Initial Apple TV / tvOS support.

The Apple TV remote is currently exposed as a joystick with its touch surface treated as two axes. Key presses are also generated when its buttons and touch surface are used.

A new hint has been added to help deal with deciding whether to background the app when the remote's menu button is pressed: SDL_HINT_APPLE_TV_CONTROLLER_UI_EVENTS.

src/power/uikit/SDL_syspower.m

@@ -30,6 +30,7 @@
 #include "SDL_assert.h"
 #include "SDL_syspower.h"
 
+#if !TARGET_OS_TV
 /* turn off the battery monitor if it's been more than X ms since last check. */
 static const int BATTERY_MONITORING_TIMEOUT = 3000;
 static Uint32 SDL_UIKitLastPowerInfoQuery = 0;
@@ -46,10 +47,22 @@ SDL_UIKit_UpdateBatteryMonitoring(void)
         }
     }
 }
+#else
+void
+SDL_UIKit_UpdateBatteryMonitoring(void)
+{
+    /* Do nothing. */
+}
+#endif /* !TARGET_OS_TV */
 
 SDL_bool
 SDL_GetPowerInfo_UIKit(SDL_PowerState * state, int *seconds, int *percent)
 {
+#if TARGET_OS_TV
+    *state = SDL_POWERSTATE_NO_BATTERY;
+    *seconds = -1;
+    *percent = -1;
+#else /* TARGET_OS_TV */
     @autoreleasepool {
         UIDevice *uidev = [UIDevice currentDevice];
 
@@ -88,8 +101,10 @@ SDL_GetPowerInfo_UIKit(SDL_PowerState * state, int *seconds, int *percent)
 
         const float level = uidev.batteryLevel;
         *percent = ( (level < 0.0f) ? -1 : ((int) ((level * 100) + 0.5f)) );
-        return SDL_TRUE; /* always the definitive answer on iOS. */
     }
+#endif /* TARGET_OS_TV */
+
+    return SDL_TRUE; /* always the definitive answer on iOS. */
 }
 
 #endif /* SDL_POWER_UIKIT */