Windows: start Direct3D 12 first, and Vulkan only without a D3D12 GPU (#1190)

* Windows: start Direct3D 12 first, and Vulkan only without a D3D12 GPU

wgpu started Vulkan, D3D12 and OpenGL together and preferred Vulkan, so
every Windows start loaded all installed Vulkan drivers. An old Intel
Vulkan driver (igvk64.dll) crashed 0.10.1 at startup inside the driver.

The app now probes D3D12, then Vulkan, then OpenGL, one backend at a
time, and starts only the first with a hardware adapter (WARP when none
has one). WGPU_BACKEND still wins; graphics.json's "backend" sets the
order by hand; the software renderer (safe mode, the retry) uses D3D12
alone. A new Windows CI job starts the real app under several settings.

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

* CI: a test filter YAML parses

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

* CI: the startup smoke test writes graphics.json where the app reads it

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

* CI: run the WARP shader tests one at a time

WARP's shader JIT (d3d10warp.dll) crashed twice in 124 runs of the gpu
tests with four test threads, with a null read inside its own optimizer
while several devices compiled compute pipelines at once. Serial runs
did not crash.

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

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>

apps/solidcraft/Cargo.toml

@@ -29,6 +29,8 @@ log = { workspace = true }
 rfd = { workspace = true }
 # Checks eframe's settings file (app.ron) before eframe reads it (src/startup.rs).
 ron = "0.12"
+# Waits for wgpu's adapter list when choosing the graphics backend before the window opens.
+pollster = { workspace = true }
 getrandom = "0.3"
 # The update check (docs/updates.md): HTTPS with rustls, certificates from the operating system.
 ureq = { version = "3.4", default-features = false, features = ["rustls-no-provider", "platform-verifier"] }
@@ -50,8 +52,5 @@ block2 = "0.6"
 [target.'cfg(all(unix, not(target_os = "macos")))'.dependencies]
 winit = { version = "0.30", default-features = false, features = ["x11"] }
 
-[dev-dependencies]
-pollster = { workspace = true }
-
 [build-dependencies]
 embed-resource = "3.0.11"

apps/solidcraft/src/main.rs

@@ -276,11 +276,19 @@ fn adopt_settings(
     Ok(())
 }
 
+/// `graphics.json`, read before the window opens.
+fn graphics() -> Option<serde_json::Value> {
+    graphics_path().and_then(|p| std::fs::read_to_string(p).ok()).and_then(|s| serde_json::from_str::<serde_json::Value>(&s).ok())
+}
+
+/// The graphics backend preference (`graphics.json`'s `backend`: `auto`, `dx12`, `vulkan`, `gl`).
+fn backend_preference() -> Option<String> {
+    graphics().and_then(|v| v.get("backend").and_then(serde_json::Value::as_str).map(str::to_string))
+}
+
 /// Anti-aliasing samples from Preferences (4 when unset).
 fn msaa() -> u16 {
-    graphics_path()
-        .and_then(|p| std::fs::read_to_string(p).ok())
-        .and_then(|s| serde_json::from_str::<serde_json::Value>(&s).ok())
+    graphics()
         .and_then(|v| v.get("msaa").and_then(serde_json::Value::as_u64))
         .and_then(|m| u16::try_from(m).ok())
         .filter(|m| [1, 2, 4, 8].contains(m))
@@ -399,7 +407,7 @@ fn main() -> eframe::Result {
             settings.as_ref().map(|d| d.join("app.ron"))
         },
         persist_window: !safe_mode,
-        wgpu_options: wgpu_options(cpu_renderer),
+        wgpu_options: wgpu_options(cpu_renderer, if safe_mode { None } else { backend_preference() }.as_deref()),
         ..Default::default()
     };
     #[cfg(all(unix, not(target_os = "macos")))]
@@ -504,11 +512,20 @@ fn main() -> eframe::Result {
     }
 }
 
-/// The renderer settings: with `cpu`, the software adapter (WARP, lavapipe, llvmpipe).
-fn wgpu_options(cpu: bool) -> eframe::egui_wgpu::WgpuConfiguration {
+/// The renderer settings: with `cpu`, the software adapter (WARP, lavapipe, llvmpipe). The
+/// backends come from `startup::choose_backends` (on Windows D3D12 first, and only the backend
+/// in use is started); `preference` is `graphics.json`'s `backend`.
+fn wgpu_options(cpu: bool, preference: Option<&str>) -> eframe::egui_wgpu::WgpuConfiguration {
     let mut options = eframe::egui_wgpu::WgpuConfiguration::default();
-    if cpu && let eframe::egui_wgpu::WgpuSetup::CreateNew(setup) = &mut options.wgpu_setup {
-        setup.native_adapter_selector = Some(std::sync::Arc::new(startup::pick_cpu_adapter));
+    if let eframe::egui_wgpu::WgpuSetup::CreateNew(setup) = &mut options.wgpu_setup {
+        let env_set = std::env::var(startup::WGPU_BACKEND_ENV).is_ok_and(|v| !v.trim().is_empty());
+        if let Some(backends) = startup::choose_backends(cfg!(target_os = "windows"), env_set, cpu, preference, startup::has_hardware_adapter) {
+            eprintln!("SolidCraft graphics: starting {backends:?}");
+            setup.instance_descriptor.backends = backends;
+        }
+        if cpu {
+            setup.native_adapter_selector = Some(std::sync::Arc::new(startup::pick_cpu_adapter));
+        }
     }
     options
 }

apps/solidcraft/src/startup.rs

@@ -110,6 +110,68 @@ pub fn pick_cpu_adapter(adapters: &[eframe::wgpu::Adapter], surface: Option<&efr
         })
 }
 
+/// `WGPU_BACKEND`: when set, wgpu picks the backends from it and the order below is not used.
+pub const WGPU_BACKEND_ENV: &str = "WGPU_BACKEND";
+
+/// The graphics backends to start with, or `None` to leave it to wgpu (`WGPU_BACKEND`, or all
+/// the backends it was built with).
+///
+/// On Windows, D3D12 comes first, then Vulkan, then OpenGL, and only the first one with a
+/// hardware adapter is started at all. wgpu would otherwise start Vulkan, D3D12 and OpenGL
+/// together and prefer Vulkan, and starting Vulkan loads every installed Vulkan driver: Intel's
+/// (`igvk64.dll`) crashed SolidCraft at startup that way, inside the driver, before anything
+/// could be reported. D3D12 is Windows' own graphics API, the one its drivers are tested with.
+/// `has_hardware(backends)` says whether those backends have an adapter that isn't software
+/// (it is only asked about the backends being tried, one at a time).
+///
+/// - `WGPU_BACKEND` set (`env_set`): `None`, whatever it says wins.
+/// - The software renderer (`cpu`, safe mode): D3D12 alone on Windows (WARP); `None` elsewhere.
+/// - `preference` (`graphics.json`'s `backend`: `dx12`, `vulkan`, `gl` or a comma list; `auto`
+///   or empty for the order above): those backends, on any system.
+/// - Elsewhere than Windows: `None`.
+/// - No hardware adapter at all: D3D12 (WARP, Windows' software renderer).
+pub fn choose_backends(
+    windows: bool,
+    env_set: bool,
+    cpu: bool,
+    preference: Option<&str>,
+    mut has_hardware: impl FnMut(eframe::wgpu::Backends) -> bool,
+) -> Option<eframe::wgpu::Backends> {
+    use eframe::wgpu::Backends;
+    if env_set {
+        return None;
+    }
+    if cpu {
+        return windows.then_some(Backends::DX12);
+    }
+    if let Some(p) = preference.map(str::trim).filter(|p| !p.is_empty() && !p.eq_ignore_ascii_case("auto")) {
+        let chosen = Backends::from_comma_list(p);
+        if !chosen.is_empty() {
+            return Some(chosen);
+        }
+        log::warn!("graphics: unknown backend preference `{p}`; using the default order");
+    }
+    if !windows {
+        return None;
+    }
+    Some(WINDOWS_ORDER.into_iter().find(|b| has_hardware(*b)).unwrap_or(Backends::DX12))
+}
+
+/// The order backends are tried in on Windows.
+pub const WINDOWS_ORDER: [eframe::wgpu::Backends; 3] = [eframe::wgpu::Backends::DX12, eframe::wgpu::Backends::VULKAN, eframe::wgpu::Backends::GL];
+
+/// Whether `backends` (started on their own, nothing else) have a hardware adapter.
+pub fn has_hardware_adapter(backends: eframe::wgpu::Backends) -> bool {
+    let mut desc = eframe::wgpu::InstanceDescriptor::new_without_display_handle();
+    desc.backends = backends;
+    desc.flags = eframe::wgpu::InstanceFlags::from_build_config().with_env();
+    let instance = eframe::wgpu::Instance::new(desc);
+    let adapters = pollster::block_on(instance.enumerate_adapters(backends));
+    let found: Vec<String> = adapters.iter().map(|a| format!("{} ({:?})", a.get_info().name, a.get_info().device_type)).collect();
+    log::info!("graphics: {backends:?} adapters: {found:?}");
+    adapters.iter().any(|a| a.get_info().device_type != eframe::wgpu::DeviceType::Cpu)
+}
+
 /// The message shown when no window could be opened at all.
 pub fn no_window_message(error: &str, settings: Option<&Path>) -> String {
     let folder = settings.map(|d| d.display().to_string()).unwrap_or_else(|| "the SolidCraft settings folder".into());
@@ -182,6 +244,65 @@ mod tests {
         let _ = std::fs::remove_dir_all(&d);
     }
 
+    #[test]
+    fn windows_starts_d3d12_first_and_vulkan_only_when_d3d12_has_no_gpu() {
+        use eframe::wgpu::Backends;
+        let probe = |with: &'static [Backends]| {
+            move |b: Backends| {
+                assert!(b == Backends::DX12 || b == Backends::VULKAN || b == Backends::GL, "one backend at a time: {b:?}");
+                with.contains(&b)
+            }
+        };
+        // D3D12 works: Vulkan and OpenGL are never even asked about (starting Vulkan loads
+        // its drivers, which is what crashed).
+        let mut asked = Vec::new();
+        let chosen = choose_backends(true, false, false, None, |b| {
+            asked.push(b);
+            b == Backends::DX12
+        });
+        assert_eq!(chosen, Some(Backends::DX12));
+        assert_eq!(asked, [Backends::DX12]);
+        // Everything works: still D3D12 alone.
+        assert_eq!(choose_backends(true, false, false, None, probe(&[Backends::DX12, Backends::VULKAN, Backends::GL])), Some(Backends::DX12));
+        // No D3D12 hardware adapter: Vulkan, else OpenGL, else D3D12's software adapter (WARP).
+        assert_eq!(choose_backends(true, false, false, None, probe(&[Backends::VULKAN, Backends::GL])), Some(Backends::VULKAN));
+        assert_eq!(choose_backends(true, false, false, None, probe(&[Backends::GL])), Some(Backends::GL));
+        assert_eq!(choose_backends(true, false, false, None, probe(&[])), Some(Backends::DX12));
+        // `auto` and blanks are the default order.
+        assert_eq!(choose_backends(true, false, false, Some(" auto "), probe(&[Backends::DX12])), Some(Backends::DX12));
+        assert_eq!(choose_backends(true, false, false, Some(""), probe(&[Backends::GL])), Some(Backends::GL));
+    }
+
+    #[test]
+    fn wgpu_backend_the_preference_and_the_software_renderer_override_the_order() {
+        use eframe::wgpu::Backends;
+        let never = |b: Backends| -> bool { panic!("no probing expected, asked about {b:?}") };
+        // WGPU_BACKEND: wgpu reads it itself, nothing is probed.
+        assert_eq!(choose_backends(true, true, false, Some("gl"), never), None);
+        assert_eq!(choose_backends(true, true, true, None, never), None);
+        // The software renderer (safe mode, the retry): WARP through D3D12 alone, never Vulkan.
+        assert_eq!(choose_backends(true, false, true, Some("vulkan"), never), Some(Backends::DX12));
+        assert_eq!(choose_backends(false, false, true, None, never), None);
+        // The preference, on any system, without probing.
+        assert_eq!(choose_backends(true, false, false, Some("vulkan"), never), Some(Backends::VULKAN));
+        assert_eq!(choose_backends(true, false, false, Some("GL"), never), Some(Backends::GL));
+        assert_eq!(choose_backends(true, false, false, Some("dx12,vulkan"), never), Some(Backends::DX12 | Backends::VULKAN));
+        assert_eq!(choose_backends(false, false, false, Some("vulkan"), never), Some(Backends::VULKAN));
+        // An unknown preference is the default order.
+        assert_eq!(choose_backends(true, false, false, Some("glide"), |b| b == Backends::DX12), Some(Backends::DX12));
+        // Elsewhere: wgpu's own choice.
+        assert_eq!(choose_backends(false, false, false, None, never), None);
+        assert_eq!(choose_backends(false, false, false, Some("auto"), never), None);
+    }
+
+    #[test]
+    fn probing_a_backend_alone_never_panics() {
+        // Whatever this machine has (often nothing): an answer, not a crash.
+        for b in WINDOWS_ORDER {
+            let _ = has_hardware_adapter(b);
+        }
+    }
+
     #[test]
     fn the_message_names_the_settings_folder_and_safe_mode() {
         let m = no_window_message("no adapter", Some(Path::new("/x/SolidCraft")));