/*!
\page page_preview-actions Preview Actions

The preview action is an action that allows the application to generate a preview of the action before
the action is applied. The preview is controlled by the HUD UI.

PreviewActions contain one or more parameters which form the preview parameters of the action.

The PreviewAction has additional extra requirements compared to other Actions:
- It can have multiple parameters whose values can be seen and changed over the bus
- The parameters' ordering can be specified by client code
- It adds new signals to control the preview mode: started, cancelled, resetted

The ordering of the parameters is specified by the order in which the actions are defined in the parameters list.

PreviewAction does not have a value of it's own. Instead the values of the parameters provide the information
on which the preview is generated.

\image html hud_parameters.jpg "HUD UI showing Color Balance action with four slider parameters"

\section sec_control_signals Control Signals
Diagram describing when the different signals are emitted:
\image html preview_action_signals.png

<i>started</i> signal informs the application that it must set up a preview view and start updating the
preview based on the values of the defined preview parameters.

<i>resetted</i> signal informs the application that it has to reset the parameter values to their original values.

<i>cancelled</i> signal informs the application that the user cancelled the PreviewAction. At this point the application
must return the the state it was in at the time the <i>started()</i> signal was triggered without applying any changes.

<i>triggered</i> signal informs the application the user wants the changes to be applied.

\section sec_example Example

This example shows how to create a PreviewAction with a single range parameter.

First a PreviewAction is created and set up:
\snippet preview-action/preview-action.cpp create previewaction

Then a PreviewRangeParameter:
\snippet preview-action/preview-action.cpp create rangeparameter

After all the parameters have been created they are added to the PreviewAction:
\snippet preview-action/preview-action.cpp set previewaction parameters

And finally the PreviewAction is added to the ActionManager:
\snippet preview-action/preview-action.cpp add to manager

Then hooking up the control signals:
\snippet preview-action/preview-action.cpp connect previewaction signals

And not forgetting the parameter value updates:
\snippet preview-action/preview-action.cpp connect parameter signals

---

The complete example:
\include examples/preview-action/preview-action.cpp

*/
