Now, platform mapping is not much different from mapping for regular Half-Life, all you have to think about is that the player will only be seeing from one angle. (Represented by the camera in the picture below)
The camera distance is definable with a trigger_set_camera, but it defaults to 256 units. So, the player will be seeing everything 256 units right from the player entity.
Remember to nullify backfaces, as there will be alot of them!
The player's angles MUST be set to 0, 180, 90 or 270 in Hammer. Using any other angles will bork everything.
Another important thing to think about is that all monsters, items etc must be perfectly aligned with the player, as he can't move sideways, but that's pretty self-explainatory.
The player can be turned to any of the four cardinal points using a trigger_turn_player. (Set angle to 0, 180, 90 or 270!)
The angle of monsters should always be set to 0, 180, 90 or 270 in Hammer! Monsters are locked to the angle they are set to in Hammer. So, if you set the angle of a monster to 90 or 270, he will only be able to move North and South. If you set it to 0 or 180, he will only be able to move West and East. If you set any other angle, he won't move at all. (Unless the Allow Unaligned flag is set)
You CAN turn a monster ingame, using a scripted_sequence. Sequenced movement will always ignore restrictions. A monster with the "Allow Unaligned" flag set will totally ignore restrictions.
Don't forget to place info_nodes where monsters can walk, it greatly improves their manouverability!
Note that monsters REQUIRE info_nodes to move at all in platform mode!