[Bug 59587] New: win32u: Native Vulkan float16 swapchains not implicitly treated as scRGB

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=59587

            Bug ID: 59587
           Summary: win32u: Native Vulkan float16 swapchains not
                    implicitly treated as scRGB
           Product: Wine
           Version: 11.5
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: win32u
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Native Vulkan games that create swapchains with VK_FORMAT_R16G16B16A16_SFLOAT
and VK_COLOR_SPACE_SRGB_NONLINEAR_KHR expect Windows DWM behavior where this
combination is implicitly treated as scRGB (linear Rec.709 with extended
range). On Linux, some compositors take the sRGB tag literally (e.g., Mutter),
resulting in blown-out oversaturated colors.

Microsoft documents this behavior explicitly:
https://learn.microsoft.com/en-us/windows/win32/direct3darticles/high-dynami...

"By default, a swap chain created with a floating point pixel format is treated
as if it uses the DXGI_COLOR_SPACE_RGB_FULL_G10_NONE_P709 color space."

DXVK already handles this for D3D11 games by remapping the color space in PR
#3911:
https://github.com/doitsujin/dxvk/pull/3911

However, games using native Vulkan renderers (e.g. Hunt: Showdown / CryEngine)
bypass DXVK entirely and go through win32u's Vulkan layer, which does not
perform this remapping.

Affected game: Hunt: Showdown 1896 (AppID 594650, CryEngine native Vulkan
renderer)

The game creates swapchains with:
- imageFormat = VK_FORMAT_R16G16B16A16_SFLOAT (97)
- imageColorSpace = VK_COLOR_SPACE_SRGB_NONLINEAR_KHR (0)

With HDR enabled, this results in completely oversaturated/blown-out colors
because the compositor interprets the HDR pixel values (> 1.0) as sRGB.

I tested a prototype fix in win32u_vkCreateSwapchainKHR that remaps
SRGB_NONLINEAR to EXTENDED_SRGB_LINEAR when the format is R16G16B16A16_SFLOAT
(mirroring DXVK). This fixes the oversaturation and produces correct colors and
contrast. Full tone mapping of highlights depends on compositor scRGB support
(KDE KWin supports this, GNOME Mutter does not yet).

Tested on: Fedora 44, Linux 6.19, GNOME 50, Mesa 26.0.3, AMD RX 9070 XT.

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