... cannon.h contains the CannonField class definition . ... We have moved the painting of the cannon to a separate function and have also put the defintion of the cannon's enclosing rectangle in a separate function. int ang; int f; }; . ... QPainter tmp; . ... We place the force LCDRange widget below the angle widget and specify the range to 10..50. connect ( force,SIGNAL(valueChanged(int)), cannonField,SLOT(setForce(int))); connect ( cannonField,SIGNAL(forceChanged(int)), force,SLOT(setValue(int))); ....