Kehitys/Oppikurssit/Qt 4 oppikurssi/Kappale 10

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    Development/Tutorials/Qt4 Ruby Tutorial/Chapter 10


    Sileää kuin silkki
    Tutorial Series   Qt4 Ruby -oppikurssi
    Previous   Oppikurssi 9 - Kanuunalla onnistuu
    What's Next   Oppikurssi 11 - Annetaan sille laukaus
    Further Reading   n/a

    Smooth as Silk

    Files:

    Overview

    In this example, we add a force control.

    Line by Line Walkthrough

    cannon.rb

    The CannonField now has a force value in addition to the angle.

    signals 'angleChanged(int)', 'forceChanged(int)'
    slots 'setAngle(int)', 'setForce(int)'
    

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

    def initialize(parent = nil)
      super()
    
      @currentAngle = 45
      @currentForce = 0
    
      setPalette(Qt::Palette.new(Qt::Color.new(250, 250, 200)))
      setAutoFillBackground(true)
    end
    

    The force @currentForce is initialized to zero.

    def setAngle(angle)
      if angle < 5
        angle = 5
      elsif angle > 70
        angle = 70
      end
    
      if @currentAngle == angle
        return
      end
    
      @currentAngle = angle
      update(cannonRect())
      emit angleChanged(@currentAngle)
    end
    

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

    def setForce(force)
      if force < 0
        force = 0
      end
      if @currentForce == force
        return
      end
    
      @currentForce = force
      emit forceChanged(@currentForce)
    end
    

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

    def paintEvent(event)
      painter = Qt::Painter.new(self)
    
      painter.setPen(Qt::NoPen)
      painter.setBrush(Qt::Brush.new(Qt::blue))
    
      painter.translate(0, height())
      painter.drawPie(Qt::Rect.new(-35, -35, 70, 70), 0, 90 * 16)
      painter.rotate(-@currentAngle)
      painter.drawRect(Qt::Rect.new(30, -5, 20, 10))
      painter.end()
    end
    

    We paint as in Chapter 9.

    def cannonRect()
      result = Qt::Rect.new(0, 0, 50, 50)
      result.moveBottomLeft(rect().bottomLeft())
      return result
    end
    

    The cannonRect() 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 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).

    t10.rb

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

    force = LCDRange.new()
    force.setRange(10, 50)
    

    We add a second LCDRange, which will be used to set the force.

    connect(force, SIGNAL('valueChanged(int)'),
             cannonField, SLOT('setForce(int)'))
    connect(cannonField, SIGNAL('forceChanged(int)'),
             force, SLOT('setValue(int)'))
    

    We connect the force widget and the cannonField widget, just like we did for the angle widget.

    leftLayout = Qt::VBoxLayout.new()
    leftLayout.addWidget(angle)
    leftLayout.addWidget(force)
    
    gridLayout = Qt::GridLayout.new()
    gridLayout.addWidget(quit, 0, 0)
    gridLayout.addLayout(leftLayout, 1, 0)
    gridLayout.addWidget(cannonField, 1, 1, 2, 1)
    gridLayout.setColumnStretch(1, 10)
    

    In Chapter 9, we put angle 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 angle and range in the vertical box.

    force.setValue(25)
    

    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 Left and Right keys work, change that too. [Hint: Reimplement Qt::Widget::keyPressEvent().]