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HostedAudioProcessorParameter Struct Referenceabstract

A parameter with functions that are useful for plugin hosts. More...

#include <juce_HostedAudioProcessorParameter.h>

Inheritance diagram for HostedAudioProcessorParameter:

Public Member Functions

virtual String getParameterID () const =0
 Returns an ID that is unique to this parameter.
 AudioProcessorParameter () noexcept=default
 AudioProcessorParameter (int versionHint)
 The version hint supplied to this constructor is used in Audio Unit plugins to aid ordering parameter identifiers when JUCE_FORCE_USE_LEGACY_PARAM_IDS is not enabled.
- Public Member Functions inherited from AudioProcessorParameter
 AudioProcessorParameter () noexcept=default
 AudioProcessorParameter (int versionHint)
 The version hint supplied to this constructor is used in Audio Unit plugins to aid ordering parameter identifiers when JUCE_FORCE_USE_LEGACY_PARAM_IDS is not enabled.
virtual ~AudioProcessorParameter ()
virtual float getValue () const =0
 Called by the host to find out the value of this parameter.
virtual void setValue (float newValue)=0
 The host will call this method to change the value of a parameter.
void setValueNotifyingHost (float newValue)
 A processor should call this when it needs to change one of its parameters.
void beginChangeGesture ()
 Sends a signal to the host to tell it that the user is about to start changing this parameter.
void endChangeGesture ()
 Tells the host that the user has finished changing this parameter.
virtual float getDefaultValue () const =0
 This should return the default value for this parameter.
virtual String getName (int maximumStringLength) const =0
 Returns the name to display for this parameter, which should be made to fit within the given string length.
virtual String getLabel () const =0
 Some parameters may be able to return a label string for their units.
virtual int getNumSteps () const
 Returns the number of steps that this parameter's range should be quantised into.
virtual bool isDiscrete () const
 Returns whether the parameter uses discrete values, based on the result of getNumSteps, or allows the host to select values continuously.
virtual bool isBoolean () const
 Returns whether the parameter represents a boolean switch, typically with "On" and "Off" states.
virtual String getText (float normalisedValue, int) const
 Returns a textual version of the supplied normalised parameter value.
virtual float getValueForText (const String &text) const =0
 Should parse a string and return the appropriate value for it.
virtual bool isOrientationInverted () const
 This can be overridden to tell the host that this parameter operates in the reverse direction.
virtual bool isAutomatable () const
 Returns true if the host can automate this parameter.
virtual bool isMetaParameter () const
 Should return true if this parameter is a "meta" parameter.
virtual Category getCategory () const
 Returns the parameter's category.
int getParameterIndex () const noexcept
 Returns the index of this parameter in its parent processor's parameter list.
virtual String getCurrentValueAsText () const
 Returns the current value of the parameter as a String.
virtual StringArray getAllValueStrings () const
 Returns the set of strings which represent the possible states a parameter can be in.
int getVersionHint () const
void addListener (Listener *newListener)
 Registers a listener to receive events when the parameter's state changes.
void removeListener (Listener *listener)
 Removes a previously registered parameter listener.
void sendValueChangedMessageToListeners (float newValue)

Additional Inherited Members

- Public Types inherited from AudioProcessorParameter
enum  Category {
  genericParameter = (0 << 16) | 0 , inputGain = (1 << 16) | 0 , outputGain = (1 << 16) | 1 , inputMeter = (2 << 16) | 0 ,
  outputMeter = (2 << 16) | 1 , compressorLimiterGainReductionMeter = (2 << 16) | 2 , expanderGateGainReductionMeter = (2 << 16) | 3 , analysisMeter = (2 << 16) | 4 ,
  otherMeter = (2 << 16) | 5

Detailed Description

A parameter with functions that are useful for plugin hosts.

Member Function Documentation

◆ getParameterID()

virtual String HostedAudioProcessorParameter::getParameterID ( ) const
pure virtual

Returns an ID that is unique to this parameter.

Parameter indices are unstable across plugin versions, which means that the parameter found at a particular index in one version of a plugin might move to a different index in the subsequent version.

Unlike the parameter index, the ID returned by this function should be somewhat stable (depending on the format of the plugin), so it is more suitable for storing/recalling automation data.

Implemented in AudioProcessorParameterWithID.

◆ AudioProcessorParameter() [1/2]

AudioProcessorParameter::AudioProcessorParameter ( )

◆ AudioProcessorParameter() [2/2]

AudioProcessorParameter::AudioProcessorParameter ( int versionHint)

The version hint supplied to this constructor is used in Audio Unit plugins to aid ordering parameter identifiers when JUCE_FORCE_USE_LEGACY_PARAM_IDS is not enabled.

When adding a parameter that is not present in a previous version of the Audio Unit, you must ensure that the version hint supplied is a number higher than that of any parameter in any previous plugin version.

For example, in the first release of a plugin, every parameter was created with "1" as a version hint. If you add some parameters in the second release of the plugin, all of the new parameters should have "2" as a version hint. Additional parameters added in subsequent plugin versions should have "3", "4", and so forth, increasing monotonically.

Note that adding or removing parameters with a version hint that is lower than the maximum version hint of all parameters will break saved automation in some hosts, so be careful!

A version hint of "0" will be treated as though the version hint has not been set explicitly. When targeting the AU format, the version hint may be checked at runtime in debug builds to ensure that it has been set.


According to Apple's Documentation:

‍An audio unit parameter is uniquely identified by the combination of its scope, element, and ID.

However, Logic Pro and GarageBand have a known limitation that causes them to use parameter indices instead of IDs to identify parameters. The effect of this is that adding parameters to a later version of a plugin can break automation saved with an earlier version of the plugin if the indices of existing parameters are changed. It is always unsafe to remove parameters from an Audio Unit plugin that will be used in one of these hosts, because removing a parameter will always modify the indices of following parameters.

In order to work around this limitation, parameters in AUv2 plugins are sorted first by their version hint, and then by the hash of their string identifier. As long as the parameters from later versions of the plugin always have a version hint that is higher than the parameters from earlier versions of the plugin, recall of automation data will work as expected in Logic and GarageBand.

Note that we can't just use the JUCE parameter index directly in order to preserve ordering. This would require all new parameters to be added at the end of the parameter list, which would make it impossible to add parameters to existing parameter groups. It would also make it awkward to structure code sensibly, undoing all of the benefits of string-based parameter identifiers.

At time of writing, AUv3 plugins seem to be affected by the same issue, but there does not appear to be any API to control parameter indices in this format. Therefore, when building AUv3 plugins you must not add or remove parameters in subsequent plugin versions if you wish to support Logic and GarageBand.

The documentation for this struct was generated from the following file:
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