From f0a4fea89f984d031fef00c39fa22d7221fed814 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Thu, 25 Apr 2019 14:17:07 -0700
Subject: [PATCH] Fixed bug 4608 - Android: not getting
 SDL_WINDOWEVENT_FOCUS_GAINED on start of our app

Dan Ginsburg

I've seen this on several devices including Moto Z running Android 7 and a Snapdragon 845 running Android 9.

What happens is as follows:

SDLActivity.onWindowFocusChanged(true) happens pretty early on, but it's before we've done SDL_CreateWindow and so Android_Window is 0x0 thus this message does not get sent:

JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeFocusChanged)(
                                    JNIEnv *env, jclass cls, jboolean hasFocus)
{
    SDL_LockMutex(Android_ActivityMutex);

    if (Android_Window) {
        __android_log_print(ANDROID_LOG_VERBOSE, "SDL", "nativeFocusChanged()");
        SDL_SendWindowEvent(Android_Window, (hasFocus ? SDL_WINDOWEVENT_FOCUS_GAINED : SDL_WINDOWEVENT_FOCUS_LOST), 0, 0);
    }

    SDL_UnlockMutex(Android_ActivityMutex);
}

When the window does get created, in Android_CreateWindow it does this:

 window->flags &= ~SDL_WINDOW_RESIZABLE;     /* window is NEVER resizeable */
    window->flags &= ~SDL_WINDOW_HIDDEN;
    window->flags |= SDL_WINDOW_SHOWN;          /* only one window on Android */
    window->flags |= SDL_WINDOW_INPUT_FOCUS;    /* always has input focus */

    /* One window, it always has focus */
    SDL_SetMouseFocus(window);
    SDL_SetKeyboardFocus(window);

The SDL_SetKeyboardFocus does send an SDL_WINDOWEVENT_FOCUS_GAINED message, but it gets eaten in SDL_SendWindowEvent because we've forced SDL_WINDOW_INPUT_FOCUS beforehand:

 case SDL_WINDOWEVENT_FOCUS_GAINED:
        if (window->flags & SDL_WINDOW_INPUT_FOCUS) {
            return 0;
        }
        window->flags |= SDL_WINDOW_INPUT_FOCUS;
        SDL_OnWindowFocusGained(window);
        break;

I can fix the problem if I comment out this line from Android_CreateWindow:

    window->flags |= SDL_WINDOW_INPUT_FOCUS;    /* always has input focus */

I would propose that as a fix unless there is a reason not to.
---
 src/video/android/SDL_androidwindow.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/video/android/SDL_androidwindow.c b/src/video/android/SDL_androidwindow.c
index 5e34c284a97e4..c99ca7035b993 100644
--- a/src/video/android/SDL_androidwindow.c
+++ b/src/video/android/SDL_androidwindow.c
@@ -61,7 +61,6 @@ Android_CreateWindow(_THIS, SDL_Window * window)
     window->flags &= ~SDL_WINDOW_RESIZABLE;     /* window is NEVER resizeable */
     window->flags &= ~SDL_WINDOW_HIDDEN;
     window->flags |= SDL_WINDOW_SHOWN;          /* only one window on Android */
-    window->flags |= SDL_WINDOW_INPUT_FOCUS;    /* always has input focus */
 
     /* One window, it always has focus */
     SDL_SetMouseFocus(window);