Doc: Documented the Move Blocks example.

Reviewed-by: Andreas Aardal Hanssen

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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
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+****************************************************************************/
+
+/*!
+    \example animation/moveblocks
+    \title Move Blocks Example
+
+    The Move Blocks example shows how to animate items in a
+    QGraphicsScene using a QStateMachine with a custom transition.
+
+    \image moveblocks-example.png
+
+    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:
+
+    \list
+        \o \c StateSwitcher inherits QState and can add
+              \c {StateSwitchTransition}s to other states.
+              When entered, it will randomly transition to one of these
+              states. 
+        \o \c StateSwitchTransition is a custom transition that
+           triggers on \c{StateSwitchEvent}s.
+        \o \c StateSwitchEvent is a QEvent that trigger \c{StateSwitchTransition}s.
+        \o \c QGraphicsRectWidget is a QGraphicsWidget that simply
+           paints its background in a solid \l{Qt::}{blue} color.
+    \endlist
+
+    The blocks are instances of \c 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 \c main().
+    Let's look at the \c main() function first.
+
+    \section1 The \c main() Function
+
+    After QApplication has been initialized, we set up the
+    QGraphicsScene with its \c{QGraphicsRectWidget}s.
+
+    \snippet examples/animation/moveblocks/main.cpp 1
+
+    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.
+
+    \image move-blocks-chart.png
+
+    Note that the \c 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 \c group state:
+
+    \snippet examples/animation/moveblocks/main.cpp 2
+
+    The timer is used to add a delay between each time the blocks are
+    moved. The timer is started when \c group is entered. As we will
+    see later, \c group has a transition back to the \c StateSwitcher
+    when the timer times out. \c group is the initial state in the
+    machine, so an animation will be scheduled when the example is
+    started.
+
+    \snippet examples/animation/moveblocks/main.cpp 3
+    \dots
+    \snippet examples/animation/moveblocks/main.cpp 4
+
+    \c createGeometryState() returns a QState that will set the
+    geometry of our items upon entry. It also assigns \c 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.
+
+    \snippet examples/animation/moveblocks/main.cpp 5
+
+    We move the items in parallel. Each item is added to \c
+    animationGroup, which is the animation that is inserted into the
+    transitions.
+
+    \snippet examples/animation/moveblocks/main.cpp 6 
+
+    The sequential animation group, \c subGroup, helps us insert a
+    delay between the animation of each item.
+
+    \snippet examples/animation/moveblocks/main.cpp 7
+    \dots
+    \snippet examples/animation/moveblocks/main.cpp 8
+
+    A StateSwitchTransition is added to the state switcher
+    in \c 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
+    \c {StateSwitchTransition}s.
+
+    As mentioned previously, we add a transition to the state switcher
+    that triggers when the timer times out.
+
+    \snippet examples/animation/moveblocks/main.cpp 9
+
+    Finally, we can create the state machine, add our initial state,
+    and start execution of the state graph.
+
+    \section2 The \c createGemetryState() Function
+
+    In \c createGeometryState(), we set up the geometry for each
+    graphics item.
+
+    \snippet examples/animation/moveblocks/main.cpp 13
+
+    As mentioned before, QAbstractTransition will set up an animation
+    added with \l{QAbstractTransition::}{addAnimation()} using
+    property values set with \l{QState::}{assignProperty()}.
+
+    \section1 The StateSwitcher Class
+
+    \c StateSwitcher has state switch transitions to each \l{QState}s
+    we created with \c createGemetryState(). Its job is to transition
+    to one of these states at random when it is entered.
+
+    All functions in \c StateSwitcher are inlined. We'll step through
+    its definition.
+
+    \snippet examples/animation/moveblocks/main.cpp 10
+
+    \c StateSwitcher is a state designed for a particular purpose and
+    will always be a top-level state. We use \c m_stateCount to keep
+    track of how many states we are managing, and \c m_lastIndex to
+    remember which state was the last state to which we transitioned. 
+
+    \snippet examples/animation/moveblocks/main.cpp 11
+    
+    We select the next state we are going to transition to, and post a
+    \c StateSwitchEvent, which we know will trigger the \c
+    StateSwitchTransition to the selected state.
+
+    \snippet examples/animation/moveblocks/main.cpp 12
+
+    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.
+
+    \section1 The StateSwitchTransition Class
+
+    \c StateSwitchTransition inherits QAbstractTransition and triggers
+    on \c{StateSwitchEvent}s. It contains only inline functions, so
+    let's take a look at its \l{QAbstractTransition::}{eventTest()}
+    function, which is the only function that we define..
+
+    \snippet examples/animation/moveblocks/main.cpp 14
+
+    \c 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).
+
+    \section1 The StateSwitchEvent Class
+
+    \c StateSwitchEvent inherits QEvent, and holds a number that has
+    been assigned to a state and state switch transition by \c
+    StateSwitcher. We have already seen how it is used to trigger \c
+    \c{StateSwitchTransition}s in \c StateSwitcher.
+
+    \snippet examples/animation/moveblocks/main.cpp 15
+
+    We only have inlined functions in this class, so a look at its
+    definition will do.
+
+    \section1 The QGraphicsRectWidget Class
+
+    QGraphicsRectWidget inherits QGraphicsWidget and simply paints its
+    \l{QWidget::}{rect()} blue. We inline \l{QWidget::}{paintEvent()},
+    which is the only function we define. Here is the
+    QGraphicsRectWidget class definition:
+
+    \snippet examples/animation/moveblocks/main.cpp 16
+
+    \section1 Moving On
+
+    The technique shown in this example works equally well for all
+    \l{QPropertyAnimation}s. 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.
+*/
+