SKSpriteKit, detect non-transparency parts

问题

I am making a game in SKSpriteKit, I am trying to make a foreground object with this Image, http://minus.com/i/OQ0boloElnCr

if an object touches the non-transparency in the picture(the ceiling and rock paths), the object dies. Is it possible in Sprite kit to detect the ceiling, the non-transparency parts of the image

来源：https://stackoverflow.com/questions/20089846/skspritekit-detect-non-transparency-parts