Window transparency support on Android

Implements per-pixel transparency feature on Android.
Allows plugins to do specific rendering and render godot UI on top
(useful for camera support with drawing on top).

doc/classes/OS.xml

@@ -970,10 +970,10 @@
 			If [code]true[/code], the window is minimized.
 		</member>
 		<member name="window_per_pixel_transparency_enabled" type="bool" setter="set_window_per_pixel_transparency_enabled" getter="get_window_per_pixel_transparency_enabled" default="false">
-			If [code]true[/code], the window background is transparent and window frame is removed.
+			If [code]true[/code], the window background is transparent and the window frame is removed.
 			Use [code]get_tree().get_root().set_transparent_background(true)[/code] to disable main viewport background rendering.
-			[b]Note:[/b] This property has no effect if [b]Project &gt; Project Settings &gt; Display &gt; Window &gt; Per-pixel transparency &gt; Allowed[/b] setting is disabled.
-			[b]Note:[/b] This property is implemented on HTML5, Linux, macOS and Windows.
+			[b]Note:[/b] This property has no effect if [member ProjectSettings.display/window/per_pixel_transparency/allowed] setting is disabled.
+			[b]Note:[/b] This property is implemented on HTML5, Linux, macOS, Windows, and Android. It can't be changed at runtime for Android. Use [member ProjectSettings.display/window/per_pixel_transparency/enabled] to set it at startup instead.
 		</member>
 		<member name="window_position" type="Vector2" setter="set_window_position" getter="get_window_position" default="Vector2( 0, 0 )">
 			The window position relative to the screen, the origin is the top left corner, +Y axis goes to the bottom and +X axis goes to the right.

doc/classes/ProjectSettings.xml

@@ -447,10 +447,14 @@
 			If [code]true[/code], the home indicator is hidden automatically. This only affects iOS devices without a physical home button.
 		</member>
 		<member name="display/window/per_pixel_transparency/allowed" type="bool" setter="" getter="" default="false">
-			If [code]true[/code], allows per-pixel transparency in a desktop window. This affects performance, so leave it on [code]false[/code] unless you need it.
+			If [code]true[/code], allows per-pixel transparency for the window background. This affects performance, so leave it on [code]false[/code] unless you need it.
+			See [member OS.window_per_pixel_transparency_enabled] for more details.
+			[b]Note:[/b] This feature is implemented on HTML5, Linux, macOS, Windows, and Android.
 		</member>
 		<member name="display/window/per_pixel_transparency/enabled" type="bool" setter="" getter="" default="false">
 			Sets the window background to transparent when it starts.
+			See [member OS.window_per_pixel_transparency_enabled] for more details.
+			[b]Note:[/b] This feature is implemented on HTML5, Linux, macOS, Windows, and Android.
 		</member>
 		<member name="display/window/size/always_on_top" type="bool" setter="" getter="" default="false">
 			Forces the main window to be always on top.

platform/android/export/export_plugin.cpp

@@ -2552,6 +2552,11 @@ void EditorExportPlatformAndroid::get_command_line_flags(const Ref<EditorExportP
 		command_line_strings.push_back("--debug_opengl");
 	}
 
+	bool translucent = ProjectSettings::get_singleton()->get("display/window/per_pixel_transparency/enabled");
+	if (translucent) {
+		command_line_strings.push_back("--translucent");
+	}
+
 	if (command_line_strings.size()) {
 		r_command_line_flags.resize(4);
 		encode_uint32(command_line_strings.size(), &r_command_line_flags.write[0]);

platform/android/java/lib/src/org/godotengine/godot/Godot.java

@@ -130,6 +130,7 @@ public class Godot extends Fragment implements SensorEventListener, IDownloaderC
 	private boolean use_32_bits = false;
 	private boolean use_immersive = false;
 	private boolean use_debug_opengl = false;
+	private boolean translucent = false;
 	private boolean mStatePaused;
 	private boolean activityResumed;
 	private int mState;
@@ -357,7 +358,7 @@ private void onVideoInit() {
 		// ...add to FrameLayout
 		containerLayout.addView(edittext);
 
-		mView = new GodotView(activity, this, xrMode, use_gl3, use_32_bits, use_debug_opengl);
+		mView = new GodotView(activity, this, xrMode, use_gl3, use_32_bits, use_debug_opengl, translucent);
 		containerLayout.addView(mView, new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
 		edittext.setView(mView);
 		io.setEdit(edittext);
@@ -608,6 +609,8 @@ public void onCreate(Bundle icicle) {
 				use_32_bits = true;
 			} else if (command_line[i].equals("--debug_opengl")) {
 				use_debug_opengl = true;
+			} else if (command_line[i].equals("--translucent")) {
+				translucent = true;
 			} else if (command_line[i].equals("--use_immersive")) {
 				use_immersive = true;
 				if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) { // check if the application runs on an android 4.4+

platform/android/java/lib/src/org/godotengine/godot/GodotView.java

@@ -76,7 +76,7 @@ public class GodotView extends GLSurfaceView {
 	private final GodotRenderer godotRenderer;
 
 	public GodotView(Context context, Godot godot, XRMode xrMode, boolean p_use_gl3,
-			boolean p_use_32_bits, boolean p_use_debug_opengl) {
+			boolean p_use_32_bits, boolean p_use_debug_opengl, boolean p_translucent) {
 		super(context);
 		GLUtils.use_gl3 = p_use_gl3;
 		GLUtils.use_32 = p_use_32_bits;
@@ -86,7 +86,8 @@ public GodotView(Context context, Godot godot, XRMode xrMode, boolean p_use_gl3,
 		this.inputHandler = new GodotInputHandler(this);
 		this.detector = new GestureDetector(context, new GodotGestureHandler(this));
 		this.godotRenderer = new GodotRenderer();
-		init(xrMode, false, 16, 0);
+
+		init(xrMode, p_translucent, 16, 0);
 	}
 
 	public void initInputDevices() {
@@ -139,6 +140,7 @@ private void init(XRMode xrMode, boolean translucent, int depth, int stencil) {
 				 * is interpreted as any 32-bit surface with alpha by SurfaceFlinger.
 				 */
 				if (translucent) {
+					this.setZOrderOnTop(true);
 					this.getHolder().setFormat(PixelFormat.TRANSLUCENT);
 				}
 

platform/android/os_android.cpp

@@ -161,6 +161,8 @@ Error OS_Android::initialize(const VideoMode &p_desired, int p_video_driver, int
 		}
 	}
 
+	transparency_enabled = p_desired.layered;
+
 	if (gl_initialization_error) {
 		OS::get_singleton()->alert("Your device does not support any of the supported OpenGL versions.\n"
 								   "Please try updating your Android version.",

platform/android/os_android.h

@@ -66,6 +66,8 @@ class OS_Android : public OS_Unix {
 
 	int video_driver_index;
 
+	bool transparency_enabled = false;
+
 public:
 	// functions used by main to initialize/deinitialize the OS
 	virtual int get_video_driver_count() const;
@@ -150,6 +152,9 @@ class OS_Android : public OS_Unix {
 	virtual String get_model_name() const;
 	virtual int get_screen_dpi(int p_screen = 0) const;
 
+	virtual bool get_window_per_pixel_transparency_enabled() const { return transparency_enabled; }
+	virtual void set_window_per_pixel_transparency_enabled(bool p_enabled) { ERR_FAIL_MSG("Setting per-pixel transparency is not supported at runtime, please set it in project settings instead."); }
+
 	virtual String get_unique_id() const;
 
 	virtual String get_system_dir(SystemDir p_dir, bool p_shared_storage = true) const;