how to detect touch in a circle « cocos2d for iPhone

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how to detect touch in a circle

(8 posts) (4 voices)

Started 7 months ago by phantomsri
Latest reply from itlgames

Tags:

phantomsri
Member
I really need help.
i have a circle sprite, and this code
```
-(void)ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGSize winSize =[[CCDirector sharedDirector] winSize];
    UITouch* myTouch = [touches anyObject];
    CGPoint location = [myTouch locationInView: [myTouch view]];
    location = [[CCDirector sharedDirector]convertToGL:location];

    CCSprite *circleSprite = (CCSprite*)[self getChildByTag:30];
    CGRect correctColorSprite1 = [circleSprite boundingBox];

        if (CGRectContainsPoint(correctColorSprite1, location)) {
       NSLog(@"inside");
}
```
as i know there is a bounding box, when i touch slightly outside of the top circle it will still detect the touch.
Now i need help to eliminate this, i have read this post from this link http://www.cocos2d-iphone.org/forum/topic/8803.

But after reading it I'm confused how to incorporate it. Currently my circle size is in 50 points.
I hope someone can help me out give me some snippets of a improved code to detect the touch only in the circle.
Posted 7 months ago #

Well that post explains pretty clear, you just need to detect the distance between the touch and the centre of your circle.

Ok, let's assume the diameter of your circle is the width of your PNG (so the circle on your png has no extra margins), assuming the anchor point of the circle is on middle of sprite (the default value) you could do:

-(void)ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGSize winSize =[[CCDirector sharedDirector] winSize];
    UITouch* myTouch = [touches anyObject];
    CGPoint location = [myTouch locationInView: [myTouch view]];
    location = [[CCDirector sharedDirector]convertToGL:location];

    CCSprite *circleSprite = (CCSprite*)[self getChildByTag:30];

    BOOL inside = ( ccpDistance(circleSprite.position, location) < circleSprite.contentSize.width/2.0f );

     if (inside) {
        NSLog(@"inside");
     }
}

EDIT: you could just check the square root distance to optimise, but I'm sure any device can deal with a square calculation on each touch!

Posted 7 months ago #

phantomsri
Member

Thanks for your kind help itlgames.
I actually learning a lot from this forums. I am really new in this field of programming.

Posted 7 months ago #
andrew
Member

manucorporat posted a more efficient method a while back: http://www.cocos2d-iphone.org/forum/topic/12453#post-70037

Posted 7 months ago #
itlgames
Moderator

Yes @andrew, the square root distance, I also told on my reply, but not really any difference on a touch event, more like if you would call it every frame. And since the OP wasn't very clear with the original post about the circle distance, better keep things simple to explain the concept.

Posted 7 months ago #
atfield
Member

then, the button became a unregular shape

Posted 7 months ago #
phantomsri
Member

thanks guys, the code provided by @itlgames its good enough for know. I have plans to use this code to be used on a hexagon shape.
I also thank @andrew for the other link.

Posted 7 months ago #
itlgames
Moderator
To check the square root on your code use:
```
BOOL inside = (ccpLengthSQ(ccpSub(circleSprite.position, location)) < (circleSprite.contentSize.width*circleSprite.contentSize.width) / 4.0f );
```
I think on cocos2d v1.1 you have a ccpDistanceSQ so:
```
BOOL inside = (ccpDistanceSQ(circleSprite.position, location) < (circleSprite.contentSize.width*circleSprite.contentSize.width) / 4.0f );
```
Note now cos we don't calculate the square root of the distance (to save the calculation) we have to compare against the pow2 of the radius, or as I did just the pow2 of the diameter divided by 4: (diameter/2)*(diameter/2) = (diameter*diameter)/4

But as I said, this is done on the touch event, so to be honest you won't note any performance difference.
Posted 7 months ago #

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