Fixed bug 4702 - Android back button does not send SDL_KEYDOWN event

fallback when event.getSource() is SOURCE_UNKNOWN

android-project/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -1799,6 +1799,10 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
     // Key events
     @Override
     public boolean onKey(View  v, int keyCode, KeyEvent event) {
+
+        int deviceId = event.getDeviceId();
+        int source = event.getSource();
+
         // Dispatch the different events depending on where they come from
         // Some SOURCE_JOYSTICK, SOURCE_DPAD or SOURCE_GAMEPAD are also SOURCE_KEYBOARD
         // So, we try to process them as JOYSTICK/DPAD/GAMEPAD events first, if that fails we try them as KEYBOARD
@@ -1806,20 +1810,25 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
         // Furthermore, it's possible a game controller has SOURCE_KEYBOARD and
         // SOURCE_JOYSTICK, while its key events arrive from the keyboard source
         // So, retrieve the device itself and check all of its sources
-        if (SDLControllerManager.isDeviceSDLJoystick(event.getDeviceId())) {
+        if (SDLControllerManager.isDeviceSDLJoystick(deviceId)) {
             // Note that we process events with specific key codes here
             if (event.getAction() == KeyEvent.ACTION_DOWN) {
-                if (SDLControllerManager.onNativePadDown(event.getDeviceId(), keyCode) == 0) {
+                if (SDLControllerManager.onNativePadDown(deviceId, keyCode) == 0) {
                     return true;
                 }
             } else if (event.getAction() == KeyEvent.ACTION_UP) {
-                if (SDLControllerManager.onNativePadUp(event.getDeviceId(), keyCode) == 0) {
+                if (SDLControllerManager.onNativePadUp(deviceId, keyCode) == 0) {
                     return true;
                 }
             }
         }
 
-        if ((event.getSource() & InputDevice.SOURCE_KEYBOARD) != 0) {
+        if (source == InputDevice.SOURCE_UNKNOWN) {
+            InputDevice device = InputDevice.getDevice(deviceId);
+            source = device.getSources();
+        }
+
+        if ((source & InputDevice.SOURCE_KEYBOARD) != 0) {
             if (event.getAction() == KeyEvent.ACTION_DOWN) {
                 //Log.v("SDL", "key down: " + keyCode);
                 if (SDLActivity.isTextInputEvent(event)) {
@@ -1835,7 +1844,7 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
             }
         }
 
-        if ((event.getSource() & InputDevice.SOURCE_MOUSE) != 0) {
+        if ((source & InputDevice.SOURCE_MOUSE) != 0) {
             // on some devices key events are sent for mouse BUTTON_BACK/FORWARD presses
             // they are ignored here because sending them as mouse input to SDL is messy
             if ((keyCode == KeyEvent.KEYCODE_BACK) || (keyCode == KeyEvent.KEYCODE_FORWARD)) {