Patent Publication Number: US-6222558-B1

Title: System and method for efficiently transmitting and processing object information between and among a plurality of networked computers

Description:
This is a continuation of application Ser. No. 08/670,525 filed Jun. 27, 1996 now U.S. Pat. No. 5,886,707, which is a Division of U.S. patent application Ser. No. 07/615,986, filed Nov. 20, 1990, now U.S. Pat. No. 5,544,317. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to graphics and drawing applications for computers, and more particularly to a method for the interactional presentation of graphics through a coupled network of intelligent computer work stations. 
     2. Brief Description of the Prior Art 
     Many presentation graphics and drawing applications exist for computers. Some notable examples are MACDRAW™ for APPLE™ MACINTOSH™ computers and SUNDRAW™ for Sun Microsystems work stations. These programs allow the user to prepare graphical drawings depicting virtually any subject matter. However, they are limited in that they allow only one person to work on the drawing at a time; they do not allow interactive networking of the graphical drawings. 
     Methods and computer programs do exist which allow users to share information over a network simultaneously, but these are not graphically oriented. The most notable example of this is a program called TALK, which is available as part of 4.3 BSD UNIX. This program allows one user using a work station to initiate a conversation with another user on a different work station. The program allows only the transfer of textual information. Once a conversation is started, the program splits the screen horizontally. The characters inputted by user A appear on the top half of A&#39;s screen, and simultaneously appear on the lower half of the screen on the user B&#39;s work station. In like manner, when user B types on B&#39;s work station, the input appears on the top half of B&#39;s screen and the bottom half of user A&#39;s screen. In addition to the fact that the TALK program only allows sharing of textual information, it is limited in that the conversation can be between only two users. 
     There is also a freely available public domain program for the X-Windows system called WScrawl which allows users to share graphical information. However, it works by taking advantage of special features of X-Windows. A simple program is run which opens a single window on each of multiple machines. Then graphics drawn in one window is replicated in the other windows by making identical X-Windows protocol requests. This differs from the current invention in several ways. First, there is only one program being run. Second, the graphics being drawn is not reduced to its essence and then transmitted. Rather, the graphics are merely drawn in multiple windows which are located on different machines. This approach has many disadvantages. First of all, there is no way to distinguish between what multiple users have drawn; everything is merged together. Second, since the essence of the graphic is not transmitted, there is no way for another user to “grab” the image and modify it. Third, and possibly most importantly, this scheme will work only under the X-Windows system. There is no way to make it interoperate with other windowing systems such as Apple&#39;s MacOS™ or Microsoft&#39;s MICROSOFT WINDOWS™. The current invention has none of these restrictions. 
     Finally, the POSTSCRIPT™ page description language has been used to transmit graphical information over a network, most notably in Sun Microsystems NEWS™ (Network Extensible Windowing System). However, POSTSCRIPT™ has not facilities for describing the interactions which a use might engage in when using a drawing program. For example, POSTSCRIPT™ has no means of indicating that a specific object has moved from one location to another, or that an object has been cut. In fact, the notion of a graphical object is alien to PostScript, which is suited mainly to describing static images so they can be printed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to allow the simultaneous, real-time sharing of graphical information over a network between two or more intelligent work stations on a network. 
     It is another object of the present invention to minimize the data necessary to describe the graphical information, for the rapid transmittal of the data between work stations. 
     It is a further object of the present invention to avoid using pixel-by-pixel description and transmission of data describing a graphical image, such that the speed of transmission is increased. 
     It is yet another object of the present invention to develop and utilize a protocol including a series of commands each having a fixed data bit length portion and a description portion having a variable data bit length. 
     It is yet a further object of the present invention to provide a series of commands which describe the type of graphical manipulation that is being conducted, the type of graphical figure upon which it is being conducted and the location of the screen bits at which it is being conducted, such that each of the terminals in the network are provided with sufficient information to replicate the graphical production of the generating work station. 
     It is still another object of the present invention to provide a simplified set of commands which is concise for rapid transmission and reception. 
     The user of a work station (user A) has a means of inputting graphical information to a work station, such as a graphical drawing program. As graphical information is input by user A, it is reduced to a minimal description and an identifier is assigned to it. This description and identifier is termed an object description, and the object description plus other information is formulated into a command that is then transmitted via the network to all other work stations engaged in the conversation. When the other work stations in the conversation receive the command over the network from work station A, they depict that information from the command on the local display in an area (window or canvas) designated for that purpose. 
     Each command involves a division of instructions into a command type portion having a fixed length and a graphical object description portion having a variable length, in order to transmit data structures that describe graphical objects and operations on those objects. 
     It is an advantage of the present invention that it allows the simultaneous, real-time sharing of graphical information over a network between two or more intelligent work stations on a network. 
     It is another advantage of the present invention that it minimizes the data necessary to describe the graphical information, for the rapid transmittal of the data between work stations. 
     It is a further advantage of the present invention that it avoids using pixel-by-pixel description and transmission of data describing a graphical image, such that the speed of transmission is increased. 
     It is yet another advantage of the present invention that it develops and utilizes a protocol including a series of commands each having a fixed data bit length portion and a description portion having a variable data bit length. 
     It is a further advantage of the present invention that it provides a series of commands which describe the type of graphical manipulation that is being conducted, the type of graphical figure upon which it is being conducted and the location of the screen bits at which it is being conducted, such that each of the terminals in the network are provided with sufficient information to replicate the graphical production of the generating work station. 
     It is still another advantage of the present invention that it provides a simplified set of commands which is concise for rapid transmission and reception. 
     The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments which make reference to the several figures of the drawing. 
    
    
     IN THE DRAWING 
     FIG. 1 is a schematic diagram of the communication of graphical information between work stations; 
     FIG. 2 is a further schematic diagram of the communication of graphical information between work stations; 
     FIG. 3 is a schematic diagram of the method for moving a graphical object depicted upon the computer screens; 
     FIG. 4 is a schematic diagram of the method for resizing an object depicted upon the computer screens; 
     FIG. 5 is a schematic diagram of the method for deleting a graphical object depicted upon the computer screens; 
     FIG. 6 is a schematic diagram of the method for aggregating graphical objects depicted on the computer screens; and 
     FIG. 7 is a schematic diagram of the method for disaggregating graphical objects depicted upon the computer screens. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, when a session or conversation is begun between two or more work stations, they exchange certain information. This information includes a list of other users already involved in the conversation, the revision level each program is using, and possibly details such as the size of the canvas (virtual drawing area) each is using locally. This is referred to as the initial parameter exchange  12 . 
     A work station which is becoming involved in the conversation for the first time will attempt to connect to the other members of the conversation. After the initial parameter exchange, the work station newly added to the conversation will be sent a complete description of all objects on the screen of each of the work stations already involved. With this method, new parties can be included in the conversation in a real-time, on demand basis. 
     The user of a work station (user A) has a means of inputting graphical information into A&#39;s work station, such as a graphical drawing program  14 . As graphical information is input by user A, it is reduced to a minimal object description  16  and an object identifier  18  is assigned to it. This object description  16  and object identifier  18  plus other information described below is combined in an add new object command  20 , and the command  20  is then transmitted  24  via the network to all other work stations engaged in the conversation, such as work stations B and C in FIG.  1 . When the other work stations in the conversation receive the information over the network from work station A, they store the information  26  in a portion of memory reserved for work station A, and they depict that information from the command on the local display in an area (window or canvas) designated for that purpose  28 . 
     In like manner, as depicted in FIG. 2, when a user of a remote machine, such as work station B, inputs graphical information  30 , the object is depicted on her machine, reduced to its essence as an object description  31  and an object identifier  33 , and it is combined in an add new object command  32 , and transmitted  34  to all other work stations in the conversation, such as work stations A and C in FIG. 2, for memory storage  36  and for display in windows  40  reserved for input from work station B. A user can&#39;t modify another users drawing on the other user&#39;s work station, but a user can pick up a received drawing and copy it from memory  36  to her drawing area. She can then modify the copied drawing and it is transmitted to the other work stations. 
     When a user copies the drawing of another user to her drawing area, the preexisting drawing in her drawing area is erased from the screen. In the preferred embodiment, the sequence of commands that were utilized to create the erased drawing are retained in the user&#39;s memory storage. At a later time, the user can recall the erased drawing to her computer screen for further modification. Because the entire sequence of commands which were utilized to create the drawing are retained in computer memory, further commands to modify the drawing can be initiated based upon the object identifiers that are associated with the command sequence of the recalled drawing. 
     For the purposes of drawing graphical objects, there are at least 5 basic operations which a user would perform: creation, resizing, movement, aggregation and deletion. When an object is created on machine A, an indication of the creation of a new object is sent to every other machine in the conversation, including a description of the object  16 , and a unique object identifier  18  is sent with the new object. That information forms the basis of each command. The object identifier  18  is used subsequently if the object is referred to in a subsequent operation (e.g., deleted, etc.). When each other machine receives notification of the creation of a new object on machine A, it adds the object to the list of objects it maintains in memory  36  for machine A and draws that object on its screen that represents the output of work station A. 
     For some objects, most notably text, it is more efficacious for the information about the object to be disseminated as the object is being created. For such instances, an indication of the commencement of object creation is sent, followed by data describing the development of the object and terminated by an indication of object completion. 
     If the user of machine A performs another operation (resizing, movement, etc.) on an object, a command  20  reflecting this operation is constructed by selecting a command type  41  that is sent to all other machines, this command  20  includes the unique identifier  18  for the object, and a complete description of what was done. For example, as depicted in FIG. 3, suppose user A moves an object she has already drawn from one place to another ( 42 ). An object move command is constructed  44  specifying the object identifier of the object moved and the relative displacement of the new location of the object  44 . This is transmitted to work stations B and C  46 . Work stations B and C independently look up the object specified in the move command  48 . The object location maintained in the object description data structure in machines B and C is updated  50 . Work stations B and C erase the depiction of the object in the old location  52 . Then work stations B &amp; C draw the object in the new location  54 . 
     If user A resizes an object  56 , as depicted in FIG. 4, an object resize command containing the object identifier and information describing the new object size and shape is constructed  58 . This is transmitted to work stations B and C  60 . Work stations B and C look up the object  62 . They update the object information  64 ; then they erase the old object  66  and draw the resized object  68 . 
     Similarly, if user A deletes (cuts) an object  70 , as depicted in FIG. 5, an object cut command is constructed  72 . This command is transmitted to work stations B and C  74 . Work stations B and C look up the object  76 . They then erase the object on the screen  78  and remove the object from their list of user A&#39;s objects  79 . The memory associated with the object is then freed  80 . 
     If user A aggregates (combines with another) an object  82 , an object aggregation command is constructed  84 , see FIG.  6 . This command is transmitted to work stations B and C  86 . Work stations B and C look up the aggregate object to which the other object is to be added, and the other object to add as well  88 . The object to aggregate is then added to the list of objects comprising the aggregate  90  and is deleted from the list of independent objects for work station A  92 . 
     If user A disaggregates an object  94 , an object disaggregation command is constructed  96 , see FIG.  7 . This command is transmitted to work stations B and C. Work stations B and C look up the aggregate on their list of user A&#39;s objects  100 . They then look up the object to disaggregate on the object list associated with the aggregate  102 . They then remove the object from the aggregate&#39;s list  104  and add it to the main list  106  of independent objects for work station A. Aggregate objects can also be nested. That is, an aggregate object can consist of other aggregate objects, which can in turn consist of other aggregate objects. 
     In order to accomplish the sharing of graphical information over a network, a protocol is necessary to allow each machine to describe what is happening locally to every other machine in the conversation. This protocol consists of a set of commands which are transmitted over the network. Some of the commands refer to graphical objects. The essence of a particular set of commands is to transmit the contents of a screen in terms of the objects on the screen and operations on the objects. Objects are described in the most concise fashion necessary to capture their essence. In the preferred embodiment, each command consists of a fixed length portion followed by a (possibly empty) variable length portion. The fixed length portion describes the type of command and the length of the variable portion. The variable portion contains the detailed information needed to properly process the command. For example, for moving an object, the fixed length portion will identify the type of command and the length of the variable length portion. The variable portion will contain the identifier for the object as well as the displacement of the object. 
     The protocol consists of the following type of commands. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Command 
                 Description 
               
               
                   
                   
               
             
            
               
                   
                 Add New Object 
                 A new object has been 
               
               
                   
                   
                 added to the local screen 
               
               
                   
                 Move Object 
                 An object has been moved 
               
               
                   
                 Resize Object 
                 An object&#39;s size has been 
               
               
                   
                   
                 changed 
               
               
                   
                 Cut Object 
                 An object has been deleted 
               
               
                   
                   
                 from the local screen 
               
               
                   
                 Add Object to Aggregate 
                 An object has been added 
               
               
                   
                 Object 
                 to an aggregate 
               
               
                   
                 Remove Object From 
                 An object has been removed 
               
               
                   
                 Aggregate 
                 from an aggregation 
               
               
                   
                 Clear Screen 
                 All objects have been 
               
               
                   
                   
                 removed from the local 
               
               
                   
                   
                 screen 
               
               
                   
                 Begin special mode 
                 A special mode (e.g., Text 
               
               
                   
                   
                 Entry) has been entered 
               
               
                   
                 Special mode data 
                 Data corresponding to an 
               
               
                   
                   
                 already-entered special 
               
               
                   
                   
                 mode 
               
               
                   
                 End special mode 
                 The previously entered 
               
               
                   
                   
                 special mode has been 
               
               
                   
                   
                 terminated 
               
               
                   
                   
               
            
           
         
       
     
     Commands are not limited to this set and additional commands can be added as needed. For example, commands to rotate and duplicate an object could be added, and commands to change aspects of an object description, such as fill pattern, line style or color can also be added. 
     As described above, each command consists of a fixed length portion followed by a variable length portion. The fixed length portion of a command is described by the following table, wherein each field is 32 bits in length in the preferred embodiment. It is not necessary to specify a user identifier in a command since a separate logical connection is used between each pair of machines in a conversation. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 Command Type 
               
               
                 Command Detail 
               
               
                 Length 
               
               
                 Command Detail 
               
               
                 Pointer 
               
               
                   
               
            
           
         
       
     
     The contents of the variable length portion, called the command details, varies depending on the type of command and object, as described in the following table: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 COMMAND DETAILS 
               
               
                   
                 Command 
                 (VARIABLE LENGTH) 
               
               
                   
                   
               
             
            
               
                   
                 Add New Object 
                 Object Description 
               
               
                   
                 Move Object 
                 Object Identifier; 
               
               
                   
                   
                 Displacement to new location 
               
               
                   
                 Resize Object 
                 Object Description Details 
               
               
                   
                 Cut Object 
                 Object Identifier 
               
               
                   
                 Add Object to Aggregate 
                 Object Identifier of 
               
               
                   
                 Object 
                 Aggregate Object; Object 
               
               
                   
                   
                 Identifier of Object 
               
               
                   
                   
                 added to Aggregate 
               
               
                   
                 Remove object From 
                 Object Identifier of 
               
               
                   
                 Aggregate 
                 Aggregate Object; Object 
               
               
                   
                   
                 Identifier of Object 
               
               
                   
                   
                 removed from Aggregate 
               
               
                   
                 Clear Screen 
                 None 
               
               
                   
                 Begin special mode 
                 Special mode type 
               
               
                   
                   
                 indicator; 
               
               
                   
                   
                 Location 
               
               
                   
                 Special mode data 
                 Depends on mode type 
               
               
                   
                 End special mode 
                 Object Identifier with 
               
               
                   
                   
                 which to tag resultant 
               
               
                   
                   
                 object 
               
               
                   
                   
               
            
           
         
       
     
     The object description portion of a command detail (used for the add new object command) also consists of a fixed length portion and a variable length portion. The fixed length portion contains information which is not specific to a particular type of object, while the variable portion contains information which is unique to objects of that type. For example, the fixed length portion of the object description contains the object identifier, the object type and the object location. In the preferred embodiment, the fields of the fixed length portion are 32 bits in length. Location information consists of 16 bits each for horizontal (x coordinate) and vertical (y coordinate) position. 
     A fixed length portion of an object description is as follows: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 Object Identifier 
               
               
                 Object Type 
               
               
                 Object Location 
               
               
                 Object Detail Length 
               
               
                 Object Bounding Box 
               
               
                 Object Detail Pointer 
               
               
                   
               
            
           
         
       
     
     The object bounding box is the rectangle which fully contains the object. It is used in the object selection logic to facilitate local object editing. If a point in a window is not in an object&#39;s bounding box, then that point can not be used to select the object for editing. Additional elements can be added to the fixed length portion as needed. For example, it is possible to add elements such as line width, line style, fill pattern and color. 
     The contents of the variable length portion of the object description depends on the object type. For example, for a circle, the variable length object details consist of the location of the center of the circle and its radius. The variable length object details for several possible objects are described in the following table: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Point List; 
               
               
                   
                 Scribble 
                 Point Count 
               
               
                   
                   
               
             
            
               
                   
                 String 
                 Array of characters in string; 
               
               
                   
                   
                 Length of character array; 
               
               
                   
                   
                 Location of string; 
               
               
                   
                   
                 Location of current character 
               
               
                   
                 Text 
                 Array of strings in text; 
               
               
                   
                   
                 Length of string array 
               
               
                   
                 Square 
                 Location of upper left; 
               
               
                   
                   
                 Length of side 
               
               
                   
                 Rectangle 
                 Location of upper left; 
               
               
                   
                   
                 Width; 
               
               
                   
                   
                 Height 
               
               
                   
                 Circle 
                 Location of center; 
               
               
                   
                   
                 Radius 
               
               
                   
                 Ellipse 
                 Location of center; 
               
               
                   
                   
                 Width; 
               
               
                   
                   
                 Height 
               
               
                   
                   
               
            
           
         
       
     
     Additional objects can be added as needed, And the description of an object can change. For example, strings could be modified to include the font to use to render the string. 
     Structuring the description of a graphical object in this fashion allows a virtually infinite variety of different types to be represented, since the object details can be of whatever length is necessary to fully describe any object and since the object details can be interpreted in any manner necessary, depending on the object type. Furthermore, structuring object descriptions in this fashion allow their transmission over a network in relatively simple fashion. 
     In the preferred embodiment, when the object description is transmitted and received, the fixed length portion and variable length portion are contiguous. When the object description is received, the buffer containing its description may be decomposed into the fixed length portion and variable length portion. The object header and details are not necessarily stored in contiguous memory. In fact, the detail information may not be in contiguous memory either. The detail information may contain pointers to other areas in memory. This is the case with text, which is stored as an array of pointers to character strings. 
     There are two traditional problems with networking protocols which exchange binary data, as does the present invention. The first is byte ordering, and the second is holes due to data alignment. Byte ordering refers to the manner in which different machines store quantities of more than 8 bits in length. Some processors (such as DEC VAX processors and Intel 8086-family processors) store the high order portion in high memory. Other processors (Sun SPARC, Motorola 68000 and 88000) store the high order portion in low memory. Networking protocols generally have a “canonical,” or standard way of transmitting such quantities. For example, TCP/IP always transmits the high order byte first, proceeding to the low order byte. Network canonical presentation of 16 and 32 bit quantities are adhered to in the preferred embodiment. 
     The other problem occurs in processors which force alignment on half word (16 bit) or full word (32 bit) boundaries within structures. Since the protocol information is being transmitted in a binary format, it is important for structures to be stored identically on all machines in a conversation. When this is not possible, it will be the responsibility of each machine to convert received data structures into a format usable locally. This problem will be minimized by designing the data structures to be used so that each field is naturally aligned on an appropriate boundary without holes. 
     For example, in the preferred embodiment, single byte quantities are not followed by half or full word quantities, and half word quantities are not followed by full word quantities. Two single byte quantities can be followed either by a half word quantity, or two single byte quantities. A half word quantity can be followed by either another half word quantity or two single byte quantities. 
     This protocol represents a significant improvement over fax technology, which transmits a bit map of a graphical image. Instead of transmitting a bit by bit description of the image, we transmit a description of each of the objects (e.g., squares, circles, text, etc.) which make up the image. This has two advantages. The first is concision. Describing a square by its upper left hand corner and length of side is considerably more concise than describing each bit the square contains. An image of 1000 pixels by 1000 pixels represents a million bits of information if the image is black and white, and potentially as much as 24 million bits if the image is in color. This represents a huge amount of data to transmit over a network, and would bring all but the fastest existing networks to their knees in short order. 
     The second advantage to this approach is preservation of information. When a bit map is transferred, there is a resultant loss of information as to the essence of the image. What was created as a set of geometric objects becomes a bunch of unrelated bits. The receiver of this bunch of bits has no way to determine from it the original constituent parts as they were drawn. All that is known is that some bits are on and some are off, but not that some of the bits represent a circle, a square, some text, etc. 
     In the present invention, there is another further refinement in concision. A typical computer program which stored graphical information would probably use a data structure known as a union. This type of data structure can be used to store multiple different kinds of data, while consuming only the amount of space required for the largest kind. A union can only be used for one type of data at time, since the fields representing different types may overlap. It would be impractical to use such a data structure to transmit a description over a network because potentially large parts of the union would be unused. By dividing the description of a graphical object into a fixed and variable length portion, this problem can be avoided. Only as much data as is necessary to describe a specific object is transmitted, instead of the amount necessary to describe the most detailed object. This approach has other advantages, too. The description of an object may be distributed throughout the memory of the machine on which it was created. However, in order to transmit it to another machine, it must be gathered together. Since we can accommodate descriptions of varying length, this becomes practical. 
     A final advantage of this approach is that it simplifies reading and writing of commands and descriptions over a network. When writing, the fixed and variable portions of a command and/or object are collected into a contiguous block of memory. They can then be written in one write operation. When a command is read, it is read in two operations. This is necessary since only the size of the fixed length portion is known. This is read in, and it indicates the length of the variable length portion (if any). This allows the variable length portion to then be read in. 
     Taking this approach becomes very important when communicating over a network in a graphics program. Network throughput can become constipated. Under normal circumstances, this causes read and write operations to block; that is, to cause the process requesting them to become idled until the operation can be completed. This is not acceptable for graphics programs, since the user may be in the midst of drawing something on her screen, and does not want that to be interrupted due to network constipation. Thus, the communication endpoints must be configured as non-blocking. This means that if the read or write operation cannot be completed, the operating system reports how much was transferred and returns to the calling program. This introduces a level of complexity to the application, as it must now manage the processing of partially complete operations. Doing so becomes much simpler if the data being transferred is of fixed size. Since this is not possible, the next best approach is to divide the data into a fixed length portion and a variable length portion. 
     Since the data sequences are in contiguous memory on writes, the process of writing the data can be essentially handled as if it was of a fixed length; that is, the complete length is known a priori. If the operation cannot be completed at once, the amount of data actually transferred is recorded. When the operation can be re-attempted, the program knows from where to resume writing, and how much to write. While the network is constipated, the commands which correspond to the user&#39;s actions are accumulated in a first-in first-out queue. When the network becomes unconstipated, the writing of the command which was partially written is completed, and subsequently queued commands are then written, until there are no more queued commands or the network again becomes constipated. 
     On reading, the problem is a bit more complex, since the reader does not know the length of the complete sequence. However, since there are only two parts, the operation is greatly simplified. If a read completes only partially, the amount of data read is recorded, in addition to which part of the message (either the fixed or variable) was being read. When the operation can be re-attempted, the program knows not only how much to read, but also which part of the message was being read. 
     The underlying mechanism of the network is not significant. Many networking protocols exist, including proprietary solutions such as DECNET and non-proprietary solutions such as DoD Internet Protocols (TCP/IP). The only requirement is that the network provide services to reliably transfer data between two machines in a timely fashion. If more than one machine is involved in the conversation, each pair of machines will have its own network connection. Further, while one preferred embodiment of this invention assumes that a connection-oriented transport service is being provided between machines, this is not necessary. A connection-less (or datagram) service can suffice. In the same way that the exact nature of the network service used is not relevant to the invention, neither is the nature of the computers involved. The productive use of this invention is not limited to work stations or personal computers. It is intended to be used in any application where graphical information is to be shared between machines on a real-time basis. 
     Similarly, the invention is not limited to simply displaying graphical information. For example, the graphical input may be sent to another machine to be translated into text and then sent back for redisplay. Another application of this technology would be in an environment where a computer generates a series of images for sequential display and a work station is used to display the image. The computer could essentially generate animated sequences by defining a set of objects and then sending commands which describe their movement and other changes to them (removal or cutting, resizing, rotation, etc.). Another application of this technology is in presenting graphical animation. A script describing a sequence of images could be prepared, stored and then replayed on a single machine using a single program. 
     The invention is in essence a means of sharing graphical information between machines. This is done by reducing the graphical information to the minimal amount of data required to represent it, and transmitting that data between machines. While the invention has been shown and described with reference to particular preferred embodiments, it will be understood by those skilled in the art that various alterations and modifications in form and detail may be made therein. 
     Accordingly, it is intended that the following claims cover all such alterations and modifications as may fall within the true spirit and scope of the invention.