from the absolute position mode to the relative position mode may be performed automatically when the amount of cursor movement per unit time on the screen of the local monitor device  30  drops to or below a predetermined value. With regard to this judgment for this automatic switching, for example, the CPU  40  in the display control device  16  makes the judgment and sends switching information, which indicates switching from the absolute position mode to the relative position mode, to the input operation device  12 , and, once the input operation device  12  receives the switching information, the input operation device  12  subsequently sends the second cursor movement information to the display control device  16 . 
     As above, although the present invention has been described in terms of the individual embodiments described above, the technical scope of the present invention is not limited to the scope described in the individual embodiments described above. It is possible to add various alterations or improvements to the individual embodiments described above within a range that does not depart from the spirit of the invention, and the technical scope of the present invention also encompasses forms to which such alterations or improvements are added. 
     For example, although the individual embodiments described above have been described in terms of the case in which the input operation devices  12  send the drawing request information to the display control device  16  by adding the priority level information, which indicates the priority level, as well as the deletion possibility information, the present invention is not limited thereto, and a form in which the drawing request information is sent to the display control device  16  from the input operation devices  12  without adding the priority level information or the deletion possibility information may be employed. In such a form, the display control device  16  stores, in the HDD  46  in advance, priority level tables indicating the priority level and deletion possibility for each type of the drawing request information, as shown in Table 1 and Table 2 prepared in advance, and, in the sorting processing, the display control device  16  sorts the drawing request information stored in the buffer  52  in the order of priority level on the basis of the priority level tables. 
     Although the individual embodiments described above have been described in terms of the case in which, in the sorting processing, every time the display control device  16  receives the drawing request information, the display control device  16  judges whether or not real-time responsiveness will be lost in updating the display contents at the shared display device  18 , the present invention is not limited thereto, and a form in which whether or not real-time responsiveness will be lost in updating the display contents in the shared display device  18  is judged at predetermined time intervals (for example, every one second) may be employed. 
     Although the individual embodiments described above have been described in terms of the case in which, in the sorting processing, the drawing request information stored in the buffer  52  is sorted in the order of the priority level when real-time responsiveness will be lost in updating the display contents in the shared display device  18 , the present invention is not limited thereto, and it is permissible to employ a form in which, for example, the drawing request information stored in the buffer  52  is sorted in the order of the priority level every time the display control device  16  receives the drawing request information and stores it in the buffer  52 , without judging whether or not real-time responsiveness will be lost in updating the display contents in the shared display device  18 . 
     Although the individual embodiments described above have been described for the case in which a FIFO buffer is employed as the buffer  52 , the present invention is not limited thereto, and an other type of buffer may be employed as the buffer  52  so long as it is a buffer that is capable of reading out the drawing request information in the order of priority level.