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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.

HUD UI showing Color Balance action with four slider parameters

# Control Signals

Diagram describing when the different signals are emitted:

started 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.

resetted signal informs the application that it has to reset the parameter values to their original values.

cancelled 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 started() signal was triggered without applying any changes.

triggered signal informs the application the user wants the changes to be applied.

# Example

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

First a PreviewAction is created and set up:

PreviewAction *previewAction = new PreviewAction(this);
previewAction->setText("Exposure");

Then a PreviewRangeParameter:

PreviewRangeParameter *range = new PreviewRangeParameter(this);
range->setText("Exposure Amount");
range->setMinimumValue(-50);
range->setMaximumValue(50);
range->setValue(0);

After all the parameters have been created they are added to the PreviewAction:

previewAction->addParameter(range);

And finally the PreviewAction is added to the ActionManager:

ActionManager *manager = new ActionManager(this);
manager->addAction(previewAction);

Then hooking up the control signals:

connect(previewAction, &PreviewAction::triggered, [=]() {
// action was completed.
// apply the action with the values of the parameters
qDebug() << "Preview triggered.";
});
connect(previewAction, &PreviewAction::cancelled, [=]() {
// action was cancelled
qDebug() << "Preview cancelled.";
});
connect(previewAction, &PreviewAction::started, [=]() {
// action was activated in the HUD UI.
// do the necessary initialization and start providing preview
// based on the values of the parameters.
qDebug() << "Preview started.";
});
connect(previewAction, &PreviewAction::resetted, [=]() {
// reset the parameter values
qDebug() << "Preview reset(ted).";
});

And not forgetting the parameter value updates:

connect(range, &PreviewRangeParameter::valueChanged, [=](float value) {
// gets the values from the HUD UI when user interacts with the slider
// Application then updates the preview based on this value
qDebug() << "range value:" << value;
});

The complete example:

/* This file is part of lomiri-action-api
* Copyright 2013 Canonical Ltd.
*
* lomiri-action-api is free software: you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License version 3,
* as published by the Free Software Foundation.
*
* lomiri-action-api is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranties of
* MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
* PURPOSE. See the GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <QApplication>
#include <QMainWindow>
#include <lomiri/action/ActionManager>
#include <lomiri/action/PreviewAction>
#include <lomiri/action/PreviewRangeParameter>
#include <QDebug>
using namespace lomiri::action;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
};
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
PreviewAction *previewAction = new PreviewAction(this);
previewAction->setText("Exposure");
PreviewRangeParameter *range = new PreviewRangeParameter(this);
range->setText("Exposure Amount");
range->setMinimumValue(-50);
range->setMaximumValue(50);
range->setValue(0);
previewAction->addParameter(range);
ActionManager *manager = new ActionManager(this);
manager->addAction(previewAction);
connect(previewAction, &PreviewAction::triggered, [=]() {
// action was completed.
// apply the action with the values of the parameters
qDebug() << "Preview triggered.";
});
connect(previewAction, &PreviewAction::cancelled, [=]() {
// action was cancelled
qDebug() << "Preview cancelled.";
});
connect(previewAction, &PreviewAction::started, [=]() {
// action was activated in the HUD UI.
// do the necessary initialization and start providing preview
// based on the values of the parameters.
qDebug() << "Preview started.";
});
connect(previewAction, &PreviewAction::resetted, [=]() {
// reset the parameter values
qDebug() << "Preview reset(ted).";
});
connect(range, &PreviewRangeParameter::valueChanged, [=](float value) {
// gets the values from the HUD UI when user interacts with the slider
// Application then updates the preview based on this value
qDebug() << "range value:" << value;
});
}
MainWindow::~MainWindow()
{}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
#include "preview-action.moc"
lomiri::action::ActionManager
Definition lomiri-action-manager.h:32
lomiri::action::ActionManager::addAction
Q_INVOKABLE void addAction(lomiri::action::Action *action)
Definition lomiri-action-manager.cpp:426
lomiri::action::PreviewAction
previewable action
Definition lomiri-preview-action.h:30
lomiri::action::PreviewAction::addParameter
Q_INVOKABLE void addParameter(lomiri::action::PreviewParameter *parameter)
Definition lomiri-preview-action.cpp:181
lomiri::action::PreviewRangeParameter
Definition lomiri-preview-range-parameter.h:29