uSightRead: Music Theory on the Go

I had an opportunity last night to work on the input component of uSightRead. The main part of the game is a single scene, with layers for the individual parts. There is a main game display layer and an input layer. The input layer consists of keys from a piano that respond to touches. Initially I had thought that each sprite would be able to handle its own touches and then simply pass a message up. This is not how it works. With cocos2d-iphone only a layer can receive touches. I discovered this in a answer to this question on Stack Overflow, which the answer goes into how to do bounds checking.

If you note the highest rated answer shows how to compute where the point touched within your layer, and then determine if the touch was inside a label. This is doing a basic rectangle point intersection. The example code uses a compound if statement, but I simply built a rectangle based on my sprite, and used the CGRectContainsPoint function found. You can read about the built-in geometry functions here. Here’s what my code looks like:

CGRect spriteRect =
  CGRectMake(self.position.x - spriteWidth / 2,
                   self.position.y - spriteHeight / 2,
                   spriteWidth,
                   spriteHeight);

if(CGRectContainsPoint(spriteRect, cLoc)
{
  NSLog(@"Sprite was touched");
  return kEventHandled;
}
else
{
  return kEventIgnored;
}

The one thing to note is the subtraction of half the width and height to compute the postion. This is because the position is actually the center of the Sprite.