Development/Tutorials/Qt4 Ruby Tutorial/Chapter 12 - Revision history

AnneW at 14:23, 18 July 2012

2012-07-18T14:23:29Z

AnneW: Marked this version for translation

2011-07-02T14:56:04Z

Marked this version for translation

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Aspotashev: add translate tags

2011-07-01T23:46:04Z

add translate tags

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Neverendingo: Text replace - "" to ""

2011-06-29T20:55:56Z

Text replace - "</code>" to "</syntaxhighlight>"

Neverendingo: Text replace - "`" to ""`


2011-06-29T20:43:16Z
Text replace - "<code ruby>" to "<syntaxhighlight lang="ruby">"

				
				
				
				
			
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			Revision as of 20:43, 29 June 2011
			
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  '''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/lcdrange.rb lcdrange.rb]'''   '''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/lcdrange.rb lcdrange.rb]'''
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def initialize(s, parent = nil)   def initialize(s, parent = nil)
     super(parent)      super(parent)
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  This constructor first calls '''<tt>init()</tt>''' and then sets the label text. '''<tt>init()</tt>''' is a separate function performing initialization mosty because of function overloading matters in the original C++ version.   This constructor first calls '''<tt>init()</tt>''' and then sets the label text. '''<tt>init()</tt>''' is a separate function performing initialization mosty because of function overloading matters in the original C++ version.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def init()   def init()
     lcd = Qt::LCDNumber.new(2)      lcd = Qt::LCDNumber.new(2)
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  The setup of '''<tt>lcd</tt>''' and '''<tt>slider</tt>''' is the same as in the previous chapter. Next we create a [http://doc.qt.nokia.com/latest/qlabel.html Qt::Label] and tell it to align the contents centered horizontally and to the top vertically. The [http://doc.qt.nokia.com/latest/qobject.html#connect Qt::Object::connect()] calls have also been taken from the previous chapter.   The setup of '''<tt>lcd</tt>''' and '''<tt>slider</tt>''' is the same as in the previous chapter. Next we create a [http://doc.qt.nokia.com/latest/qlabel.html Qt::Label] and tell it to align the contents centered horizontally and to the top vertically. The [http://doc.qt.nokia.com/latest/qobject.html#connect Qt::Object::connect()] calls have also been taken from the previous chapter.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def setText(s)   def setText(s)
     @label.setText(s)      @label.setText(s)
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  The '''<tt>CannonField</tt>''' now has two new signals: '''<tt>hit()</tt>''' and '''<tt>missed()</tt>'''. In addition, it contains a target.   The '''<tt>CannonField</tt>''' now has two new signals: '''<tt>hit()</tt>''' and '''<tt>missed()</tt>'''. In addition, it contains a target.
    
− <code ruby> + <syntaxhighlight lang="ruby">
     signals 'hit()', 'missed()' #...      signals 'hit()', 'missed()' #...
  </code>   </code>
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  The '''<tt>hit()</tt>''' signal is emitted when a shot hits the target. The '''<tt>missed()</tt>''' signal is emitted when the shot moves beyond the right or bottom edge of the widget (i.e., it is certain that it has not and will not hit the target).   The '''<tt>hit()</tt>''' signal is emitted when a shot hits the target. The '''<tt>missed()</tt>''' signal is emitted when the shot moves beyond the right or bottom edge of the widget (i.e., it is certain that it has not and will not hit the target).
    
− <code ruby> + <syntaxhighlight lang="ruby">
       newTarget()        newTarget()
  </code>   </code>
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  This line has been added to the constructor. It creates a "random" position for the target. In fact, the '''<tt>newTarget()</tt>''' function will try to paint the target. Because we are in a constructor, the '''<tt>CannonField</tt>''' widget is invisible. Qt guarantees that no harm is done when calling [http://doc.qt.nokia.com/latest/qwidget.html#update Qt::Widget::update()] on a hidden widget.   This line has been added to the constructor. It creates a "random" position for the target. In fact, the '''<tt>newTarget()</tt>''' function will try to paint the target. Because we are in a constructor, the '''<tt>CannonField</tt>''' widget is invisible. Qt guarantees that no harm is done when calling [http://doc.qt.nokia.com/latest/qwidget.html#update Qt::Widget::update()] on a hidden widget.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  @@first_time = true   @@first_time = true
    
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  By experimentation we have found this to always be in reach of the shot.   By experimentation we have found this to always be in reach of the shot.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def moveShot()   def moveShot()
     region = Qt::Region.new(shotRect())      region = Qt::Region.new(shotRect())
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  This part of the timer event has not changed from the previous chapter.   This part of the timer event has not changed from the previous chapter.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  if shotR.intersects(targetRect())     if shotR.intersects(targetRect())  
     @autoShootTimer.stop()      @autoShootTimer.stop()
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  This '''<tt>if</tt>''' statement checks whether the shot rectangle intersects the target rectangle. If it does, the shot has hit the target (ouch!). We stop the shoot timer and emit the '''<tt>hit()</tt>''' signal to tell the outside world that a target was destroyed, and return. Note that we could have created a new target on the spot, but because the '''<tt>CannonField</tt>''' is a component we leave such decisions to the user of the component.   This '''<tt>if</tt>''' statement checks whether the shot rectangle intersects the target rectangle. If it does, the shot has hit the target (ouch!). We stop the shoot timer and emit the '''<tt>hit()</tt>''' signal to tell the outside world that a target was destroyed, and return. Note that we could have created a new target on the spot, but because the '''<tt>CannonField</tt>''' is a component we leave such decisions to the user of the component.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  elsif shotR.x() > width() || shotR.y() > height()   elsif shotR.x() > width() || shotR.y() > height()
     @autoShootTimer.stop()      @autoShootTimer.stop()
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  This is the same as in the previous chapter, except that it now emits the '''<tt>missed()</tt>''' signal to tell the outside world about the failure.   This is the same as in the previous chapter, except that it now emits the '''<tt>missed()</tt>''' signal to tell the outside world about the failure.
    
− <code ruby> + <syntaxhighlight lang="ruby">
     else      else
       region = region.unite(Qt::Region.new(shotR))        region = region.unite(Qt::Region.new(shotR))
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  '''<tt>CannonField::paintEvent()</tt>''' is as before, except that this has been added:   '''<tt>CannonField::paintEvent()</tt>''' is as before, except that this has been added:
    
− <code ruby> + <syntaxhighlight lang="ruby">
       paintTarget(painter)        paintTarget(painter)
  </code>   </code>
  This line makes sure that the target is also painted when necessary.   This line makes sure that the target is also painted when necessary.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def paintTarget(painter)   def paintTarget(painter)
     painter.setBrush(Qt::Brush.new(Qt::red))      painter.setBrush(Qt::Brush.new(Qt::red))
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  This function paints the target; a rectangle filled with red and with a black outline.   This function paints the target; a rectangle filled with red and with a black outline.
    
− <code ruby> + <syntaxhighlight lang="ruby">
  def targetRect()   def targetRect()
     result = Qt::Rect.new(0, 0, 20, 10)      result = Qt::Rect.new(0, 0, 20, 10)
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  There are no new members in the '''<tt>MyWidget</tt>''' class, but we have slightly changed the constructor to set the new '''<tt>LCDRange</tt>''' text labels.   There are no new members in the '''<tt>MyWidget</tt>''' class, but we have slightly changed the constructor to set the new '''<tt>LCDRange</tt>''' text labels.
    
− <code ruby> + <syntaxhighlight lang="ruby">
       angle = LCDRange.new(tr('ANGLE'))        angle = LCDRange.new(tr('ANGLE'))
  </code>   </code>
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  We set the angle text label to "ANGLE".   We set the angle text label to "ANGLE".
    
− <code ruby> + <syntaxhighlight lang="ruby">
       force  = LCDRange.new(tr('FORCE'))        force  = LCDRange.new(tr('FORCE'))
  </code>   </code>



Alisha at 03:04, 13 January 2010
2010-01-13T03:04:17Z


				
				
				
				
			
			← Older revision
			Revision as of 03:04, 13 January 2010
			
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  === Running the Application ===   === Running the Application ===
−  
  The '''<tt>LCDRange</tt>''' widgets look a bit strange: When resizing '''<tt>MyWidget</tt>''', the built-in layout management in [http://doc.qt.nokia.com/latest/qvboxlayout.html Qt::VBoxLayout] gives the labels too much space and the rest not enough; making the space between the two '''<tt>LCDRange</tt>''' widgets change size. We'll fix that in the next chapter   The '''<tt>LCDRange</tt>''' widgets look a bit strange: When resizing '''<tt>MyWidget</tt>''', the built-in layout management in [http://doc.qt.nokia.com/latest/qvboxlayout.html Qt::VBoxLayout] gives the labels too much space and the rest not enough; making the space between the two '''<tt>LCDRange</tt>''' widgets change size. We'll fix that in the next chapter
    
  === Exercises ===   === Exercises ===
−  
  Make a cheat button that, when pressed, makes the '''<tt>CannonField</tt>''' display the shot trajectory for five seconds.   Make a cheat button that, when pressed, makes the '''<tt>CannonField</tt>''' display the shot trajectory for five seconds.
    
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  Not easy; make it possible to have several shots in the air at the same time. [Hint: Make a '''<tt>Shot</tt>''' class.]   Not easy; make it possible to have several shots in the air at the same time. [Hint: Make a '''<tt>Shot</tt>''' class.]
  + 
  + [[Category:Ruby]]



Alisha at 10:32, 31 December 2009
2009-12-31T10:32:09Z

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Alisha: Created page with '{{Template:I18n/Language Navigation Bar|Development/Tutorials/Qt4 Ruby Tutorial/Chapter 12}}  {{TutorialBrowser|  series=[[Development/Tutorials/Qt4_Ruby_Tutorial|Qt4 Ruby Tutori...'
2009-12-31T04:04:55Z
Created page with '{{Template:I18n/Language Navigation Bar|Development/Tutorials/Qt4 Ruby Tutorial/Chapter 12}}  {{TutorialBrowser|  series=[[Development/Tutorials/Qt4_Ruby_Tutorial|Qt4 Ruby Tutori...'
New page
{{Template:I18n/Language Navigation Bar|Development/Tutorials/Qt4 Ruby Tutorial/Chapter 12}}



{{TutorialBrowser|



series=[[Development/Tutorials/Qt4_Ruby_Tutorial|Qt4 Ruby Tutorial]]|



name=Hanging in the Air the Way Bricks Don't|



pre=[[Development/Tutorials/Qt4_Ruby_Tutorial/Chapter_11|Tutorial 11 - Giving It a Shot]]|



next=[[Development/Tutorials/Qt4_Ruby_Tutorial/Chapter_13|Tutorial 13 - Game Over]]

}}

== Hanging in the Air the Way Bricks Don't ==

[[Image:Qt4_Ruby_Tutorial_Screenshot_12.png|center]]

Files:

* [http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/lcdrange.rb lcdrange.rb]

* [http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/t12.rb t12.rb]

* [http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/cannon.rb cannon.rb]



=== Overview ===

In this example, we extend our LCDRange class to include a text label. We also provide something to shoot at.  



=== Line by Line Walkthrough ===

'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/lcdrange.rb lcdrange.rb]'''



  def initialize(s, parent = nil)

    super(parent)

    init()

    setText(s)

  end



This constructor first calls init() and then sets the label text. init() is a separate function performing initialization mosty because of function overloading matters in the original C++ version.



  def init()

    lcd = Qt::LCDNumber.new(2)

    lcd.setSegmentStyle(Qt::LCDNumber::Filled)



    @slider = Qt::Slider.new(Qt::Horizontal)

    @slider.setRange(0, 99)

    @slider.setValue(0)



    @label = Qt::Label.new()

    @label.setAlignment(Qt::AlignHCenter.to_i | Qt::AlignTop.to_i)



    connect(@slider, SIGNAL('valueChanged(int)'),

    lcd, SLOT('display(int)'))

    connect(@slider, SIGNAL('valueChanged(int)'),

    self, SIGNAL('valueChanged(int)'))



    layout = Qt::VBoxLayout.new()

    layout.addWidget(lcd)

    layout.addWidget(@slider)

    layout.addWidget(@label)

    setLayout(layout)



    setFocusProxy(@slider)

  end



The setup of lcd and slider is the same as in the previous chapter. Next we create a Qt::Label and tell it to align the contents centered horizontally and to the top vertically. The Qt::Object::connect() calls have also been taken from the previous chapter.



  def setText(s)

    @label.setText(s)

  end



This function sets the label text.



'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/cannon.rb cannon.rb]'''



The CannonField now has two new signals: hit() and missed(). In addition, it contains a target.



  signals 'hit()', 'missed()' #...



The hit() signal is emitted when a shot hits the target. The missed() signal is emitted when the shot moves beyond the right or bottom edge of the widget (i.e., it is certain that it has not and will not hit the target).



    newTarget()



This line has been added to the constructor. It creates a "random" position for the target. In fact, the newTarget() function will try to paint the target. Because we are in a constructor, the CannonField widget is invisible. Qt guarantees that no harm is done when calling Qt::Widget::update() on a hidden widget.



  @@first_time = true



  def newTarget()

    if @@first_time

      @@first_time = false

      midnight = Qt::Time.new(0, 0, 0)

      srand(midnight.secsTo(Qt::Time.currentTime()))

    end



    @target = Qt::Point.new(200 + rand(190), 10 + rand(255))

    update()

  end



This function creates a target center point at a new random position.



We create the Qt::Time object midnight, which represents the time 00:00:00. Next we fetch the number of seconds from midnight until now and use it as a random seed. See the documentation for Qt::Date, Qt::Time, and Qt::DateTime for more information.



Finally we calculate the target's center point. We keep it within the rectangle (x = 200, y = 35, width = 190, height = 255), i.e., the possible x and y values are 200 to 389 and 35 to 289, respectively) in a coordinate system where we put y position 0 at the bottom edge of the widget and let y values increase upwards x is as normal, with 0 at the left edge and with x values increasing to the right.



By experimentation we have found this to always be in reach of the shot.



  def moveShot()

    region = Qt::Region.new(shotRect())

    @timerCount += 1



    shotR = shotRect()



This part of the timer event has not changed from the previous chapter.



    if shotR.intersects(targetRect()) 

      @autoShootTimer.stop()

      emit hit()



This if statement checks whether the shot rectangle intersects the target rectangle. If it does, the shot has hit the target (ouch!). We stop the shoot timer and emit the hit() signal to tell the outside world that a target was destroyed, and return. Note that we could have created a new target on the spot, but because the CannonField is a component we leave such decisions to the user of the component.



    elsif shotR.x() > width() || shotR.y() > height()

      @autoShootTimer.stop()

      emit missed()



This is the same as in the previous chapter, except that it now emits the missed() signal to tell the outside world about the failure.



    else

      region = region.unite(Qt::Region.new(shotR))

    end

    

    update(region)

  end



And the rest of the function is as before.



CannonField::paintEvent() is as before, except that this has been added:



    paintTarget(painter)



This line makes sure that the target is also painted when necessary.



  def paintTarget(painter)

    painter.setBrush(Qt::Brush.new(Qt::red))

    painter.setPen(Qt::Pen.new(Qt::Color.new(Qt::black)))

    painter.drawRect(targetRect())

  end



This function paints the target; a rectangle filled with red and with a black outline.



  def targetRect()

    result = Qt::Rect.new(0, 0, 20, 10)

    result.moveCenter(Qt::Point.new(@target.x(), height() - 1 - @target.y()))

    return result

  end





This private function returns the enclosing rectangle of the target. Remember from newTarget() that the target point uses y coordinate 0 at the bottom of the widget. We calculate the point in widget coordinates before we call Qt::Rect::moveCenter().



The reason we have chosen this coordinate mapping is to fix the distance between the target and the bottom of the widget. Remember that the widget can be resized by the user or the program at any time.



'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t12/t12.rb t12.rb]'''



There are no new members in the MyWidget class, but we have slightly changed the constructor to set the new LCDRange text labels.



    angle = LCDRange.new(tr('ANGLE'))



We set the angle text label to "ANGLE".



    force  = LCDRange.new(tr('FORCE'))



We set the force text label to "FORCE".



=== Running the Application ===



The LCDRange widgets look a bit strange: When resizing MyWidget, the built-in layout management in Qt::VBoxLayout gives the labels too much space and the rest not enough; making the space between the two LCDRange widgets change size. We'll fix that in the next chapter



=== Exercises ===



Make a cheat button that, when pressed, makes the CannonField display the shot trajectory for five seconds.



If you did the "round shot" exercise from the previous chapter, try changing the shotRect() to a shotRegion() that returns a Qt::Region so you can have really accurate collision detection.



Make a moving target.



Make sure that the target is always created entirely on-screen.



Make sure that the widget cannot be resized so that the target isn't visible. [Hint: Qt::Widget::setMinimumSize() is your friend.]



Not easy; make it possible to have several shots in the air at the same time. [Hint: Make a Shot class.]

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