How can i ignore touch event on a transparent area?

Hi, i’m a beginner from flash development. I found that a blank area in a layer will also trigger a touch event. Then i have a problem. There are two layers: layer_bottom and layer_top, the latter is on the top of the former. The visual elements in the layer_top just cover one part of the screen, layer_bottom is full filled. When i click the screen where the layer_top doesn’t cover, the layer_bottom should receive the touch event, layer_bottom not, while click the screen where the layer_top covers, the layer_bottom should not receive the touch event, only the layer_top receives.
It is default in flash, what should i do in cocos2dx in a simple way?
Thanks everyone!

See that topic: http://cocos2d-x.org/forums/6/topics/19694