The problem is :
I have two cameras, A for the main 3d scene, B for renderering guis behind the main 3d scene. The reseon two use two cameras is GUITEXTURE and GUITEXT are always on top of the main scene.
for A I set Clear flags to depth only, depth to -1, culling mask to the main 3D scene
for B I set clera flags to solid color, depth to -3, culling mask to the layer I define for the guis,rendering path is forward.
The problem is that if I set A's rendering path to forward, everything goes fine. If I set it to "deferred lighting", It seems only can see the 3D scene, and everything without any depth values becomes black and can not see the behind guis. Seems "depth only" does not work in defered lighting mode. Is that a bug on something?