Compatibility Report

• Name of the game with compatibility issues: Imperium of the Stars Demo
• Steam AppID of the game: 5198340

System Information

• GPU: AMD Radeon RX 6800 XT (RADV NAVI21)
• Video driver version: Mesa 26.2.4 (radv)
• Kernel version: 7.2.8-zen1-2-zen
• CPU / RAM: Ryzen 9 7950X, 64 GB. Arch Linux, KDE Plasma Wayland session (game runs under XWayland), Steam Runtime 1.0.20260714.251828
• Link to full system information report as Gist (Steam System Information); Steam Runtime Diagnostics: Gist
• Proton version: Proton Experimental (experimental-11.0-20261014). Also reproduced with Proton 10.0 (test app only; see below)

I confirm:

• [x] that I haven't found an existing compatibility report for this game.
• [x] that I have checked whether there are updates for my system available.

steam-5198340.log.gz

imperium-msaa-repro.zip

.)

Symptoms

The game's 3D views (galaxy map, etc.) are completely blank; the Vue UI around them renders normally. There is no in-game GPU
warning and no errors in the Chromium console or from Dawn. Setting Settings > Graphics > Anti-aliasing to off or SMAA fixes it;
the default, 4x MSAA, breaks it.

The game is an Electron 42.7.1 / Chromium 148 app rendering with three.js's WebGPU renderer. With the game's own
--enable-logging=stderr --log-level=0 output in the Proton log, the renderer compiles ~147 shader programs and issues draws with no
validation errors, but nothing reaches the screen.

I reduced it to a small WebGPU page run in the same Electron build under Proton: in Dawn's D3D12 backend on vkd3d-proton, every
render pass with a 4-sample color attachment and a resolveTarget leaves the resolve target untouched.

(24 = color rgba8unorm/rgba16float/bgra8unorm x depth none/depth24plus-stencil8/depth32float/depth24plus x storeOp store/discard.)

With Dawn's nonzero_clear_resources_on_creation_for_testing toggle on, the failing resolve targets read back the fill pattern
(255,255,255,255) unchanged, so the resolve is skipped or a no-op rather than being cleared later. These Dawn toggles did not help:
emulate_store_and_msaa_resolve, clear_color_with_draw, lazy_clear_resource_on_first_use (disabled), d3d12_create_not_zeroed_heap
(disabled), d3d12_use_64kb_alignment_msaa_texture, always_resolve_into_zero_level_and_layer. Chromium --disable-gpu-compositing,
--disable-direct-composition, --in-process-gpu did not help either.

Raw D3D12 test (no Dawn)

A small D3D12 program (d3d12-repro/resolve.cpp) that clears a 4x MSAA texture and resolves it with ResolveSubresource,
ResolveSubresourceRegion and a render-pass ending-access resolve works on vkd3d-proton in all 64 combinations I tried (RGBA8 and
RGBA16F; typed and typeless; created in RENDER_TARGET/RESOLVE_DEST or COMMON with explicit barriers; with and without
CREATE_NOT_ZEROED). One silent failure mode I found: if the MSAA source is not transitioned to RESOLVE_SOURCE before
ResolveSubresource, vkd3d-proton does nothing and leaves the destination unchanged, which matches the symptom. I could not capture
Dawn's actual D3D12 call sequence (vkd3d-proton release builds have no trace output), so I don't know whether Dawn issues an unusual
state sequence or vkd3d-proton mishandles a legal one.

Reproduction

Game:

1. Install "Imperium of the Stars Demo" (5198340), run with Proton Experimental, start a new game.
2. Leave Anti-aliasing on the default (4x MSAA): the 3D view is blank. Switch to off or SMAA: it renders.

Without the game (attached imperium-msaa-repro.zip):

1. Download Electron 42.7.1 for Windows (electron-v42.7.1-win32-x64.zip from the Electron GitHub releases).
2. In a Proton prefix run electron.exe <path to webgpu-repro> <path to results.json> (e.g. proton run electron.exe ...).
3. In results.json, configs entries with samples: 4 have "ok": false and read back zeros; manual entries are "ok": true.
   (The present entries are window-capture checks and are unreliable on some setups.)

Log: PROTON_LOG=1 %command% --enable-logging=stderr --log-level=0 run with AA on the default 4x MSAA is attached as
steam-5198340.log.gz. It was taken on Proton Experimental (experimental-11.0-20261014) with
WINEDEBUG=-all,+debugstr to keep it small (the default PROTON_LOG=1 +seh,+unwind output reached 10 GB in ten minutes on Proton 10.0
and stalled shader warm-up). It shows vkd3d-proton build 0bb64c56c8f0dcc, DXVK v3.1.1-97-ga78a467, RADV on the RX 6800 XT, and the game
compiling 151 shader programs without errors while the 3D view stays blank.