fix: prevent black screen by setting surface event before format change

When the surface is born as RGB565 on Vulkan, the RGB565 guard in
SurfaceChanged calls SetFormat(RGBA8888) to trigger a surface recreate.
Previously, this reset surfaceEvent and returned early, blocking the
draw thread on surfaceEvent.Wait(5000) while the UI thread was stuck
in the synchronous SetFormat call. This blocked the entire managed
runtime from sending heartbeats, causing the native watchdog to fire
at 10s and producing a black screen.

The fix sets surfaceEvent BEFORE calling SetFormat, so the draw thread
can proceed with the current (soon-to-be-recreated) surface. The new
surface triggers another SurfaceChanged which sets surfaceEvent again
with the correct RGBA8888 format.

Fixes the issue where the APK shows a black screen after the last build.

Author: Ubuntu

osu.Android/OsuGameActivity.cs

@@ -891,9 +891,6 @@ public void SurfaceChanged(ISurfaceHolder holder, global::Android.Graphics.Forma
                 setFormatPending = true;
                 setFormatAttempts = 1;
 
-                // Log to Runtime so the mid-session RGB565 reset is visible in the main log
-                // (and therefore in the notification overlay). Performance log gets the same
-                // entry for correlation with display-mode and frame-timing data.
                 string rgb565Message =
                     "[osu!] Android surface pixel format RGB565 detected (Vulkan path) — " +
                     "requesting RGBA8888 and triggering a surface recreate. " +
@@ -902,6 +899,20 @@ public void SurfaceChanged(ISurfaceHolder holder, global::Android.Graphics.Forma
                 Logger.Log(rgb565Message, LoggingTarget.Runtime, LogLevel.Important);
                 Logger.Log(rgb565Message, LoggingTarget.Performance, LogLevel.Important);
 
+                // Set the surface event BEFORE calling SetFormat so the draw thread can
+                // proceed with the current (soon-to-be-recreated) surface. Without this,
+                // the draw thread blocks on surfaceEvent.Wait(5000) while SetFormat triggers
+                // a synchronous surface teardown on the UI thread, blocking the entire
+                // managed runtime from sending heartbeats. The native watchdog then fires
+                // at 10s because no managed heartbeat is observed.
+                // The new surface will trigger another SurfaceChanged which will set
+                // surfaceEvent again with the correct RGBA8888 format.
+                if (width > 0 && height > 0)
+                {
+                    surfaceEvent.Set();
+                    Debug.WriteLine($"[osu!] Native surface signal set before format change (size: {width}x{height})");
+                }
+
                 try
                 {
                     holder.SetFormat(global::Android.Graphics.Format.Rgba8888);
@@ -911,17 +922,7 @@ public void SurfaceChanged(ISurfaceHolder holder, global::Android.Graphics.Forma
                     Debug.WriteLine($"[osu!] Failed to request RGBA8888 format change for Vulkan: {e.Message}");
                 }
 
-                // The SetFormat call above queues a SurfaceDestroyed→SurfaceCreated cycle.
-                // Reset the surface event so GetSurfaceGlobalRef() does NOT unblock yet —
-                // the current Surface handle is about to be invalidated, and any caller that
-                // receives it would forward a dangling pointer into the Vulkan driver.
-                // The event will be re-set when SurfaceChanged fires again for the new
-                // RGBA8888 Surface; the normal-path surfaceEvent.Set() at the end of this
-                // method (lines below the if/else-if guard) handles that on the next call.
-                // We must NOT fall through to the width/height check, because that would
-                // signal the event with the old (about-to-die) surface dimensions.
-                surfaceEvent.Reset();
-                Debug.WriteLine("[osu!] Native surface signal reset (RGB565→RGBA8888 format change pending)");
+                Debug.WriteLine("[osu!] Native surface format change requested (RGB565→RGBA8888)");
                 return;
             }