Illusory Bridges
By Jason Harper, JasonHarper@pobox.com
From the "Missed Island" map

Next is a purely visual effect. Proceed to the next terminal, paying close attention to the room that you'll pass through twice. I'll bet you've never seen a bridge in Marathon that looked quite that realistic. This is your last chance to come up with a guess as to how it was done... (Editors Note: In the Missed Island tutorial you will pass through the room pictured above. You will walk under the bridge, exit the room through the door you are facing, climb some steps and reenter the room through the door to the upper right allowing you to cross over the bridge. - gls)

Actually, it was a total fake. You went through two separate rooms, one with the passage under the bridge and one with the walkway on top, that are precisely overlapped in 5D space. In the first room you went through, the apparent open space above the passageway is actually a solid column, with the landscape texture applied to all sides so that you couldn't distinguish it from the room's ceiling. Shown here are screen shots taken from normally inaccessible positions within each room, with the central column in the first room retextured so that you can see it. The lava texture is used for all surfaces you can't see in normal passage through the rooms.

This trick is quite effective visually, but does have some severe limitations on its use:

• The room's top must be open to the sky. Otherwise, there would be no way to conceal the central pillar in the 'under' version of the room.
• It's usable in solo levels only. If there were two players, one in each version of the room, they'd wonder why they couldn't see each other.
• It should only be used at a point in a scenario where the player can't possibly have an assault rifle or missile launcher, since trying to grenade-hop up or down a level would completely spoil the illusion.
• If there's any combat in the rooms, it must be with creatures (such as Compilers) that leave no corpse. Otherwise, there would be a noticeable inconsistency between the two versions of the room due to different placement of corpses.

If you'd like to examine the rooms more closely, open the map in Forge where you have a Jump key. You'll need to set a starting point closer to the rooms (by command-clicking in a polygon), since you can't reach them from the start of the level (due to a chip insertion switch that can't be activated in Forge).

Missed Island