Cocos2D CCNode position in absolute screen coordinates

Question

I've been looking around for a while, and I have not been able to find an answer to this for some reason. It seems simple enough, but maybe I just can't find the right function in the library.

I have a scene with a layer that contains a bunch of CCNodes with each one CCSprite in them.

During the application, I move around the position of the main layer, so that I "pan" around a camera in a way. (i.e. I translate the entire layer so that the viewport changes).

Now I want to determine the absolute position of a CCNode in screen coordinates. The position property return the position relative to the parent node, but I really would like this transformed to its actual position on screen.

Also, as an added bonus, it would be awesome if I could express this position as coordinate system where 0,0 maps to the upper left of the screen, and 1,1 maps to the lower right of the screen. (So I stay compatible with all devices)

Edit: Note that the solution should work for any hierarchy of CCNodes preferably.

nash nash · Accepted Answer · 2011-04-24T09:46:52

Every CCNode, and descendants thereof, has a method named convertToWorldSpace:(CGPoint)p

This returns the coordinates relative to your scene.

When you have this coordinate, flip your Y-axis, as you want 0,0 to be in the top left.

CCNode * myNode = [[CCNode alloc] init];
myNode.position = CGPointMake(150.0f, 100.0f);

CCSprite * mySprite = [[CCSprite alloc] init]; // CCSprite is a descendant of CCNode
[myNode addChild: mySprite];
mySprite.position = CGPointMake(-50.0f, 50.0f);

// we now have a node with a sprite in in. On this sprite (well, maybe
// it you should attack the node to a scene) you can call convertToWorldSpace:
CGPoint worldCoord = [mySprite convertToWorldSpace: mySprite.position];

// to convert it to Y0 = top we should take the Y of the screen, and subtract the worldCoord Y
worldCoord = CGPointMake(worldCoord.x, ((CGSize)[[CCDirector sharedDirector] displaySizeInPixels]).height - worldCoord.y);

// This is dry coded so may contain an error here or there.
// Let me know if this doesn't work.

[mySprite release];
[myNode release];

Cocos2D CCNode position in absolute screen coordinates

1 Answers