General
Like with any puzzle, there is generally one intended solution (or family of nearly identical solutions that share the same "checkpoints") to a Portal chamber. While it may be possible to reach the exit using alternative solutions, this is not intentional, and generally something a well-designed chamber attempts to prevent if at all possible. Therefore, a "legitimate" solution is one that maps to (one of) the intended one(s). Merely having reached the exit does not make the solution valid; by reaching the chamberlock via an unintended series of actions, you have not actually solved the chamber, only bypassed it.With that in mind, it is useful to categorize specific "tricks" (often called "moves" in the Portal community), as themselves valid or not. Many of these are ones I (and often many others) actively avoid ever using, and so any solution that employs them can be readily identified as illegitimate. Knowing this can remove ambiguity during the solving process, where you have an idea on a possible solution step but wonder if my solutions would ever include such a thing. I often find myself in the same situation, and never feel good about having solved a chamber but not being sure it was a legitimate solution due to it using questionable moves (or alternatively being stuck because I discounted any ideas using such moves).
Borderline Moves
These are moves which are not certain to be unintended, but are rarely employed by my chambers, and as such it is unlikely they are part of the solution. Often, this is moves that I know I have used but try to avoid using, or only know of it being intended in some of my older maps. This includes:- Funnel/bridge Climbing
Repeatedly moving a bridge or funnel you are on/in in a direction and using its autocenter to carry you in that direction - Interacting through grating
- Placing portals while flying through the air
- Raising a cube over your head, like to carry it over a fizzler or put it on a ledge or through an elevated portal
- Toppling a laser cube to aim upwards
- Precise (< 10 degrees) laser aiming
- Precise (< 1/2 of a PeTI voxel/< 64 units) portal placement
- Cube stacking
- Walking with a lit laser cube, keeping it aimed at a target
Illegitimate Moves
These are moves that I never use in my chambers, and any use of them to solve the level is guaranteed to be an exploit. This includes:- Hitbox abuse, such as clipping cubes into walls or the player into models, or getting a laser to go through an object by placing the cube's "lens" inside a barrier's clip bounds
- Portal Bumping
Engine ExploitForcing a portal through a barrier like glass or a fizzler by placing the previous in a tight location - Funnel FlyingEngine ExploitUsing a funnel/sneak interaction bug to grant the ability to fly everywhere
- Portal PeekingEngine ExploitMoving a portal while using it by firing at the perfect moment
- Seam GlitchEngine ExploitFiring portals/lasers/etc into a tiny gap between solid geometry
- Wall ClimbingEngine Exploit
- ReportalingEngine ExploitMoving portals you are falling into or coming out of to gain a momentum boost
- Bunny HoppingEngine ExploitExploiting physics glitches to gain massively increased jump distance
- Floating laser cubesEngine ExploitExploiting the fact that lit laser cubes remain floating if untouched
- Grating phasingEngine ExploitExploiting the fact that cubes can pass through grating on the other side of a portal
- Exploiting turret sleep/wake cycle
- Using cubes as turret shields
- Anything involving blindly tossing/pushing an item (especially spheres) in a direction and hoping it ends up in a specific location
- Anything involving high-speed "ninja" moves, portal shots, or similar, especially involving tight timings or difficult aiming
- Using cubes as a platform to stand or jump on
- Cube Throwing
- Abusing "laser receiver glancing"Engine ExploitActivating multiple things with a laser that merely glances yet lights a laser receiver
- Leaps over pits or goo that are just barely possible, in either distance or due to complex strafing
Preventing Unintended Solutions
I try to remove unintended solutions from my chambers, provided doing so does not massively compromise their quality in other ways, for example by making the intended solution obvious. However, there is a specific exception: I do not bother with game-level exploits. That is, any issue above with the '' tag above is something I will make no attempt to address. Not only are such issues rarely fixable without extremely onerous and heavy-handed enforcement (if even then), they are so far removed from the obvious intent of a puzzle that their usage is blatant cheating. They are not worth addressing, and even if I did have a fix, those who seriously consider them "valid" solution steps would probably just start using the console instead and consider that the new solution.