Level Transitions

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Level transitions allow you transfer the player from one map to another, essentially making two separate levels seem like one larger map.

Why change levels?

The Source Engine, while expansive, still has limits as to the the amount data that can be processed. Breaking up levels also helps split up the work load and compile times during the design process.

Types of level transitions

Two way transitions

A two way level transition allows a player to travel back and forth between two connected maps.

One way transitions

One way transitions prevent the player from traveling back to previously explored areas after being completed. An obstacle or chain of events makes a previous area inaccessible.

Methods / Styles of transitioning


  • Example:
    • A door or hallway connecting two rooms


  • Example:
    • A portal connecting two worlds
    • A character getting knocked unconscious and dragged into a new area

Example of a seamless transition in-game

To create a seamless transition, parts of one level are included inside the next level being loaded. The exception being "teleportation" style transitions, where the players are transported into an entirely new world or environment. Below is an example from Half-Life 2's d1_trainstation_01, the first level of the game.
D1 trn sta 01.jpg D1 trn sta 02.jpg D1 trn sta 03.jpg D1 trn sta 04.jpg D1 trn sta 05.jpg

  • In the 1st image you can see the trigger_changelevel in the doorway that loads the next map.
  • In the 2nd image, zoomed out you can see the map actually ends at the staircase just beyond the door in the first picture. Most of the level lies on the right of the picture here.
  • Once the player touches the changelevel, they're greeted by a loading seen as demonstrated in the 3rd image, the next map is loaded over the current map.
  • Now the player is in an entirely new map, but from the other side of the door, it appears the old level is still there.
  • However, if you zoom out, you can see that a new level was loaded and the original level was almost entirely removed. There is no longer the any parts of the level that were in the right from the zoomed out screenshot above, but an entirely new area in the upper left.

Creating a seamless transition

To start, you must have:

First, have the exact same brushes and entities in the visible area. This will make the level change seamless.

Next, in both levels, place an info_landmark in the exact same location relative to the map. Name them Level01-Level02 (This can be changed)

Next, create a trigger_changelevel in both levels. This can be named anything. Link them to the corresponding info_landmark inside the properties panel. Note: do not have these in the same relative area. This will create a looping effect, and when you get into one level you immediately are teleported back. Set the new map name to either the previous or next level, depending on which level the trigger_changelevel is located within.

Finally, in both levels create a trigger_transition. This will be the area where props will be taken between levels. These should be named the same as the info_landmarks.

Creating a displacement transition

There are 4 different methods:

Method 1

Follow the steps for a seamless transition, but do not include the same level geometry. You can disable the trigger_changelevel to the previous level if required.

Method 2

To start, you must have:

First, create a small brush with the trigger texture in the first level. This will be the trigger_changelevel. Set the new map name to the second map. Set the landmark name to the name of the landmark. Then, create a landmark somewhere. This may take some trial and error to figure out where this should be best placed as to not cause issues with changing level into a wall in level 2. Next, if you want props to carry over, create a trigger_transition and call it the same name as the info_landmark. This volume is where any entities will transfer over to the next level. You can then create a logic_relay pointing at your trigger_changelevel. Set the Target Input to ChangeLevel. You can put this somewhere where the player cannot contact it. Within the second level, add the info_landmark (named the same as the previous one). You will have to create a second trigger_changelevel in the second map, but this can be disabled and out of the player's reach. Set the new map name to the first map. Set the landmark name to the name of the landmark.

Method 3

([Portal 2] Only) To start you must have:

Add the point_changelevel, and create an input with the input set to ChangeLevel, with the parameter as the map name. Nothing else is required.

Method 4

(<Left 4 Dead>, <Left 4 Dead 2> Only) To start you must have:

First, create an info_landmark in both levels. Set it to the same name in both levels. Finally, Create an info_changelevel brush over the saferoom. Set the new map name to the next map. Set the landmark name keyvalue to the name of the landmark.

See Also