Qt Tutorial #1 Add-on Part II

Hi guys,

For this tutorial here,

http://doc.trolltech.com/4.2/tutorial-t11.html

At the end of the tutorial, there's an exercise that says:

"Change the color of the cannon when a shot is in the air."

How do we achieve that? I tried it for like 2-3 hours, but still couldnt get it to work.

In the following function you have to see if the cannon is in the air, meaning autoShootTimer->isActive().

Code:

---

void CannonField::paintCannon(QPainter &painter)
{
   painter.setPen(Qt::NoPen);
   if( autoShootTimer->isActive() //bullet is in the air
       painter.setBrush( Qt::red );
   else //bullet is not in the air
       painter.setBrush(Qt::blue);     
   painter.save();
   painter.translate(0, height());
   painter.drawPie(QRect(-35, -35, 70, 70), 0, 90 * 16);
   painter.rotate(-currentAngle);
   painter.drawRect(barrelRect);
   painter.restore();
 }

---

Regards

Hi,

Has anybody tried this modification? I'm not sure if I did something, but this is what I have tried before and my cannon's color never changed each time I pressed the shoot button.

Here's the simple code modification that didnt work for me:

Code:

---

void CannonField::paintCannon( QPainter& painter )
{
   painter.setPen( Qt::NoPen );
 
   if( autoShootTimer->isActive() )//bullet is in the air
   {
	   painter.setBrush( Qt::red );
   }
   else //bullet is not in the air
   {
	   painter.setBrush(Qt::blue);  
   }
 
   painter.save();
   painter.translate(0, height());
   painter.drawPie(QRect(-35, -35, 70, 70), 0, 90 * 16 );
   painter.rotate(-currentAngle);
   painter.drawRect(barrelRect);
   painter.restore();
}

---

Actually the cannon rect wasn't updated at repaint. Try this

Code:

---

void CannonField::moveShot()
 {
     QRegion region = shotRect();
     ++timerCount;
 
     QRect shotR = shotRect();
     QRect cannonR = cannonRect();
 
     if (shotR.x() > width() || shotR.y() > height()) {
         autoShootTimer->stop();
     } else {
         region = region.unite(shotR);
         region = region.unite(cannonR);
     }
     update(region);
 }

---

Regards

Hi Marcel,

Thank you. Now that I added that code, the cannon changes from blue to red. However, it stays red even when the shot is off screen. Is there a remedy to re-paint it blue?

Actually, it is, if you modify the code above a bit:

Code:

---

void CannonField::moveShot()
 {
     QRegion region = shotRect();
     ++timerCount;
 
     QRect shotR = shotRect();
     QRect cannonR = cannonRect();
     if (shotR.x() > width() || shotR.y() > height()) {
         autoShootTimer->stop();
     } else {
         region = region.unite(shotR);
     }
     region = region.unite( cannonR );
     update(region);
 }

---

This way the cannon will be updated even after the timer is stopped ( the bullet is off-screen ). If the timer is stopped, then the cannon will be painted with the original color.

Regards.