Pretty much the solution goes:
1) Hide everything except the Room. Set Room to Alpha 1
2) Render 3D room normally to imprint the ZBuffer
3) Draw the 2D pre-rendered image onto the backbuffer
4) Set the camera to not clear Zbuffer/Backbuffer with CameraClsMode.
5) Unhide everything and set room to Alpha 0
Render everything! (But the room is hidden)
2D Resident Evil in a can.
1) Hide everything except the Room. Set Room to Alpha 1
2) Render 3D room normally to imprint the ZBuffer
3) Draw the 2D pre-rendered image onto the backbuffer
4) Set the camera to not clear Zbuffer/Backbuffer with CameraClsMode.
5) Unhide everything and set room to Alpha 0
Render everything! (But the room is hidden)
2D Resident Evil in a can.