Android: decouple video/audio subsystems from JNI initialization

[HTRamsey]

Summary

Allows Android embedders to use SDL without the full video/audio Java layer by gating subsystem-specific code behind SDL_VIDEO_DISABLED and SDL_AUDIO_DISABLED preprocessor flags.

This enables applications that only need joystick/gamepad support (e.g. Qt-based apps like QGroundControl) to build SDL without shipping stub Java classes for unused subsystems. Currently, QGC maintains a full set of stubbed-out SDLActivity.java, SDLAudioManager.java, and SDLInputConnection.java files just to satisfy SDL's JNI requirements, even though it only uses the controller/HID subsystem.

Changes

C layer (SDL_android.c, SDL_android.h)

• Split SDLActivity_tab JNI method table into core (20 entries: lifecycle, hints, permissions, file dialog) and video (24 entries: surface, input, clipboard, orientation)
• JNI_OnLoad: conditionally register SDLActivity_video_tab, SDLInputConnection, and SDLAudioManager classes
• checkJNIReady(): no longer requires mAudioManagerClass when SDL_AUDIO_DISABLED is defined
• nativeSetupJNI(): method ID resolution split into core (always) vs video (guarded)
• All audio JNI methods and function implementations: #ifndef SDL_AUDIO_DISABLED
• All video JNI callbacks and function implementations: #ifndef SDL_VIDEO_DISABLED
• Display orientation accessors (GetDisplayNaturalOrientation, GetDisplayCurrentOrientation) remain outside video guard, needed by camera subsystem
• SDL_SendAndroidBackButton() compiles as no-op when video disabled (public API, must always link)
• Video-specific includes (SDL_androidkeyboard.h, etc.) guarded

Java layer (SDL.java)

• Added SDL_INIT_* flag constants matching include/SDL3/SDL_init.h values
• New setupJNI(int subsystems) and initialize(int subsystems) methods for selective initialization
• Zero-arg overloads preserved for full backwards compatibility

Build config (SDL_build_config_android.h)

• Wrapped SDL_VIDEO_DRIVER_ANDROID, OpenGL ES, Vulkan, and GPU defines in #ifndef SDL_VIDEO_DISABLED, matching the existing pattern used for audio/joystick/haptic/sensor/camera

Usage

Embedders can now build SDL with -DSDL_VIDEO_DISABLED=1 -DSDL_AUDIO_DISABLED=1 and initialize from Java:

SDL.setupJNI(SDL.SDL_INIT_JOYSTICK | SDL.SDL_INIT_HAPTIC);
SDL.initialize(SDL.SDL_INIT_JOYSTICK | SDL.SDL_INIT_HAPTIC);
SDL.setContext(myActivity);

No SDLAudioManager.java, SDLInputConnection.java, SDLDummyEdit.java, or SDLSurface.java required. SDLActivity.java only needs core methods (getContext, isAndroidTV, isChromebook, isDeXMode, isTablet, sendMessage, etc.).

Test plan

• Full SDL Android build with default flags (no behavioral change)
• Build with -DSDL_VIDEO_DISABLED=1: video Java classes not required, joystick/gamepad still works
• Build with -DSDL_AUDIO_DISABLED=1: audio Java class not required
• Build with both disabled: minimal Java surface (SDLActivity core + SDLControllerManager + HIDDeviceManager)
• Camera subsystem still compiles when video is disabled (uses unguarded orientation accessors)
• SDL.setupJNI() zero-arg call still works identically to before

[slouken]

I'm marking this draft until CI passes and the test plan is complete.

[1bsyl]

There are going lots of merge conflicts with #14962
It's sound much easier to apply 14962 first and then disable things with ifdef.

[HTRamsey]

Not really. Also most of the changes in this are trivial so rebase conflicts would be very easy to fix

[1bsyl]

it's a lot of idef indeed, but not so easy to test for someone who's not running SDL without video/audio

[AntTheAlchemist]

I'm very interested in this and can test with audio disabled.

Would proguard see the final ints and strip out unused code from SDLAudioManager.java? Or can more compile conditions be put in?

[MoNTE48]

I'm also interested in this because I use OpenAl-Soft directly and don't seem to be using SDL_VIDEO anywhere.