Fix android low processor usage mode flicker 3.x

main/main.cpp

@@ -2117,7 +2117,7 @@ bool Main::start() {
 uint64_t Main::last_ticks = 0;
 uint32_t Main::frames = 0;
 uint32_t Main::frame = 0;
-bool Main::force_redraw_requested = false;
+uint32_t Main::force_redraw_frames = 0;
 int Main::iterating = 0;
 bool Main::agile_input_event_flushing = false;
 
@@ -2178,6 +2178,8 @@ bool Main::iteration() {
 	uint64_t physics_process_ticks = 0;
 	uint64_t idle_process_ticks = 0;
 
+	bool draw = false;
+
 	frame += ticks_elapsed;
 
 	last_ticks = ticks;
@@ -2240,15 +2242,25 @@ bool Main::iteration() {
 	VisualServer::get_singleton()->sync(); //sync if still drawing from previous frames.
 
 	if (OS::get_singleton()->can_draw() && VisualServer::get_singleton()->is_render_loop_enabled()) {
-		if ((!force_redraw_requested) && OS::get_singleton()->is_in_low_processor_usage_mode()) {
+		draw = true;
+		if (OS::get_singleton()->is_in_low_processor_usage_mode()) {
 			if (VisualServer::get_singleton()->has_changed()) {
-				VisualServer::get_singleton()->draw(true, scaled_step); // flush visual commands
-				Engine::get_singleton()->frames_drawn++;
+				draw = true;
+#ifdef ANDROID_ENABLED
+				// On Android in low_processor_usage_mode there can be horrible flickering when it stops drawing
+				// Fix by force drawing 2 more frames after last changed frame.
+				force_redraw_frames = 3; // needs to be 3 to draw 2 more after this frame
+#endif
+			} else {
+				draw = false;
 			}
-		} else {
+		}
+
+		if (draw || force_redraw_frames > 0) {
 			VisualServer::get_singleton()->draw(true, scaled_step); // flush visual commands
 			Engine::get_singleton()->frames_drawn++;
-			force_redraw_requested = false;
+			if (force_redraw_frames > 0)
+				force_redraw_frames--;
 		}
 	}
 
@@ -2328,8 +2340,8 @@ bool Main::iteration() {
 	return exit || auto_quit;
 }
 
-void Main::force_redraw() {
-	force_redraw_requested = true;
+void Main::force_redraw(uint32_t frames) {
+	force_redraw_frames = frames;
 }
 
 /* Engine deinitialization

main/main.h

@@ -40,7 +40,7 @@ class Main {
 	static uint64_t last_ticks;
 	static uint32_t frames;
 	static uint32_t frame;
-	static bool force_redraw_requested;
+	static uint32_t force_redraw_frames;
 	static int iterating;
 	static bool agile_input_event_flushing;
 
@@ -52,7 +52,7 @@ class Main {
 	static bool start();
 
 	static bool iteration();
-	static void force_redraw();
+	static void force_redraw(uint32_t frames = 1);
 
 	static bool is_iterating();
 

platform/android/os_android.cpp

@@ -386,6 +386,7 @@ void OS_Android::init_video_mode(int p_video_width, int p_video_height) {
 void OS_Android::set_display_size(Size2 p_size) {
 	default_videomode.width = p_size.x;
 	default_videomode.height = p_size.y;
+	Main::force_redraw(3); // fix flicker if in low_processor_mode
 }
 
 Error OS_Android::shell_open(String p_uri) {