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The implementation of '''<tt>setForce()</tt>''' is quite similar to that of '''<tt>setAngle()</tt>'''. The only difference is that because we don't show the force value, we don't need to repaint the widget.‎

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We paint as in Chapter 9.‎

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The '''<tt>cannonRect()</tt>''' function returns the rectangle enclosing the cannon in widget coordinates. First we create a rectangle with the size 50 x 50 and then move it so its bottom-left corner is equal to the widget's own bottom-left corner.‎

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The [http://doc.qt.nokia.com/latest/qwidget.html#rect-prop Qt::Widget::rect()] function returns the widget's enclosing rectangle in the widget's own coordinates. The top-left corner of the rectangle is always (0, 0).‎

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The constructor is mostly the same, but some new bits have been added.‎

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We add a second '''<tt>LCDRange</tt>''', which will be used to set the force.‎

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We connect the '''<tt>force</tt>''' widget and the '''<tt>cannonField</tt>''' widget, just like we did for the '''<tt>angle</tt>''' widget.‎

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In Chapter 9, we put '''<tt>angle</tt>''' in the lower-left cell of the layout. Now we want to have two widgets in that cell, so we make a vertical box, put the vertical box in the grid cell, and put each of '''<tt>angle</tt>''' and '''<tt>range</tt>''' in the vertical box.‎

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We initialize the force value to 25.‎

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=== Running the Application ===‎

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We now have a force control.‎

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=== Exercises === Make the size of the cannon barrel be dependent on the force.‎

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Put the cannon in the bottom-right corner.‎

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Try adding a better keyboard interface. For example, make + and - increase and decrease the force and enter shoot. If you're bothered by the way the '''<tt>Left</tt>''' and '''<tt>Right</tt>''' keys work, change that too. [Hint: Reimplement [http://doc.qt.nokia.com/latest/qwidget.html#keyPressEvent Qt::Widget::keyPressEvent()].]‎

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[[Category:Ruby]]‎

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