DroidDeck/docs/development/game-environment.md

Steam game environment

Open Games → Game environment, directly below FEX preset, in Steam settings or the in-session drawer. Choose all Proton games, an installed game, or enter a Steam app ID. For a non-Steam shortcut, use its numeric compatdata directory ID (unsigned 32-bit). The drawer opens the editor on its selected game profile. That editing scope stays fixed if Steam's selected game changes in the background; use the editor's own profile picker to switch deliberately. Changes apply on the next game launch, including when Steam is already running. A running game must be restarted. Native Linux games and Steam itself are outside this editor's scope.

The Components page also has a Configuration dropdown. Default profile owns the default Proton and FEX preset. An installed game can inherit those defaults or choose its own Proton and FEX preset. Proton choices are applied through Steam's per-app compatibility mapping, including while Steam is running when its live compatibility helper is attached. A newly installed Proton that the running client has not discovered yet applies when Steam next starts.

Each game can also override the stored FEX, DXVK and VKD3D-Proton package used by its selected Proton. The launch wrapper applies that game’s component files immediately before Proton starts, removes managed files that are absent from the selection, and restores Default component choices for the next game. Use Default removes the game override. Component packages must first be downloaded or imported on the Default Components page.

Before publishing game component choices, DroidDeck preserves each Proton build's original components, including an explicitly empty bundle when a component is not shipped. Those restore choices remain after the last override is cleared. A missing or unreadable original is an error, not permission to delete the component's files. If an original is missing after a build may already have used a game override, DroidDeck refuses to capture those potentially modified files as originals.

Component selections and the launch table are saved with a recovery record. Publishing the launch table commits the selection: if the app stops before its settings file is updated, the next component read recovers the matching settings. An interruption before publication leaves the previous selections in place. Unused staged packages are removed only after both files have been saved.

Reset game profile removes all overrides owned by the selected game: Proton, FEX preset, component packages, environment variables, texture filtering and Windows components. The game then inherits the Default profile again.

The order is inherited process environment, selected FEX preset and built-in settings, shared edits, then game-specific edits. Editor entries therefore win over matching Steam launch-option variables. Remove explicitly unsets a variable. Restore inherited settings removes the override. The environment editor's Clear environment overrides action clears only the selected environment entries and is intentionally narrower than Reset game profile. Values are literal strings, with no shell expansion; quotes are only needed when the consuming program expects them.

Defaults and available suggestions

The initial configuration enables Mesa shader caching with MESA_SHADER_CACHE_DISABLE=false, sets VKD3D_FEATURE_LEVEL=12_2 and VKD3D_SHADER_MODEL=6_9, and preserves the selected FEX preset. Existing edits and explicit removals take precedence over these defaults. FEX's own default remains the default preset. Shader caching in VKD3D/DXVK, synchronization, ray tracing and diagnostic logging otherwise retain the runtime's defaults.

On an Adreno 6xx, Turnip does not expose storageBuffer8BitAccess, which DXVK 3 requires. A Steam or desktop session installs DXVK 2.7.1 into any Proton whose DXVK is still the copy that Proton shipped, including after a Proton update put that copy back. A DXVK package chosen in Components stays for that Proton build.

The variable-name picker offers 24 predefined variables and a Custom entry. Like WinNative, known variables use toggles, value dropdowns, multi-select lists, or numeric/text fields. Feature-level and shader-model dropdowns also accept custom values. Custom variables have editable names and literal values.

Variable	Use
VKD3D_FEATURE_LEVEL	D3D12 capability override; defaults to 12_2.
VKD3D_SHADER_MODEL	Shader-model override; defaults to 6_9.
VKD3D_CONFIG	Per-game workarounds such as nodxr; not a universal performance preset.
MESA_SHADER_CACHE_MAX_SIZE	Storage budget for Mesa's shader cache, for example 1G.
mesa_glthread	OpenGL threading; test with the affected game.
DXVK_CONFIG	DXVK configuration options; recent builds accept dxvk.maxFrameRate = 60.
VKD3D_FRAME_RATE	D3D12 frame-rate limit.
DXVK_HUD, PROTON_LOG	Optional diagnostics; leave unset for ordinary play.
PROTON_USE_WINED3D	D3D9–11 OpenGL fallback for compatibility testing.
PROTON_USE_XALIA	Proton's gamepad-navigation helper toggle.

Forcing 12_2 or 6_9 changes reported capabilities; it cannot implement a missing Vulkan feature. Remove either entry to use automatic detection for that capability. Other picker suggestions are editable starting values and are enabled only when added and saved. Older or custom components can support a different set of options. Android Wine wrapper, ALSA-server, Box64 and patched async-DXVK options are identified in the editor as requiring a different/custom component; custom entries remain allowed. The old DXVK_FRAME_RATE environment variable was removed from current DXVK, so it is not offered as a suggestion. Prefer the session frame limiter for ordinary play.

Launch path and references

WinNative's Linux session filters Android-only options, merges user variables over the FEX preset, and passes the result to env -i before starting Steam. Its Windows/Wine graphics helper also maps the selected feature level to VKD3D_FEATURE_LEVEL. Reviewed source: WinNative Linux session, variable editor, graphics configuration.

DroidDeck instead publishes an atomic JSON snapshot at /root/.config/droiddeck/game-environment.json. Both its Valve ARM64 Proton wrapper and adopted third-party Proton wrappers execute droiddeck-game-env, which reads that snapshot for each real game launch and uses execvpe to start Proton. Probe prefix compatdata/0 and non-launch verbs are unchanged. Malformed configuration falls back to the inherited environment without evaluating its contents. Both component and environment selection normalize signed non-Steam prefix IDs to unsigned IDs.

The published file also carries generated dxvkConfig and dxvkConfigGames values the app's own file never has. The session menu's texture filtering (core/TextureFiltering) becomes d3d9/d3d11.samplerAnisotropy and samplerLodBias options. Default choices apply to games without overrides; each game can save either choice independently or return it to Use Default. The launcher appends the selected options to DXVK_CONFIG after the environment profile, so a user's own DXVK_CONFIG entry keeps its options. "Auto" texture sharpness is -log2(panel / session), derived when the session is sized, and applies from the next launch.

Upstream references: VKD3D capability parsing, VKD3D options, Proton runtime options, Mesa variables, DXVK variables, DXVK frame-limiter changes.

Validation: ./gradlew testDebugUnitTest and python3 -m unittest discover -s tools/tests -p test_game_environment.py. Actual game compatibility depends on the installed Proton, VKD3D and Vulkan driver; these checks do not establish that every device supports feature level 12_2 or SM 6_9.