info_mapgate is an entity which works with Quoth’s Mapindex system.
The Session Mapindex is a number which is preserved over map changes and updated by trigger_changelevel entities. The simplest use of the Session Mapindex is to have a hub level which changes according to the other levels which have been visited (like the quake start map after you complete an episode), but the system is flexible enough to allow other uses as well.
info_mapgate acts like a trigger_relay which fires at the start of the level, conditionally on the value of the session mapindex. Set the
mapindex key on the info_mapgate to a bit-flag (1,2,4,8…), and it will trigger if that flag is set on the Session Mapindex. If you set multiple flags on a single info_mapgate, the trigger will fire if any of them are set. For detection of the presence of all of a set of flags, see info_endgate.
If you apply spawnflag 1 to an info_mapgate the trigger condition is inverted, so it will always fire unless the mapindex condition is met.