openFSX

An independent, experimental runtime for content from Microsoft Flight Simulator X, inspired by the approach of openOMSI.

Research prototype with airborne and runway starts. Current work includes content inspectors, a textured MDLX viewer and keyboard-controlled flight using a limited CFG/AIR dynamics subset. Three fixed-wheel contacts support test-plane ground roll and departure. It is not a complete FSX replacement: reference-flight comparison, broader ground/landing behavior, scenery loading, gauges and add-on APIs remain ahead.

Repository · Website

Approach

Build a new engine in Rust, read content from the user's own FSX installation, and establish compatibility through reproducible tests. No original executable code, aircraft, textures, scenery or SDK binaries belong in this repository. The local FSX/ directory is ignored by Git.

The viewer uses wgpu and winit, with Windows x64 as the first target and automatic graphics-backend selection. The first offscreen render was verified on an NVIDIA RTX 2080 through Vulkan. Full compatibility with existing aircraft and native add-ons is a long-term research goal, not an existing feature.

The compatibility target is FSX 1:1, including interface, flight behavior, content and supported APIs. This is an acceptance target, not a description of current coverage. Each subsystem needs reference comparisons before claiming parity.

Quick start

Install stable Rust and the Windows MSVC C++ build tools. Run from the repository root:

# Easiest start: with no arguments the menu opens for an FSX folder beside or
# above the executable (for example this repository's ./FSX). FLY NOW starts on
# the runway in the virtual cockpit, with live C172 instruments when
# target/fsx-gauge-host.exe has been built (scripts/build-gauge-host.ps1).
cargo run -p fsx-app --features viewer --bin openfsx-viewer

# Open the experimental FSX-style Free Flight menu (Windows / WebView2).
cargo run -p fsx-app --features viewer --bin openfsx-viewer -- "./FSX" --menu

# List variants in your own FSX installation.
cargo run -- inspect "./FSX" --windows-1252

# Inspect geometry and available LODs.
cargo run -- inspect-model "./FSX/SimObjects/Airplanes/C172/model/cessna172sp.mdl"

# Inspect panel placements and native-interior texture bindings (variant 0).
cargo run -- inspect-panel "./FSX/SimObjects/Airplanes/C172" --windows-1252

# Inspect a native gauge library as data; no DLL loading or execution.
cargo run -- inspect-gauges "./FSX/Gauges/Cessna172.dll" --windows-1252

# Decode CAB resources and inspect ACE XML/image references without executing scripts.
cargo run -- inspect-cabinet "./FSX/Gauges/n_number_plaque.cab"

# Open the experimental native viewer.
cargo run -p fsx-app --features viewer --bin openfsx-viewer -- "./FSX/SimObjects/Airplanes/C172/model/cessna172sp.mdl" --lod 150 --texture-dir "./FSX/SimObjects/Airplanes/C172/texture.1"

# Start an airborne C172 test with keyboard controls.
cargo run -p fsx-app --features viewer --bin openfsx-viewer -- "./FSX/SimObjects/Airplanes/C172" --fly --variant 0 --windows-1252 --lod 150

# Start on a real airport runway from the installed scenery. Build
# scripts/build-terrain-host.ps1 once to add the installed FSX elevation mesh.
cargo run -p fsx-app --features viewer --bin openfsx-viewer -- "./FSX/SimObjects/Airplanes/C172" --fly --airport KSEA --cockpit --native-gauges --windows-1252

# Start on the original test runway, with parking brake applied.
cargo run -p fsx-app --features viewer --bin openfsx-viewer -- "./FSX/SimObjects/Airplanes/C172" --fly --ground --windows-1252 --lod 150

Drag to orbit, scroll to zoom, use arrow keys to rotate, press R to reset and Esc to close. The viewer displays bind-pose geometry with diffuse DDS textures and approximate alpha blending. DXT1/3/5 and masked 32-bit RGB DDS top mips are decoded; texture.cfg fallback directories are searched. Missing textures fall back to diffuse color and are reported. Bounded RPN evaluates model visibility and XAPC animation expressions; static inspection stays read-only, while temporal animation can use instance-local numeric values and scratch registers. Explicit variable inspection also supports XAPS scale/bias bindings. Flight now drives center steering and the native throttle expression, with simulation-clock Lag limits for supported bindings. Control-surface percent mappings, RPM, Standard autoplay and skin deformation remain incomplete. Use --animation N --frame N to inspect authored rotation/translation keys; [ / ] scrub the selected clip. The inspector lists file-local animation IDs. See the viewer guide.

The CFG inspector reads title values from [fltsim.N] under SimObjects/Airplanes. --windows-1252 explicitly selects that code page for every file; omit it for ASCII/UTF-8 installations. Encodings are not guessed. The presence of fsx.exe checks directory structure, not license ownership. Neither tool launches FSX or modifies its installation.

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