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POWhy am not getting collision detection with CGRectIntersectsRect in IOS?
 

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  1. POWhy am not getting collision detection with CGRectIntersectsRect in IOS?
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    <p>I have 4 elements: greenball, yellowball, orangeball, and redball that fall from the top of the screen</p> <p>I also have an element, blueball, that follows my touch. </p> <p>All of these things are working great! :D</p> <p>However, I want to detect when the greenball intersects with the blueball</p> <p>my blue ball is placed in the view at viewDidLoad, the 4 balls are placed on the view based on an nstimer that calls onTimer.</p> <p>All 5 balls are created on the same layer:</p> <pre><code>[self.view insertSubview:greenImage belowSubview:bottomBar] </code></pre> <p>I can detect when the redball and greenball collide:</p> <pre><code>if (CGRectIntersectsRect(greenImage.frame, redImage.frame)) { UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"title" message:@"points" delegate:nil cancelButtonTitle:@"cool" otherButtonTitles:nil]; [message show]; [message release]; } </code></pre> <p>If I replace "redImage" for "blueball" I don't get the alert. I assume this may be because they aren't declared in the same method. </p> <p>Any ideas on how to detect this collision?</p> <p>thanks!</p> <p><strong>--- EDIT ---</strong></p> <p>Using the suggestion below I'm doing the following:</p> <pre><code> greenImage = [[UIImageView alloc] initWithImage:green]; greenImage.frame = CGRectMake(startX,0,43,43); [self.view insertSubview:greenImage belowSubview:bottomBar]; [UIView beginAnimations:nil context:greenImage]; [UIView setAnimationDuration:5 * speed]; greenImage.frame = CGRectMake(startX, 500.0, 43,43); CGFloat r1 = greenImage.frame.size.width * .5; CGFloat r2 = blueBall.frame.size.width * .5; if(CGPointDistance(greenImage.center, blueBall.center) &lt; (r1 + r2)){ UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"notice" message:@"hit!" delegate:nil cancelButtonTitle:@"cool" otherButtonTitles:nil]; [message show]; [message release]; } </code></pre> <p>below this method I have:</p> <pre><code>CGFloat CGPointDistance(CGPoint p1, CGPoint p2) { return sqrtf((p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y)); } </code></pre> <p>get an error:</p> <blockquote> <p>conflicting types for 'CGPointDistance'</p> </blockquote> <p>and a warning:</p> <blockquote> <p>implicit declaration of function 'CGPointDistance'</p> </blockquote>
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      1. POWhy am not getting collision detection with CGRectIntersectsRect in IOS?
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    1. CORect intersections is quite a bad way of doing collision detection on balls. Instead you could compare the distances of the centers of the balls with the sum of the radii. This will correctly determine when the balls collide.
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    2. COOk, can you point me to a explanation on how to recognize the images as a circle by getting the center (redImage.center maybe?) and setting the radii? I understand how that can be a better option just need a better of understanding on setting/detection for circles/balls. Thanks, again.
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    3. COAssuming that the ball fill up the image, the radius would be (the width of the image) / 2. If there is some inset you will have to account for it: (width-inset)/2
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