How I can define the edges? - iphone

Question

I have made a code for scrolling a background in Cocos2d to create an effect of a camera, but I cant prevent the camera going beyond the edges of my background. My background is an image that is 1440*1080. My code is:
+(id) scene
{
CCScene* scene = [CCScene node];
TileDemo* layer = [TileDemo node];
[scene addChild: layer];
return scene;
}
-(id) init
{
if ((self = [super init]))
{
self.isTouchEnabled = YES;
CCSprite *Nivel1 = [CCSprite spriteWithFile:#"Nivel1.png"];
Nivel1.position = ccp(0.5f, 0.5f);
[self addChild:Nivel1 z:0 tag:1];
}
return self;
}
-(void) dealloc
{
[super dealloc];
}
-(void) registerWithTouchDispatcher
{
[[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:YES];
}
-(BOOL) ccTouchBegan:(UITouch*)touch withEvent:(UIEvent*)event
{
return YES;
}
-(void) ccTouchEnded:(UITouch*)touch withEvent:(UIEvent*)event
{
}
-(void) ccTouchCancelled:(UITouch*)touch withEvent:(UIEvent*)event
{
}
-(void) ccTouchMoved:(UITouch*)touch withEvent:(UIEvent*)event
{
CGPoint touchLocation = [touch locationInView: [touch view]];
CGPoint prevLocation = [touch previousLocationInView: [touch view]];
touchLocation = [[CCDirector sharedDirector] convertToGL: touchLocation];
prevLocation = [[CCDirector sharedDirector] convertToGL: prevLocation];
CGPoint diff = ccpSub(touchLocation,prevLocation);
CCNode* node = [self getChildByTag:1];
CGPoint currentPos = [node position];
[node setPosition: ccpAdd(currentPos, diff)];
}
#end

Answer 1

you have to calculate maximum and minimum posiible position of your sprite and check it in your touchMoved:withEvent: method. On my mind, it is easier to calculate these values, when anchorPoint of your sprite is in (0.f, 0.f), instead of standard (0.5f, 0.5f). then your positions will be
CGPoint maxPos = ccp(0.f, 0.f);
CGPoint minPos = ccp((spriteWidth - screenWidth) * (-1), (spriteHeight - screnHeight) * (-1));
then just check if your sprite's new position is in valid range before set it.