doc: Polish documentation for state machine framework

Fix some examples and wording, and add some clarification based on
comments in documentation review session.

Reviewed-by: Kent Hansen

1 files changed, 50 insertions, 54 deletions

diff --git a/doc/src/frameworks-technologies/statemachine.qdoc b/doc/src/frameworks-technologies/statemachine.qdoc
index ed8bc85..ac10314 100644
--- a/doc/src/frameworks-technologies/statemachine.qdoc
+++ b/doc/src/frameworks-technologies/statemachine.qdoc
@@ -75,6 +75,11 @@
   states can be configured to set properties and invoke methods on QObjects.
   Qt's event system is used to drive the state machines.
 
+  The state graph in the State Machine framework is hierarchical. States can be nested inside of
+  other states, and the current configuration of the state machine consists of the set of states
+  which are currently active. All the states in a valid configuration of the state machine will
+  have a common ancestor.
+
   \section1 Classes in the State Machine Framework
 
   These classes are provided by qt for creating event-driven state machines.
@@ -269,9 +274,17 @@
 
   When a parallel state group is entered, all its child states will be
   simultaneously entered. Transitions within the individual child states
-  operate normally. However, any of the child states may take a transition
-  outside the parent state. When this happens, the parent state and all of its
-  child states are exited.
+  operate normally. However, any of the child states may take a transition which exits the parent
+  state. When this happens, the parent state and all of its child states are exited.
+
+  The parallelism in the State Machine framework follows an interleaved semantics. All parallel
+  operations will be executed in a single, atomic step of the event processing, so no event can
+  interrupt the parallel operations. However, events will still be processed sequentially, since
+  the machine itself is single threaded. As an example: Consider the situation where there are two
+  transitions that exit the same parallel state group, and their conditions become true
+  simultaneously. In this case, the event that is processed last of the two will not have any
+  effect, since the first event will already have caused the machine to exit from the parallel
+  state.
 
   \section1 Detecting that a Composite State has Finished
 
@@ -414,16 +427,7 @@
 
   Take the following code:
   \code
-    QStateMachine machine;
-    machine.setGlobalRestorePolicy(QStateMachine::RestoreProperties);
-
-    QState *s1 = new QState();
-    s1->assignProperty(object, "fooBar", 1.0);
-    machine.addState(s1);
-    machine.setInitialState(s1);
-
-    QState *s2 = new QState();
-    machine.addState(s2);
+  \snippet doc/src/snippets/statemachine/main5.cpp 0
   \endcode
 
   Lets say the property \c fooBar is 0.0 when the machine starts. When the machine is in state
@@ -434,19 +438,7 @@
   If we are using nested states, the parent defines a value for the property which is inherited by
   all descendants that do not explicitly assign a value to the property.
   \code
-    QStateMachine machine;
-    machine.setGlobalRestorePolicy(QStateMachine::RestoreProperties);
-
-    QState *s1 = new QState();
-    s1->assignProperty(object, "fooBar", 1.0);
-    machine.addState(s1);
-    machine.setInitialState(s1);
-
-    QState *s2 = new QState(s1);
-    s2->assignProperty(object, "fooBar", 2.0);
-    s1->setInitialState(s2);
-
-    QState *s3 = new QState(s1);
+  \snippet doc/src/snippets/statemachine/main5.cpp 2
   \endcode
 
   Here \c s1 has two children: \c s2 and \c s3. When \c s2 is entered, the property \c fooBar
@@ -461,13 +453,7 @@
 
   Say we have the following code:
   \code
-    QState *s1 = new QState();
-    QState *s2 = new QState();
-
-    s1->assignProperty(button, "geometry", QRectF(0, 0, 50, 50));
-    s2->assignProperty(button, "geometry", QRectF(0, 0, 100, 100));
-
-    s1->addTransition(button, SIGNAL(clicked()), s2);
+  \snippet doc/src/snippets/statemachine/main5.cpp 3
   \endcode
 
   Here we define two states of a user interface. In \c s1 the \c button is small, and in \c s2
@@ -477,14 +463,7 @@
   object.
 
   \code
-    QState *s1 = new QState();
-    QState *s2 = new QState();
-
-    s1->assignProperty(button, "geometry", QRectF(0, 0, 50, 50));
-    s2->assignProperty(button, "geometry", QRectF(0, 0, 100, 100));
-
-    QSignalTransition *transition = s1->addTransition(button, SIGNAL(clicked()), s2);
-    transition->addAnimation(new QPropertyAnimation(button, "geometry"));
+  \snippet doc/src/snippets/statemachine/main5.cpp 4
   \endcode
 
   Adding an animation for the property in question means that the property assignment will no
@@ -504,28 +483,45 @@
   property can potentially have any value, depending on the animation.
 
   In some cases, it can be useful to be able to detect when the property has actually been assigned
-  the value defined by a state. For this, we can use the state's polished() signal.
+  the value defined by a state.
+
+  Say we have the following code:
   \code
-    QState *s1 = new QState();
-    s1->assignProperty(button, "geometry", QRectF(0, 0, 50, 50));
+  \snippet doc/src/snippets/statemachine/main5.cpp 5
+  \endcode
 
-    QState *s2 = new QState();
+  When \c button is clicked, the machine will transition into state \c s2, which will set the
+  geometry of the button, and then pop up a message box to alert the user that the geometry has
+  been changed.
+
+  In the normal case, where animations are not used, this will operate as expected. However, if
+  an animation for the \c geometry of \c button is set on the transition between \c s1 and \c s2,
+  the animation will be started when \c s2 is entered, but the \c geometry property will not
+  actually reach its defined value before the animation is finished running. In this case, the
+  message box will pop up before the geometry of the button has actually been set.
 
-    s1->addTransition(s1, SIGNAL(polished()), s2);
+  To ensure that the message box does not pop up until the geometry actually reaches its final
+  value, we can use the state's polished() signal. The polished() signal will be emitted when the
+  the property is assigned its final value, whether this is done immediately or after the animation
+  has finished playing.
+  \code
+  \snippet doc/src/snippets/statemachine/main5.cpp 6
   \endcode
 
-  The machine will be in state \c s1 until the \c geometry property has been set. Then it will
-  immediately transition into \c s2. If the transition into \c s1 has an animation for the \c
-  geometry property, then the machine will stay in \c s1 until the animation has finished. If there
-  is no animation, it will simply set the property and immediately enter state \c s2.
+  In this example, when \c button is clicked, the machine will enter \c s2. It will remain in state
+  \c s2 until the \c geometry property has been set to \c QRect(0, 0, 50, 50). Then it will
+  transition into \c s3. When \c s3 is entered, the message box will pop up. If the transition into
+  \c s2 has an animation for the \c geometry property, then the machine will stay in \c s2 until the
+  animation has finished playing. If there is no such animation, it will simply set the property and
+  immediately enter state \c s3.
 
-  Either way, when the machine is in state \c s2, the property \c geometry has been assigned the
-  defined value.
+  Either way, when the machine is in state \c s3, you are guaranteed that the property \c geometry
+  has been assigned the defined value.
 
   If the global restore policy is set to QStateMachine::RestoreProperties, the state will not emit
   the polished() signal until these have been executed as well.
 
-  \section1 What happens if a state is exited before the animation has finished
+  \section1 What Happens If A State Is Exited Before The Animation Has Finished
 
   If a state has property assignments, and the transition into the state has animations for the
   properties, the state can potentially be exited before the properties have been assigned to the
@@ -545,7 +541,7 @@
 
   If the target state does not assign any value to the property, there are two
   options: By default, the property will be assigned the value defined by the state it is leaving
-  (the value it would have been assigned if the animation had been permitted to finish playing.) If
+  (the value it would have been assigned if the animation had been permitted to finish playing). If
   a global restore policy is set, however, this will take precedence, and the property will be
   restored as usual.