Visual Programming: Advanced Cantata Capabilities

A Hands-on Approach to Visual Programming

1. Variables: the variables subform is used to define variables and evaluate expressions. Once variables have been defined they can be used in place of integer, float, and double arguments of glyphs. Valid expressions may include variables, standard arithmetic operators, and logicals, as well as predefined constants and functions. To define a variable, follow the format:
   variable = expression

   EX: Predefined Constants:
       log2e  (value = 1.4426950408889634074)
   EX: Predefined Functions: 
       gnoise (gnoise[x] Gaussian noise function)
   EX: Logical Operators: 
       == or .EQ. see if two expressions are equal
   EX: Instruction or Statement:
       i=(i>10)?0:i+1 
   EX: User Defined Functions:
       f(x,y)=cos(sqrt(x**2+y**2)*exp(0.0-sqrt(x**2+y**2)/4)
       enter f(0,0) to evaluate the function at x=0 and y=0
   EX: Arithmetic Operators:
       *, /, -, +, **
   EX: Arithmetic Bit-wise Operators:
       <<  shift first expression to the left by the second
   EX: Arithmetic Assignment Operators:
       ^= bit wise XOR
   

   
   Variables subform

   • Expression: this is a string selection field to set variables or to enter an expression.
   • Result of Evaluation: the result of the mathematical expression parser is displayed here.
   • Evaluate button: to evaluate an expression or set a variable click on this button.
   • Delete Variable(s): click on this button to delete variable(s). A list of variable(s) will be displayed, select the variable(s) to be deleted and then click the "Use" button.

     
     Delete variable(s) list

   • Variables Defined: list the varibales defined for the current workspace.
   • Workspace Defining Scope: in visual programs having procedures, while loops, or count loops, each workspace in the hierarchy will be listed in this space. By clicking on the different workspaces the valid variables will be displayed in the "Variables Defined" field.
     Then scope of the variables can be set via the Attributes submenu.
2. Procedures (subroutines): hierarchy within cantata is supported via procedures. Procedures are ONLY valid within the current workspace. In order to share procedures across different workspaces, you should first create the procedure and then create a Encapsulated Workspace from it.

   
   Click inside the image to see inside the Procedure

   • To create a procedure:
     1. select the set of glyphs that constitute your procedure
     2. select Create Procedure from the Workspace submenu or click on the equivalent switch found in the "Workspace Command Bar".

        
        Create Procedure switch

     3. place the created by clicking at the desired position in the workspace.
   • To open a procedure click on the "Open Workspace" button .
   • To rename a procedure, click on the current name "Procedure" that appears underneath the procedure glyph and a prompt in which you can enter a new name will appear.
   • If desired, procedures can be nested.
3. Control Structures: these structures provide constructs to direct the flow (control and data) of a visual program. Two types of constructs: conditional and looping.
   • Conditional: flow will be directed one way or another depending on the variables defined for the workspace.

     The available conditional constructs include:

     • If/Else: directs data flow to one path if a specified condition is met, to another path if the condition is not met.

       
       If/Else conditional construct

       To use the if/else construct:

       1. Create an If/Else glyph.
       2. Use the "Variables" subform to define and initialize a boolean variable to be used in the conditional expression of the If/Else operator. NOTE: every time you change the value of a variable, reset your workspace environment before a new execution of your visual program.
       3. Open the pane of the If/Else operator and type in the condition.
       4. Close the pane and connect the If/Else glyph in your visual program.
       If/Else construct example.
     • Merge: directs data flow from two separate paths to the same path, whether data arrives from the first path, the second path, or both; no condition is involved.

       
       Merge conditional construct

       To use the merge construct:

       1. Create a Merge glyph.
       2. Connect the glyph in your visual program.
       Merge construct example.
     • Switch: selects one of two inputs for use by the visual network, depending on the value of a conditional statement.

       
       Switch conditional construct

       To use the switch construct:

       1. Create an Switch glyph.
       2. Use the "Variables" subform to define and initialize a boolean variable to be used in the conditional expression of the Switch operator. NOTE: every time you change the value of a variable, reset your workspace environment before a new execution of your visual program.
       3. Open the pane of the Switch operator and type in the condition.
       4. Close the pane and connect the Switchglyph in your visual program.
       Switch construct exmaple.
     • Trigger: delays execution of a glyph until data is made available by another glyph which is not otherwise connected to the dependent glyph.

       
       Trigger conditional construct

       To use the trigger construct:

       1. Create a Trigger glyph.
       2. Connect the glyph in your visual program.
       Trigger construct example.
     • Expression: sets the value of a variable; used in conjunction with other control structures for purposes of variable initialization and/or modification.

       
       Expression conditional construct

       To use the expression construct:

       1. Create an Expression glyph.
       2. Open the pane of the Expression operator and type in the expression that is to be used to define, initialize, or modify the value of a variable.
       3. Close the pane and connect the Expression glyph in your visual program.
       Expression construct example.
   • Looping: flow will iterate through a particular section of the visual program multiple times defined by the varibles of the workspace.

     To create a loop construct:

     1. Select only the set of glyphs to be incorporated into the loop construct.
     2. Create the loop construct (Count, While). The selected glyphs will be removed from the workspace and the loop cronstruct will be created.
     3. Place the new loop glyph by clicking at the desired location in the workspace. After you place the glyph, all network connections will be redrawn.

     The available looping constructs include:

     • Count: causes data flow to iterate through a particular section of a network a specified number of times.

       
       Count looping construct

       After the count loop construct has been created, open the pane to specify the loop parameters. Provide a variable, and initial, final and increment values. Close the count loop pane and it is ready for execution.

       
       Count Loop pane and parameters

       Execute sample visual program with Count loop construct.

     • While: causes data flow to iterate through a particular section of a network as long as a particular condition is met.

       
       While looping construct

       After the while loop construct has been created, open the pane to specify the loop parameters. Provide the conditional expression that determines the number of times the loop will be executed. If desired, you may also provide an initial expression, and an update expression. Close the while loop pane and it is ready for execution.

       
       While Loop pane and parameters

       Execute sample visual program with While loop construct.

4. Encapsulated Workspaces: the process of creating an independent application from a visual program is referred to as encapsulating a workspace. The functionality of a visual program is "stored" as a new Khoros program called an encapsulated workspace. This new encapsulated workspace can be brought into cantata as a new operator, accessible via Toolbox Menus, teh Accelerated Routines list, and the Accelerated Finder list, just like any other Khoros program. The new independent application can be run without display of the network of glyphs that define the visual program. Once the a visual program is ready for encapsulation, the command line user interface and the graphical user interface for the new program must be defined.

   NOTE: for Encapsulated Workspaces you need to be familiar with the Khoros software development tools (guise, composer, craftsman).

   An encapsulated workspace is a software object, i.e., it is a pane object. It is NOT composed of either C code or a scripting language interpretaion if the visual program. The key components of an encapsulated workspace are:

   • Network of glyphs as they appear in the cantata workspace, written out as a saved regular workspace file.
   • The *.pane file that simnultaneously defines the workspace GUI and the CLUI of the encapsulated workspace.
   • An automatically generated shell script with a number of comments and a single line of code that executes kexec.

   Creation of Encapsulated Workspaces.

5. Data Transport and Distributed Processing: (not available yet)

In summary, cantata is used by the visual programmer to interactively develop visual programs by combining glyphs into a visual program or network.