SDL2 on macOS detects joysticks only with SDL2_INIT_VIDEO

[EliaCereda]

It appears that SDL can detect joysticks connected at startup only if SDL2_INIT_VIDEO is also initialised.

When only SDL_INIT_JOYSTICK is initialised, for some reason gamepads are detected correctly if they're hot plugged while the program is running (e.g. inside the while(true) loop below), but not if they are already connected at startup.

SDL version: 2.32.54
macOS version: 14.7.4 arm64

Reproduction code (from https://github.com/ros-drivers/joystick_drivers/blob/ros2/joy/src/joy_enumerate_devices.cpp)

// On Windows, we have to be sure that SDL doesn't generate its own main.
#define SDL_MAIN_HANDLED
#include <SDL.h>

#include <cstdio>
#include <stdexcept>

int main()
{
  // SDL_INIT_GAMECONTROLLER implies SDL_INIT_JOYSTICK
  if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMECONTROLLER | SDL_INIT_HAPTIC ) < 0) {
    fprintf(stderr, "SDL could not be initialized: %s\n", SDL_GetError());
    return 1;
  }

  fprintf(stdout, "SDL initialized. Joystick subsystem version: %d.%d.%d\n", 
    SDL_MAJOR_VERSION, SDL_MINOR_VERSION, SDL_PATCHLEVEL);

  while (true) {
    SDL_PumpEvents();

    fprintf(
      stdout,
      "ID : GUID                             : GamePad : Mapped : Joystick Device Name\n");
    fprintf(
      stdout,
      "-------------------------------------------------------------------------------\n");
    for (int i = 0; i < SDL_NumJoysticks(); ++i) {
      SDL_JoystickGUID joystick_guid;
      const char * joystick_name = "Unknown";
      const char * has_mapping_string = "false";
      const char * is_gamepad = "false";

      if (SDL_IsGameController(i)) {
        SDL_GameController * controller = SDL_GameControllerOpen(i);
        joystick_guid = SDL_JoystickGetGUID(SDL_GameControllerGetJoystick(controller));
        joystick_name = SDL_GameControllerName(controller);
        if (nullptr != SDL_GameControllerMapping(controller)) {
          has_mapping_string = "true";
        }
        is_gamepad = "true";

      } else {
        joystick_name = SDL_JoystickNameForIndex(i);
        joystick_guid = SDL_JoystickGetDeviceGUID(i);
      }

      char guid_string[33];
      SDL_JoystickGetGUIDString(joystick_guid, guid_string, sizeof(guid_string));

      fprintf(
        stdout, "%2d : %32s : %7s : %6s : %s\n", i, guid_string, is_gamepad, has_mapping_string,
        joystick_name);
    }

    SDL_Delay(1000);
  }

  SDL_Quit();

  return 0;
}

Output with SDL2_INIT_VIDEO:

SDL initialized. Joystick subsystem version: 2.32.54
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
 0 : 05005d8eac0500000400000065706d04 :    true :   true : Logitech Cordless RumblePad 2

Output without SDL2_INIT_VIDEO:

SDL initialized. Joystick subsystem version: 2.32.54
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
ID : GUID                             : GamePad : Mapped : Joystick Device Name
-------------------------------------------------------------------------------
[... never detects it ...]

[slouken]

This is almost certainly a GCController quirk where it requires full window event integration to work properly. I notice from your SDL version that this affects SDL3 as well.

Can you throw some debug messages in SDL_mfijoystick.m to confirm?

[EliaCereda]

Thanks for the quick feedback, I'm running a pre-built copy of SDL so I can't do it easily, I'd have to look back over the next few days for that.

[EliaCereda]

It appears this is the known behaviour of GameController.framework, but it was quite hard to find before knowing where to look.

https://stackoverflow.com/questions/55226373/how-do-i-use-apples-gamecontroller-framework-from-a-macos-command-line-tool
https://stackoverflow.com/questions/65042693/gccontroller-controllers-does-not-contain-any-controllers-that-were-connecte?noredirect=1&lq=1

Do you have any pointers to the SDL2_INIT_VIDEO macOS initialization code to double check what changes?

[slouken]

Do you have any pointers to the SDL2_INIT_VIDEO macOS initialization code to double check what changes?

I'm not sure what you're asking?

[EliaCereda]

I was looking for these:

• SDL/src/joystick/apple/SDL_mfijoystick.m

  Line 759 in 5b1e92a

  connectObserver = [center addObserverForName:GCControllerDidConnectNotification

• SDL/src/video/cocoa/SDL_cocoaevents.m

  Line 506 in 5b1e92a

  void Cocoa_RegisterApp(void)

• SDL/src/video/cocoa/SDL_cocoaevents.m

  Line 594 in 5b1e92a

  NSEvent *event = [NSApp nextEventMatchingMask:NSEventMaskAny untilDate:expiration inMode:NSDefaultRunLoopMode dequeue:YES];

Am I correct that without the video subsystem, SDL never interacts with either the CoreFoundation or Foundation runloops? In other words there are no calls to CFRunLoopRunInMode or [NSRunLoop run] or similar?

[slouken]

Am I correct that without the video subsystem, SDL never interacts with either the CoreFoundation or Foundation runloops? In other words there are no calls to CFRunLoopRunInMode or [NSRunLoop run] or similar?

That's correct. It might be worth doing an experiment to see if calling those in the joystick update loop if video isn't initialized fixes this.