Rectangle and Circle collision detection - ios

Question

I am trying to do collision detection between a rectangle and a circle. I came up with this method:
-(BOOL) isCollidingRect:(CCSprite *) spriteOne WithSphere:(CCSprite *) spriteTwo {
float diff = ccpDistance(spriteOne.position, spriteTwo.position);
float obj1Radii = [spriteOne boundingBox].size.width/2;
float obj2Radii = [spriteTwo boundingBox].size.width/2;
if (diff < obj1Radii + obj2Radii) {
return YES;
} else {
return NO;
}
}
and this is how I check it:
if ([self isCollidingRect:player WithSphere:blocker] == true) {
[self playerdeathstart];
}
This seems to work properly on the side of the rectangle but it doesn't above or below it. On the top and bottom, the collision occurs too early.
Is there a way I can get this collision to detected properly? Thank you for your help.

Answer 1

You can use CGRectIntersectsRect to achieve this.
-(BOOL) isCollidingRect:(CCSprite *) spriteOne WithSphere:(CCSprite *) spriteTwo {
return CGRectIntersectsRect([spriteOne boundingBox],[spriteTwo boundingBox]);
}
It is not pixel perfect but as i understand that is not necessary in this case.

Answer 2

This is not a solution for those who use Cocos2d-ObjC, but will help for Cocos2d-x devs (for instance, personally I found this topic because was searching for the same for my c++ game).
Cocos2d-x has method "intersectsCircle" for Rect class.
Here is how I solved in my c++ project almost the same problem as one described by you:
bool ObstacleEntity::hasCollisionAgainst(cocos2d::Sprite *spr)
{
cocos2d::Rect rect = cocos2d::Rect( spr->getPositionX(), spr->getPositionY(), spr->getBoundingBox().size.width, spr->getBoundingBox().size.height);
float rw = this->getBoundingBox().size.width / 2;
float rh = this->getBoundingBox().size.height / 2;
float radius = ( rw > rh ) ? rw : rh;
cocos2d::Vec2 center( this->getPositionX() + rw, this->getPositionY() + rh );
return rect.intersectsCircle( center, radius );
}
Passed Sprite here is rectangle, while ObstacleEntity always is almost ideally round.
Note that anchor points for all entities are set to lower left corner in my case.