Viadeo Twitter Google Bookmarks ! Facebook Digg del.icio.us MySpace Yahoo MyWeb Blinklist Netvouz Reddit Simpy StumbleUpon Bookmarks Windows Live Favorites 
Logo Documentation Qt ·  Page d'accueil  ·  Toutes les classes  ·  Toutes les fonctions  ·  Vues d'ensemble  · 

Move Blocks Example

Files:

The Move Blocks example shows how to animate items in a QGraphicsScene using a QStateMachine with a custom transition.

The example animates the blue blocks that you can see in the image above. The animation moves the blocks between four preset positions.

The example consists of the following classes:

  • StateSwitcher inherits QState and can add StateSwitchTransitions to other states. When entered, it will randomly transition to one of these states.
  • StateSwitchTransition is a custom transition that triggers on StateSwitchEvents.
  • StateSwitchEvent is a QEvent that triggers StateSwitchTransitions.
  • QGraphicsRectWidget is a QGraphicsWidget that simply paints its background in a solid blue color.

The blocks are instances of QGraphicsRectWidget and are animated in a QGraphicsScene. We do this by building a state graph, which we insert animations into. The graph is then executed in a QStateMachine. All this is done in main(). Let's look at the main() function first.

The main() Function

After QApplication has been initialized, we set up the QGraphicsScene with its QGraphicsRectWidgets.

     QGraphicsRectWidget *button1 = new QGraphicsRectWidget;
     QGraphicsRectWidget *button2 = new QGraphicsRectWidget;
     QGraphicsRectWidget *button3 = new QGraphicsRectWidget;
     QGraphicsRectWidget *button4 = new QGraphicsRectWidget;
     button2->setZValue(1);
     button3->setZValue(2);
     button4->setZValue(3);
     QGraphicsScene scene(0, 0, 300, 300);
     scene.setBackgroundBrush(Qt::black);
     scene.addItem(button1);
     scene.addItem(button2);
     scene.addItem(button3);
     scene.addItem(button4);

After adding the scene to a QGraphicsView, it is time to build the state graph. Let's first look at a statechart of what we are trying to build.

Note that the group has seven sub states, but we have only included three of them in the diagram. The code that builds this graph will be examined line-by-line, and will show how the graph works. First off, we construct the group state:

     QStateMachine machine;

     QState *group = new QState();
     group->setObjectName("group");
     QTimer timer;
     timer.setInterval(1250);
     timer.setSingleShot(true);
     QObject::connect(group, SIGNAL(entered()), &timer, SLOT(start()));

The timer is used to add a delay between each time the blocks are moved. The timer is started when group is entered. As we will see later, group has a transition back to the StateSwitcher when the timer times out. group is the initial state in the machine, so an animation will be scheduled when the example is started.

     QState *state1;
     QState *state2;
     QState *state3;
     QState *state4;
     QState *state5;
     QState *state6;
     QState *state7;

     state1 = createGeometryState(button1, QRect(100, 0, 50, 50),
                                  button2, QRect(150, 0, 50, 50),
                                  button3, QRect(200, 0, 50, 50),
                                  button4, QRect(250, 0, 50, 50),
                                  group);
     ...
     state7 = createGeometryState(button1, QRect(0, 0, 50, 50),
                                  button2, QRect(250, 0, 50, 50),
                                  button3, QRect(0, 250, 50, 50),
                                  button4, QRect(250, 250, 50, 50),
                                  group);
     group->setInitialState(state1);

createGeometryState() returns a QState that will set the geometry of our items upon entry. It also assigns group as the parent of this state.

A QPropertyAnimation inserted into a transition will use the values assigned to a QState (with QState::assignProperty()), i.e., the animation will interpolate between the current values of the properties and the values in the target state. We add animated transitions to the state graph later.

     QParallelAnimationGroup animationGroup;
     QSequentialAnimationGroup *subGroup;

     QPropertyAnimation *anim = new QPropertyAnimation(button4, "geometry");
     anim->setDuration(1000);
     anim->setEasingCurve(QEasingCurve::OutElastic);
     animationGroup.addAnimation(anim);

We move the items in parallel. Each item is added to animationGroup, which is the animation that is inserted into the transitions.

     subGroup = new QSequentialAnimationGroup(&animationGroup);
     subGroup->addPause(100);
     anim = new QPropertyAnimation(button3, "geometry");
     anim->setDuration(1000);
     anim->setEasingCurve(QEasingCurve::OutElastic);
     subGroup->addAnimation(anim);

The sequential animation group, subGroup, helps us insert a delay between the animation of each item.

     StateSwitcher *stateSwitcher = new StateSwitcher(&machine);
     stateSwitcher->setObjectName("stateSwitcher");
     group->addTransition(&timer, SIGNAL(timeout()), stateSwitcher);
     stateSwitcher->addState(state1, &animationGroup);
     stateSwitcher->addState(state2, &animationGroup);
     ...
     stateSwitcher->addState(state7, &animationGroup);

A StateSwitchTransition is added to the state switcher in StateSwitcher::addState(). We also add the animation in this function. Since QPropertyAnimation uses the values from the states, we can insert the same QPropertyAnimation instance in all StateSwitchTransitions.

As mentioned previously, we add a transition to the state switcher that triggers when the timer times out.

     machine.addState(group);
     machine.setInitialState(group);
     machine.start();

Finally, we can create the state machine, add our initial state, and start execution of the state graph.

The createGeometryState() Function

In createGeometryState(), we set up the geometry for each graphics item.

 QState *createGeometryState(QObject *w1, const QRect &rect1,
                             QObject *w2, const QRect &rect2,
                             QObject *w3, const QRect &rect3,
                             QObject *w4, const QRect &rect4,
                             QState *parent)
 {
     QState *result = new QState(parent);
     result->assignProperty(w1, "geometry", rect1);
     result->assignProperty(w2, "geometry", rect2);
     result->assignProperty(w3, "geometry", rect3);
     result->assignProperty(w4, "geometry", rect4);

     return result;
 }

As mentioned before, QAbstractTransition will set up an animation added with addAnimation() using property values set with assignProperty().

The StateSwitcher Class

StateSwitcher has state switch transitions to each QStates we created with createGeometryState(). Its job is to transition to one of these states at random when it is entered.

All functions in StateSwitcher are inlined. We'll step through its definition.

 class StateSwitcher : public QState
 {
     Q_OBJECT
 public:
     StateSwitcher(QStateMachine *machine)
         : QState(machine), m_stateCount(0), m_lastIndex(0)
     { }

StateSwitcher is a state designed for a particular purpose and will always be a top-level state. We use m_stateCount to keep track of how many states we are managing, and m_lastIndex to remember which state was the last state to which we transitioned.

     virtual void onEntry(QEvent *)
     {
         int n;
         while ((n = (qrand() % m_stateCount + 1)) == m_lastIndex)
         { }
         m_lastIndex = n;
         machine()->postEvent(new StateSwitchEvent(n));
     }
     virtual void onExit(QEvent *) {}

We select the next state we are going to transition to, and post a StateSwitchEvent, which we know will trigger the StateSwitchTransition to the selected state.

     void addState(QState *state, QAbstractAnimation *animation) {
         StateSwitchTransition *trans = new StateSwitchTransition(++m_stateCount);
         trans->setTargetState(state);
         addTransition(trans);
         trans->addAnimation(animation);
     }

This is where the magic happens. We assign a number to each state added. This number is given to both a StateSwitchTransition and to StateSwitchEvents. As we have seen, state switch events will trigger a transition with the same number.

The StateSwitchTransition Class

StateSwitchTransition inherits QAbstractTransition and triggers on StateSwitchEvents. It contains only inline functions, so let's take a look at its eventTest() function, which is the only function that we define..

     virtual bool eventTest(QEvent *event)
     {
         return (event->type() == QEvent::Type(StateSwitchEvent::StateSwitchType))
             && (static_cast<StateSwitchEvent *>(event)->rand() == m_rand);
     }

eventTest is called by QStateMachine when it checks whether a transition should be triggered--a return value of true means that it will. We simply check if our assigned number is equal to the event's number (in which case we fire away).

The StateSwitchEvent Class

StateSwitchEvent inherits QEvent, and holds a number that has been assigned to a state and state switch transition by StateSwitcher. We have already seen how it is used to trigger StateSwitchTransitions in StateSwitcher.

 class StateSwitchEvent: public QEvent
 {
 public:
     StateSwitchEvent()
         : QEvent(Type(StateSwitchType))
     {
     }

     StateSwitchEvent(int rand)
         : QEvent(Type(StateSwitchType)),
           m_rand(rand)
     {
     }

     enum { StateSwitchType = QEvent::User + 256 };

     int rand() const { return m_rand; }

 private:
     int m_rand;
 };

We only have inlined functions in this class, so a look at its definition will do.

The QGraphicsRectWidget Class

QGraphicsRectWidget inherits QGraphicsWidget and simply paints its rect() blue. We inline paintEvent(), which is the only function we define. Here is the QGraphicsRectWidget class definition:

 class QGraphicsRectWidget : public QGraphicsWidget
 {
 public:
     void paint(QPainter *painter, const QStyleOptionGraphicsItem *,
                QWidget *)
     {
         painter->fillRect(rect(), Qt::blue);
     }
 };

Moving On

The technique shown in this example works equally well for all QPropertyAnimations. As long as the value to be animated is a Qt property, you can insert an animation of it into a state graph.

QState::addAnimation() takes a QAbstractAnimation, so any type of animation can be inserted into the graph.

Publicité

Best Of

Actualités les plus lues

Semaine
Mois
Année
  1. « Quelque chose ne va vraiment pas avec les développeurs "modernes" », un développeur à "l'ancienne" critique la multiplication des bibliothèques 64
  2. Apercevoir la troisième dimension ou l'utilisation multithreadée d'OpenGL dans Qt, un article des Qt Quarterly traduit par Guillaume Belz 0
  3. Les développeurs ignorent-ils trop les failles découvertes dans leur code ? Prenez-vous en compte les remarques des autres ? 17
  4. BlackBerry 10 : premières images du prochain OS de RIM qui devrait intégrer des widgets et des tuiles inspirées de Windows Phone 0
  5. Quelles nouveautés de C++11 Visual C++ doit-il rapidement intégrer ? Donnez-nous votre avis 10
  6. Adieu qmake, bienvenue qbs : Qt Building Suite, un outil déclaratif et extensible pour la compilation de projets Qt 17
  7. La rubrique Qt a besoin de vous ! 1
Page suivante

Le blog Digia au hasard

Logo

Déploiement d'applications Qt Commercial sur les tablettes Windows 8

Le blog Digia est l'endroit privilégié pour la communication sur l'édition commerciale de Qt, où des réponses publiques sont apportées aux questions les plus posées au support. Lire l'article.

Communauté

Ressources

Liens utiles

Contact

  • Vous souhaitez rejoindre la rédaction ou proposer un tutoriel, une traduction, une question... ? Postez dans le forum Contribuez ou contactez-nous par MP ou par email (voir en bas de page).

Qt dans le magazine

Cette page est une traduction d'une page de la documentation de Qt, écrite par Nokia Corporation and/or its subsidiary(-ies). Les éventuels problèmes résultant d'une mauvaise traduction ne sont pas imputables à Nokia. Qt 4.6
Copyright © 2012 Developpez LLC. Tous droits réservés Developpez LLC. Aucune reproduction, même partielle, ne peut être faite de ce site et de l'ensemble de son contenu : textes, documents et images sans l'autorisation expresse de Developpez LLC. Sinon, vous encourez selon la loi jusqu'à 3 ans de prison et jusqu'à 300 000 E de dommages et intérêts. Cette page est déposée à la SACD.
Vous avez déniché une erreur ? Un bug ? Une redirection cassée ? Ou tout autre problème, quel qu'il soit ? Ou bien vous désirez participer à ce projet de traduction ? N'hésitez pas à nous contacter ou par MP !
 
 
 
 
Partenaires

Hébergement Web