Quickly Build a Frame-by-Frame Game - Beginning iOS6 Games Development - page 98

viper = [Viper01 new];
CGRect frame = [self.view frame];
viper.center = CGPointMake(frame.size.width/2.0, frame.size.height/2.0);
[self.view addSubview:viper];
[viper setMoveToPoint:viper.center];
displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateScene)];
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
}
In Listing 5-3, after setting the title, we create a UITapGestureRecognizer and add it to the root
associated with this UIViewController . Adding the UITapGestureRecognizer to the UIView will
viewTapped: to be called when the user taps the screen, giving us a chance to update
Viper01 and place it in the center of the root UIView .
moveToPoint property of viper to the center of the screen, so the viper starts out
CADisplayLink and
updateScene . Once we call addToRunLoop , updateScene will be called every time
CADisplayLink and NSRunLoop and
updateScene , as shown in Listing 5-4.
Listing 5-4. Example01Controller.m (updateScene)
-(void)updateScene{
[viper updateLocation];
}
In Listing 5-4, in the task updateScene , we simply call updateLocation on the object viper . In future
examples we will do more in the task updateScene , but for now let's just look at how we implement
moving the one ship.
Moving the Spaceship
Each time updateScene is called, we have to update the location of the spaceship. This is
accomplished with a little geometry to figure out the new location of the ship for each frame of the
animation. Let's just look at updateLocation and understand how that task moves the spaceship.
See Listing 5-5.
Listing 5-5. Viper01.m (updateLocation)
-(void)updateLocation{
CGPoint c = [self center];