坐标系问题

cocos2d-x C++
#1

CCSprite test = ;
test.position = ccp;
;
CCSpritechild = [CCSprite spriteWithFile:@“Icon-small.png”];
child.color = ccRED;
child.position = ccp(20,20); // 基于test的坐标
[test addChild:child];

test.rotation = –90;

怎么得到child在整个layer的坐标点。