Difference between revisions of "Development/Tutorials/Qt4 Ruby Tutorial/Chapter 10"

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'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t10/cannon.rb cannon.rb]'''
 
'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t10/cannon.rb cannon.rb]'''
  
The CannonField now has a force value in addition to the angle.
+
The '''<tt>CannonField</tt>''' now has a force value in addition to the angle.
  
 
<code ruby>
 
<code ruby>
Line 45: Line 45:
 
</code>
 
</code>
  
The force @currentForce is initialized to zero.
+
The force '''<tt>@currentForce</tt>''' is initialized to zero.
  
 
<code ruby>
 
<code ruby>
  def setAngle(angle)
+
def setAngle(angle)
    if angle < 5
+
  if angle < 5
      angle = 5
+
    angle = 5
    elsif angle > 70
+
  elsif angle > 70
      angle = 70
+
    angle = 70
    end
+
  end
 
+
    if @currentAngle == angle
+
      return
+
    end
+
  
    @currentAngle = angle
+
  if @currentAngle == angle
     update(cannonRect())
+
     return
    emit angleChanged(@currentAngle)
+
 
   end
 
   end
 +
 +
  @currentAngle = angle
 +
  update(cannonRect())
 +
  emit angleChanged(@currentAngle)
 +
end
 
</code>
 
</code>
  
We have made a slight change in the setAngle() function. It repaints only the portion of the widget that contains the cannon.
+
We have made a slight change in the '''<tt>setAngle()</tt>''' function. It repaints only the portion of the widget that contains the cannon.
  
 
<code ruby>
 
<code ruby>
  def setForce(force)
+
def setForce(force)
    if force < 0
+
  if force < 0
      force = 0
+
    force = 0
    end
+
    if @currentForce == force
+
      return
+
    end
+
 
+
    @currentForce = force
+
    emit forceChanged(@currentForce)
+
 
   end
 
   end
 +
  if @currentForce == force
 +
    return
 +
  end
 +
 +
  @currentForce = force
 +
  emit forceChanged(@currentForce)
 +
end
 
</code>
 
</code>
  
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.
+
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.
  
 
<code ruby>
 
<code ruby>
  def paintEvent(event)
+
def paintEvent(event)
    painter = Qt::Painter.new(self)
+
  painter = Qt::Painter.new(self)
  
    painter.setPen(Qt::NoPen)
+
  painter.setPen(Qt::NoPen)
    painter.setBrush(Qt::Brush.new(Qt::blue))
+
  painter.setBrush(Qt::Brush.new(Qt::blue))
  
    painter.translate(0, height())
+
  painter.translate(0, height())
    painter.drawPie(Qt::Rect.new(-35, -35, 70, 70), 0, 90 * 16)
+
  painter.drawPie(Qt::Rect.new(-35, -35, 70, 70), 0, 90 * 16)
    painter.rotate(-@currentAngle)
+
  painter.rotate(-@currentAngle)
    painter.drawRect(Qt::Rect.new(30, -5, 20, 10))
+
  painter.drawRect(Qt::Rect.new(30, -5, 20, 10))
    painter.end()
+
  painter.end()
  end
+
end
 
</code>
 
</code>
  
Line 101: Line 101:
  
 
<code ruby>
 
<code ruby>
  def cannonRect()
+
def cannonRect()
    result = Qt::Rect.new(0, 0, 50, 50)
+
  result = Qt::Rect.new(0, 0, 50, 50)
    result.moveBottomLeft(rect().bottomLeft())
+
  result.moveBottomLeft(rect().bottomLeft())
    return result
+
  return result
  end
+
end
 
</code>
 
</code>
  
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 '''<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 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 [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).
  
 
'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t10/t10.rb t10.rb]'''
 
'''[http://www.darshancomputing.com/qt4-qtruby-tutorial/tutorial/t10/t10.rb t10.rb]'''
Line 121: Line 121:
 
</code>
 
</code>
  
We add a second LCDRange, which will be used to set the force.
+
We add a second '''<tt>LCDRange</tt>''', which will be used to set the force.
  
 
<code ruby>
 
<code ruby>
    connect(force, SIGNAL('valueChanged(int)'),
+
connect(force, SIGNAL('valueChanged(int)'),
            cannonField, SLOT('setForce(int)'))
+
        cannonField, SLOT('setForce(int)'))
    connect(cannonField, SIGNAL('forceChanged(int)'),
+
connect(cannonField, SIGNAL('forceChanged(int)'),
            force, SLOT('setValue(int)'))
+
        force, SLOT('setValue(int)'))
 
</code>
 
</code>
  
We connect the force widget and the cannonField widget, just like we did for the angle widget.
+
We connect the '''<tt>force</tt>''' widget and the '''<tt>cannonField</tt>''' widget, just like we did for the '''<tt>angle</tt>''' widget.
  
 
<code ruby>
 
<code ruby>
Line 144: Line 144:
 
</code>
 
</code>
  
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.
+
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.
  
 
<code ruby>
 
<code ruby>
Line 162: Line 162:
 
Put the cannon in the bottom-right corner.
 
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().]
+
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()].]

Revision as of 02:18, 31 December 2009


Contents

Development/Tutorials/Qt4 Ruby Tutorial/Chapter 10


Smooth as Silk
Tutorial Series   Qt4 Ruby Tutorial
Previous   Tutorial 9 - With Cannon You Can
What's Next   Tutorial 11 - Giving It a Shot
Further Reading   n/a

Smooth as Silk

Qt4 Ruby Tutorial Screenshot 10.png

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().]


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