Portal Placement Tricks

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Revision as of 04:40, 29 December 2021 by Fyrestorm (talk | contribs) (Added Seam Shot section, added "out of bounds" note to relevant "Uses of Trick" entries for all tricks)

Portal Placement Tricks


Overview

Portal 2 has several techniques for placing portals in ways not intended by the developers. These tricks can create shortcuts by reaching portalable surfaces early, or even creating portals on surfaces not intended to support them. This page describes each trick, explains the trick's execution and mechanics, and lists currently-known places where that trick can be used in routing.

Portal Bumping

Portal bumping is an intended mechanic with some unintended uses. When a player has an existing portal on a surface and shoots their other portal at the same location, rather than replacing the existing portal or allowing both portals to overlap, the game will reposition (or "bump") the second portal to the closest available space on that portable surface, if such a space exists.

When portal bumping, the new portal will be bumped away from the centre of the existing portal, based on where you aimed the new portal. E.g. if you shoot to the left of the existing portal's centre, the new portal will be bumped to the left (assuming there is space available in that direction). If you aim above the existing portal's centre, the new portal will be bumped upwards etc.

Portal bumping works in both single player and cooperative, but you can only portal bump off your own portals reliably (when you try to portal bump off another player's portal, you will usually replace their portal unless you aim precisely around the edge).

Execution of Trick

Video 2.1.A - Portal 1 and Portal 2 portal bumps by MrCatMcFly (Portal 2 routes start at 10:28).


Portal bumping can be exploited as it ignores some checks when placing the new portal. Firstly, the portal can only be bumped a short distance, but this is enough to cross thin obstacles, and the game does not check if there are any obstacles between the existing portal and new portal. This can easily be seen in Turret Sabotage, where a beginner route involves firing a portal beside the door where Wheatley breaks the glass, then bumping the other portal past the door instead of waiting for Wheatley's actions to finish. This is demonstrated in Video 2.1.A at the 10:28 mark.

Portals can sometimes be bumped out of bounds ("OoB" for short) as well. One example of this is in Bridge Fling, which is demonstrated in Video 2.1.A at the 11:15 mark.

Video 2.1.B - Laser Platform portal bump by swagatron (happens at 5 seconds, easy to miss without playing in slow motion).


Secondly, portals can be bumped onto a portalable surface that is normally too small to support a portal. One example of this is in Laser Platform, where a portal can be bumped slightly nearer the player early in the chamber, as demonstrated in Video 2.1.A at the 10:44 mark (while only saving a fraction of a second, this was used to set a world record in Video 2.1.B).

Uses of Trick

Single Player, Speedrun:

Cooperative, Speedrun:

Miscellaneous:

  • Various observation rooms can be portal bumped into if there is a portable ceiling outside of them (e.g. in Turret Intro)

Placement Helper Abuse

Placement helpers (also called portal aligners) are an invisible entity intentionally placed within levels by the developers, some of which have unintended uses. Placement helpers are meant to help players correctly place portals when making a precise shot, and will redirect portals that land inside a helper's radius to appear at the centre of the helper. This is intended to avoid the frustration of e.g. missing a close jump or failing to redirect a laser to its target due to a slight misalignment.

Execution of Trick

Video 3.1.A - Portal 2 Mechanics - Placement Helpers by Krzyhau.


Placement helpers can be exploited as they have relatively simple checks when redirecting a portal. In most official levels, for a helper to affect a portal, the following conditions must be met:

  1. The portal must land on a surface within the helper's radius (each helper has its own radius)
  2. The portal must land on a surface facing the same way as the surface the helper is aligned against (e.g. the surfaces must be parallel, but one can be further forward / back from the other)
  3. The surface the helper is aligned against must be suitable (e.g. flat, portalable, big enough to hold a portal). In official levels this effectively means it must not already be occupied by a differently-coloured portal
  4. The player must be facing the helper when they fire the portal

Helpers with unusual placements (e.g. in custom levels) may have additional criteria. See Video 3.1.A for explanations.

While the above conditions are detailed, they leave several gaps for exploits:

  • The surface the portal lands on does not need to be portalable (only the surface the helper redirects it to needs to be)
  • The game does not check for obstacles between the surface the portal lands on and the surface the helper is aligned against

Due to these gaps, some helpers with an oversized radius can redirect portals to a surface the player cannot hit directly from their current position. One notable example of this is in PotatOS, as demonstrated in Video 3.1.A at the 4:14 mark.

Although placement helpers are common in official levels, each case where they can be abused for routing is unique. While not allowed in runs, the following console commands can be used to make helpers and their radius visible for practice or research:

  1. developer 1
  2. sv_cheats 1 (if in challenge mode)
  3. ent_rbox info_placement_helper

Uses of Trick

Single Player, Speedrun:

Single Player, Least Portals:

Grate Shot

Video 4.0.A - Funnel Catch grate shot by Rex.


"Grate shot" is a design oversight, where shooting a small area with portal shot collision (too small to support a portal) can place a portal on a nearby larger area that does not have portal shot collision, but is still flagged as a portabable surface.

Grate shot is named after the level feature that typically enables it, which is a mesh floor grate (no portal shot collision) that is surrounded by a white metal outline (has portal shot collision). Firing a portal onto the latter can place it on the former. One example of this is in Funnel Catch (singleplayer), which is demonstrated in Video 4.0.A at 6 seconds.

Execution of Trick

Video 4.1.A - Portal 2 Speedrun Tutorial - Chapter 8 by Can't Even (Funnel Catch starts at 20:21).


Performing a grate shot simply requires hitting the correct part of the white solid outline around the grate. This is a very small target, and there are several grate assets used in Portal 2. An example of the setup for Funnel Catch (singleplayer) is demonstrated in Video 4.1.A (trick setup starts at 20:43, actual shot starts at 21:05). For specific details of each grate shot used in routing, see the level the shot appears in (listed below).

Uses of Trick

Single Player, Speedrun:

Cooperative, Speedrun:

Seam Shot

"Seam shots" are a design oversight, where two pieces of level geometry are placed in direct contact with no gap, but due to a mistake in the portal collision code, it is possible to fire a portal "between" these pieces, as if through an invisible seam.

The full explanation of what makes seam shots possible is technically complex. In brief, all basic level geometry in Portal 2 is made up of 3D shapes, called brushes (e.g. walls, floors, stairs, railings). There are 2 categories of brushes in Portal 2:

  • Simple Brushes: Every facing of a simple brush needs to be "axis-aligned", which means perfectly aligned with the X, Y and Z cardinal directions on the map. This generally means a cube or cuboid shape, although one brush made of multiple cubes (such as the steps on a staircase) can have each facing axis-aligned.
  • Complex Brushes: Any brush that is not simple is instead complex. This includes every brush with a diagonal facing, as well as brushes that may be cubes or cuboids, but are not axis-aligned. For example, two cubic metal containers may have identical dimensions, and one may be axis-aligned with the map, but the other may be "skewed" sideways, which makes it not axis-aligned.

Note that "simple" or "complex" is a quality of the entire brush. This means that even when some facings of a brush are axis-aligned, a brush may be flagged "complex" due to other facings.

Portal 2's code uses different logic to check for collisions with simple and complex brushes. Due to these differences and an oversight in the complex brush code, it is possible to fire a shot near the point where a simple and complex brush touch, and have each collision check fail to detect any obstacles, allowing the portal shot to pass through a "gap" between the brushes.

Execution of Trick

Video 5.1.A - Seamshot Tutorial // Portal 2 by fin.

Performing a seam shot requires firing a portal at a precise target and angle to have it slip through the seam. Also, while a lot of seams exist in Portal 2 official levels, they can only be used for a seam shot if a portable surface can be hit on the other side of the seam. Due to these factors, seam shots normally require large amounts of in-depth research to discover, and executing one often requires the use of on-screen coordinates / specific setups to hit targets that are not visually evident.

The easiest seam shot currently used in routing is in Incinerator, which is demonstrated in Video 3.1.A at the 5:01 mark. Note that this seam shot (and the other seam shot in Incinerator) is an out of bounds shot ("OoB" for short), which are not allowed in some "in bounds" categories of speedrunning.

If you are using the SAR (Source Auto Record) speedrun plugin tool, the console command sar_seamshot_finder 1 can be used to enable a tool that highlights seam shot locations (use sar_seamshot_finder 0 to disable the tool).

Uses of Trick

Single Player, Speedrun:

Single Player, Least Portals:

  • Incinerator (2 different routes, both out of bounds, both suboptimal but beginner-friendly routes)
  • Crazy Box (suboptimal but beginner-friendly route)
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