juce::ParameterAttachment Class Reference

Used to implement 'attachments' or 'controllers' that link a plug-in parameter to a UI element. More...

#include <juce_ParameterAttachments.h>

Inheritance diagram for juce::ParameterAttachment:

Collaboration diagram for juce::ParameterAttachment:

Public Member Functions
	ParameterAttachment (RangedAudioParameter &parameter, std::function< void(float)> parameterChangedCallback, UndoManager *undoManager=nullptr)
	Listens to a parameter and calls the the provided function in response to parameter changes. More...
	~ParameterAttachment () override
	Destructor. More...
void	beginGesture ()
	Begins a gesture on the managed parameter. More...
void	endGesture ()
	Ends a gesture on the managed parameter. More...
void	sendInitialUpdate ()
	Calls the parameterChangedCallback function that was registered in the constructor, making the UI reflect the current parameter state. More...
void	setValueAsCompleteGesture (float newDenormalisedValue)
	Triggers a full gesture message on the managed parameter. More...
void	setValueAsPartOfGesture (float newDenormalisedValue)
	Updates the parameter value during a gesture. More...

Private Member Functions
template<typename Callback >
void	callIfParameterValueChanged (float newDenormalisedValue, Callback &&callback)
void	cancelPendingUpdate () noexcept
	This will stop any pending updates from happening. More...
void	handleAsyncUpdate () override
	Called back to do whatever your class needs to do. More...
void	handleUpdateNowIfNeeded ()
	If an update has been triggered and is pending, this will invoke it synchronously. More...
bool	isUpdatePending () const noexcept
	Returns true if there's an update callback in the pipeline. More...
float	normalise (float f) const
void	parameterGestureChanged (int, bool) override
	Indicates that a parameter change gesture has started. More...
void	parameterValueChanged (int, float) override
	Receives a callback when a parameter has been changed. More...
void	triggerAsyncUpdate ()
	Causes the callback to be triggered at a later time. More...

Private Attributes
ReferenceCountedObjectPtr< AsyncUpdaterMessage >	activeMessage
std::atomic< float >	lastValue { 0.0f }
RangedAudioParameter &	parameter
std::function< void(float)>	setValue
UndoManager *	undoManager = nullptr

Detailed Description

Used to implement 'attachments' or 'controllers' that link a plug-in parameter to a UI element.

To implement a new attachment type, create a new class which includes an instance of this class as a data member. Your class should pass a function to the constructor of the ParameterAttachment, which will then be called on the message thread when the parameter changes. You can use this function to update the state of the UI control. Your class should also register as a listener of the UI control and respond to respond to changes in the UI element by calling either setValueAsCompleteGesture or beginGesture, setValueAsPartOfGesture and endGesture.

Make sure to call sendInitialUpdate at the end of your new attachment's constructor, so that the UI immediately reflects the state of the parameter.

@tags{Audio}

Constructor & Destructor Documentation

ParameterAttachment()

juce::ParameterAttachment::ParameterAttachment	(	RangedAudioParameter &	parameter,
		std::function< void(float)>	parameterChangedCallback,
		UndoManager *	undoManager = nullptr
	)

Listens to a parameter and calls the the provided function in response to parameter changes.

If an undoManager is supplied beginNewTransaction will be called on it whenever the UI requests a parameter change via this attachment.

Parameters

parameter	The parameter to which this attachment will listen
parameterChangedCallback	The function that will be called on the message thread in response to parameter changes
undoManager	The UndoManager that will be used to begin transactions when the UI requests a parameter change.

~ParameterAttachment()

juce::ParameterAttachment::~ParameterAttachment ( )

override

Destructor.

Member Function Documentation

beginGesture()

void juce::ParameterAttachment::beginGesture

(

)

Begins a gesture on the managed parameter.

Call this when the UI is about to begin a continuous interaction, like when the mouse button is pressed on a slider.

Referenced by juce::SliderParameterAttachment::sliderDragStarted().

callIfParameterValueChanged()

template<typename Callback >

void juce::ParameterAttachment::callIfParameterValueChanged ( float  newDenormalisedValue, Callback &&  callback  )

private

cancelPendingUpdate()

void juce::AsyncUpdater::cancelPendingUpdate ( )

noexceptinherited

This will stop any pending updates from happening.

If called after triggerAsyncUpdate() and before the handleAsyncUpdate() callback happens, this will cancel the handleAsyncUpdate() callback.

Note that this method simply cancels the next callback - if a callback is already in progress on a different thread, this won't block until the callback finishes, so there's no guarantee that the callback isn't still running when the method returns.

endGesture()

void juce::ParameterAttachment::endGesture

(

)

Ends a gesture on the managed parameter.

Call this when the UI has finished a continuous interaction, like when the mouse button is released on a slider.

Referenced by juce::SliderParameterAttachment::sliderDragEnded().

handleAsyncUpdate()

void juce::ParameterAttachment::handleAsyncUpdate ( )

overrideprivatevirtual

Called back to do whatever your class needs to do.

This method is called by the message thread at the next convenient time after the triggerAsyncUpdate() method has been called.

Implements juce::AsyncUpdater.

handleUpdateNowIfNeeded()

void juce::AsyncUpdater::handleUpdateNowIfNeeded ( )

inherited

If an update has been triggered and is pending, this will invoke it synchronously.

Use this as a kind of "flush" operation - if an update is pending, the handleAsyncUpdate() method will be called immediately; if no update is pending, then nothing will be done.

Because this may invoke the callback, this method must only be called on the main event thread.

isUpdatePending()

bool juce::AsyncUpdater::isUpdatePending ( ) const

noexceptinherited

Returns true if there's an update callback in the pipeline.

normalise()

float juce::ParameterAttachment::normalise ( float  f ) const

inlineprivate

References juce::RangedAudioParameter::convertTo0to1(), juce::gl::f, and parameter.

parameterGestureChanged()

void juce::ParameterAttachment::parameterGestureChanged ( int  parameterIndex, bool  gestureIsStarting  )

inlineoverrideprivatevirtual

Indicates that a parameter change gesture has started.

E.g. if the user is dragging a slider, this would be called with gestureIsStarting being true when they first press the mouse button, and it will be called again with gestureIsStarting being false when they release it.

IMPORTANT NOTE: This will be called synchronously, and many audio processors will call it during their audio callback. This means that not only has your handler code got to be completely thread-safe, but it's also got to be VERY fast, and avoid blocking. If you need to handle this event on your message thread, use this callback to trigger an AsyncUpdater or ChangeBroadcaster which you can respond to later on the message thread.

Implements juce::AudioProcessorParameter::Listener.

parameterValueChanged()

void juce::ParameterAttachment::parameterValueChanged ( int  parameterIndex, float  newValue  )

overrideprivatevirtual

Receives a callback when a parameter has been changed.

IMPORTANT NOTE: This will be called synchronously when a parameter changes, and many audio processors will change their parameter during their audio callback. This means that not only has your handler code got to be completely thread-safe, but it's also got to be VERY fast, and avoid blocking. If you need to handle this event on your message thread, use this callback to trigger an AsyncUpdater or ChangeBroadcaster which you can respond to on the message thread.

Implements juce::AudioProcessorParameter::Listener.

sendInitialUpdate()

void juce::ParameterAttachment::sendInitialUpdate

(

)

Calls the parameterChangedCallback function that was registered in the constructor, making the UI reflect the current parameter state.

This function should be called after doing any necessary setup on the UI control that is being managed (e.g. adding ComboBox entries, making buttons toggle-able).

setValueAsCompleteGesture()

void juce::ParameterAttachment::setValueAsCompleteGesture

(

float

newDenormalisedValue

)

Triggers a full gesture message on the managed parameter.

Call this in the listener callback of the UI control in response to a one-off change in the UI like a button-press.

setValueAsPartOfGesture()

void juce::ParameterAttachment::setValueAsPartOfGesture

(

float

newDenormalisedValue

)

Updates the parameter value during a gesture.

Call this during a continuous interaction, like a slider value changed callback.

triggerAsyncUpdate()

void juce::AsyncUpdater::triggerAsyncUpdate ( )

inherited

Causes the callback to be triggered at a later time.

This method returns immediately, after which a callback to the handleAsyncUpdate() method will be made by the message thread as soon as possible.

If an update callback is already pending but hasn't happened yet, calling this method will have no effect.

It's thread-safe to call this method from any thread, BUT beware of calling it from a real-time (e.g. audio) thread, because it involves posting a message to the system queue, which means it may block (and in general will do on most OSes).

Member Data Documentation

activeMessage

ReferenceCountedObjectPtr<AsyncUpdaterMessage> juce::AsyncUpdater::activeMessage

privateinherited

lastValue

std::atomic<float> juce::ParameterAttachment::lastValue { 0.0f }

private

parameter

RangedAudioParameter& juce::ParameterAttachment::parameter

private

Referenced by normalise().

setValue

std::function<void (float)> juce::ParameterAttachment::setValue

private

undoManager

UndoManager* juce::ParameterAttachment::undoManager = nullptr

private

---

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

• juce_ParameterAttachments.h