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/*!

    \example statemachine/trafficlight

    \title Traffic Light Example

    The Traffic Light example shows how to use \l{The State Machine Framework}

    to implement the control flow of a traffic light.

    \image trafficlight-example.png

    In this example we write a TrafficLightWidget class. The traffic light has

    three lights: Red, yellow and green. The traffic light transitions from

    one light to another (red to yellow to green to yellow to red again) at

    certain intervals.

    \snippet examples/statemachine/trafficlight/main.cpp 0

    The LightWidget class represents a single light of the traffic light. It

    provides an \c on property and two slots, turnOn() and turnOff(), to turn

    the light on and off, respectively. The widget paints itself in the color

    that's passed to the constructor.

    \snippet examples/statemachine/trafficlight/main.cpp 1

    The TrafficLightWidget class represents the visual part of the traffic

    light; it's a widget that contains three lights arranged vertically, and

    provides accessor functions for these.

    \snippet examples/statemachine/trafficlight/main.cpp 2

    The createLightState() function creates a state that turns a light on when

    the state is entered, and off when the state is exited. The state uses a

    timer, and as we shall see the timeout is used to transition from one

    LightState to another. Here is the statechart for the light state:

    \img trafficlight-example1.png

    \omit

    \caption This is a caption

    \endomit

    \snippet examples/statemachine/trafficlight/main.cpp 3

    The TrafficLight class combines the TrafficLightWidget with a state

    machine.  The state graph has four states: red-to-yellow, yellow-to-green,

    green-to-yellow and yellow-to-red. The initial state is red-to-yellow;

    when the state's timer times out, the state machine transitions to

    yellow-to-green. The same process repeats through the other states.

    This is what the statechart looks like:

    \img trafficlight-example2.png

    \omit

    \caption This is a caption

    \endomit

    \snippet examples/statemachine/trafficlight/main.cpp 4

    The main() function constructs a TrafficLight and shows it.

*/