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It has never been officially used by Valve, who simply call it "sticky gel" or "stick paint". It is often referred to by the community as "Adhesion Gel". The code for sticky gel is still in the game, although disabled by default, and can be re-enabled with this mod (archived download) that requires an older version of the game. It was later shown by Valve with the effects working in a presentation here. A video of the leftovers (albeit after the effects were removed) can be found here.
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Because of this, several community map-makers have tried (with varying success) to implement it in their maps. All of the Sticky Gel-related textures and particles remain in the final game. The gel is purple, however it is not known whether this would be the final color.
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This led to it being cut from the game and eventually replaced by reflection gel in the PeTI update. While this may sound neat, it proved to be disorienting and cause motion sickness among playtesters.
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Going through game_sounds_music_a2.txt will reveal the internal, possibly original, name for the "Turret Wife Serenade" track.Ī gel which, when used with portals, would allow the player to walk on the walls and ceiling of test chambers. However, when played together it's clear they aren't meant to accompany, as they are in different keys with different chord progressions. Based on the name of the file (sp_under_potatos_x1_01) this file is related to the above. An atmospheric bass line to an unknown track.
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