Re-enable per-pixel transparency support on Linux, macOS, and Windows.

[bruvzg]

Seems like new Vulkan drivers have support for transparency, so it can be re-enabled.

So far I have tested it on Windows (with NVIDIA RTX 2070 Super), Linux (Fedora 36, NVIDIA RTX 2070 Super) and M1 mac.

To use:

• Enable display/window/per_pixel_transparency/allowed in the project settings.
• Disable viewport background get_viewport().transparent_bg = true.
• Set transparent flag for a window DisplayServer.window_set_flag(DisplayServer.WINDOW_FLAG_TRANSPARENT, true, window_id).

Transparency for the splash screen will probably require some additional changes.

Fixes #50626

[TokisanGames]

Would this help anything listed in this issue #63675?

[fire]

Wanted to repost that @you-win depends on this transparent desktop windows feature for https://github.com/virtual-puppet-project/vpuppr

[bruvzg]

Would this help anything listed in this issue #63675?

Actually, it's completely unrelated, so ignore my previous comment, I was looking at a wrong tab. This is for enabling semi-transparent windows, it's not affecting rendering in any way.

[akien-mga]

Thanks!

[MarianoGnu]

I tested the example project, turned out it had the transparent_background flag disabled and made me think the movie maker was working wrong, but it indeed recorded with transparent background. However the window itself does not show with transparent background and renders the skybox when running, this behavior is quite unexpected

EDIT: i am updating my gpu drivers right now, uldate later

[Calinou]

I tested the example project, turned out it had the transparent_background flag disabled and made me think the movie maker was working wrong, but it indeed recorded with transparent background. However the window itself does not show with transparent background and renders the skybox when running, this behavior is quite unexpected

Which operating system are you using? On Linux, you must have composting enabled in your window manager for transparency to be visible. This is the case by default on most desktop environments, but not always – especially on "lightweight" ones such as Xfce or LXQt.

[MarianoGnu]

I just updated my nvidia drivers to confirm it is not a driver issue, the problem still persists
System Information:
Godot Engine v4.0.2.stable.official.7a0977ce2 - https://godotengine.org
Vulkan API 1.3.236 - Forward+ - Using Vulkan Device #1: NVIDIA - NVIDIA GeForce RTX 3060 Laptop GPU
Windows 11 Home, 64 bits

[Calinou]

I wonder if the fact this is hybrid graphics (NVIDIA Optimus) causes an issue with per-pixel transparency. Try updating the Intel integrated graphics' drivers as well (from Intel, not your laptop OEM or Windows Update).

[MarianoGnu]

I disabled the nvidia drivers from Device manager to force the use of Intel GPU (without updating it), as result, i have per pixel transparency, but not as expected, instead environment is half transparent

[MarianoGnu]

Changing the environment to use clear color instead of skubox seems to work for the usecase of the test example, except it affects lighting a lot, in my personal project i intend to use an skybox for affecting lighting on 3D world

[MarianoGnu]

when using a non fully black color as clear color the issue appears again, it seems windows is using grayscale for transparency instead of alpha, or maybe is using AGBR instead of RGBA format

[GK-GreyGhost]

I'm running into the problem even with a fully black clear color, its seems the godot window blend mode is some sort of additive blend? if the window behind godot is black it becomes opaque, 50% gray is transparent and white almost completely disappears

this image is a default cube in godot in front of affinity designer (graphics editing program) showing a black page with a gray and white stripe. happy to upload a video if needed

edit: going to investigate the source tomorrow starting with VkCompositeAlphaFlagBitsKHR

Windows 10, Godot 4.0.2

[Calinou]

as result, i have per pixel transparency, but not as expected, instead environment is half transparent

This is because Godot uses premultiplied alpha for transparent windows. Fully transparent pixels use additive blending, fully opaque pixels use "mix" blending. This means that fully transparent non-black pixels will be visible, but with additive blending.

Premultiplied alpha should be preferred over straight alpha, as it allows for antialiased borders to look correct. (You can check this by having an unshaded white cube in a transparent window, then moving this transparent window on a white background. Make sure to enable MSAA to some degree.)

[GK-GreyGhost]

Thank you @Calinou, that solved it for me, 1 material in the scene was "corrupting" everything else by having subsurface scattering turned on

I think this is a bug? if not could we add a warning? "SSS causes scene to use additive blending with per-pixel transparency enabled"

[Calinou]

@GK-GreyGhost The SSS issue may be a bug. Please open an issue with a minimal reproduction project attached.

[GK-GreyGhost]

@Calinou copy that, I will shortly, thanks!