added documentation with an image

source/RobotAPI/gui_plugins/PlatformUnitPlugin/JoystickControlWidget.h

@@ -79,6 +79,38 @@ namespace armarx
 
     /**
      * @brief Provides a simple joystick control.
+     *
+     * The widget emits signals when the control is moved.
+     *
+     * The signal
+     * @code{.cpp}
+     * positionChanged(QPointF)
+     * @endcode
+     * passes the nibble's current position.
+     * The position is in the unit circle.
+     * The x-axis is horizontal and increases to the right.
+     * The y-axis is vertical and increases upwards.
+     *
+     * The signal
+     * @code{.cpp}
+     * rotationChanged(double)
+     * @endcode
+     * passes the position vectors rotation in polar coordinates (-pi,pi].
+     * The up position is 0.
+     * The down position is pi.
+     * The Quadrants 1 and 4 have positive value.
+     *
+     * If the constructor is called with useQuadrant3and4==true the control is the whole unit circle.
+     * If the constructor is called with useQuadrant3and4==false the control is the unit circle's upper semicircle. (y>=0)
+     *
+     * Possible positions can be influenced with
+     * \code{.cpp}
+     * setSteps(int steps);
+     * \endcode
+     *      - steps>0 : only position vectors with a length from {n/steps | n in {0,1,...,steps} are valid. The nibble snaps to a valid position.
+     *      - steps<=0: all positions in the unit circle are valid.
+     *
+     * @image html JoystickControlWidget_widget.png "Left: A widget with 2 steps using the whole unit circle. Right: A widget using the unit circle's upper semi circle." width=300px
      */
     class JoystickControlWidget : public QWidget
     {