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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#the-function">The <tt>main()</tt> Function</a></li>
<li class="level2"><a href="#the-function">The <tt>createGeometryState()</tt> Function</a></li>
<li class="level1"><a href="#the-stateswitcher-class">The StateSwitcher Class</a></li>
<li class="level1"><a href="#the-stateswitchtransition-class">The StateSwitchTransition Class</a></li>
<li class="level1"><a href="#the-stateswitchevent-class">The StateSwitchEvent Class</a></li>
<li class="level1"><a href="#the-qgraphicsrectwidget-class">The QGraphicsRectWidget Class</a></li>
<li class="level1"><a href="#moving-on">Moving On</a></li>
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<h1 class="title">Move Blocks Example</h1>
<span class="subtitle"></span>
<!-- $$$animation/moveblocks-description -->
<div class="descr"> <a name="details"></a>
<p>Files:</p>
<ul>
<li><a href="animation-moveblocks-main-cpp.html">animation/moveblocks/main.cpp</a></li>
<li><a href="animation-moveblocks-moveblocks-pro.html">animation/moveblocks/moveblocks.pro</a></li>
</ul>
<p>The Move Blocks example shows how to animate items in a <a href="qgraphicsscene.html">QGraphicsScene</a> using a <a href="qstatemachine.html">QStateMachine</a> with a custom transition.<p class="centerAlign"><img src="images/moveblocks-example.png" alt="" /></p><p>The example animates the blue blocks that you can see in the image above. The animation moves the blocks between four preset positions.</p>
<p>The example consists of the following classes:</p>
<ul>
<li><tt>StateSwitcher</tt> inherits <a href="qstate.html">QState</a> and can add <tt>StateSwitchTransition</tt>s to other states. When entered, it will randomly transition to one of these states.</li>
<li><tt>StateSwitchTransition</tt> is a custom transition that triggers on <tt>StateSwitchEvent</tt>s.</li>
<li><tt>StateSwitchEvent</tt> is a <a href="qevent.html">QEvent</a> that triggers <tt>StateSwitchTransition</tt>s.</li>
<li><tt>QGraphicsRectWidget</tt> is a <a href="qgraphicswidget.html">QGraphicsWidget</a> that simply paints its background in a solid <a href="qt.html#GlobalColor-enum">blue</a> color.</li>
</ul>
<p>The blocks are instances of <tt>QGraphicsRectWidget</tt> and are animated in a <a href="qgraphicsscene.html">QGraphicsScene</a>. We do this by building a state graph, which we insert animations into. The graph is then executed in a <a href="qstatemachine.html">QStateMachine</a>. All this is done in <tt>main()</tt>. Let's look at the <tt>main()</tt> function first.</p>
<a name="the-function"></a>
<h2>The <tt>main()</tt> Function</h2>
<p>After <a href="qapplication.html">QApplication</a> has been initialized, we set up the <a href="qgraphicsscene.html">QGraphicsScene</a> with its <tt>QGraphicsRectWidget</tt>s.</p>
<pre class="cpp"> <span class="type">QGraphicsRectWidget</span> <span class="operator">*</span>button1 <span class="operator">=</span> <span class="keyword">new</span> <span class="type">QGraphicsRectWidget</span>;
<span class="type">QGraphicsRectWidget</span> <span class="operator">*</span>button2 <span class="operator">=</span> <span class="keyword">new</span> <span class="type">QGraphicsRectWidget</span>;
<span class="type">QGraphicsRectWidget</span> <span class="operator">*</span>button3 <span class="operator">=</span> <span class="keyword">new</span> <span class="type">QGraphicsRectWidget</span>;
<span class="type">QGraphicsRectWidget</span> <span class="operator">*</span>button4 <span class="operator">=</span> <span class="keyword">new</span> <span class="type">QGraphicsRectWidget</span>;
button2<span class="operator">-</span><span class="operator">></span>setZValue(<span class="number">1</span>);
button3<span class="operator">-</span><span class="operator">></span>setZValue(<span class="number">2</span>);
button4<span class="operator">-</span><span class="operator">></span>setZValue(<span class="number">3</span>);
<span class="type"><a href="qgraphicsscene.html">QGraphicsScene</a></span> scene(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">300</span><span class="operator">,</span> <span class="number">300</span>);
scene<span class="operator">.</span>setBackgroundBrush(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>black);
scene<span class="operator">.</span>addItem(button1);
scene<span class="operator">.</span>addItem(button2);
scene<span class="operator">.</span>addItem(button3);
scene<span class="operator">.</span>addItem(button4);</pre>
<p>After adding the scene to a <a href="qgraphicsview.html">QGraphicsView</a>, it is time to build the state graph. Let's first look at a statechart of what we are trying to build.</p>
<p class="centerAlign"><img src="images/move-blocks-chart.png" alt="" /></p><p>Note that the <tt>group</tt> 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 <tt>group</tt> state:</p>
<pre class="cpp"> <span class="type"><a href="qstatemachine.html">QStateMachine</a></span> machine;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>group <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>();
group<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"group"</span>);
<span class="type"><a href="qtimer.html">QTimer</a></span> timer;
timer<span class="operator">.</span>setInterval(<span class="number">1250</span>);
timer<span class="operator">.</span>setSingleShot(<span class="keyword">true</span>);
<span class="type"><a href="qobject.html">QObject</a></span><span class="operator">::</span>connect(group<span class="operator">,</span> SIGNAL(entered())<span class="operator">,</span> <span class="operator">&</span>timer<span class="operator">,</span> SLOT(start()));</pre>
<p>The timer is used to add a delay between each time the blocks are moved. The timer is started when <tt>group</tt> is entered. As we will see later, <tt>group</tt> has a transition back to the <tt>StateSwitcher</tt> when the timer times out. <tt>group</tt> is the initial state in the machine, so an animation will be scheduled when the example is started.</p>
<pre class="cpp"> <span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state1;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state2;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state3;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state4;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state5;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state6;
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state7;
state1 <span class="operator">=</span> createGeometryState(button1<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">100</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button2<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">150</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button3<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">200</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button4<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">250</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
group);
...
state7 <span class="operator">=</span> createGeometryState(button1<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button2<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">250</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button3<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">0</span><span class="operator">,</span> <span class="number">250</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
button4<span class="operator">,</span> <span class="type"><a href="qrect.html">QRect</a></span>(<span class="number">250</span><span class="operator">,</span> <span class="number">250</span><span class="operator">,</span> <span class="number">50</span><span class="operator">,</span> <span class="number">50</span>)<span class="operator">,</span>
group);
group<span class="operator">-</span><span class="operator">></span>setInitialState(state1);</pre>
<p><tt>createGeometryState()</tt> returns a <a href="qstate.html">QState</a> that will set the geometry of our items upon entry. It also assigns <tt>group</tt> as the parent of this state.</p>
<p>A <a href="qpropertyanimation.html">QPropertyAnimation</a> inserted into a transition will use the values assigned to a <a href="qstate.html">QState</a> (with <a href="qstate.html#assignProperty">QState::assignProperty</a>()), 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.</p>
<pre class="cpp"> <span class="type"><a href="qparallelanimationgroup.html">QParallelAnimationGroup</a></span> animationGroup;
<span class="type"><a href="qsequentialanimationgroup.html">QSequentialAnimationGroup</a></span> <span class="operator">*</span>subGroup;
<span class="type"><a href="qpropertyanimation.html">QPropertyAnimation</a></span> <span class="operator">*</span>anim <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpropertyanimation.html">QPropertyAnimation</a></span>(button4<span class="operator">,</span> <span class="string">"geometry"</span>);
anim<span class="operator">-</span><span class="operator">></span>setDuration(<span class="number">1000</span>);
anim<span class="operator">-</span><span class="operator">></span>setEasingCurve(<span class="type"><a href="qeasingcurve.html">QEasingCurve</a></span><span class="operator">::</span>OutElastic);
animationGroup<span class="operator">.</span>addAnimation(anim);</pre>
<p>We move the items in parallel. Each item is added to <tt>animationGroup</tt>, which is the animation that is inserted into the transitions.</p>
<pre class="cpp"> subGroup <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qsequentialanimationgroup.html">QSequentialAnimationGroup</a></span>(<span class="operator">&</span>animationGroup);
subGroup<span class="operator">-</span><span class="operator">></span>addPause(<span class="number">100</span>);
anim <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpropertyanimation.html">QPropertyAnimation</a></span>(button3<span class="operator">,</span> <span class="string">"geometry"</span>);
anim<span class="operator">-</span><span class="operator">></span>setDuration(<span class="number">1000</span>);
anim<span class="operator">-</span><span class="operator">></span>setEasingCurve(<span class="type"><a href="qeasingcurve.html">QEasingCurve</a></span><span class="operator">::</span>OutElastic);
subGroup<span class="operator">-</span><span class="operator">></span>addAnimation(anim);</pre>
<p>The sequential animation group, <tt>subGroup</tt>, helps us insert a delay between the animation of each item.</p>
<pre class="cpp"> StateSwitcher <span class="operator">*</span>stateSwitcher <span class="operator">=</span> <span class="keyword">new</span> StateSwitcher(<span class="operator">&</span>machine);
stateSwitcher<span class="operator">-</span><span class="operator">></span>setObjectName(<span class="string">"stateSwitcher"</span>);
group<span class="operator">-</span><span class="operator">></span>addTransition(<span class="operator">&</span>timer<span class="operator">,</span> SIGNAL(timeout())<span class="operator">,</span> stateSwitcher);
stateSwitcher<span class="operator">-</span><span class="operator">></span>addState(state1<span class="operator">,</span> <span class="operator">&</span>animationGroup);
stateSwitcher<span class="operator">-</span><span class="operator">></span>addState(state2<span class="operator">,</span> <span class="operator">&</span>animationGroup);
...
stateSwitcher<span class="operator">-</span><span class="operator">></span>addState(state7<span class="operator">,</span> <span class="operator">&</span>animationGroup);</pre>
<p>A StateSwitchTransition is added to the state switcher in <tt>StateSwitcher::addState()</tt>. We also add the animation in this function. Since <a href="qpropertyanimation.html">QPropertyAnimation</a> uses the values from the states, we can insert the same <a href="qpropertyanimation.html">QPropertyAnimation</a> instance in all <tt>StateSwitchTransition</tt>s.</p>
<p>As mentioned previously, we add a transition to the state switcher that triggers when the timer times out.</p>
<pre class="cpp"> machine<span class="operator">.</span>addState(group);
machine<span class="operator">.</span>setInitialState(group);
machine<span class="operator">.</span>start();</pre>
<p>Finally, we can create the state machine, add our initial state, and start execution of the state graph.</p>
<a name="the-function"></a>
<h3>The <tt>createGeometryState()</tt> Function</h3>
<p>In <tt>createGeometryState()</tt>, we set up the geometry for each graphics item.</p>
<pre class="cpp"> <span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>createGeometryState(<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>w1<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qrect.html">QRect</a></span> <span class="operator">&</span>rect1<span class="operator">,</span>
<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>w2<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qrect.html">QRect</a></span> <span class="operator">&</span>rect2<span class="operator">,</span>
<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>w3<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qrect.html">QRect</a></span> <span class="operator">&</span>rect3<span class="operator">,</span>
<span class="type"><a href="qobject.html">QObject</a></span> <span class="operator">*</span>w4<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qrect.html">QRect</a></span> <span class="operator">&</span>rect4<span class="operator">,</span>
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>parent)
{
<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>result <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qstate.html">QState</a></span>(parent);
result<span class="operator">-</span><span class="operator">></span>assignProperty(w1<span class="operator">,</span> <span class="string">"geometry"</span><span class="operator">,</span> rect1);
result<span class="operator">-</span><span class="operator">></span>assignProperty(w2<span class="operator">,</span> <span class="string">"geometry"</span><span class="operator">,</span> rect2);
result<span class="operator">-</span><span class="operator">></span>assignProperty(w3<span class="operator">,</span> <span class="string">"geometry"</span><span class="operator">,</span> rect3);
result<span class="operator">-</span><span class="operator">></span>assignProperty(w4<span class="operator">,</span> <span class="string">"geometry"</span><span class="operator">,</span> rect4);
<span class="keyword">return</span> result;
}</pre>
<p>As mentioned before, <a href="qabstracttransition.html">QAbstractTransition</a> will set up an animation added with <a href="qabstracttransition.html#addAnimation">addAnimation()</a> using property values set with <a href="qstate.html#assignProperty">assignProperty()</a>.</p>
<a name="the-stateswitcher-class"></a>
<h2>The StateSwitcher Class</h2>
<p><tt>StateSwitcher</tt> has state switch transitions to each <a href="qstate.html">QState</a>s we created with <tt>createGeometryState()</tt>. Its job is to transition to one of these states at random when it is entered.</p>
<p>All functions in <tt>StateSwitcher</tt> are inlined. We'll step through its definition.</p>
<pre class="cpp"> <span class="keyword">class</span> StateSwitcher : <span class="keyword">public</span> <span class="type"><a href="qstate.html">QState</a></span>
{
Q_OBJECT
<span class="keyword">public</span>:
StateSwitcher(<span class="type"><a href="qstatemachine.html">QStateMachine</a></span> <span class="operator">*</span>machine)
: <span class="type"><a href="qstate.html">QState</a></span>(machine)<span class="operator">,</span> m_stateCount(<span class="number">0</span>)<span class="operator">,</span> m_lastIndex(<span class="number">0</span>)
{ }</pre>
<p><tt>StateSwitcher</tt> is a state designed for a particular purpose and will always be a top-level state. We use <tt>m_stateCount</tt> to keep track of how many states we are managing, and <tt>m_lastIndex</tt> to remember which state was the last state to which we transitioned.</p>
<pre class="cpp"> <span class="keyword">virtual</span> <span class="type">void</span> onEntry(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>)
{
<span class="type">int</span> n;
<span class="keyword">while</span> ((n <span class="operator">=</span> (qrand() <span class="operator">%</span> m_stateCount <span class="operator">+</span> <span class="number">1</span>)) <span class="operator">=</span><span class="operator">=</span> m_lastIndex)
{ }
m_lastIndex <span class="operator">=</span> n;
machine()<span class="operator">-</span><span class="operator">></span>postEvent(<span class="keyword">new</span> StateSwitchEvent(n));
}
<span class="keyword">virtual</span> <span class="type">void</span> onExit(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>) {}</pre>
<p>We select the next state we are going to transition to, and post a <tt>StateSwitchEvent</tt>, which we know will trigger the <tt>StateSwitchTransition</tt> to the selected state.</p>
<pre class="cpp"> <span class="type">void</span> addState(<span class="type"><a href="qstate.html">QState</a></span> <span class="operator">*</span>state<span class="operator">,</span> <span class="type"><a href="qabstractanimation.html">QAbstractAnimation</a></span> <span class="operator">*</span>animation) {
StateSwitchTransition <span class="operator">*</span>trans <span class="operator">=</span> <span class="keyword">new</span> StateSwitchTransition(<span class="operator">+</span><span class="operator">+</span>m_stateCount);
trans<span class="operator">-</span><span class="operator">></span>setTargetState(state);
addTransition(trans);
trans<span class="operator">-</span><span class="operator">></span>addAnimation(animation);
}</pre>
<p>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.</p>
<a name="the-stateswitchtransition-class"></a>
<h2>The StateSwitchTransition Class</h2>
<p><tt>StateSwitchTransition</tt> inherits <a href="qabstracttransition.html">QAbstractTransition</a> and triggers on <tt>StateSwitchEvent</tt>s. It contains only inline functions, so let's take a look at its <a href="qabstracttransition.html#eventTest">eventTest()</a> function, which is the only function that we define..</p>
<pre class="cpp"> <span class="keyword">virtual</span> <span class="type">bool</span> eventTest(<span class="type"><a href="qevent.html">QEvent</a></span> <span class="operator">*</span>event)
{
<span class="keyword">return</span> (event<span class="operator">-</span><span class="operator">></span>type() <span class="operator">=</span><span class="operator">=</span> <span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>Type(StateSwitchEvent<span class="operator">::</span>StateSwitchType))
<span class="operator">&</span><span class="operator">&</span> (<span class="keyword">static_cast</span><span class="operator"><</span>StateSwitchEvent <span class="operator">*</span><span class="operator">></span>(event)<span class="operator">-</span><span class="operator">></span>rand() <span class="operator">=</span><span class="operator">=</span> m_rand);
}</pre>
<p><tt>eventTest</tt> is called by <a href="qstatemachine.html">QStateMachine</a> 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).</p>
<a name="the-stateswitchevent-class"></a>
<h2>The StateSwitchEvent Class</h2>
<p><tt>StateSwitchEvent</tt> inherits <a href="qevent.html">QEvent</a>, and holds a number that has been assigned to a state and state switch transition by <tt>StateSwitcher</tt>. We have already seen how it is used to trigger <tt>StateSwitchTransition</tt>s in <tt>StateSwitcher</tt>.</p>
<pre class="cpp"> <span class="keyword">class</span> StateSwitchEvent: <span class="keyword">public</span> <span class="type"><a href="qevent.html">QEvent</a></span>
{
<span class="keyword">public</span>:
StateSwitchEvent()
: <span class="type"><a href="qevent.html">QEvent</a></span>(Type(StateSwitchType))
{
}
StateSwitchEvent(<span class="type">int</span> rand)
: <span class="type"><a href="qevent.html">QEvent</a></span>(Type(StateSwitchType))<span class="operator">,</span>
m_rand(rand)
{
}
<span class="keyword">enum</span> { StateSwitchType <span class="operator">=</span> <span class="type"><a href="qevent.html">QEvent</a></span><span class="operator">::</span>User <span class="operator">+</span> <span class="number">256</span> };
<span class="type">int</span> rand() <span class="keyword">const</span> { <span class="keyword">return</span> m_rand; }
<span class="keyword">private</span>:
<span class="type">int</span> m_rand;
};</pre>
<p>We only have inlined functions in this class, so a look at its definition will do.</p>
<a name="the-qgraphicsrectwidget-class"></a>
<h2>The QGraphicsRectWidget Class</h2>
<p>QGraphicsRectWidget inherits <a href="qgraphicswidget.html">QGraphicsWidget</a> and simply paints its <a href="qwidget.html#rect-prop">rect()</a> blue. We inline <a href="qwidget.html#paintEvent">paintEvent()</a>, which is the only function we define. Here is the QGraphicsRectWidget class definition:</p>
<pre class="cpp"> <span class="keyword">class</span> <span class="type">QGraphicsRectWidget</span> : <span class="keyword">public</span> <span class="type"><a href="qgraphicswidget.html">QGraphicsWidget</a></span>
{
<span class="keyword">public</span>:
<span class="type">void</span> paint(<span class="type"><a href="qpainter.html">QPainter</a></span> <span class="operator">*</span>painter<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstyleoptiongraphicsitem.html">QStyleOptionGraphicsItem</a></span> <span class="operator">*</span><span class="operator">,</span>
<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>)
{
painter<span class="operator">-</span><span class="operator">></span>fillRect(rect()<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>blue);
}
};</pre>
<a name="moving-on"></a>
<h2>Moving On</h2>
<p>The technique shown in this example works equally well for all <a href="qpropertyanimation.html">QPropertyAnimation</a>s. As long as the value to be animated is a Qt property, you can insert an animation of it into a state graph.</p>
<p>QState::addAnimation() takes a <a href="qabstractanimation.html">QAbstractAnimation</a>, so any type of animation can be inserted into the graph.</p>
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