Merge origin/main into profile-gain-table-map (RENDER_CACHE_VERSION: main's 21 + 1 = 22)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/gpu/src/backend.rs

@@ -121,6 +121,30 @@ pub fn window_backends() -> Backends {
     resolve(choice, default, wgpu::Instance::enabled_backend_features()).unwrap_or(default)
 }
 
+/// The DX12 shader compiler: FXC (`d3dcompiler_47.dll`, part of Windows) unless
+/// `WGPU_DX12_COMPILER` (`wgpu`, wgpu's own variable: `fxc`, `dxc`, `auto`…) names another.
+///
+/// Issue #471: wgpu's default (`Auto`) loads whichever `dxcompiler.dll` the DLL search path finds
+/// first — LightCraft ships none, so it is some other program's (an SDK's, a folder on `PATH`). A
+/// copy without its `dxil.dll` beside it warns that the DXIL is unsigned; wgpu takes the warning for
+/// a compile error, its own validation pipelines fail, the device is lost and the window never
+/// opens. FXC is always there and compiles everything LightCraft's shaders need.
+pub fn dx12_compiler(env: Option<&str>) -> wgpu::Dx12Compiler {
+    let Some(v) = env else { return wgpu::Dx12Compiler::Fxc };
+    v.parse().unwrap_or_else(|e| {
+        log::warn!("gpu: WGPU_DX12_COMPILER={v} ignored: {e}");
+        wgpu::Dx12Compiler::Fxc
+    })
+}
+
+/// wgpu's backend options for every instance LightCraft creates — the window's and the compute
+/// devices': wgpu's environment variables, with the DX12 compiler from [`dx12_compiler`].
+pub fn backend_options() -> wgpu::BackendOptions {
+    let mut o = wgpu::BackendOptions::from_env_or_default();
+    o.dx12.shader_compiler = dx12_compiler(std::env::var("WGPU_DX12_COMPILER").ok().as_deref());
+    o
+}
+
 /// `LIGHTCRAFT_GPU_BACKEND=off`.
 pub(crate) fn env_off() -> bool {
     env_choice() == BackendChoice::Off
@@ -211,6 +235,20 @@ mod tests {
         assert!(default_window_backends("linux").contains(Backends::VULKAN | Backends::GL));
     }
 
+    /// Issue #471: DX12 shaders compile with FXC, never a `dxcompiler.dll` found on the search path,
+    /// unless `WGPU_DX12_COMPILER` asks for it.
+    #[test]
+    fn dx12_compiles_with_fxc_unless_asked() {
+        assert!(matches!(dx12_compiler(None), wgpu::Dx12Compiler::Fxc));
+        assert!(matches!(dx12_compiler(Some("bogus")), wgpu::Dx12Compiler::Fxc));
+        assert!(matches!(dx12_compiler(Some("FXC")), wgpu::Dx12Compiler::Fxc));
+        assert!(matches!(dx12_compiler(Some("dxc")), wgpu::Dx12Compiler::DynamicDxc { .. }));
+        assert!(matches!(dx12_compiler(Some("auto")), wgpu::Dx12Compiler::Auto));
+        if std::env::var_os("WGPU_DX12_COMPILER").is_none() {
+            assert!(matches!(backend_options().dx12.shader_compiler, wgpu::Dx12Compiler::Fxc));
+        }
+    }
+
     #[test]
     fn resolves_against_the_build() {
         let compiled = Backends::DX12 | Backends::VULKAN;

crates/gpu/src/ctx.rs

@@ -282,6 +282,8 @@ impl Gpu {
         let mut desc = wgpu::InstanceDescriptor::new_without_display_handle();
         // only these drivers are loaded (`crate::backend`: never Vulkan on Windows unless asked)
         desc.backends = backends;
+        // DX12 shaders compile with FXC (issue #471)
+        desc.backend_options = crate::backend::backend_options();
         let instance = wgpu::Instance::new(desc);
         let adapter = pollster::block_on(
             instance.request_adapter(&wgpu::RequestAdapterOptions { power_preference: wgpu::PowerPreference::HighPerformance, ..Default::default() }),

crates/gpu/src/nn.rs

@@ -76,6 +76,8 @@ fn create_device() -> Result<Dev, String> {
 fn make_device(backends: wgpu::Backends) -> Result<Dev, String> {
     let mut desc = wgpu::InstanceDescriptor::new_without_display_handle();
     desc.backends = backends;
+    // DX12 shaders compile with FXC (issue #471)
+    desc.backend_options = crate::backend::backend_options();
     let instance = wgpu::Instance::new(desc);
     let wanted = std::env::var("LIGHTCRAFT_GPU_ADAPTER").ok().map(|s| s.trim().to_lowercase()).filter(|s| !s.is_empty());
     let adapter = match &wanted {