Abstract:
A system and method for interactive design of user manipulable graphic elements. A computer has display and stored tasks wherein the appearance of graphic elements and methods for their manipulation are defined. Each graphic element is defined by at least one figure specification, one mask specification and one map specification. An interactive display editor program defines specifications of said graphic elements. An interactive program editor program defines programming data and methods associated with said graphic elements. A display program uses the figure, map and mask specifications for assembling graphic elements upon the display and enabling user manipulation of said graphic elements.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to systems and methods for design of interactive interfaces for computer programs. 
     Computer programs are a series of instructions that direct the operation of a computer. They are written by computer programmers to achieve a desired purpose. The instructions, taken as a whole, may define a computer application such as a word processing system, an accounting system, an inventory system or an arcade game. Most programs require interaction with the user of the computer program. In the case of a word processing program, the user keys text, formats and prints documents. In the case of an accounting program, the user enters the desired debits and credits and appropriate documentation, posts and selects reports. The schemes used to prompt the computer user to input data and to output information generated by the computer program to the computer user are known as human/computer interfaces. 
     This application relates to systems and methods that facilitate the computer programmer&#39;s task of writing programs with human/computer interfaces that are readily understandable and easy to use. 
     More and more, human/computer interfaces (whatever the application) make use of certain devices such as menus, windows, scroll bars, graphical displays, in addition to the traditional and still essential keypad and keyboard. Especially popular are direct manipulation interfaces (DMI) which are human/computer interfaces that allow the user to command the computer by selecting and manipulating pictures (sometimes called icons), usually with a pointing device such as a mouse. (A mouse is simply an input device which, when moved over a surface, &#34;drags&#34; a mouse pointer over the computer display. Typically, a mouse has several buttons which when pressed, initiate an input relating the button pusher and the location of the mouse cursor upon the computer display. The pressing or releasing of a mouse button is often referred to as a &#34;mouse event&#34;.) The pictures of a DMI are designed to behave somewhat like the objects they represent. The Apple Macintosh employs direct manipulation extensively and is widely considered one of the easiest computers to use for people who are not necessarily computer specialists. The advantages of direct manipulation are widely recognized. 
     Unfortunately, direct manipulation interfaces are difficult to construct and difficult to modify once they are constructed. The programmer needs to write programs to create the pictures, move the pictures around the screen, determine what pictures the mouse is pointing to, what the pictures on the screen represent, what to do when a picture is selected and so forth. Although some programming languages and tools provide commands for drawing geometric figures and ways of sensing the mouse events, these basic capabilities are only the beginnings of a direct manipulation interface. Traditional programming languages leave the programmer to construct more sophisticated objects, such as menus. This is time consuming and often leads to complex and idiosyncratic interfaces. 
     User interface management systems are known which are computer programs that provide a collection of interface elements such as menus and dialog boxes and often include interactive tools for building prototype interfaces. See, for example, &#34;Software Frameworks&#34; Byte December 1984, describing Apple Computers Toolkit/32; &#34;Macapp: An Application Framework&#34;, Byte August 1986; and &#34;Objects, Icons and Software-ICS&#34;, Byte August 1986. 
     If a user interface management system has an interactive interface itself, it may be possible to create entire application interfaces without programming. For some applications, a good user interface management system may be sufficient. However, it is not always clear what interface elements and interactive tools will be needed and the interface elements and tools may not be readily modified or modified at all to suit the specific application. 
     Current estimates indicate that interface design can consume 50 percent of the time on a large programming project. Interfaces produced are usually difficult to debug and modify. Even though carefully thought out, interfaces are likely to need to be redesigned when tried with real users. 
     SUMMARY OF THE INVENTION to simplify the development of sophisticated interfaces. 
     It is a further advantage to cut the time needed to implement an interface by as much as a factor of 10. 
     It is yet another advantage to allow interfaces to be quickly and easily designed, thoroughly tested and then discarded for more effective redesigns. 
     It is an advantage according to this invention that graphic elements on computer displays can be created, displayed and manipulated directly. The displays comprising the interface can be simply saved and restored. 
     It is an advantage according to this invention to allow the programmer to treat an interface as an object for inspection, manipulation and design. 
     According to this invention, the programmer uses graphic editors to mock up interface designs by drawing and arranging objects that appear on the computer display. The application underneath the interface is created by &#34;building inward&#34; from this mock-up. Typically, the programmer is building a direct manipulation interface which allows the user to command the computer by moving and selecting icons designed to behave like the objects they represent. 
     Briefly, according to this invention, there is provided a system for the interactive design of user manipulable graphic elements. The system comprises a computer having a bit and stored tasks. The appearance or sensitivity of graphic elements are defined by at least one figure specification and one other type specification, such as a mask specification or a map specification. Figure specifications define the outline and shading of graphic elements. Mask specifications define the transparent and nontransparent portions of graphic elements. Map specifications define the sensitive, for example, mouse pointer sensitive areas of graphic elements. An interactive display editor program is provided for defining the specifications of said graphic elements. An interactive program editor program is provided for programming data and methods associated with said graphic elements. A display program using the figure specifications and the other type specifications is provided for assembling graphic elements upon the display and enabling user manipulation of said graphic elements. Preferably, the figure, map and mask specifications are bit mapped specifications. 
     It is most preferred, according to this invention, that the display editor be capable of copying specifications of one type for use in generating specifications of another type. In other words, once the figure specification has been generated, the mask and map specifications can be generated by copying and modifying the figure specification. This results in rapid programming and insures alignment of the various specifications. 
     According to one embodiment of this invention, multiple sets of figure, map and mask specifications are generated. The copying feature of the display editor enables the generation of alternate sets of specifications where they have common features and require alignment. 
     In one preferred embodiment according to this invention, the computer has stored tasks comprising an object oriented programming environment wherein the appearance of said graphic elements and methods for their manipulation are defined by display objects, each said display object comprising at least one figure specification instance variable and one other type specification instance variable. 
     Where the other type specification is a mask specification defining the nontransparent portions of said graphic element, the display editor or said program editor is used to establish a list defining occlusion priorities of graphic elements. The display program for assembling graphic elements upon the display comprises an algorithm for controlling the display such that the masked portions of graphic elements with a higher occlusion priority mask the overlaid portions of a graphic elements with a lower occlusion priority. 
     Where the other type specification comprises map specifications defining mouse sensitive portions of said graphic element, it may comprise a plurality of specifications organized as a tagged list or list tree of bit maps. The program editor is used for defining methods activated when the mouse is used to bring the mouse cursor over the mouse sensitive areas of the graphics element and a mouse button is pushed. The display program has algorithms for recognizing when a mouse button has been pushed while the mouse cursor is within a mouse sensitive area. The algorithm preferably comprises a depth first search of the tagged list tree. 
     There is also provided, according to this invention, a computer assisted process for the interactive design of user manipulable graphic elements displayed upon a computer display. The method requires an interactive display editor program for defining specifications of graphic elements, a program editor for programming data and methods associated with graphic elements, and a display program for assembling graphic elements upon the display and enabling the manipulation of graphic elements. The method comprises a first step of using the display editor to interactively define the figure specification of a graphic element and a subsequent step of the display editor to interactively define at least one other type specification. According to a preferred embodiment, the method requires a computer having an object oriented programming environment wherein the appearance of said graphic elements and methods for their manipulation are defined by display objects, an interactive display editor program for defining specifications of display objects, a program editor program for programming data and methods assigned to display objects and other program objects, and a display program for assembling graphic elements upon the display and enabling the interactive positioning and repositioning of graphic elements at locations within a window. The method comprises the step of invoking the display editor to interactively define the figure specification of a graphic element, the data for which is stored in at least one instance variable associated with a display object, the step of using the display editor to interactively define a mask specification defining the transparent and nontransparent portions of said graphic element, or to interactively define a map specification defining sensitive areas, the data for which is stored in at least one instance variable associated with said display object, and repeating prior steps to define a plurality of display objects. 
     An additional step may comprise using either the display editor or the program editor to assign occlusion priorities to each display object such that when the display program is invoked to move one graphic element to the same position as another, the masked portions of a graphic element with a higher occlusion priority mask the overlaid portions of the graphic elements with a lower occlusion priority. 
     Yet another additional step may comprise invoking the program editor to define methods or messages activated when the mouse is used to bring the mouse cursor over the mouse sensitive areas of the graphic element and a mouse button is pushed. 
     In an especially preferred method, the display editor is used to copy an existing specification for generating another specification by the modification thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and other objects and advantages will become apparent from the following description made with reference to the drawings in which: 
     FIGS. 1(a) and 1(b), respectively, illustrate figure and mask specifications; 
     FIGS. 2(a), 2(b) and 2(c) illustrate the process of erasing a mask and painting a figure; 
     FIG. 3(a) illustrates a figure specification and FIGS. 3(b), 3(c), 3(d) and 3(e) illustrate possible map specifications corresponding to FIG. 3(a); 
     FIG. 4 illustrates the tree structure of the map specification; and 
     FIG. 5 illustrates three icons assembled upon a computer display illustrating the appearance of three dimensions. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While not entirely essential to the implementation of the applicants&#39; invention, it is most easily implemented in object oriented programming environments. The nature of object oriented programming has been explained in detail in the literature. For example, SmallTalk 80: The Language and its Implementation, Goldberg and Robeson, 1983; numerous articles in the August 1981 and August 1986 issues of Byte; &#34;Object-Oriented programming: Themes and Variations&#34;, Stefik and Bobrow, The AI Magazine, Winter 1986. 
     In an object oriented programming language, the fundamental data structures of the language are objects, programming elements that contain a specification of both data and actions. Data are specified in local variables referred to as instance variable (or IVs, for short) contained within the object. Actions or methods are subprograms that operate on the variables. Methods are invoked by messages sent from one object to itself or other objects. 
     There are two fundamental kinds of objects: classes and instances. Classes define a set of variables and methods and can be thought of as templates for object types. Instances are particular instantiations of a class. An instance provides storage for variables defined in its class. Each instance has its own version of those variables. When a message is sent to an instance, the instance looks to methods defined in its class to specify how the message is to be executed. 
     Classes are defined in terms of class hierarchy. A class inherits all variables and methods from classes referred to as superclasses. The variables and methods inherited from a superclass are available to the inheriting class as if they were defined within the inheriting class. A class can be referred to as a subclass or a child class of its superclasses. Note, that if a subclass has multiple superclasses, all the variables and methods from each superclass are inherited. This is often referred to as multiple inheritance. 
     There are two kinds of variables that can be defined within a class. Class variables, which are referred to as CVs, define variables whose storage is shared by all instances of the defining class. Class variables are typically used for coordination between classes instances. Instance variables (IVs define variables where a separate storage space is allocated for each instance. All instances have their own copy of instance variables. 
     Methods specify the action to be performed when a message is sent to an object. When the message is sent to an object, the message name is matched against method names defined for that object. The method actually executed is the method with the same name as the message that is defined lowest in that object&#39;s class hierarchy. 
     Messages can have parameters. When a message is sent, all actual parameters are fully evaluated before a method is located for that message. Methods have formal parameters, corresponding to the actual parameters in the message, and temporary variables. Temporary variables may be created when a message is executed, are available only within the scope of that method while the method is executing. 
     Programs perform by sending messages to objects which invoke a method in an object&#39;s class. Often methods send messages to other objects invoking other methods. Each method returns a result to the sender. At the heart of many languages and especially an object oriented language is a program segment for interpreting and evaluating messages and keeping track of where to return when messages call other messages. The applicants, invention does not reside in the particular implementation of this program segment. 
     Object oriented programming can be implemented with any number of programming languages. Object oriented programming environments have been implemented in the LISP language, in the C language and in others. For example, Interlisp-D has been extended to provide the LOOPS programming environment. See &#34;Object-Oriented Programming: Themes and Variations&#34;, Stefik and Bobrow, The AI Magazine, Winter 1986 and The LOOPS Manual, Bobrow and Stefik, Xerox Corporation 1983. 
     Interlisp-D/LOOPS runs on a Xerox 1100 Series Work station. A work station is simply a single user computer with a large graphics display, several megabytes of memory, a high speed processor and a device for pointing to objects on the display, such as a mouse. Work stations have bit mapped displays. In a bit mapped display, a portion of the computers memory is dedicated to storing the screen bit map. Each pixel on the display corresponds to at least one bit of memory in the screen bit map. In the case of a CRT display, as the raster is scanned, the video signal for any given pixel is controlled by the corresponding bit or bits in the screen bit map. Programs and apparatus for reading the screen bit map and feeding the information therein to the video input of the CRT in synchronism with the horizontal and video scanning signals are well known and form no part of this invention. 
     Systems software for work stations typically comprises a number of operations for transferring scratch bit maps to the screen bit map and for combining scratch bit maps. A popular tool for manipulating bit maps is BITBLT also known as RasterOp. BITBLT is a general purpose procedure for copying, moving and combining portions of bit maps. It is described in Principles of Interactive Computer Graphics, Newman and Sproull, McGraw Hill 1979. See also &#34;The SmallTalk Graphics Kern&#34;, Byte Magazine August 1981, and &#34;Raster Operations&#34;, Byte Magazine, November 1985. 
     Bit maps may be generated directly with bit map editors that display a large pixel representation of the bit map upon a display screen and allow the programmer to black in or clear individual pixels. Use of such a bit map editor is obviously tedious. Another form of graphics editor is known as a object graphics editor. Object graphics editors respond to commands to draw and erase lines and circles and other shapes and to fill and clear specified areas. The graphics editor builds a list of commands for describing an image. Before the object graphics generated image can be displayed on a bit mapped display, it must be converted to a bit map. Object graphics editors often include such a utility. An object graphics editor known as &#34;Sketch&#34; is available as a drawing program for the Interlisp-D environment. It enables the interactive construction of figures from a combination of text and graphics. A sketch created by the &#34;Sketch&#34; program consists of elements such as text, lines and curves, boxes, circles and ellipses. Each element has one or more positions that determine the location and shape and a set of properties that determine how it looks. Sketch is an interactive graphics editor in that locations upon the display may be designated by use of a mouse cursor and mouse events. Object graphics editors are known in the art. &#34;Sketch&#34; is described in A Users Guide To Sketch-The Interlisp Drawing System, Xerox Corporation, 1985. &#34;McDraw&#34; is an object graphics editor widely known to Apple Macintosh users. 
     Common to most object oriented programming environments are commands that may be issued from the keyboard or with the mouse pointer for creating and modifying classes and specializing classes to create new objects. &#34;Systems classes&#34; define how objects, instances, instance variables (IVs), classes, class variables (CVs) and messages can be created, destroyed, edited or manipulated. For example, the highest level of class may be named &#34;Object&#34; having no parent class and no IVs. Its methods may comprise setting the name of an Object or destroying an Object. The system classes may include a class named &#34;Class&#34; which has only the parent class of Object. It has no IVs and provides methods for specialization of classes, modification of classes and so forth. The system classes may also include a class named &#34;File&#34; which provides for files containing object oriented code and includes methods for creating, saving and loading such files. 
     Also common to most object oriented programming environments are certain &#34;tool classes&#34; that aid the developer (computer programmer) in designing, implementing and debugging applications. Tool classes might include a class named &#34;CodeEditor&#34; that enables the user to interactively edit code, a class named &#34;BreakWindow&#34; that enables the programmer to observe the performance of a section of code by observing bindings of variables within a method, a class named &#34;ClassBrowser&#34; which is a window that displays the portions of a class hierarchy associated with the file or group of files and shows the order between classes graphically and allows more detailed viewing and modification of classes. Still further, the tool classes of a typical object oriented programming environment may include a class named &#34;Dependence/Browser&#34; which is an editing window that enables the user to graphically view the dependencies (and hierarchies, if any) between specified objects, and a class named &#34;Object Inspector&#34; which is an editing window that shows the IVs, names, and values of IVs, allowing the user to perform interactive editing. The specific names of the system classes and tool classes identified in this paragraph are arbitrary and the name and functionality vary from environment to environment. The Interlisp-D/Loops programming environment provides variations of the system classes and tool classes described in this paragraph and was used by the applicants to implement a specific embodiment of the invention disclosed herein. That embodiment is described in Chips: A Tool for Developing Software Interfaces Interactively, Cunningham, Corbett and Bonar, (Technical Report No. LSP-4 supported by Office of Naval Research dated Oct. 23, 1987). 
     In the practice of this invention, certain special &#34;tool classes&#34; and &#34;user interface classes&#34; are used to implement the inventive systems and procedures. One class of objects may be referred to as &#34;DomainObjects&#34;. This class defines special objects in the application domain--the domain for which the interface is being built. DomainObjects provide the functionality of describing situations, processes or objects from the application domain for which the program is being built. In addition, DomainObjects connect themselves to other domain objects, defining their behavior in terms of other domain objects, saving themselves to a file, and editing their behavior and properties interactively. 
     Each instance of a subclass of DomainObject defines one or more instances of the class &#34;DisplayObject&#34; that determines how the domain object is to be displayed. The domain object corresponds to an object in the application domain, while the display object determines how the domain object will display itself on the screen. For example, there might be a class of domain objects called LightBulb. It has display objects associated with it that determine how it will show up on the screen. The domain object instance itself determines the objects behavior (for example, is it &#34;on&#34; or &#34;off&#34;). It determines how to process inputs, controls its display objects in response to inputs, and connects to other domain objects. Display objects are stored in the DomainObject classes IV, &#34;displayObjects&#34;, as an associated list of the form ((tag 1  displayObjectInstance 1 ) . . . (tag n  displayObjectInstance n )). Where tag i  is a name for the display objected. For the domain object LightBulb, displayObjectInstance1, may be the image of an unilluminated light bulb and displayObjectInstance2, might be an image of an illuminated light bulb. The domain object, depending upon its condition (&#34;on&#34; or &#34;off&#34;) sends one or the other display object instance to the screen. Each instance of DomainObject class stores one or more display objects in its displayObjects IV. These display objects instances are copies of those stored in the classes display objects IV. 
     As already stated, the display objects determine how a domain object will display itself on the screen. Display objects are the basic user interface object in the applicants&#39; system. The class DisplayObject provides functionality for the overlapping display of irregularly shaped, noncontinuous objects, the functionality for button detection in response to buttoning (mouse events). Preferably, anything that is displayed on the screen in the applicants&#39; system is either an instance of or an instance of a specification of, the class DisplayObject. Applicants&#39; invention can be implemented by combining the functions described above for domain objects and display objects into a single type object. 
     Preferred instance variables and messages or methods for display objects according to this invention are set forth in the following table. 
     
                       TABLE I______________________________________DISPLAY OBJECT______________________________________Parents:ObjectIVS:figure specification            bitmap version of imagemask specification            bitmap version of maskmap specification            (tag1 offset1 bitmap1 tagn            offsetn bitmapn . . .)position         screen positionresponsesToSelection            (tag1 button msgOrCode1 . . .            tagn button msgOrCoden)occludesMe       list of display objects that            occludes this one.occludedByMe     list of display objects that            this one occludes.Messages: ##STR1## ##STR2## ##STR3## ##STR4## ##STR5## ##STR6## ##STR7## ##STR8## ##STR9## ##STR10## ##STR11## ##STR12## ##STR13## ##STR14## ##STR15## ##STR16## ##STR17## ##STR18## ##STR19## ##STR20##______________________________________ 
    
     In the Table, the message names are to the right of the arrow followed by message parameters in parentheses. The type of instance to which the message can be sent is to the left of the arrow. The arrow could be read as &#34;sent to&#34; where the message description is read right to left. 
     The figure specification, mask specification and each element of the map specification of a display object each comprise at least one bit map. Figure, map and mask bit map specifications are themselves objects and preferably have at least the instance variables and methods as generally described in Table II. 
     
                       TABLE II______________________________________BITMAP______________________________________Parents:ObjectIVS:width              width of bitmapheight             height of bitmapMessages: ##STR21## ##STR22## ##STR23## ##STR24## ##STR25## ##STR26## ##STR27##______________________________________ 
    
     In a preferred embodiment of this invention, the figure, map and mask specifications may comprise two different specifications, namely, a display representation which is the bit map representation already described and an editor representation which is a list of object graphic commands in a format recognized by the display editor (to be described). The object graphics commands are more easily edited; however, the edit representation comprising a list of object graphic commands must be converted to a bit map representation for it to be displayed. 
     The figure specification defines the way the display object will appear on the display (outlines, color, shading). The mask of the display object defines which areas of the display object are to be opaque. Referring to FIGS. 1(a) and 1(b), the figure specification and mask specification, respectively, for a SmileFace display object are shown. 
     Using this scheme, it is possible to display a figure of arbitrary shape on an arbitrary background. Referring now to FIG. 2(a), there is shown a background defined by a scratch bit map which is an instance of the class BitMap. (See Table II). The mask specification of the SmileFace object can be sent the message Erase with the scratch bit map as a destination parameter. The result is shown in FIG. 2(b). Next, the figure specification is sent the message Paint with the scratch bit map as a destination parameter. The result in shown in FIG. 3. Finally, the image of the SmileFace object can be transferred to the screen bit map be sending the scratch bit map the message Paint with the screen bit map as the destination parameter. The erasing and painting procedure using a scratch bit map is called double buffering and avoids flicker associated with erasing from the screen bit map. 
     The system, according to this invention, creates the illusion that display objects assembled upon the screen overlap one another as though the screen had depth and some display objects are closer than others. An ordered &#34;contents&#34; list is maintained of all display objects assembled on the screen bit map and, therefore, the screen at any time. When the screen is first displayed (as when the file containing the application is loaded or when the screen is redisplayed) each display object in the order contents list is sent the message PlaceOnScreen starting with the last display object in the list and proceeding to the first. As each display object is placed on the screen, its mask and figure bit maps are erased and painted, respectively, on the screen bit map. The occludesMe list is an ordered list of all display objects that are nearer to the front of the contents list than the display object and at an overlapping screen location. The occludedByMe list is an ordered list of all display objects in the contents list further from the front of contents list than the display object and at a screen position overlapped by the display object. The purpose of keeping the occludesMe and occludedByMe list will become apparent. 
     When a display object is sent the message Move to a new position defined by the parameters x and y (pixel coordinates measured from the lower left corner of the screen), each display object in the occludedByMe IV is sent the message Replace with a scratch bit map (having the same height and width as the display object being moved) as the destination parameter. Then, the message Replace is sent to each display object in the occludedByMe IV. The same registry of the display objects on the screen is maintained on the scratch bit map. (Consider that other display objects may only partially overlap the display object being Moved.) The scratch bit map is then Replaced on the screen bit map. The occludesMe and occludedByMe list of each overlapped and overlapping display object are then updated and everything is removed from the moved display objects own occludesMe IV and occludedByMe IV. The moved display object is now placed at the front of the contents list. (Note, to this point the Move method may be identical with the RemoveFromScreen method except that the RemoveFromScreen procedure also removes the display object from the contents list). The next step in the Move method is to send each display object in the contents list the message OnYou? using the new coordinates of the display object as the parameters. It then sends the message PlaceOnScreen to each display object upon which it landed and then to itself. Finally, it adds itself to the front of the occludesMe list of each display object upon which it landed and it adds each display object upon which it landed to its occludedByMe list. The occludesMe and occludedByMe list enable the rapid moving or removal of display objects from the screen. 
     There are any number of other sequences that could implement the Move method described above and the procedure is illustrative of just one. 
     The map specification of a display object comprises one or more bit mapped objects in a tag list or a tagged list tree. FIG. 3(a) shows the figure specification for a display object and FIGS. 3(b)-3(e) show the outlines of the map specifications associated with the same object and the tags therefor. The tree structure of the tagged tree list is shown in FIG. 4. The root of the tree is the region surrounding the entire display. 
     When a mouse event takes place, each display object in the contents list starting from the front is sent the message OnYou? with the x, y position of the mouse cursor. If a display object is found at the cursor position, the OnYou? message returns a list of itself and the part selected. Each bit map comprising a member of the map tree of the selected display object is sent the message OnYou? with the relative coordinates of the mouse cursor. The OnYou? messages are sent in a depth first search. In other words, if the coordinates of the OnYou? message fall within the small circle on the bit map shown as FIG. 3(d), the tag scir would be returned and the search ended. The selected display object is then sent the message RespondToSelection with the tag and button event (left, middle, right) and the x, y coordinates to the selected display object. 
     A RespondToSelection method attempts to match the tag and button event with a member of the list in the responsesToSelection IV. If it does, it sands the associated method to the selected display object. 
     As shown in FIG. 5, three display objects are positioned upon a window upon the screen. The display object of the class ChocolateChip looks like a chocolate chip cookie, the display object of the class FooChip looks like a man in the moon and the display object of the class WasherChip looks like a washer with a hole in the middle. The ChocolateChip is partially occluded by the WasherChip but can been seen through the hole in the WasherChip. Preferably, according to this invention, selection of these display objects with the mouse cursor exactly corresponds to their visual representation on the window. Selecting the part of the FooChip that is not occluded selects this display object. Selecting any part of the WasherChip&#39;s display object selects it. Selecting any part of the ChocolateChip that can be seen, including the part that is seen through the hole in the WasherChip, selects it. To implement this selection process, it is necessary that the map specification include in its tagged list a bit mapped specification identical or substantially identical to the mask specification bit map. When a mouse event takes place, if a true is not returned when the OnYou? is sent to the display object, the next display object on the contents list is polled with the OnYou? message. 
     Two additional user interface classes facilitate design of computer interfaces according to this invention. One called &#34;Pointer&#34; relates to mouse event inputs and another called &#34;GroupPresentationObject&#34; relates to management of a portion of the screen displaying multiple objects. The IVs and methods for these classes are described in Tables III and IV. 
     
                       TABLE III______________________________________POINTER______________________________________Parents:ObjectIVs:xHot            the x coordinate of the hot           spotyHot            the y coordinate of the hot           spotimageBM         bit map of imagemaskBM          bit map of maskbutton          button pressedMessages: ##STR28## ##STR29## ##STR30## ##STR31## ##STR32##______________________________________ 
    
     
                       TABLE IV______________________________________GroupedPresentationObject______________________________________Description:An object that is composed of several graphics objects,bitmaps, and/or strings.Parents:ObjectIVs:objList(pos1 presObjn . . . posn presObjn)Messages: ##STR33## ##STR34## ##STR35## ##STR36## ##STR37## ##STR38## ##STR39## ##STR40## ##STR41##______________________________________ 
    
     Interrupt driven functions maintain the current xHot, yHot and button IVs of an instance of Pointer. The current status of these IVs can be determined by sending a pointer object the messages GetPosition or GetButtons. 
     It should be apparent that the Drag method of a display object can be implemented as a series of moves with the new position for each move being supplied by the mouse similar to the move method. 
     When the Drag method is invoked, messages are repeatedly sent to a pointer object to determine the status of the button IV and the cursor position (the xHot and yHot IVs). If the status of the button IV indicates dragging is to continue, the display object is deleted from its present position and painted at the newly determined xHot, yHot position. When the button IV indicated that dragging is completed, the Drag method finishes with a &#34;settle-in&#34; procedure that updates OccludesMe and OccludedByMe lists and paints the object at its new location taking into consideration the occlusion priorities. 
     It should be apparent that an instance of GroupPresentationObject can very nicely manage the entire screen where the destination bit map, dspBM, is the screen bit map. The objList IV is then the &#34;contents&#34; list earlier referred to. This class enables the entire screen display to be treated as an object. 
     In addition to the user interface classes, special tool classes aid in the implementation of the systems and methods according to this invention. The DisplayObjectEditor class is generally described in the following Table V. 
     
                       TABLE V______________________________________DisplayObjectEditor______________________________________Parents:WindowIVs:dspObj         displayObject being editedimagePlane     collection of graphic objects          describing the image of the          displayObjectshadowPlane    collection of graphic objects          describing the opaque potion of          the displayObjectmapPlane       collection of graphic objects          describing the selectable          regions of the displayObjectotherPlane     list of collections of graphic          objects describing the          selectable subregions of the          displayObjectcontrolMenu    menu which allows user to          select plant to editMessages: ##STR42## ##STR43## ##STR44## ##STR45## ##STR46## ##STR47## ##STR48## ##STR49## ##STR50## ##STR51## ##STR52## ##STR53## ##STR54## ##STR55## ##STR56## ##STR57## ##STR58## ##STR59## ##STR60## ##STR61## ##STR62## ##STR63## ##STR64## ##STR65## ##STR66## ##STR67## ##STR68## ##STR69## ##STR70## ##STR71## ##STR72## ##STR73##______________________________________ 
    
     The Window class in the parents list of Table V is simply a subclass of displayObject. The methods of the displayObjectEditor that implement features of this invention are the MoveToPlane, MovePlane and CopyPlane methods. The MoveToPlane method allows an element to be transferred from one imaged specification to another. The CopyToPlane method allows a copy of an element on one image specification to be placed upon another. The MovePlane and CopyPlane methods are similar except that entire specifications are moved or copied. In the preferred implementation, the image specifications being moved or copied are lists of object graphic commands since these are much easier to manipulate and change. Eventually, the bit mapped version of the image specification must be stored in the figure, map and mask specifications. 
     The specific computer code for carrying out the various methods for the objects described in this application depends upon the computer language being used and the preferences of the programmer. The methods can all be written by normally skilled programmers given the descriptions provided herein. Attached to his specification as Appendix A is the description of certain objects and the code for the essential methods of those objects as this invention was implemented in the Interlisp-D/Loops environment. 
     As used in the following claims, the term &#34;object-oriented environments&#34; refers to a programming environment in which program code segments are considered objects that interact by sending messages to one another. &#34;Objects&#34; are combinations of data structures and methods. A portion of the data structure includes the &#34;instance variables&#34; that distinguish objects from similar objects of the same type. A &#34;message&#34; is a command to an object that causes the object to execute a method or send a message. A &#34;method&#34; (not used interchangeably with &#34;process&#34;) is a subroutine used by an object upon receipt of a message. 
     A &#34;task&#34; or &#34;program&#34; is a series of instructions stored in a computers main or mass storage memory which can be executed by the computer. 
     A computer &#34;display&#34; is a two dimensional interactive output device such as a video screen. A &#34;window&#34; is all or a portion of the surface of the display. 
     &#34;Interactive&#34; editors as used in the claims refers to editors in which as editing takes place, the completed portions of the graphic element appear upon the display to be used as reference points for further editing. ##SPC1##