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An excursion funnel in Portal 2.

[Portal 2] prop_tractor_beam is a point entity available in Portal 2. It is a model that emits a projected_tractor_beam_entity.

Excursion funnels are a puzzle element of Portal 2 that work like tractor beams. Objects (like turrets and cubes) and players that touch blue funnels slowly drift away from the emitter, unaffected by gravity, or towards the emitter if the funnel is orange. Players can remove objects and themselves from the funnel but can not move against the flow.

Like bridges and lasers, funnels can be extended through portals.


Linear Force <float>
Linear force to apply to objects in the beam. The color and direction of spin will automatically change when the value becomes negative. Most Valve created Excursion Funnels have a linear force of 250, so likewise the reverse funnel should be -250.
Disable Emitter Particles <boolean>
Disable the whirly particles on the emitter.
Use 128 model <Boolean>
Use the tractor beam projector model that fits within a 128 unit square (the default model is 167 units wide)


Name <string>
The targetname that other entities refer to this entity by.
Entity Scripts <scriptlist> (New with Left 4 Dead 2)
Space delimited list of VScript files (without file extension) that are executed after all entities have spawned. The scripts are all executed in the same script scope, later ones overwriting any identical variables and functions.
Script think function <string> (New with Left 4 Dead 2)
Name of a function in this entity's script which will be called automatically every 100 milliseconds (ten times a second) for the duration of the script. It can be used to create timers or to simulate autonomous behavior. The return value (if present) will set the time until the next call.
Note:Try to avoid expensive operations in this function, as it may cause performance problems.


Parent (parentname) <targetname>
Specifies a movement parent. An entity will maintain its initial offset from its parent. An attachment point can be added to the end of the name, separated by a comma.


Pitch Yaw Roll (Y Z X) <angle>
This entity's orientation in the world. Pitch is rotation around the Y axis, yaw is the rotation around the Z axis, roll is the rotation around the X axis.


Start Enabled <boolean>
If the projector should start enabled.
Disable Placement Helper <boolean>
Disable the automatically created placement helper to prevent it from fighting with a custom one.


Render in Fast Reflections <boolean> (New with Portal 2)
If enabled, causes this entity/prop to to render in fast water reflections (i.e. when a water material specifies $reflectonlymarkedentities) and in the world impostor pass.


SetLinearForce  <float>
Set the linear force applied to objects in the beam.


Removes this entity and any entities parented to it from the world.
Functions the same as Kill, although this entity and any entities parented to it are killed on the same frame, being marginally faster than Kill.
AddOutput  <string>
Evaluates a keyvalue/output on this entity. It can be potentially very dangerous, use with care.
Format: <key> <value>
Format: <output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
FireUser1 to FireUser4
Fire the OnUser outputs; see User Inputs and Outputs.
Use  !FGD
Same as a player invoking +use; may not do anything. Can also be invoked by creating an output that does not specify an input.
This input is not included in Valve's FGDs.
RunScriptFile  <script> (New with Left 4 Dead 2)
Execute a VScript file from disk, without file extension. The script contents are merged with the script scope of the receiving entity.
RunScriptCode  <string> (New with Left 4 Dead 2)
Execute a string of VScript source code in the scope of the entity receiving the input. String quotation may be needed when fired via console.
Bug: In <Left 4 Dead 2>, the code is executed in the script scope of the entity that fires the output, not the one receiving the input.
Warning: Never try to pass string parameters to a script function with this input. It will corrupt the VMF structure because of the nested quotation marks, which then must be removed manually with a text editor.
CallScriptFunction  <string> (New with Left 4 Dead 2) !FGD
Execute a VScript function in the scope of the receiving entity.
SetLocalOrigin  <coordinates> (New with Alien Swarm) !FGD
Send this entity to a spot in the map. If the entity is parented to something, it will be offset from the parent by this amount.
SetLocalAngles  <angles> (New with Alien Swarm) !FGD
Set this entity's angles.


SetParent  <string>
Move with this entity. See Entity Hierarchy (parenting).
SetParentAttachment  <string>
Change this entity to attach to a specific attachment point on its parent. The entity will teleport so that the position of its root bone matches that of the attachment. Entities must be parented before being sent this input.
SetParentAttachmentMaintainOffset  <string>
As above, but without teleporting. The entity retains its position relative to the attachment at the time of the input being received.
Removes this entity from the the movement hierarchy, leaving it free to move independently.


Enables projection from this projector.
Disables projection from this projector.


DisableDrawInFastReflection  (New with Portal 2)
Turns off rendering of this entity in reflections when using $reflectonlymarkedentities in water material.
EnableDrawInFastReflection  (New with Portal 2)
Turn on rendering of this entity in reflections when using $reflectonlymarkedentities in water material.



OnUser1 to OnUser4
These Outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.
OnKilled  (Only in the Left 4 Dead series)
This Output fires when the entity is killed and removed from the game.


Each funnel consists of a prop_tractor_beam and a player clip in front. Funnels often have a light in front of them for a soft blue glow (with an approximate brightness of 50 120 250 50). This is sometimes left out when the beam is reversible because it conflicts with the orange color of the funnel; a simple workaround, however, is to place two lights - one blue, one orange - and have them be enabled/disabled by the same event as that which reverses the funnel.

Grating Walls

In order to create a wall that will let the tractor beam to go through it but it will block players or a prop_weighted_cube from passing through, three separate brushes/entities must be combined.

  • func_brush brush entity with a Solidity property set to "Never Solid" (will be the only visible brush to the player)
  • player clip brush will block player's movements
  • func_clip_vphysics brush entity will block weighted cube movement

If Paint Bombs are present, a filter_activator_class will be needed to allow the paint to pass through the grating.

External links

Example map with a VMF included.