I've searched - but how to check for collision with rotated CGRect?

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I've searched - but how to check for collision with rotated CGRect?

(15 posts) (8 voices)

Started 1 year ago by MrMojo
Latest reply from col55

Tags:

MrMojo
Member

Hi there - I've searched the forums, and found the a few posts talking about how to test if a rotated sprite collides with a cgrect, but have tried the solutions posted and got no results ;-(

e.g.
http://www.cocos2d-iphone.org/forum/topic/1693#post-10649

What I want to do is test if a ROTATED sprite collides with a touched location, but it doesn't seem to work - it still sees the sprite as not rotated when I do my collision test. I've added the following to my sprite class as suggested by most of the approaches i saw:

-(CGRect) realContentRect
{
  CGRect rect = CGRectMake(0, 0, contentSize_.width, contentSize_.height);
  return CGRectApplyAffineTransform(rect, [self nodeToParentTransform]);
}

-(BOOL) intersectsRect:(CGRect) targetRect
{
  return CGRectIntersectsRect([self realContentRect], targetRect);
}

-(BOOL) intersectsPt:(CGPoint) targetPt
{
  CGRect targetRect = CGRectMake(targetPt.x, targetPt.y, 1, 1);
  return [self intersectsRect:targetRect];
}

and my touchesEnded event tests for collision with my rotated player like so:

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

	if ([player intersectsPoint:location])
	{
		NSLog(@"clicked on rotated player");
	}
}

any ideas why this doesnt work? it works as if the player sprite isn't rotated. thanks so much for any pointers!

Posted 1 year ago #

MrMojo
Member

Note that I also tried using the "boundingBox" as the rotated rect, but that's identical to the "realContentRect" mentioned above, so it doesn't seem to make a difference. any ideas on why this doesn't let me detect a touch in a rotated sprite?

Posted 1 year ago #
Codemattic
Moderator

I think Solution 3 would work best:

http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/

Posted 1 year ago #
Dunc
Member

Ray Wenderleich posted a nice tutorial a while back which shows how you can use box2d as a convenient approach to collision detection. Not sure if it'll be overkill for what you are trying to achieve, but here it is just in case: http://www.raywenderlich.com/606/how-to-use-box2d-for-just-collision-detection-with-cocos2d-iphone

Posted 1 year ago #
mobilebros
Moderator
Given that position is the position of the Rect and width and height are the dimensions, and rotation is the rotation in degrees.
```
cpVect centerpt = cpvadd(position, cpv(width*0.5f, height*0.5f));

pt = cpvadd(centerpt, cpvrotate(cpvsub(pt, centerpt), cpvforangle(-CC_DEGREES_TO_RADIANS(rotation))));

BOOL contains = CGRectContainsPoint(CGRectMake(position.x, position.y, width, height), pt);
```
I use cpVect functions, but they should map easily to CGPoint functions. So all I do here is rotate the point around the center of the rectangle to match the rotated coord system of the rect.

Note: Probably using anchorPoint instead of a hard-coded (0.5f, 0.5f) would be better.
Posted 1 year ago #

MrMojo
Member

thanks for all the suggestions! i got something working using both the original concept (CGPointApplyAffineTransform) and the concept posted by @mobilebros. I have all of the following methods on my sprite class, but it may work at a higher level too (CCNode?). Thanks again for all your pointers! the code below is still ignoring the anchor point though, and I do believe could be easily extended to include scaling,etc using the transform approach, now that I have rotation working.

// Supporting method. Returns a rect that represents the top left corner of a node, and it's width and height. Anchor Point ignored.
-(CGRect) getExtentsRect
{
	CGRect rectBounds = CGRectMake(self.position.x-(self.contentSize.width*0.5f), self.position.y-(self.contentSize.width*0.5f), self.contentSize.width, self.contentSize.height);
	return rectBounds;
}	

// Rotates a point (targetPt) about another point (anchorPt) by an angle (degrees) using a transform
-(CGPoint) rotatePointAboutPoint:(CGPoint) targetPt anchorPt:(CGPoint) anchorPt angle:(float) angle
{
	CGRect rectExtents = [self getExtentsRect];

	CGPoint targetPtRelativeToSelf = ccpSub(targetPt, anchorPt);
	CGPoint RotatedPt = CGPointApplyAffineTransform(targetPtRelativeToSelf, CGAffineTransformMakeRotation(-CC_DEGREES_TO_RADIANS(angle)));
	RotatedPt = ccpAdd(self.position, RotatedPt);

	return RotatedPt;
}

// SOLUTION 1: Returns whether or not a point intersects another point using CGPointApplyAffineTransform.
-(BOOL) intersectsPointUsingTransform:(CGPoint) pt
{
	CGRect extentsRect = [self getExtentsRect];
	CGPoint rotatedPt = [self rotatePointAboutPoint:pt anchorPt:self.position angle:self.rotation];
	return CGRectContainsPoint(extentsRect, rotatedPt);
}

// SOLUTION 2: Returns whether or not a point intersects another point using basic trig.
-(BOOL) intersectsPointUsingTrig: (CGPoint) pt
{
	CGRect rectExtents = [self getExtentsRect];
	CGPoint rotatedPt = ccpRotateByAngle(pt, self.position, -CC_DEGREES_TO_RADIANS(self.rotation));
	return CGRectContainsPoint(rectExtents, rotatedPt);
}

Posted 1 year ago #

col55
Member

hi cant seem to get them to work any help would be great. i have a rotated sprite and need to test for a small sprite intersects it.thanks colyn

Posted 7 months ago #
col55
Member

hi i figured it out for some reason the angle getting passed in rotate point about point method was wrong not sure if this is to do with im running latest cocos2d and this post was from a year ago but to get it to work i had to do the following , see amended code.also thanks to mrmojo for the start.

`-(CGPoint) rotatePointAboutPoint:(CGPoint) targetPt anchorPt:(CGPoint) anchorPt angle:(float) angle
{
//CGRect rectExtents = [self getExtentsRect];
angle +=(180-(angle + angle));//this is new line.

CGPoint targetPtRelativeToSelf = ccpSub(targetPt, anchorPt);
CGPoint RotatedPt = CGPointApplyAffineTransform(targetPtRelativeToSelf, CGAffineTransformMakeRotation(-CC_DEGREES_TO_RADIANS(angle)));
RotatedPt = ccpAdd(self.position, RotatedPt);

return RotatedPt;

}'

Posted 7 months ago #
praveencastelino
Member

Try the following code...

-(void)ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch=[touches anyObject];
CGPoint loc=[touch locationInView:[touch view]];
// world space
loc=[[CCDirector sharedDirector] convertToGL:loc];
NSLog(@"world %g,%g",loc.x,loc.y);

//node space
CCSprite *rotatedSprite=(CCSprite *)[self getChildByTag:77];
loc=[rotatedSprite convertToNodeSpace:loc];
NSLog(@"node %g,%g",loc.x,loc.y);

// check if the touched location is within the rect of the node
if (CGRectContainsPoint([rotatedSprite textureRect], loc)) {
NSLog(@"inside");
} else {
NSLog(@"outside");
}
}

Posted 7 months ago #
col55
Member

Thanks fo the reply but I'm not using touches just checking for collision of a rotated sprite with another sprite.
Exampl. Bullet hitting an enemy sprite after the sprite has been rotated.
Any change you can explain what's happening in your code as it looks a lot nicer than what I'm using.

Posted 7 months ago #
praveencastelino
Member

1. Get the touch
CGPoint loc=[touch locationInView:[touch view]];
2.Convert to OpenGL coordinate space. (this would convert it to either portrait or landscape)
loc=[[CCDirector sharedDirector] convertToGL:loc];
3. Convert the point to node space from world space
loc=[rotatedSprite convertToNodeSpace:loc];
4. hit test
if (CGRectContainsPoint([rotatedSprite textureRect], loc))

Posted 7 months ago #
col55
Member

thanks much apretiated but had the same problem with that code that the angle was all screwy as if sprite was 45 degress the returning angle would be 135 degrees but i ahve a working method now so thanks, its not pretty but works lol

Posted 7 months ago #
Gray Olson
Member

Could you share with the community? I think others could find it useful.

Posted 7 months ago #
Birkemose
Member
For some reason I havent been able to find a ccp... function that calculates the angle between two points, and I use it all the time.
If your player is position a, and your badguy is position b, it returns the angle.
If you want to rotate the sprite, you of cause have to add 180 / M_PI, as cocos2d for some reason uses 360 degress.
```
-( float )angle:( CGPoint )a b:( CGPoint )b {
	float distance, result;

	// get distance between points
	distance = ccpDistance( a, b );
	// calculate angle
	result = ( b.x - a.x ) / distance;
	if ( ( b.y - a.y ) <= 0 ) {
		result = -asinf( result );
	} else {
		result = M_PI + asinf( result );
	}
	//
	return( result );
}
```
Posted 7 months ago #
col55
Member

Gray Olson just look at my post above that I made works a treat just not very streamlined add it as an extension to ccsprite

Posted 7 months ago #

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