When it comes to volunteers porting games to platforms they weren’t officially released for, it’s usually Doom and Quake that are the main characters because Id Software has released many of their graphics engines as free software. However, that is not to say that they are the only titles that can be unofficially ported, as a Reddit user named zbios has managed to run Half-Life 2 natively on Raspberry Pi and Apple Silicon.
Currently Half-Life 2 continues to support macOS or at least that’s what the game’s file on Steam says, but if the compilation is for Intel processors, it will work on Rosetta, the compatibility layer and with architecture emulation developed by Apple to run applications compiled for x86 (Intel) on Apple Silicon processors used by the latest generations of Mac computers.
Returning to the topic at hand, the execution of Half-Life 2 on Raspberry Pi and natively on Apple Silicon (that is, it is compiled for Apple’s ARM architecture) has been possible thanks to the source code of the Source engine being publicly available as a result of the Team Fortress 2 source code leak in 2018.
The leaked source code has ended up being published on GitHub under a ban on using it for commercial purposes, but if Valve hasn’t authorized that, the reality is that any reuse of that source code may be illegal. Regardless of the legal situation, from a technical point of view the scenario is not essentially different from what was seen on other occasions with Doom and Quake.
According to the Reddit user, the performance of Half-Life 2 is quite uneven on each of the platforms. On a Raspberry Pi 4 it has achieved a frame rate per second between 15 and 20 at 720p and 10fps at 1080p, although the experience has apparently been stable. About Apple Silicon, more specifically a Apple M2, the situation changes radically by achieving a frame rate per second of between 300 and 400 in the Ravenholm section depending on your version.
Despite being both ARM processors, the profile of each one is very different. The Reddit user does not rule out that other games like Portal can be ported, but some like Garry’s Mod are out of reach due to the modifications they have in the engine itself.
Will these initiatives encourage Valve to officially port Steam and its games to Android and other ARM-based platforms? From a technical point of view, it seems that it is totally feasible, but another thing is that the company sees interest and/or commercial viability.