cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   Dynex
   Member

   Hi guys,

   I am looking for a way to create a reference point on a sprite. I am using it's anchorpoint with CCScale, but now I need another point of reference to check for collision detection. My game does not require complex CD, just whether or not a point has intersected a rect or a path. But in order to do that, I need to create a reference point, that stays relative to the sprite after rotating/scaling. Has anyone does this before?

   Posted 6 months ago #
2. 

   Dynex
   Member

   For example, how do I compare the bottom middle of a sprite (that has been rotated and scaled) with another sprite? (Say, usingCGRectContainsPoint) What point would I reference to?

   Posted 6 months ago #
3. 

   HiRez
   Member

   You could attach an empty node as a child at the reference location (before you translate/scale/rotate it), then read the position off that. Don't know if that's the best or only way to do it, just something I thought of.

   Posted 6 months ago #
4. 

   Birkemose
   Administrator

   The way @HiRez describes it, would be the way to do it.

   Posted 6 months ago #
5. 

   Dynex
   Member

   I tried this a couple times now, but no success. How exactly do I do this? Am I adding the CCNode as a child to the sprite? And how do I attach it to a reference location?

   CCSprite *growingStick = [CCSprite spriteWithFile@"stick.png"];
   growingStick.position = ccp ( 240, 320 ); //top middle of screen
   growingStick.anchorpoint = ccp ( 0.5, 1.0 ); //top middle of stick
   [self addChild: growingStick];
   
   CCNode *endPoint = [CCNode new];
   endPoint.position = ??
   [??? addChild: endPoint];

   Anyway I try, it doesn't work :(
   Basically I need to create another anchorpoint that I can use for myself.

   Posted 6 months ago #
6. 

   IgnatiusCore
   Member

   You can do:
   

   CCNode *endPoint = [CCNode node];
   endPoint.position = ccp(0,0);
   [growingStick addChild: endPoint];

   That will attach the endPoint to the bottom right of the sprite.
   Note: ccp(0.5*(growingSticks Width), growingSticks Height) would give you the same position point as the growing stick.
   Then to get it's position you'd say something like:
   

   CGPoint pos = [growingStick convertToWorldSpace: endPoint.position];

   I find it's helpful for testing purposes to do something like:
   

   NSLog(@"Node Position:(%f, %f)",pos.x, pos.y);

   To see where it goes in your log navigator output.
   or
   

   NSLog(@"Node Position:(%i, %i)",(int)pos.x,(int)pos.y);

   If you don't like decimal places. :)

   Posted 6 months ago #
7. 

   Dynex
   Member

   Thank you so much! I messed around with convertToWorldSpace but never got it working... Thanks! There is no rep system here is there? I'd +1 you

   Posted 6 months ago #
8. 

   Lam
   Moderator

   You converting to and from worldspace to node space is pretty cool once you have the hang of it.

   The trick I always remember is ["parent of that node" convertToWorldSpace: "node".position];

   So if you keep that in mind, "parent of that node converts the node's position to world space", it'll always work out.

   Posted 6 months ago #
9. 

   HiRez
   Member

   Good tip, Lam. Always found convertToWorldSpace a little confusing. Knowing you call it on the parent of the node whose position you want converted helps.

   Posted 6 months ago #

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