Tooltip windows render with opaque black backgrounds and stale content in Unreal Engine 5.6 editor (Conan Exiles dev kit)

Software / project

https://github.com/user-attachments/assets/9a734be4-fa66-4735-8206-8104b9d31c21

Conan Exiles Mod Devkit — a custom Unreal Engine 5.6 fork distributed by Funcom and run via Steam. The dev kit is shipped Windows-only; this report is for running it on Linux through Proton.

The editor is forced onto the D3D12 RHI by the project's DefaultEngine.ini and by hard plugin dependencies (DLSS / Streamline). Switching to UE's Vulkan RHI is not viable: it crashes at RHI.cpp:1351 GRHIGlobals.GpuInfo.VendorId != 0 when the NGX Streamline plugins are loaded, and removing those plugins breaks other plugins that hard-depend on them. So D3D12 → vkd3d-proton is the only working path.

vkd3d-proton / Proton version

Reproduces on every Proton version I've tried:

• Proton-Hotfix (current)
• Proton-Experimental
• Proton 10.0.4
• Proton 9.0

vkd3d.log

steam-9466428251963392000.tar.gz

Bundled vkd3d-proton version: - vkd3d-proton: 3.0.0 (build 21a49c975df83a7 — v3.0b release, December 2025)

System

• GPU: NVIDIA GeForce RTX 4080 Super
• NVIDIA driver: 595.58.03
• Distro: Kubuntu 26.04
• Kernel: 7.0.0-15-generic
• DE / session: KDE Plasma plasmashell 6.6.4 on Wayland

Description

UE5's Slate UI creates a separate top-level HWND with its own D3D12 swapchain for each tooltip popup. In the Blueprint editor, hovering over node pins, asset thumbnails, or details-panel entries produces tooltips that exhibit two related artifacts:

1. Opaque black region around the tooltip. A black rectangle, typically much larger than the tooltip text itself, renders alongside or extending from the tooltip. Looks consistent with the tooltip HWND's swapchain backbuffer being presented as opaque black instead of with proper alpha or background colour.
2. Stale content / multiple tooltips overlaid. Successive tooltips appear to render on top of each other — text from previous tooltips remains visible behind the current one. Consistent with the swapchain not being cleared/overwritten between presents.
3. Visible flicker on mouse movement as Slate shows/hides tooltips in quick succession.

Screenshot attached.

vkd3d-proton trace pattern

A VKD3D_DEBUG=info capture during the bug shows the exact pattern: Slate is creating per-HWND swapchains for tooltips and then rapidly resizing them via ChangeProperties as the tooltip content changes. Each resize triggers recreate_swapchain_in_present_task on a separate worker thread.

Excerpt from `vkd3d.log` while hovering over Blueprint pins:

    0170:info:dxgi_vk_swap_chain_init: Creating swapchain (8 x 8), BufferCount = 3.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (654 x 141), BufferCount = 3.
    02b4:info:dxgi_vk_swap_chain_recreate_swapchain_in_present_task: Got 4 swapchain images.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (512 x 253), BufferCount = 3.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (512 x 305), BufferCount = 3.
    02b4:info:dxgi_vk_swap_chain_recreate_swapchain_in_present_task: Got 4 swapchain images.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (512 x 318), BufferCount = 3.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (512 x 321), BufferCount = 3.
    02b4:info:dxgi_vk_swap_chain_recreate_swapchain_in_present_task: Got 4 swapchain images.
    0170:info:dxgi_vk_swap_chain_ChangeProperties: Reallocating swapchain (512 x 256), BufferCount = 3.
    [... continues ...]

The `0170` thread is the editor's main thread issuing geometry changes; `02b4` is the present worker chasing each resize with a swapchain recreation. The visible artifacts (opaque black region around the tooltip; content from prior tooltips remaining visible behind the current one) are consistent with the new swapchain images not being correctly initialised or with stale presented frames being shown during the resize churn. Full vkd3d log attached.

Reproduction

1. Install Conan Exiles Mod Devkit on Linux (available on Steam as a non-Steam tool, though Funcom doesn't ship Linux binaries).
2. Launch with default Proton settings — D3D12 RHI is selected automatically.
3. Open any Blueprint asset and hover a node pin or empty graph area.
4. Tooltip renders with the black box and stale-content artifacts.

Expected

Tooltip windows render with the correct background colour and content; no residual content from prior tooltips; no flicker on mouse movement.

Actual

See screenshot. Black region surrounds the tooltip; stacked stale content; flicker.

Workarounds attempted (unsuccessful)

• Wine virtual desktop via winecfg / explorer /desktop= — no effect on tooltip rendering.
• Multiple Proton versions (Hotfix, Experimental, 10.0.4, 9.0) — consistent reproduction across all.
• Switching to UE Vulkan RHI — crashes at GRHIGlobals.GpuInfo.VendorId != 0 due to NGX Streamline plugin interaction; can't realistically be disabled because of plugin dependency chains.
• Gamescope nesting — gamescope launches but does not present the editor visibly under nested KDE compositor.

Workaround that does work

Setting Slate.EnableTooltips 0 in the editor's console / ConsoleVariables.ini suppresses tooltips entirely, which avoids the artifact at the cost of tooltip functionality. Useful as a workaround but not a fix.

Logs

Full Proton and vkd3d logs attached.

Notes

If multi-swapchain-per-window is genuinely the trigger, this same pattern likely affects any UE5 editor running through vkd3d-proton, not specifically the Conan fork — happy to try reproducing on stock UE5 if that helps narrow it.