Interactive method of developing software interfaces

Claims

We claim:

1. A system for the interactive design of user manipulable graphic elements, comprising

a) a computer having a display and stored tasks wherein the appearance of said graphic elements and methods for their manipulation are defined, each said graphic element being defined by at least one figure specification defining the appearance of said graphic element and at least one other type specification defining one or more areal properties of one or more portions of said graphic element,

b) an interactive display editor program for defining the figure specification and said other type specifications of said graphic elements,

c) an interactive program editor program for programming data and said methods associated with said graphic elements, and

d) program means using the figure specification and said other type specifications for assembling said graphic elements upon the display and enabling user manipulation of said graphic elements.

2. Systems according to claim 1 wherein said display editor has means for copying said figure specification and said other type specifications to form copied specifications and for modifying said copied specifications for creating additional other type specifications.

3. A system for the interactive design of user manipulable graphic elements, comprising

a) a computer having a bit mapped display and 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 bit mapped figure specification instance variable defining the appearance of said display object and at least one other bit mapped type specification instance variable defining one or more areal properties of one or more portions of said display object,

b) an interactive display editor program for defining said bit mapped figure specification instance variables and said other bit mapped type specification instance variables of said display objects,

c) an interactive program editor program for programming data and said methods associated with said display objects and other objects of said programming environment, and

d) program means using said bit mapped figure specification instance variables and said other bit mapped type specification instance variables for assembling said graphic elements upon the display and enabling user manipulation of said graphic elements.

4. A system for the interactive design of user manipulable graphic elements, comprising

a) a computer having a bit mapped display and 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 bit mapped figure specification instance variable defining the appearance of said display object and at least one bit mapped mask specification instance variable,

b) an interactive display editor program for defining said bit mapped figure specification instance variables and said bit mapped mask specification instance variables of said display objects,

c) an interactive program editor program for programming data and said methods associated with said display objects and other objects of said programming environment, and

d) program means using said bit mapped figure specification instance variable and said bit mapped mask specification instance variables for assembling said graphic elements upon the display and enabling manipulation of said graphic elements,

said mask specification instance variables defining nontransparent portions of said graphic elements, said display editor program having means for establishing and maintaining a list defining occlusion priorities of said graphic elements, said program means for assembling said graphic elements upon the display comprising means for defining one or more collections of overlaid graphic elements, each of said collections being formed by moving one or more of said graphic elements to a position in which said moved graphic elements geometrically overlap one or more other of said graphic elements to create overlaid portions and a second program means for controlling the display such that said nontransparent portions of said graphic elements of each said collection having higher occlusion priorities mask all said overlaid portions of graphic elements having lower occlusion priorities.

5. A system for the interactive design of user manipulable graphic elements displayed upon a computer display, comprising

a) a computer having a bit mapped display, a mouse for input, said mouse having one or more mouse buttons, a keyboard input capability and 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, said display object comprising at least one bit mapped figure specification instance variable defining the appearance of said display object and at least one bit mapped map specification instance variable,

b) an interactive display editor program for defining said bit mapped figure specification instance variables and said bit mapped map specification instance variables of said display objects,

c) an interactive program editor program for programming data and said methods associated with said display objects and other objects of said programming environment, and

d) program means using said bit mapped figure specification instance variables for assembling said graphic elements upon the display and for displaying a mouse cursor within said display,

said map specification instance variables defining mouse sensitive portions of said graphic element as a tagged list or list tree of bit maps, said program editor program having means for defining one or more of said methods to be activated when the mouse is used to bring the mouse cursor over said mouse sensitive areas of said graphic element and one of said mouse buttons has been pushed while the mouse cursor is within a mouse sensitive area.

6. A system for the interactive design of user manipulable graphic elements displayed upon a computer display, comprising

a) a computer having a bit mapped display, a mouse input, said mouse having one or more mouse buttons, a keyboard input capability and stored tasks comprising an object oriented programming environment allowing messages to be exchanged between objects and 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 bit mapped figure specification instance variable defining the appearance of said display object, at least one bit mapped mask specification instance variable and at least one bit mapped map specification instance variable,

b) a display editor program for defining said bit mapped figure, mask and map specification instance variables of said display objects,

c) a program editor program for programming data and said methods assigned to said display objects and other objects of said programming environment, and

d) a program means using said bit mapped figure, mask and map specification instance variables for assembling said graphic elements upon the display and for displaying a mouse cursor within said display,

said mask specification instance variables defining nontransparent portions of said graphic element, said display editor program or said program editor program having means for assigning occlusion priorities to each said graphic element, said program means further having means for defining one or more collections of overlaid graphic elements, each of said collections being formed by moving one or more of said graphic elements to a position in which said moved graphic elements geometrically overlap one or more other of said graphic elements to create overlaid portions, and a second program means for controlling the display such that said nontransparent portions of said graphic elements of each said collection having higher occlusion priorities mask all said overlaid portions of graphic elements having lower occlusion priorities, said map specifications defining mouse sensitive portions of at least one said graphic element, said program editor having means for defining one or more of said methods or messages to be activated when the mouse is used to bring the mouse cursor over said mouse sensitive areas of said graphic element and one of said mouse buttons is pushed.

7. Systems according to any one of claims 3 to 6 wherein said display editor has means for creating multiple sets of bit mapped specification instance variables associated with a given display object which sets of specification instance variables are selectable by messages sent to the display object.

8. Systems according to any one of claims 3 to 6 wherein said display editor has means for copying said bit mapped specification instance variables to yield copied specification instance variables and modifying said copied specification instance variables for creating additional bit mapped type specification instance variables.

9. A computer assisted process for the interactive design of user manipulable graphic elements displayed on a computer display, said method requiring a computer having tasks wherein the appearance of said graphic elements and methods for their manipulation are defined, each said graphic element bring defined by at least one figure specification defining the appearance of said graphic element and at least one other type specification defining one or more areal properties of one or more portions of said graphic element, an interactive display editor program for defining the figure specification and said other type specifications of said graphic elements, a program editor program for programming data and said methods associated with said graphic elements, and a program means for assembling said graphic elements upon the display and enabling the manipulation of said graphic elements, comprising the steps of

a) using the display editor program to interactively define said figure specification of a new graphic element, and

b) using the display editor program to interactively define at least one of said other type specifications of said new graphic element.

10. A process according to claim 9 wherein figure specifications are copied and modified to define specifications of new display objects.

11. A computer assisted process for the interactive design of user manipulable graphic elements displayed upon a computer display, said method requiring a computer having an object oriented programming environment wherein the appearance of said graphic elements and methods for their manipulation are defined, each said graphic element being defined by display objects, each said display object comprising at least one bit mapped figure specification instance variable defining the appearance of said graphic element and at least one other bit mapped type specification instance variable defining one or more areal properties of one or more portions of said graphic element, an interactive display editor program for defining the figure specification instance variables and said other bit mapped type specification instance variables of said display objects, a program editor program for programming data and said methods assigned to said display objects and other objects of said programming environment, and a program means for assembling said graphic elements upon the display and enabling the manipulation of said graphic elements, comprising the steps of

a) using the display editor program to interactively define the bit mapped figure specification instance variables of a new graphic element, the data for which figure specification instance variables are associated with a display object corresponding to said new graphic element, and

b) using the display editor program to interactively define at least one other bit mapped type specification instance variables of said new graphic element, the data for which other type specification instance variables are associated with a display object corresponding to said new graphic element.

12. A computer assisted process for the interactive design of user manipulable graphic elements displayed upon a computer display, said method requiring a computer having a bit mapped display and 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 bit mapped figure specification instance variable defining the appearance of said graphic element and at least bit mapped mask specification instance variable defining nontransparent portions of said graphic element, an interactive display editor program for defining the bit mapped figure and mask specification instance variables of said display objects, a program editor program for programming data and said methods assigned to said display objects and other objects of said programming environment, and a display program means, said display program means supporting windows, for assembling said graphic elements upon the display and enabling the interactive positioning and repositioning of said graphic elements at locations within one or more of said windows, comprising the steps of

a) using the display editor program to interactively define the bit mapped figure specification instance variables of a new graphic element, the data for which figure specification instance variables are associated with a display object corresponding to said new graphic element,

b) using the display editor program to interactively define the bit mapped mask specification instance variables defining transparent and nontransparent portions of said new graphic element, the data for which map specification instance variables are associated with a display object corresponding to said new graphic element,

c) repeating steps a) and b) one or more times to define a plurality of display objects, and

d) using either the display editor program or the program editor program for assigning occlusion priorities to each display object such that when the display program means is invoked to move one or more of said new graphic elements to a position in which said moved graphic elements geometrically overlap one or more of other said graphic elements to created overlaid portions, said nontransparent portions of said graphic elements having higher occlusion priorities mask all said overlaid portions of graphic elements having lower occlusion priorities.

13. A computer assisted process for the interactive design for user manipulable graphic elements displayed upon a computer display, said method requiring a computer having a bit mapped display, a mouse for input, said mouse having one or more mouse buttons, a keyboard input capability and an object oriented programming environment allowing messages to be exchanged between objects and 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 bit mapped figure specification instance variable defining the appearance of said graphic element and at least one other bit mapped type specification instance variable defining one or more areal properties of one or more portions of said graphic element, an interactive display editor program for defining the bit mapped figure specification instance variables and said other bit mapped type specification instance variables of said display objects, a program editor program for programming data and said methods assigned to said display objects and other objects of said programming environment, and a display program means for assembling graphic elements upon the display and displaying a mouse cursor, comprising the steps of

a) using the display editor program to interactively define the bit mapped figure specification instance variables of a new graphic element, the data for which figure specification instance variables are associated with a display object corresponding to said graphic element,

b) using the display editor program and the program editor program to interactively define the bit mapped map specification instance variables defining mouse sensitive portions of at least one said new graphic element, the data for which map specification instance variables are associated with a display object corresponding to said graphic element, and

c) using the program editor program to define one or more of said methods or messages to be activated when the mouse is used to bring the mouse cursor over said mouse sensitive areas of said graphic element and one of said mouse buttons is pushed.

14. A computer assisted process for the interactive design of user manipulable graphic elements displayed upon a bit mapped computer display, said graphic elements being comprised of at least bit mapped figure specification instance variables defining the appearance of said graphic elements, bit mapped mask specification instance variables defining the transparent and nontransparent portions of said graphic elements, and bit mapped map specification instance variables defining mouse sensitive portions of said graphic elements, said process requiring a computer having a mouse for input, said mouse having one or more mouse buttons, a keyboard input capability and having an object oriented programming environment with an interactive display editor program for defining elements of display objects representing said graphic elements, a program editor program for programming data and methods for manipulating objects assigned to said display objects and to other objects of said programming environment, and a display program means, said display program means supporting windows, for assembling said graphic elements within at least one of said windows defined upon the display and enabling the interactive positioning and repositioning of said graphic elements at locations within one or more of said windows, comprising the steps of

a) using the display editor program to interactively define bit mapped figure specification instance variables of a new graphic element, the data for which figure specification instance variables are associated with a display object corresponding to said new graphic element,

b) using the display editor program to interactively define bit mapped mask specification instance variables defining transparent and nontransparent portions of said new graphic element, the data for which mask specification instance variables are associated with a display object corresponding to said new graphic element,

c) repeating steps a) and b) one or more times to define a plurality of display objects,

d) using either the display editor program or the program editor program for assigning occlusion priorities to each of said new graphic elements by storing data in at least one of said instance variables associated with each display object such that when the display program means is invoked to move one or more of said graphic elements to a position in which said moved graphic elements geometrically overlap one or more of other said graphic elements to created overlaid portions, said nontransparent portions of said graphic elements having higher occlusion priorities mask all said overlaid portions of graphic elements having lower occlusion priorities,

e) using the display editor program and the program editor program to interactively define one or more of said map specification instance variables of at least one said new graphic element, the data for which map specification instance variables are associated with a display object corresponding to said new graphic element, and

f) using the program editor program to define one or more of said methods or messages to be activated when the mouse is used to bring the mouse cursor over said mouse sensitive areas of said graphic element and one of said mouse buttons is pushed, said methods and messages being associated with a display object corresponding to said graphic element.

15. A computer assisted process for the interactive design of user manipulable graphic elements associated with an application domain and displayed upon a bit mapped computer display, said graphic elements being comprised of at least bit mapped figure specification instance variables defining the appearance of said graphic elements, bit mapped mask specification instance variables defining the transparent and nontransparent portions of said graphic elements, and bit mapped map specification instance variables defining mouse sensitive portions of said graphic elements, said graphic elements comprising the visual representations of programming items, said process requiring a computer having a mouse for input, said mouse having one or more mouse buttons, a keyboard input capability and having an object oriented programming environment with an interactive display editor program for defining elements of display objects representing said graphic elements, a program editor program for programming data and methods for manipulating objects assigned to said display objects and to other objects of said programming environment, and a display program means, said display program means supporting windows, for assembling said graphic elements within at least one of said windows defined upon the display and enabling the interactive positioning and repositioning of said graphic elements at locations within one or more of said windows, comprising the steps of

a) using the display editor program to interactively define bit mapped figure specification instance variables of a new graphic element, the data for which figure specification instance variables are associated with a display object corresponding to said new graphic element,

b) using the display editor program to interactively define bit mapped mask specification instance variables, the data for which mask specification instance variables are associated with a display object corresponding to said new graphic element,

c) repeating steps a) and b) one or more times to define a plurality of display objects,

d) using either the display editor program or the program editor program for assigning occlusion priorities to each of said new graphic elements by storing data in at least one of said instance variables associated with each display object such that when the display program means is invoked to move one or more of said graphic elements to a position in which said moved graphic elements geometrically overlap one another or more of other said graphic elements to created overlaid portions, said nontransparent portions of said graphic elements having higher occlusion priorities mask all said overlaid portions of graphic elements having lower occlusion priorities,

e) using the display editor program and the program editor program to interactively define one or more of said map specification instance variables of at least one said new graphic element, the data for which map specification instance variables are associated with a display object corresponding to said new graphic element,

f) using the program editor program to define one or more of said methods or messages to be activated when the mouse is used to bring the mouse cursor over said mouse sensitive areas of said graphic element and one of said mouse buttons is pushed, said methods and messages being stored at instance variables associated with the display object corresponding to said graphic element, and

g) using the program editor program to define methods for domain objects, said domain objects representing objects from said application domain and said methods specifying the function of said programming items and for exchanging messages with a display object defining the visual representation of said programming items.

16. A process according to any one of claims 11 to 15 wherein each display object may have multiple sets of figure specification instance variables associated therewith, said sets being selectable by messages sent to the display object.

17. A process according to any one of claims 11 to 15 wherein sets of figure specification instance variables are copied and modified to define specification instance variables of new display objects.

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'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, "drags" 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 "mouse event".) 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, "Software Frameworks" Byte December 1984, describing Apple Computers Toolkit/32; "Macapp: An Application Framework", Byte August 1986; and "Objects, Icons and Software-ICS", 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 "building inward" 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' 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; "Object-Oriented programming: Themes and Variations", 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'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'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 "Object-Oriented Programming: Themes and Variations", 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 "The SmallTalk Graphics Kern", Byte Magazine August 1981, and "Raster Operations", 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 "Sketch" 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 "Sketch" 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. "Sketch" is described in A Users Guide To Sketch-The Interlisp Drawing System, Xerox Corporation, 1985. "McDraw" 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. "Systems classes" 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 "Object" having no parent