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
-- change the parameter Scale through MIDI controller and use its value to replace the note-on velocity -- initialize variables min = 0 max = 100 maxVel = 127 defVel = 100 default = defVel / maxVel * max maxCC = 127 -- define Scale with the previous variables defineParameter("Scale", nil, default, min, max) -- use the value of Scale to replace the note-on velocity function onNote(event) event.velocity = maxVel * Scale / max postEvent(event) end -- change the value of Scale through the last incoming MIDI controller function onController(event) Scale = event.value / maxCC * max end
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. defineParameter(name, longName, default, min, max, increment, changeCallback) Creates a numeric parameter. The The automatic formatting of a value can be overridden with the defineParameter(name, longName, default, strings, changeCallback) Creates a parameter with integer indices that have a text representation given by the string values of an array. The defineParameter(name, longName, bool, changeCallback) Creates a boolean parameter. The defineParameter(name, longName, string, changeCallback) Creates a parameter with a string value. You can change the string by assigning a new string value to the parameter. defineParameter(name, longName, table, changeCallback) Creates a parameter with a table as value. The defineParameter(name, longName, parameterDefinition, changeCallback) Creates a parameter with the behavior of the specified parameterDefinition. You can use this to clone the behavior of existing parameters. defineParameter { name = "p", longName = "param", default = 0, min = 0, max = 100, increment = 0.01, onChanged = callback, type = "float", format = "%.2f", readOnly = false, writeAlways = false, automatable = true, persistent = true } 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.Numeric
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:Value Description increment = 1
The parameter will be an integer value and its value string will display no digits behind the decimal point. increment = 0.001
The parameter will be a floating point value and its value string will display three digits behind the decimal point. increment = 0
The parameter will be a floating point value and its value string will display two digits behind the decimal point. format
argument. See Additional Named Arguments for more details.Indexed String Array
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
bool
argument also defines the default value of the parameter.String
Table
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
By Named Arguments
Example 2
-- showcase different parameters -- initialize variables maxVelocity = 127 -- change callback of parameter "Name" function nameChanged() print("name changed to", Name) --print the value of the parameter end -- initialize parameters defineParameter("Scale", nil, 100) -- parameter with default 100 and range 0 to 100 defineParameter("Offset", nil, 0, -100, 100, 1) -- bipolar parameter with integer steps defineParameter("Pan", nil, 0, -100, 100, 0.1) -- bipolar parameter with 0.1 steps defineParameter("Mode", nil, 1, { "Off", "Normal", "Hyper" }) -- indexed string array defineParameter("Enable", "Enable Filter", true) -- switch with long name defineParameter("Label", nil, "untitled", nameChanged) -- string parameter defineParameter("Intervals", nil, { 0, 4, 7 }) -- table parameter defineParameter("Volume", nil, this.parent:getParameterDefinition("Level")) --[[ parameter with the same behavior as the "Level" parameter of the parent layer ]] -- use the parameters Scale and Intervals to play a chord with fixed velocity function onNote(event) fixedVelocity = maxVelocity * Scale / 100 local id1 = playNote(event.note + Intervals[1], fixedVelocity) local id2 = playNote(event.note + Intervals[2], fixedVelocity) local id3 = playNote(event.note + Intervals[3], fixedVelocity) end
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 the parameter Scale through MIDI controller and use its value to replace the note-on velocity -- the current value of Scale is printed only if changed from UI, e.g., go to the Parameter List to adjust Scale -- initialize variables min = 0 max = 100 maxVel = 127 defVel = 100 default = defVel / maxVel * max maxCC = 127 -- this callback function will only be called if you adjust Scale from the UI function valueChanged() print("Value of Scale changed to:", Scale) end -- define Scale with the previous variables defineParameter("Scale", nil, default, min, max, valueChanged) -- use the value of Scale to replace the note-on velocity function onNote(event) event.velocity = maxVel * Scale / max postEvent(event) end -- change the value of Scale through the last incoming MIDI controller function onController(event) -- assigning a value to Scale will not call the callback function Scale = event.value / maxCC * max end
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
-- define string parameter defineParameter("Name", nil, "untitled", function() nameChanged() end) --[[ if nameChanged is called inside an anonymous function, it can be declared after defineParameter ]] -- change callback of parameter "Name" function nameChanged() print("name changed to", Name) -- print the value of the parameter end
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
-- different parameters created with named arguments -- change callback of parameter "Name" function nameChanged() print("name changed to", Name) --print the value of the parameter end -- parameter with default 100 and range 0 to 100 defineParameter{ name = "Scale", default = 100 } -- bipolar parameter with integer steps defineParameter{ name = "Offset", default = 0, min = -100, max = 100, increment = 1, } -- bipolar parameter with 0.1 steps defineParameter{ name = "Pan", default = 0, min = -100, max = 100, increment = 0.1, } -- indexed string array defineParameter{ name = "Mode", default = 1, strings = { "Off", "Normal", "Hyper" }, } -- switch with long name defineParameter{ name = "Enable", longName = "Enable Filter", default = true, } -- string parameter defineParameter{ name = "Label", default = "untitled", onChanged = nameChanged, } -- table parameter defineParameter{ name = "Intervals", default = { 0, 4, 7 }, }
Creating a parameter by ParameterDefinition is not supported when using named arguments.
Additional Named Arguments
If you create a parameter by named arguments, you get access to these additional arguments:
type | The value type of the parameter (integer, float, boolean, string, variant, or envelope). The type must match the default and increment arguments. | string, optional |
format | Formats the value string of a float value using the provided arguments. Only the format specifiers for float values are supported, i.e., e, E, f, g, or G. Other format specifiers are not supported. This overrides any automatic formatting from the increment argument. | string, optional |
readOnly | The parameter can only be changed from the script if this is set to true . The argument defaults to false if no value is set. | bool, optional |
writeAlways | A parameter does not call its change callback if its value is set without being changed. Set this to true if you want to guarantee that the change callback of the parameter is called. The argument defaults to false if not set. | bool, optional |
automatable | Set this to false if you do not want the parameter to be automated. The argument defaults to true if not set. | bool, optional |
processorCallback | The parameter change callback will be executed in the processor context with high accuracy, if this is set to true . For example, this is required for automated script parameters to update correctly when using Render in Place or Export Audio. If no processor exists, the call back is still run in the controller context. | bool, optional |
persistent | The parameter will not be restored from the VST preset if this is set to false . The argument defaults to true if not set. | bool, optional |
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
-- the following parameter is read only, not automatable and not persistent defineParameter { name = "deltaTime", longName = "Delta Time", default = 0, min = 0, max = 2^31, type = "float", format = "%.3f ms", readOnly = true, automatable = false, persistent = false, } -- measure the time between subsequent notes function onNote(event) postEvent(event) t2 = getTime() if t1 then deltaTime = t2 - t1 end t1 = t2 end -- the following parameter change callback is executed in the processor context with high accuracy function onP1changed() this.parent:setParameterNormalized("Level", P1 / 100) end defineParameter{name = "P1", min=0, max=100, onChanged = onP1changed, processorCallback = true}
3 Comments
Sabine Pfeifer
proofread done
Matthias Klag
Documented additional features of defineParameter. Please re-read. Thanks!
Sabine Pfeifer
proofread done