Question

So I have a UIView called fallingBall that currently collides nicely with my UIView called theBlockView. I am using CGRectIntersectsRect(theBlockView.frame, fallingBall.frame) to detect this collision.

That’s all very well, so now I would like my fallingBall to actually be round, and I would also like the top corners of theBlockView to be rounded. To do this, I used the following code:

//round top right-hand corner of theBlockView
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:theBlockView.bounds 
                                           byRoundingCorners:UIRectCornerTopRight
                                           cornerRadii:CGSizeMake(10.0, 10.0)];
CAShapeLayer *maskLayer = [CAShapeLayer layer];
maskLayer.frame = theBlockView.bounds;
maskLayer.path = maskPath.CGPath;
theBlockView.layer.mask = maskLayer;

//round the fallingBall view
[[fallingBall layer] setCornerRadius:30];

But, funnily enough, though they look nice and rounded, the views are still rectangles.
So my question is: how can I make CGRectIntersectsRect treat them as the shapes that they look like? Is there a function that works the same but uses the view’s alpha to detect collisions?

Thanks for your time!

Answer 1

Actually, let me answer my own question!

OK, so I spent the greater part of the last 10 hours looking around, and I came across this post: Circle-Rectangle collision detection (intersection) – check out what e.James has to say!

I wrote a function to help with this: first, declare the following structs:

typedef struct
{
    CGFloat x; //center.x
    CGFloat y; //center.y
    CGFloat r; //radius
} Circle;
typedef struct
{
    CGFloat x; //center.x
    CGFloat y; //center.y
    CGFloat width;
    CGFloat height;
} MCRect;

Then add the following function:

-(BOOL)circle:(Circle)circle intersectsRect:(MCRect)rect
{

    CGPoint circleDistance = CGPointMake(abs(circle.x - rect.x), abs(circle.y - rect.y) );

    if (circleDistance.x > (rect.width/2 + circle.r)) { return false; }
    if (circleDistance.y > (rect.height/2 + circle.r)) { return false; }

    if (circleDistance.x <= (rect.width/2)) { return true; } 
    if (circleDistance.y <= (rect.height/2)) { return true; }

    CGFloat cornerDistance_sq = pow((circleDistance.x - rect.width/2), 2) + pow((circleDistance.y - rect.height/2), 2);

    return (cornerDistance_sq <= (pow(circle.r, 2)));
}

I hope this helps someone!