Building Principia for Windows XP

Back in the day when Principia originally released for Windows in 2014, the game would run on versions as far back as Windows XP. Given that Principia 1.4 was released while Windows XP still had mainstream support, this of course made sense at the time, and there was no real reason not to support it given that the tooling and dependencies at the time were still compatible with it.

Fast forward to today with Principia as an open source project. While the Windows version should still run as far back as Windows 7, our usage of modern toolchains, dependencies and system libraries such as UCRT means that hard to truly guarantee far into the future as the ecosystem moves forward. However, this has always been something I wanted to change one day, bringing Principia back onto Windows XP and producing a fully open source build of the game that can run on it.

The technical details of Principia

I suppose it would be useful to first describe the technical details of Principia that are relevant to this endeavour. Principia is a game that was originally designed to run on phones from around 2012, so it should have no problem running on very old hardware as long as it supports at least OpenGL 2.0. Principia has very few dependencies, and makes use of SDL for cross-platform support. SDL (both SDL2 and the newer SDL3) still supports Windows XP, and as previously mentioned Principia also used to run on Windows XP. So unless there have been changes I have made during my work on the open source version that broke XP compatibility, it should be possible to get it running again on XP without too many code changes.

The main issue is just the toolchain and some other dependencies which have moved on to newer Windows versions.

The Windows version of Principia only officially supports being compiled with a mingw-w64 Windows toolchain. While historically this was due to MSVC lacking support for C99 features used in Principia’s backing engine TMS, I’m not sure how the situation for this is like nowadays. However mingw-w64 also contains various polyfills for simple C functions that do not actually exist natively on Windows, and unless someone shows up with a burning interest to build Principia with MSVC this is likely not going to change anytime soon.

Regardless, FOSS toolchains tend to be the easiest to get a modern version up that can target older versions of Windows. However, the current LLVM-based mingw-w64 toolchain from MSYS2 we use for official Windows builds are unsuitable for targeting Windows XP, both due to linking against the UCRT, LLVM’s libc++ is 7+, and any other support libraries are built expecting symbols in e.g. Vista to always exist. So we will need to step out of this and find something else… Or build something from source.

Let’s build our own toolchain!

When going further back than around Vista/7, the compatibility for existing mingw-w64 toolchains you can find start to drop. Any LLVM-based toolchain has a minimum of around Windows 7 for C++ projects due to libc++ not supporting anything older, while other GCC-based toolchains are built expecting Vista+ APIs to always exist in their pre-built support libraries. While there are toolchains whose primary purpose is to target versions as old as 95, I ended up just rolling with my own. This was likely going to be the simplest, as I specifically also wanted a cross-compiling toolchain I can run on a Linux host while targeting Windows.

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