Behind the Scenes (Portal 2)/en

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This Portal 2 aesthetic theme is featured prominently during the manufacturing section of the singleplayer campaign, and is also used between test chambers and during escape sequences in Aperture Laboratories. It is characterized by unfinished construction and machinery. Catwalks, panel undersides, uncovered light fixtures, exposed wiring, and vents are common. Bottomless pits are also present in this theme. The walls are made of concrete, metal, and plastic rather than tile. The soundscapes are heavy-industrial-sounding, and often include sounds of loud, whistling Pneumatic Diversity Vents.

This theme is also used at the end of every co-op course.

Level transitions are usually placed in short corridors between two heavy security doors.


You can see a lot of tubes transporting various test elements to unknown parts of the facility in this theme.

This theme serves really only for plot advancement, so the scope for puzzles is somewhat limited here. Sure, there's the old 'portal over to that wall behind me' to traverse long distances and stretch out dialogue, but making actual puzzles out of this theme without making it feel contrived is kind of difficult. You'll see it done more successfully in co-op maps usually, due to the fact that the plot isn't quite as important and Valve tried to make the theme a puzzle rather than to leave an impact on the player.
The exception to this is if you're making a full-blown mod, maybe even with a story; as aforementioned, these can make nice interludes, and the sheer multitude of destruction sequences available for the catwalks are brilliant for action scenes. Due to the nature of this theme, the huge vistas along with numerous dynamic elements it is recommended for users with advanced knowledge of hammer.

The vast proportions of Aperture Laboratories allows a lot of free space to exist between test chambers and other rooms used for various purposes. In these in-between areas a lot of 'behind the scenes' work is done, like building and testing of test elements. Because of this the theme is more to immerse the player than to be a good puzzle environment, however, using the various 'test elements in-testing-state' as functioning test elements could make it a more interactive puzzle. Most puzzles seen in this theme tend to revolve around momentum, and they do tend to work best in co-op. However, if you have an idea for a puzzle that involves moving test elements, conveyor tracks or exceptionally big momentum puzzles, try going with this theme.

Something that is important to keep in mind when building tests for this theme is that it should look as if it was not designed to be a test. There shouldn't be a solution, as this is not a test, only a way to advance. Keeping the 'tests' looking realistic is to make the player break the rules in these parts, like walking on the reverse direction of a conveyor belt, breaking tubes that deliver test elements to other parts of the facility, etc.

Noticeable Elements

Aperture Laboratories is known to solve their problems in the most ridiculous way possible, take the Pneumatic Diversity Vents for example, seen transporting numerous test elements and garbage from one place to another.

Humans, on the other hand, use catwalks as their form of transportation, and these should be connect to every door, button stand or anywhere maintenance might be needed, like around vents and 'quality control' stations. If you don't want the player to explore an area, placing destroyed catwalks or locked doors/gates would be a good way to do this without it looking unrealistic.
All other robotic personnel use management rails, which they cannot readily be detached from.

Pneumatic Diversity Vents

The Pneumatic Diversity Vents are used extensively throughout this theme, as a mean to give further background of the facility and how it is constructed. Serving no other purpose other than decoration their use is very limited; however clever use of them had been seen in the official campaign, such as:

  • Long plot advancing 'tube ride' sequences
  • Transporting test elements
  • Destroyed to deliver gel

The tubes are not aligned to the grid; they're bent in every direction, reaching every building in the facility; but don't be alarmed, their construction is exceedingly simple. Before making a pipe remember that you don't need it to make sense, if the tube goes behind a building where the player can't see it there is no need to attach it to anything, just finish it there. Also, when making the tubes notice there are four beams surrounding the tube, make sure they are all aligned with the ones of the next model (that means only 90° Pitch Yaw Roll values).
Now let's start, first create the basic shape you want your vent to have; for example, a long straight line that has a 'T junction' at the end. Now group all the models you used to create you basic shape and rotate them freely so they would look purposeless. That's about it; with time you'd improve upon it.

Tube Rides

In the official campaign there is a part where the player and Wheatley are sucked by a vent and sent through the pipe system to GLaDOS's chamber. This was done by attaching a point_viewproxy to a 1x1x1 model which is animated to be flying through a very specific set of pipes. When you are creating your own maps, this is not necessarily required as the point_viewproxy can follow the path used to navigate the tubes.

Note.pngNote:The process may be somewhat lengthy, depending on the length and complexity of the tubes you want the player to "ride" through.
Creating a tube ride
Blank image.pngTodo: Add pictures to clarify this process and expand this section.
Note.pngNote:You will want to make sure you have the route for your tubes planned out very carefully as it can be rather time-consuming to rearrange things if the tubes end up misaligned.
Creating the path for the ride

These instructions assume you have a room to place the tubes in and connect the tubes to.

  1. Place the tubes you want the player to pass through. Use a mixture of straight tubes and turns to make it interesting.
  2. Place a path_track at roughly the height of the player's head. Name it tube_path1.
    Note.pngNote:This makes the transition to the point_viewcontrol a smooth one.
  3. Copy the path_track and move the copy to the end of the first tube section. If the first path_track doesn't link to the new one, enter the name of the new one into the Next stop target field in the properties of the path_track.
    Note.pngNote:You can actually move the copy to the first turn in the tube path if you prefer as it means fewer objects in your level. The number of path_tracks you use determines how smooth the ride will be.
  4. When you reach a corner in the tube path, place a copy of the path_track near the end of the turn.
  5. Make and move another copy of path_track into place slightly further into the turn.
  6. Move the next copy into the turn a few units, ensuring the path_tracks is not touching the sides of the tube.
  7. Make and move another copy of the path_track into the next segment.
  8. Repeat steps 2-7 above until you reach the end of your tube path.
Note.pngNote:It might be useful to make a premade instance vactube that would have all the path_tracks ready to go. Just remember to be able to set the name for the first one and the Next stop target for the last one. It is important that these names start with an @, because otherwise the instance would Fix up their names and break the system.
Making the ride function

This is the easier part. You would need a few things:

  1. Create a brush where you want the player to be "sucked" into the vactube. Convert it to a trigger_once (trigger_multiple if you want the ride to be retrigerrable).
  2. Create a smaller brush inside the trigger. Make it a func_tracktrain. Set the Next stop target to tube_path1. Name it vactube_train. Change its properties as you want.
  3. Create a point_viewproxy. Name it vactube_camera. Set the Proxy Entity to vactube_train. This will parent them together. Change the Offset type to Ease to camera if you want the player's view to be unlocked. Make sure both flags are enabled.
  4. Make a logic_auto and add an output of OnMapSpawn vactube_camera Disable 0.00. Otherwise the player would immidiately start the ride.
  5. In the trigger_once add 2 outputs:
   1. OnStartTouch vactube_camera Enable
   2. OnStartTouch vactube_train StartForward
  1. On the last path_track, add these outputs:
   1. OnPass vactube_camera TeleportPlayerToProxy 0.00. This would make the player "end" the ride at the correct place. If you don't add this output, the player would "end" back at the trigger_once.
   2. OnPass vactube_camera Disable 0.2. This disables the camera and ends the ride. 
Note.pngNote:If you want the ride to be redoable, add another output: OnPass vactube_train TeleportToPathNode tube_path1 0.3. This would make the train teleport back to the beggining, thus making it possible for it to start again.

Transporting Test Elements

In some of the maps in the official campaign these vents were used to transport bombs at the press of a button. This is a good way to interactively transport elements in the behind the scenes sections of the game, as normal cube droppers don't fit this theme.

A good puzzle introduced in the cooperative campaign had a vent that sends one cube out of it at a press of a button, one player had to press the button, while the other had to fling to catch it in time.
This map is named mp_coop_fan.

Most test elements in the vents are animated props, but since these are only good for very specific arrangement of the tubes, it is recommended to make prop_physics be transported through the tube with the help of trigger_push brushes that will be placed in the tubes, like done in the Pneumatic Diversity Vent test element.

Gel Dispensing

In some parts of the behind the scenes environment there are vents that transport gels from the Old Aperture parts to the newer parts of the facility. Some environments may require use of these gels, but like stated above, test elements are not supposed to be used in these parts, therefore another way must be found to retrieve the gel. Breaking the tube is one way of achieving this.

Use a particle effect and place it's first control point somewhere in the map close to the info_particle_system from which it originates from. You could still use it as a straight particle if the control point is directly in front of the particle_system.

Note that there are also these particle effects:

  • blob_curve_blue - for repulsion gel
  • blob_curve_orange - for propulsion gel
  • blob_curve - for conversion gel

To make a control point, you can use an info_target. Give the info_target a name, such as Gel Target 1, and put the info_target's name in Control Point 1 in the info_particle_system. Make sure that the Always transmit to client (ignore PVS) flag is checked on the info_targets, otherwise the gel particles will flow to the centre of the map.

In addition, when creating turns for the gel to go through, don't just put an info_particle_system at the start of the turn and an info_target at the end, or the particles won't stay in the vactube. Instead, have some info_particle_systems in between. Depending on the size of the corner tube, you may need to add more.

If you're making corners for the gel flow, put the info_targets in the same locations as the info_particle_systems.

Blank image.pngTodo: Explain the creation process of this in more detail

Useful Props

These are the main components of the vent system. Props with the * symbol means they have to be 'Not Solid' in order for objects to fly through them.

  • models/props_bts/vactube_128_straight.mdl
  • models/props_bts/vactube_90deg_02.mdl
  • models/props_bts/vactube_90deg_03.mdl
  • models/props_backstage/vacum_flange_a.mdl*
  • models/props_bts/vactube_connector.mdl*
  • models/props_backstage/vacum_entrance_a.mdl*

Management Rails

Management rails are the main transportation form for the many personality spheres that operate the facility. When connected to their management rails they are held by two dynamic props; one which holds the sphere, and the other connects it to the rail itself:

  • models/npcs/personality_sphere/management_rail_ball.mdl
  • models/npcs/personality_sphere/management_rail_stick.mdl

The rail is composed by either a set of props (models/props_bts/rail_horizontal...mdl), or by a set of func_detail brushes.

Blank image.pngTodo: Further investigation on how it works.

Miscellaneous tips

These are the main elements that should be used through out this theme:

There are a number of models designed for this section of the game, in the form of cables, vents and, of course, catwalks, and I recommend you use these. In the Model Browser, try looking in the props_bts, props_backstage (vacuum tube entrances/exits) and a4_destruction (for the test chamber exterior models) directories for stuff. They don't have to be anything captivating or dynamic, but a wall with cables makes a lot more sense than one without; there are, by the way, instances for detailed cable walls and such things. Also, it is very much recommended you use some of the behind-the-scenes overlays, such as the yellow numbers, 'Turret Manufacturing', etc.

See also