Decided to do a segmented run of Portal using my knowledge of the game, and managed to get a sub-20 which is pretty good I think.
I'm no speedrunner by any means, and this run has lots of mistakes, missed opportunities and outdated tactics. Still, it shows how much I've learned by playing this game for over 10 years.
No, I don't know what that white square on-screen is, and I don't know how to fix it, so don't even bother mentioning it.
Glitch explanations:
Throughout the run: ABH/Accelerated Backhopping
In some Source games, like Half-Life 2 and Portal, you can jump while crouching for some reason, which allows you to gain speed by repeatedly crouch-hopping backwards without actually holding the back key.
00:00 - Vault Skip
This involves using the radio and bed to glitch through the glass. I don't entirely understand how it works, though this tutorial sums up how to do it:
• RTA Vault Skip Tutorial
02:12 - Edge Glitch/Save Glitch
This involves getting yourself stuck inside both the wall and a portal, which separates your camera from your body, allowing you to shoot OOB. (out of bounds) Combine this with saving and loading, and you can literally phase through any surface that doesn't have a portal on it.
02:56 - Seam Shot
By lining yourself up perfectly against a corner, you can shoot a portal through a tiny gap. This skips the entirety of chambers 4 and 5.
05:32 - Advanced Peek-a-Portal
Shooting a portal while in another portal, then going through that portal at the right time brings you to the portal you just shot.
06:15 - Portal Bump
If you place a portal on top of another portal of the opposite color, it will "bump" itself to the side. This can be used in several places to get OOB, skip segments, or even skipping entire chambers.
06:48 - Semi-Save Glitch & Physics Deform
In this spot specifically, you can edge glitch your way into the observation room, which puts you in a save glitch state. By saving and loading, you can then interact with the chairs, which, when used in unison with the ability to walk through walls, can transfer insane amounts of velocity to the player in a seemingly random direction. By doing a "credit card swiping" motion, you can aim where you fling, though it's still very random. I feel like I got lucky with this skip, and was debating on straight up not doing it because of how inconsistent it is.