ogc: add env variable to support Wiimote held sideways (#60)

Applications using the SDL GameController API can easily reconfigure the
gamepad keys, but the lower-level Joystick APIs does not offer the same
option. To make life easier for applications using the plain Joystick
API, add an environment variable that automatically remaps the
directional keys to match a Wiimote held sideways.

This avoid complicating the application's input code.

src/joystick/ogc/SDL_sysjoystick.c

@@ -193,6 +193,7 @@ static bool s_hardware_queried = false;
 #ifdef __wii__
 static bool s_wii_has_new_data[MAX_WII_JOYSTICKS];
 static bool s_accelerometers_as_axes = false;
+static bool s_wiimote_sideways = false;
 
 static void SDLCALL
 on_hint_accel_as_joystick_cb(void *userdata, const char *name,
@@ -325,6 +326,12 @@ static int OGC_JoystickInit(void)
 #ifdef __wii__
     SDL_AddHintCallback(SDL_HINT_ACCELEROMETER_AS_JOYSTICK,
                         on_hint_accel_as_joystick_cb, NULL);
+    /* If this is set, the Wiimote directional keys will be translated. */
+    {
+        const char *sideways_joystick_env = getenv("SDL_WII_JOYSTICK_SIDEWAYS");
+        s_wiimote_sideways =
+            sideways_joystick_env && strcmp(sideways_joystick_env, "1") == 0;
+    }
 #endif
 
     /* Initialize the needed variables */
@@ -737,13 +744,13 @@ static void HandleWiiHats(SDL_Joystick *joystick,
         int hat = SDL_HAT_CENTERED;
 
         if (pressed & buttons[0])
-            hat |= SDL_HAT_UP;
+            hat |= s_wiimote_sideways ? SDL_HAT_LEFT : SDL_HAT_UP;
         if (pressed & buttons[1])
-            hat |= SDL_HAT_DOWN;
+            hat |= s_wiimote_sideways ? SDL_HAT_RIGHT : SDL_HAT_DOWN;
         if (pressed & buttons[2])
-            hat |= SDL_HAT_LEFT;
+            hat |= s_wiimote_sideways ? SDL_HAT_DOWN : SDL_HAT_LEFT;
         if (pressed & buttons[3])
-            hat |= SDL_HAT_RIGHT;
+            hat |= s_wiimote_sideways ? SDL_HAT_UP : SDL_HAT_RIGHT;
         SDL_PrivateJoystickHat(joystick, 0, hat);
     }
 }