Easy but poor method - if you don't want the camera to alter the distance between itself and the player, but don't want it to show what is on the other side of a wall - linepick from the player to the camera and if the linepick picks an obstacle, like a level, set the cameraprojmode to 0 to basically present a black screen. Not pretty but will do what you have said. Then set the cameraprojmode back to 1 when the linepick does not strike an object between the player and the camera.