Creating Parameters

Parameters vs. Global Variables

The function defineParameter creates a global variable that represents the value of the parameter in the script. It should be noted that:

• The rules for the naming and scope of global variables also apply for parameters.
• You can change the value of a parameter by assigning a new value to the corresponding global variable.
• The parameters that you defined for your script module are saved with the program, as opposed to global variables, which are not saved automatically.

The following example shows that parameters can be used just like global variables. After the parameter Scale has been defined, it is used to replace the note-on velocity. The value of Scale is changed by assigning the value of the last incoming MIDI controller to it.

Example 1

Parameter Characteristics

How a parameter behaves depends on its characteristics. You determine the characteristics of a parameter with the arguments of defineParameter. To create a parameter with specific characteristics, the arguments must be set in the order in which they are shown in the following syntax examples.

Numeric

Creates a numeric parameter. The default argument defines the value that the parameter will default to. The min and max arguments define the value range of the parameter. The increment argument defines the step size of the parameter. The arguments default, min, max  and increment can be any integer or floating point value. How many digits are shown behind the decimal point for a value string of a parameter is determined by the value of the increment argument. For example:

The automatic formatting of a value can be overridden with the format argument. See Additional Named Arguments for more details.

Indexed String Array

Creates a parameter with integer indices that have a text representation given by the string values of an array. The default argument defines the index that the parameter will default to. The strings argument must be an array with string values starting with index 0 or 1.

Boolean

Creates a boolean parameter. The bool argument also defines the default value of the parameter.

String

Creates a parameter with a string value. You can change the string by assigning a new string value to the parameter.

Table

Creates a parameter with a table as value. The name argument of the parameter also defines the name of the table. You can access the values of the table using the regular methods, e.g., dot notation.

By Parameter Definition

Creates a parameter with the behavior of the specified parameterDefinition. You can use this to clone the behavior of existing parameters.

By Named Arguments

Creates a parameter by named arguments. The only argument to the function is a table with the key/value pairs that define the parameter. The additional keys type, format, readOnly, writeAlways, automatable and persistent give you control over more advanced features. They can only be set with named arguments. See Defining Parameters by Named Arguments for more details.

Example 2

Parameter Change Callback

The change callback is only called if the value of the parameter was changed from the user interface, e.g., by adjusting the corresponding control on the macro page, or by calling setParameter. It is not called if the value was changed through assigning a value from inside the script. The following example revisits Example 1 to demonstrate this:

Example 3

Change Callback with Anonymous Function

In Example 2 the function nameChanged is declared before the parameter is defined. This is necessary for defineParameter in order to detect that the argument nameChanged is a function. If you want to declare the callback function after defining the corresponding parameter, you must call the callback function within an anonymous function. As the name suggests, an anonymous function is a function without a name.

Example 4

Defining Parameters By Named Arguments

When calling defineParameter with several arguments, the arguments are matched by their position and the associated values are passed on to the function. For this reason, the arguments of defineParameter must match the exact order and position when calling the function. Alternatively, you can set the arguments with the keys and values of a table. This method of passing arguments and values to a function is called named arguments.

Named arguments have the advantage that they can be set in any order you want and that optional or additional arguments can be left out without destroying the predefined order and position of the arguments to that function. The following example shows the parameters from Example 2 created with named arguments.

Example 5

Additional Named Arguments

If you create a parameter by named arguments, you get access to these additional arguments:

The arguments readOnly, writeAlways and automatable are helpful if you have a parameter that is used only for indication, but not for entering values.

Example 6