Address remaining feedback on Android background transparency

[m4gr3d]

Follow up to #106709 to address #106709 (comment)

[syntaxerror247]

@m4gr3d This looks really good now. But I'm still having one issue, the surface doesn't seems to be updated/refreshed properly.

[syntaxerror247]

Just setting the format doesn't seems to be enough. The surface needs to be updated/refreshed.
I tried refreshing it with an hack and it seems to work for vulkan but opengl is still buggy.

Before my hack (This PR):
Opengl

Screenrecorder-2025-06-13-17-16-09-513.mp4

Vulkan

Screenrecorder-2025-06-13-17-14-53-256.mp4

---

After my hack

Opengl

Screenrecorder-2025-06-13-19-28-17-173.mp4

Vulkan

Screenrecorder-2025-06-13-19-29-20-652.mp4

[syntaxerror247]

My hack is simply hiding and then showing the view. But I believe you can come up with a better solution :)

surfaceView.getHolder().setFormat(format);
surfaceView.setVisibility(View.GONE);
surfaceView.setVisibility(View.VISIBLE);

[Alex2782]

OK on Samsung Tab S7 with Mobile Renderer. (Android 13)

Godot Engine v4.5.beta.custom_build.4ca772276 (2025-06-19 02:10:56 UTC) - https://godotengine.org
Vulkan 1.1.128 - Forward Mobile - Using Device #0: Qualcomm - Adreno (TM) 650

Not on Pixel 8a, Mali GPU. (Android 16)
I think it's like in the video from @syntaxerror247 (Tested as Android export, not via editor)

---

OpenGLES/Compatibility is faulty on both devices, making it seem as if the app is frozen.

Changing surfaceView.setVisibility only partially works; on the Samsung Tab S7, the app is completely transparent at first, which seems like a crash. But touching the screen shows the UI again, without any 3D content.

[Alex2782]

Note: In the demo, application/run/low_processor_mode is enabled. If I disable it, the "visibility hack" works better.

[m4gr3d]

@syntaxerror247 @Alex2782 After some explorations, it doesn't look like we can (yet) support switching transparency at runtime.

The update to the pixel format causes the surface to be destroyed and recreated. On opengl on Android, we don't support that at all, and typically restart the app when such event occurs (see

godot/platform/android/java_godot_lib_jni.cpp

Line 239 in 4d1f26e

// Rendering context recreated because it was lost; restart app to let it reload everything

), which negates the point of being able to switch the transparency at runtime.
With vulkan, things are a bit better and we can continue without having to restart the app, but doing so still seems to create some issues as a bunch of warnings appear in the logs following the surface recreation.

TLDR; handling surface recreation is an area we'll need to improve on before we're able to enable switching transparency on/off at runtime. cc @clayjohn
As such, in the meantime transparency can only be set at start-time and is controlled by the display/window/per_pixel_transparency/allowed project setting. The display/window/size/transparent setting and the WINDOW_FLAG_TRANSPARENT flag have no effect on Android.

If display/window/per_pixel_transparency/allowed is enabled, the project can still control its transparency via get_viewport().transparent_bg.
Note however there seems to be a bug on how this is handled between vulkan and opengl. It works as expected on opengl, but on vulkan, the background seems to inherit some transparency even when get_viewport().transparent_bg == false. I'll create a bug for the rendering team for the latter issue.

Edit: I've created #108386 to track the described issue with the vulkan renderer.

[Calinou]

TLDR; handling surface recreation is an area we'll need to improve on before we're able to enable switching transparency on/off at runtime.

See also godotengine/godot-proposals#6423.

[m4gr3d]

@syntaxerror247 @Alex2782 Ping on this PR.

Note that I think I may have an approach to enable switching the transparency at runtime, but this builds on top of an upcoming large set of changes, so that capability would be 4.6 at the earliest.

In the meantime, we should move ahead with the current capability and limitations for 4.5.

[Repiteo]

Thanks!