A new video from Polygon breaks down how the team at Valve created the amazing liquid effect for the in-game bottles of Half-Life: Alyx.
The video features an interview with Matt Wilde, a VFX developer at Valve who work on Alyx and was the person behind the incredible liquid shaders that were added to the game post-launch.
Wilde says he did some preliminary work on the bottle shaders in the lead-up to Alyx’s release, however he wasn’t able to finish it in time. So the game shipped with opaque bottles that lacked the realistic outer shine and the appearance of liquid within.
However, the day of Alxy’s release — March 23 — was also the day that Washington state went into lockdown. Valve employees were now working from home, and so Wilde had a lot more time on his hands. Wilde says he spent ages just looking at bottles to understand the various tiny details of how the liquids and the surface of the bottle reacted to movement and light. He then resumed work on a pixel shader that would give the illusion of liquid within the bottles and provide more realistic interaction with light.
It all culminated in an update for Alyx in late May that added shockingly-realistic shaders to all of the game’s bottles. The liquid within the bottles looked and acted so realistic that you would be forgiven for thinking Valve had added some for of liquid simulation. However, it’s all smoke and mirrors — the entire effect is a visual change to the surface of the bottle and there’s nothing actually inside them at all.