Support the creation of an archive to be used with SDL3 on Android

[sellithy]

Since one of the recommended ways of using SDL3 on Android is through aars (see this section), I was wondering if it'd be possible to support creating an archive that'd be copied over an Android project and then the Android project would handle the linking. I think it's a good medium vs building SDL3 for Android fully

[MasonRemaley]

Thanks for the suggestion! What’s the advantage of this approach over static linking?

[sellithy]

Sorry if I'm not using terms correctly. I was saying to allow the users to produce a .a file then they copy it over to the Android project. For my own education, is this called static linking or something else?

Right now, users can skip using this repo all together and do something like

const sdl3 = ; // raw sdl from tar
const usr = "/path/to/ndk/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr";
mod.addIncludePath(sdl3.path("include"));
mod.addSystemIncludePath(.{ .cwd_relative = usr ++ "/include/aarch64-linux-android" });
mod.addSystemIncludePath(.{ .cwd_relative = usr ++ "/include" });

but I was thinking it might be better if we just support it directly from here 🤷

[MasonRemaley]

Ah no you're using the correct terminology, I just misunderstood the link--my bad!

I think your suggestion is a good idea. In practice it'd look something like this:

// Add support for -fsys=sdl, this lets the user request the system provided SDL.
// Running this line unconditionally will make sure it show sup in the help menu.
const link_system_sdl = b.systemIntegrationOption("sdl", .{});

// ...

// Forward this value along to the various platform backends
switch (target.result.os.tag) {
    .linux => linux.build(b, target.result, lib, build_config_h, link_system_sdl),
    .windows => windows.build(b, target.result, lib, build_config_h, link_system_sdl),
    .macos => macos.build(b, target.result, lib, build_config_h, link_system_sdl),
    else => @panic("target has no default config"),
}

Then in each platform.zig's build function, you'd either honor this request or panic if using the system provided SDL hasn't been implemented on the platform in question.

(Or maybe you'd just branch at the top level and never even call into the platform backends if linking the system library looks the same regardless of platform? If so that'd be much nicer!)

---

FWIW adding full support for building SDL for Android from source probably isn't that much work, I just don't have an Android dev environment to test on. There would essentially be 3 steps:

1. Branch on Abi.isAndroid() in linux.zig (or before calling into linux.zig)
2. Port SDL_build_config_android.h to a ConfigHeader just like linux.zig does for Linux
3. Provide headers for dependencies (many of these are probably already supplied by the Linux build and can be shared)

Figured it would be useful to have those steps written out if anyone reading wants try to tackle it, but an option to use the system provided library as suggested here would be good to have regardless.