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Translations:Development/Tutorials/Qt4 Ruby Tutorial/Chapter 10/Page display title/en-ca

Development/Tutorials/Qt4 Ruby Tutorial/Chapter 10

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TutorialBrowser‎

Qt4 Ruby Tutorial‎

Smooth as Silk‎

Tutorial 9 - With Cannon You Can‎

Tutorial 11 - Giving It a Shot‎

== Smooth as Silk ==‎

[[Image:Qt4_Ruby_Tutorial_Screenshot_10.png|center]]‎

Files:‎

=== Overview ===‎

In this example, we add a force control.‎

=== Line by Line Walkthrough ===‎

The '''<tt>CannonField</tt>''' now has a force value in addition to the angle.‎

The interface to the force follows the same practice as for the angle.‎

The force '''<tt>@currentForce</tt>''' is initialized to zero.‎

We have made a slight change in the '''<tt>setAngle()</tt>''' function. It repaints only the portion of the widget that contains the cannon.‎

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.‎

We paint as in Chapter 9.‎

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.‎

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).‎

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

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

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

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.‎

We initialize the force value to 25.‎

=== Running the Application ===‎

We now have a force control.‎

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

Put the cannon in the bottom-right corner.‎

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()].]‎

[[Category:Ruby]]‎

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