On Android show the system UI when an SDL window is windowed, hide the system UI when it's fullscreen, like we do on iOS.

We're increasing the Android SDK minimum version to API 19, this doesn't increase the minimum target API, which is API 14.

android-project/app/build.gradle

@@ -8,14 +8,14 @@ else {
 }
 
 android {
-    compileSdkVersion 16
+    compileSdkVersion 19
     buildToolsVersion "26.0.1"
     defaultConfig {
         if (buildAsApplication) {
             applicationId "org.libsdl.app"
         }
         minSdkVersion 14
-        targetSdkVersion 16
+        targetSdkVersion 19
         versionCode 1
         versionName "1.0"
         externalNativeBuild {

android-project/app/jni/Application.mk

@@ -5,5 +5,5 @@
 
 APP_ABI := armeabi-v7a arm64-v8a x86 x86_64
 
-# Min SDK level
+# Min runtime API level
 APP_PLATFORM=android-14

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

@@ -213,19 +213,7 @@ public class SDLActivity extends Activity {
 
         setContentView(mLayout);
 
-        /* 
+        setWindowStyle(false);
-         * Per SDL_androidwindow.c, Android will only ever have one window, and that window 
-         * is always flagged SDL_WINDOW_FULLSCREEN.  Let's treat it as an immersive fullscreen 
-         * window for Android UI purposes, as a result.
-         */
-        int iFlags = 
-            //View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY | // Only available since API 19
-            View.SYSTEM_UI_FLAG_HIDE_NAVIGATION |
-            View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION |
-            View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN |
-            View.SYSTEM_UI_FLAG_FULLSCREEN;
-
-        getWindow().getDecorView().setSystemUiVisibility(iFlags);        
 
         // Get filename from "Open with" of another application
         Intent intent = getIntent();
@@ -408,7 +396,7 @@ public class SDLActivity extends Activity {
 
     // Messages from the SDLMain thread
     static final int COMMAND_CHANGE_TITLE = 1;
-    static final int COMMAND_UNUSED = 2;
+    static final int COMMAND_CHANGE_WINDOW_STYLE = 2;
     static final int COMMAND_TEXTEDIT_HIDE = 3;
     static final int COMMAND_SET_KEEP_SCREEN_ON = 5;
 
@@ -447,6 +435,29 @@ public class SDLActivity extends Activity {
                     Log.e(TAG, "error handling message, getContext() returned no Activity");
                 }
                 break;
+            case COMMAND_CHANGE_WINDOW_STYLE:
+                if (context instanceof Activity) {
+                    Window window = ((Activity) context).getWindow();
+                    if (window != null) {
+                        if ((msg.obj instanceof Integer) && (((Integer) msg.obj).intValue() != 0)) {
+                            int flags = View.SYSTEM_UI_FLAG_LAYOUT_STABLE |
+                                        View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION |
+                                        View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN |
+                                        View.SYSTEM_UI_FLAG_HIDE_NAVIGATION |
+                                        View.SYSTEM_UI_FLAG_FULLSCREEN |
+                                        View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
+                            window.getDecorView().setSystemUiVisibility(flags);        
+                            window.addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
+                        } else {
+                            int flags = View.SYSTEM_UI_FLAG_LAYOUT_STABLE;
+                            window.getDecorView().setSystemUiVisibility(flags);        
+                            window.clearFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
+                        }
+                    }
+                } else {
+                    Log.e(TAG, "error handling message, getContext() returned no Activity");
+                }
+                break;
             case COMMAND_TEXTEDIT_HIDE:
                 if (mTextEdit != null) {
                     // Note: On some devices setting view to GONE creates a flicker in landscape.
@@ -524,6 +535,14 @@ public class SDLActivity extends Activity {
         return mSingleton.sendCommand(COMMAND_CHANGE_TITLE, title);
     }
 
+    /**
+     * This method is called by SDL using JNI.
+     */
+    public static void setWindowStyle(boolean fullscreen) {
+        // Called from SDLMain() thread and can't directly affect the view
+        mSingleton.sendCommand(COMMAND_CHANGE_WINDOW_STYLE, fullscreen ? 1 : 0);
+    }
+
     /**
      * This method is called by SDL using JNI.
      * This is a static method for JNI convenience, it calls a non-static method

docs/README-android.md

@@ -14,7 +14,7 @@ supported, but you can use the "android-project-ant" directory as a template.
  Requirements
 ================================================================================
 
-Android SDK (version 16 or later)
+Android SDK (version 19 or later)
 https://developer.android.com/sdk/index.html
 
 Android NDK r10e or later

src/core/android/SDL_android.c

@@ -209,6 +209,7 @@ static jclass mActivityClass;
 /* method signatures */
 static jmethodID midGetNativeSurface;
 static jmethodID midSetActivityTitle;
+static jmethodID midSetWindowStyle;
 static jmethodID midSetOrientation;
 static jmethodID midGetContext;
 static jmethodID midIsAndroidTV;
@@ -302,6 +303,8 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeSetupJNI)(JNIEnv* mEnv, jclass c
                                 "getNativeSurface","()Landroid/view/Surface;");
     midSetActivityTitle = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                 "setActivityTitle","(Ljava/lang/String;)Z");
+    midSetWindowStyle = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
+                                "setWindowStyle","(Z)V");
     midSetOrientation = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                 "setOrientation","(IIZLjava/lang/String;)V");
     midGetContext = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
@@ -332,7 +335,7 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeSetupJNI)(JNIEnv* mEnv, jclass c
     midGetDisplayDPI = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "getDisplayDPI", "()Landroid/util/DisplayMetrics;");
 
     if (!midGetNativeSurface ||
-       !midSetActivityTitle || !midSetOrientation || !midGetContext || !midIsAndroidTV || !midInputGetInputDeviceIds ||
+       !midSetActivityTitle || !midSetWindowStyle || !midSetOrientation || !midGetContext || !midIsAndroidTV || !midInputGetInputDeviceIds ||
        !midSendMessage || !midShowTextInput || !midIsScreenKeyboardShown ||
        !midClipboardSetText || !midClipboardGetText || !midClipboardHasText ||
        !midOpenAPKExpansionInputStream || !midGetManifestEnvironmentVariables|| !midGetDisplayDPI) {
@@ -907,6 +910,12 @@ void Android_JNI_SetActivityTitle(const char *title)
     (*mEnv)->DeleteLocalRef(mEnv, jtitle);
 }
 
+void Android_JNI_SetWindowStyle(SDL_bool fullscreen)
+{
+    JNIEnv *mEnv = Android_JNI_GetEnv();
+    (*mEnv)->CallStaticVoidMethod(mEnv, mActivityClass, midSetWindowStyle, fullscreen ? 1 : 0);
+}
+
 void Android_JNI_SetOrientation(int w, int h, int resizable, const char *hint)
 {
     JNIEnv *mEnv = Android_JNI_GetEnv();

src/core/android/SDL_android.h

@@ -34,6 +34,7 @@ extern "C" {
 
 /* Interface from the SDL library into the Android Java activity */
 extern void Android_JNI_SetActivityTitle(const char *title);
+extern void Android_JNI_SetWindowStyle(SDL_bool fullscreen);
 extern void Android_JNI_SetOrientation(int w, int h, int resizable, const char *hint);
 
 extern SDL_bool Android_JNI_GetAccelerometerValues(float values[3]);

src/video/android/SDL_androidvideo.c

@@ -120,6 +120,7 @@ Android_CreateDevice(int devindex)
 
     device->CreateSDLWindow = Android_CreateWindow;
     device->SetWindowTitle = Android_SetWindowTitle;
+    device->SetWindowFullscreen = Android_SetWindowFullscreen;
     device->DestroyWindow = Android_DestroyWindow;
     device->GetWindowWMInfo = Android_GetWindowWMInfo;
 
@@ -220,7 +221,7 @@ Android_SetScreenResolution(int width, int height, Uint32 format, float rate)
     /*
       Update the resolution of the desktop mode, so that the window
       can be properly resized. The screen resolution change can for
-      example happen when the Activity enters or exists immersive mode,
+      example happen when the Activity enters or exits immersive mode,
       which can happen after VideoInit().
     */
     device = SDL_GetVideoDevice();
@@ -234,16 +235,17 @@ Android_SetScreenResolution(int width, int height, Uint32 format, float rate)
     }
 
     if (Android_Window) {
-        SDL_SendWindowEvent(Android_Window, SDL_WINDOWEVENT_RESIZED, width, height);
-
         /* Force the current mode to match the resize otherwise the SDL_WINDOWEVENT_RESTORED event
          * will fall back to the old mode */
         display = SDL_GetDisplayForWindow(Android_Window);
 
-        display->current_mode.format = format;
+        display->display_modes[0].format = format;
-        display->current_mode.w = width;
+        display->display_modes[0].w = width;
-        display->current_mode.h = height;
+        display->display_modes[0].h = height;
-        display->current_mode.refresh_rate = rate;
+        display->display_modes[0].refresh_rate = rate;
+        display->current_mode = display->display_modes[0];
+
+        SDL_SendWindowEvent(Android_Window, SDL_WINDOWEVENT_RESIZED, width, height);
     }
 }
 

src/video/android/SDL_androidwindow.c

@@ -53,7 +53,6 @@ Android_CreateWindow(_THIS, SDL_Window * window)
     window->h = Android_ScreenHeight;
 
     window->flags &= ~SDL_WINDOW_RESIZABLE;     /* window is NEVER resizeable */
-    window->flags |= SDL_WINDOW_FULLSCREEN;     /* window is always fullscreen */
     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 */
@@ -98,6 +97,12 @@ Android_SetWindowTitle(_THIS, SDL_Window * window)
     Android_JNI_SetActivityTitle(window->title);
 }
 
+void
+Android_SetWindowFullscreen(_THIS, SDL_Window * window, SDL_VideoDisplay * display, SDL_bool fullscreen)
+{
+    Android_JNI_SetWindowStyle(fullscreen);
+}
+
 void
 Android_DestroyWindow(_THIS, SDL_Window * window)
 {

src/video/android/SDL_androidwindow.h

@@ -28,6 +28,7 @@
 
 extern int Android_CreateWindow(_THIS, SDL_Window * window);
 extern void Android_SetWindowTitle(_THIS, SDL_Window * window);
+extern void Android_SetWindowFullscreen(_THIS, SDL_Window * window, SDL_VideoDisplay * display, SDL_bool fullscreen);
 extern void Android_DestroyWindow(_THIS, SDL_Window * window);
 extern SDL_bool Android_GetWindowWMInfo(_THIS, SDL_Window * window, struct SDL_SysWMinfo * info);