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**
** Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information (qt-info@nokia.com)
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** This file is part of the $MODULE$ of the Qt Toolkit.
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** $TROLLTECH_DUAL_LICENSE$
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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 a setOn() function to turn the light on or off. It paints itself
    in the color that's passed to the constructor.

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

    The TrafficLightWidget class represents the visual part of the traffic
    light; it's a widget that contains three lights, and provides accessor
    functions for these.

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

    The LightState class represents a state that turns a light on when the
    state is entered, and off when the state is exited. The class is a timer,
    and as we shall see the timeout is used to transition from one LightState
    to another.

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

    The TrafficLight class combines the TrafficLightWidget with control flow
    based on the LightState class. 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.

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

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

*/