Cocos2d-iphone prevent physics objects overlap

gistfile1.txt

- (void)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event
{
    CGPoint touchPoint = [touch locationInView:[touch view]];
	touchPoint = [[CCDirector sharedDirector] convertToGL:touchPoint];
    
    if(isTouch){
        
        //
        // Move the flake, check into consideration finger placement
        // relative to the flake
        //
        CGPoint point = [self convertTouchToNodeSpace:touch];
        cpShape *shape = [smgr getShapeAt:point];
        if (shape && [shape->body->data class] != [cpCCSprite class]) {
            touchedFlake.shape->body->p=ccpSub(touchPoint, difTouch);
        }
        if (shape && [shape->body->data class] == [cpCCSprite class]) {
            [smgr morphShapeToActive:touchedFlake.shape mass:1];
            
            return;
            
        }
        if (shape == NULL) {
            touchedFlake.shape->body->p=ccpSub(touchPoint, difTouch);
        }

        
        [smgr rehashShape:touchedFlake.shape];
        
        
        lastMovePoint = touchPoint;
    }
}