Merge pull request #851 from rschuerer/fix/windows-display-gpu

Fix #849: draw on the GPU that drives the primary display

Cargo.lock

@@ -4344,6 +4344,7 @@ dependencies = [
  "windows",
  "winit",
  "winresource",
+ "winsafe",
 ]
 
 [[package]]
@@ -5744,6 +5745,12 @@ dependencies = [
  "version_check",
 ]
 
+[[package]]
+name = "winsafe"
+version = "0.0.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ef0ffc427f045c0cc9ebffd6f4f91153dcd2a1547b5c3c29ee3f541e16e95c6"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.57.1"

apps/vectorcraft/Cargo.toml

@@ -11,7 +11,7 @@ workspace = true
 
 [features]
 default = ["wgpu", "accessibility"]
-wgpu = ["eframe/wgpu"]
+wgpu = ["eframe/wgpu", "dep:winsafe"]
 accessibility = ["eframe/accesskit"]
 # Build with --no-default-features --features windows7 and the win7 Rust target.
 windows7 = ["eframe/glow"]
@@ -36,6 +36,10 @@ winit = { version = "0.30", default-features = false }
 
 [target.'cfg(windows)'.dependencies]
 clipboard-win = { workspace = true }
+# Which GPU drives which display (EnumDisplayDevices, src/gpu.rs), so the window is drawn on the
+# GPU that shows it: drawing on a GPU without a monitor reset the display driver. Safe wrappers over
+# Win32 (MIT); the `user` feature is User32.dll only. Only the wgpu renderer chooses an adapter.
+winsafe = { version = "0.0.29", default-features = false, features = ["user"], optional = true }
 
 # DirectWrite's system font collection (src/system_fonts.rs): fonts that font services such as
 # Adobe Fonts load in place (#579). MIT OR Apache-2.0, already in the build through accesskit.

apps/vectorcraft/src/gpu.rs

@@ -4,10 +4,21 @@
 //! The canvas is rasterized on the CPU; the GPU only composites it and draws the UI, so any
 //! adapter that can present to the window will do. [`adapter_order`] ranks the adapters: those that
 //! can't present to the window's surface never, then the one `WGPU_ADAPTER_NAME` names, hardware
-//! before software, the native backends (Vulkan, Metal, DX12) before OpenGL, the power preference
+//! before software, the native backends (Vulkan, Metal, DX12) before OpenGL, the GPU that drives a
+//! display and the one that drives the primary display ([`display_gpus`]), the power preference
 //! ([`power_preference`]) among the rest, and a GPU's DX12 adapter before its Vulkan one (#545).
 //! eframe is handed [`selector`], which takes the first of that order.
 //!
+//! A GPU without a monitor is the wrong one even when it can present: on a desktop whose monitors
+//! all hang off the discrete GPU, power saving picked the Ryzen's integrated GPU, Windows had to
+//! present every frame across adapters, and the integrated GPU's driver reset under that, which
+//! lost the graphics device, or took the desktop's compositor and every monitor down for minutes
+//! (pdfcraft#378). So, when Preferences say Automatic, the GPU that drives the display the user
+//! looks at comes first, and the power preference only orders the rest. Windows says which adapter
+//! drives which display (`EnumDisplayDevices`), Linux through sysfs; elsewhere, or when nothing
+//! matches, the order is the power preference's as before. Power Saving and High Performance,
+//! chosen by the user, order by kind as they always did.
+//!
 //! An adapter can report that it presents to the window and still fail once it does: on a hybrid
 //! Linux desktop under Wayland, the compositor runs on one GPU and may refuse the frame buffers
 //! another GPU allocates, which kills the window's Wayland connection; egui-wgpu then panics while
@@ -58,6 +69,18 @@ pub fn power_preference(pref: Option<&str>, env: Option<PowerPreference>) -> Pow
     }
 }
 
+/// Whether the adapter is the app's to choose: neither `WGPU_POWER_PREF` nor Preferences name a
+/// kind of GPU (the arguments of [`power_preference`]). Then the GPU that drives the display comes
+/// first ([`display_gpus`]); a user's own choice is kept as it is.
+pub fn automatic(pref: Option<&str>, env: Option<PowerPreference>) -> bool {
+    env.is_none() && !matches!(pref, Some("highPerformance" | "lowPower"))
+}
+
+/// The GPUs to rank first: those that drive a display, when the choice is [`automatic`].
+pub fn preferred_displays(pref: Option<&str>, env: Option<PowerPreference>) -> Vec<DisplayGpu> {
+    if automatic(pref, env) { display_gpus() } else { Vec::new() }
+}
+
 /// One adapter, as [`adapter_order`] sees it.
 #[derive(Clone, Debug)]
 pub struct Candidate {
@@ -66,6 +89,9 @@ pub struct Candidate {
     pub name: String,
     pub backend: Backend,
     pub device_type: DeviceType,
+    /// PCI vendor and device ids, to match a [`DisplayGpu`]; zero where the backend reports none
+    /// (Metal, and OpenGL's device id).
+    pub pci: (u32, u32),
     /// Reports that it can present to the window's surface.
     pub presents: bool,
 }
@@ -79,8 +105,128 @@ impl Candidate {
             name: info.name,
             backend: info.backend,
             device_type: info.device_type,
+            pci: (info.vendor, info.device),
         }
     }
+
+    /// Whether it drives one of `displays`, and whether that is the primary one.
+    fn drives(&self, displays: &[DisplayGpu]) -> (bool, bool) {
+        let shown = displays.iter().find(|g| g.pci == self.pci);
+        (shown.is_some(), shown.is_some_and(|g| g.primary))
+    }
+}
+
+/// A GPU with a monitor attached, as the system reports it ([`display_gpus`]).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct DisplayGpu {
+    /// PCI `(vendor, device)` ids, as wgpu's `AdapterInfo` reports them.
+    pub pci: (u32, u32),
+    /// Drives the display the user most likely looks at: on Windows the primary display, on Linux
+    /// a built-in panel (`eDP`, `LVDS` or `DSI`).
+    pub primary: bool,
+}
+
+impl std::fmt::Display for DisplayGpu {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:04x}:{:04x}{}", self.pci.0, self.pci.1, if self.primary { " (primary)" } else { "" })
+    }
+}
+
+/// The GPUs that drive a display, each once. Windows enumerates its display devices
+/// (`EnumDisplayDevices`: those attached to the desktop, and the primary one); Linux reads the
+/// connected connectors in `/sys/class/drm`. macOS and the rest report nothing, so the power
+/// preference decides as before; so does a system whose GPUs report no PCI ids.
+pub fn display_gpus() -> Vec<DisplayGpu> {
+    #[cfg(windows)]
+    {
+        windows_display_gpus()
+    }
+    #[cfg(target_os = "linux")]
+    {
+        linux_display_gpus(std::path::Path::new("/sys/class/drm"))
+    }
+    #[cfg(not(any(windows, target_os = "linux")))]
+    {
+        Vec::new()
+    }
+}
+
+/// Record that the GPU `pci` drives a display, merging it with its other displays.
+fn add_display_gpu(gpus: &mut Vec<DisplayGpu>, pci: (u32, u32), primary: bool) {
+    match gpus.iter_mut().find(|g| g.pci == pci) {
+        Some(gpu) => gpu.primary |= primary,
+        None => gpus.push(DisplayGpu { pci, primary }),
+    }
+}
+
+/// Windows' display devices: one per GPU output; those `ATTACHED_TO_DESKTOP` show a monitor, one
+/// of them the `PRIMARY_DEVICE`. The registry doesn't tell a user which adapter drives a display,
+/// and WMI reports a resolution for a GPU without a monitor, so this is the way.
+#[cfg(windows)]
+fn windows_display_gpus() -> Vec<DisplayGpu> {
+    use winsafe::co::DISPLAY_DEVICE as Flags;
+    let mut gpus = Vec::new();
+    // A machine has a handful of display devices; the cap only bounds a runaway enumeration.
+    for device in winsafe::EnumDisplayDevices(None, None).take(256) {
+        let device = match device {
+            Ok(d) => d,
+            // The enumeration ends with "no more items" or, from a driver, with any other error.
+            Err(e) => {
+                log::debug!("display devices: {e}");
+                break;
+            }
+        };
+        if !device.StateFlags.has(Flags::ATTACHED_TO_DESKTOP) {
+            continue;
+        }
+        // Remote Desktop and other non-PCI devices (`ROOT\BasicDisplay\0000`) are left out.
+        let Some(pci) = pci_ids(&device.DeviceID()) else { continue };
+        add_display_gpu(&mut gpus, pci, device.StateFlags.has(Flags::PRIMARY_DEVICE));
+    }
+    gpus
+}
+
+/// The PCI `(vendor, device)` of a Windows device id such as
+/// `PCI\VEN_10DE&DEV_2204&SUBSYS_40421458&REV_A1`, any case; `None` for anything else.
+fn pci_ids(device_id: &str) -> Option<(u32, u32)> {
+    let field = |key: &str| {
+        device_id.split(['\\', '&']).find_map(|part| {
+            let (name, hex) = part.split_at_checked(key.len())?;
+            if name.eq_ignore_ascii_case(key) { u32::from_str_radix(hex, 16).ok() } else { None }
+        })
+    };
+    Some((field("VEN_")?, field("DEV_")?))
+}
+
+/// Linux: every connector `cardN-CONNECTOR` under `drm` whose `status` is `connected`, with the
+/// PCI ids of its card (`cardN/device/{vendor,device}`). A built-in panel is the primary display.
+#[cfg(any(target_os = "linux", test))]
+fn linux_display_gpus(drm: &std::path::Path) -> Vec<DisplayGpu> {
+    let read_hex = |p: std::path::PathBuf| -> Option<u32> {
+        let s = std::fs::read_to_string(p).ok()?;
+        u32::from_str_radix(s.trim().trim_start_matches("0x"), 16).ok()
+    };
+    let mut gpus = Vec::new();
+    let Ok(entries) = std::fs::read_dir(drm) else { return gpus };
+    // A machine has a handful of connectors; the cap only bounds a pathological sysfs.
+    for entry in entries.flatten().take(256) {
+        let name = entry.file_name();
+        let Some((card, connector)) = name.to_str().and_then(|n| n.split_once('-')) else { continue };
+        let connected = std::fs::read_to_string(entry.path().join("status")).is_ok_and(|s| s.trim() == "connected");
+        if !connected {
+            continue;
+        }
+        let device = drm.join(card).join("device");
+        let (Some(v), Some(d)) = (read_hex(device.join("vendor")), read_hex(device.join("device"))) else { continue };
+        add_display_gpu(&mut gpus, (v, d), is_internal_panel(connector));
+    }
+    gpus
+}
+
+/// A laptop's built-in panel: an embedded DisplayPort, LVDS or DSI connector.
+#[cfg(any(target_os = "linux", test))]
+fn is_internal_panel(connector: &str) -> bool {
+    ["eDP", "LVDS", "DSI"].iter().any(|kind| connector.starts_with(kind))
 }
 
 /// `backend:vendor:device`, e.g. `Vulkan:1002:164e` (PCI ids, as `MESA_VK_DEVICE_SELECT` takes them).
@@ -97,17 +243,30 @@ fn key(backend: Backend, vendor: u32, device: u32, name: &str) -> String {
 
 /// The order to try `candidates` in (their indices): only those that present to the window and
 /// aren't in `skip`; the one whose name contains `named` (any case) first; hardware before
-/// software; native backends before OpenGL; then by `power`; then DX12 before Vulkan, keeping the
-/// system's order among equals (all of it for [`PowerPreference::None`]). Windows lists each GPU
-/// under both, and Intel's Vulkan driver made the whole window flicker black where DX12 and OpenGL
-/// didn't (#545); elsewhere there is no DX12 adapter, so the order is unchanged.
-pub fn adapter_order(candidates: &[Candidate], power: PowerPreference, named: Option<&str>, skip: &[String]) -> Vec<usize> {
+/// software; native backends before OpenGL; the GPUs that drive one of `displays`, the primary
+/// display's first; then by `power`; then DX12 before Vulkan, keeping the system's order among
+/// equals (all of it for [`PowerPreference::None`]). Windows lists each GPU under both, and Intel's
+/// Vulkan driver made the whole window flicker black where DX12 and OpenGL didn't (#545);
+/// elsewhere there is no DX12 adapter, so the order is unchanged.
+///
+/// With no `displays`, or none a candidate's PCI ids match (OpenGL reports no device id, Metal no
+/// ids at all), the order is the power preference's alone, as it was.
+pub fn adapter_order(candidates: &[Candidate], power: PowerPreference, displays: &[DisplayGpu], named: Option<&str>, skip: &[String]) -> Vec<usize> {
     let named = named.map(str::to_lowercase).filter(|n| !n.is_empty());
     let mut order: Vec<(usize, &Candidate)> = candidates.iter().enumerate().filter(|(_, c)| c.presents && !skip.contains(&c.key)).collect();
     // Stable, so equals keep the system's order.
     order.sort_by_key(|(_, c)| {
         let unnamed = named.as_ref().is_some_and(|n| !c.name.to_lowercase().contains(n));
-        (unnamed, c.device_type == DeviceType::Cpu, c.backend == Backend::Gl, power_rank(c.device_type, power), c.backend == Backend::Vulkan)
+        let (drives_display, drives_primary) = c.drives(displays);
+        (
+            unnamed,
+            c.device_type == DeviceType::Cpu,
+            c.backend == Backend::Gl,
+            !drives_display,
+            !drives_primary,
+            power_rank(c.device_type, power),
+            c.backend == Backend::Vulkan,
+        )
     });
     order.into_iter().map(|(i, _)| i).collect()
 }
@@ -151,21 +310,27 @@ impl Startup {
     }
 }
 
-/// eframe's adapter choice: the first of [`adapter_order`] for `power`, `WGPU_ADAPTER_NAME` and the
-/// adapters a restart left out. Every adapter and the choice are logged, for bug reports.
-pub fn selector(power: PowerPreference, startup: Arc<Startup>) -> NativeAdapterSelectorMethod {
+/// eframe's adapter choice: the first of [`adapter_order`] for `power`, the GPUs that drive a
+/// `displays`, `WGPU_ADAPTER_NAME` and the adapters a restart left out. Every adapter, the displays
+/// and the choice are logged: which GPU draws is the first question in every black-window report.
+pub fn selector(power: PowerPreference, displays: Vec<DisplayGpu>, startup: Arc<Startup>) -> NativeAdapterSelectorMethod {
     let named = std::env::var(NAME_ENV).ok();
     let skip = skipped();
     Arc::new(move |adapters, surface| {
         let candidates: Vec<Candidate> = adapters.iter().map(|a| Candidate::new(a, surface)).collect();
-        let order = adapter_order(&candidates, power, named.as_deref(), &skip);
+        let order = adapter_order(&candidates, power, &displays, named.as_deref(), &skip);
         let listed: Vec<String> = candidates
             .iter()
             .map(|c| {
+                let (drives_display, drives_primary) = c.drives(&displays);
                 let note = if !c.presents {
                     ", can't show the window"
                 } else if skip.contains(&c.key) {
                     ", failed before"
+                } else if drives_primary {
+                    ", drives the primary display"
+                } else if drives_display {
+                    ", drives a display"
                 } else {
                     ""
                 };
@@ -177,6 +342,13 @@ pub fn selector(power: PowerPreference, startup: Arc<Startup>) -> NativeAdapterS
         let Some((adapter, chosen)) = first else {
             return Err(format!("no graphics adapter can show the window (power preference {power:?}, {} adapters)", adapters.len()));
         };
+        let why = match chosen.drives(&displays) {
+            (_, true) => "it drives the primary display".to_string(),
+            (true, false) => "it drives a display".to_string(),
+            (false, false) if displays.is_empty() => format!("power preference {power:?}"),
+            (false, false) => format!("no adapter matches a display GPU, so power preference {power:?}"),
+        };
+        log::info!("drawing on {} ({:?}, {:?}): {why}", chosen.name.trim(), chosen.backend, chosen.device_type);
         // Set once; eframe picks the adapter once.
         let _ = startup.adapter.set(chosen.key.clone());
         Ok(adapter.clone())
@@ -248,13 +420,222 @@ mod tests {
     use super::*;
 
     fn gpu(name: &str, backend: Backend, device_type: DeviceType) -> Candidate {
-        Candidate { key: format!("{backend:?}:{name}"), name: name.into(), backend, device_type, presents: true }
+        Candidate { key: format!("{backend:?}:{name}"), name: name.into(), backend, device_type, pci: (0, 0), presents: true }
     }
 
     fn names(c: &[Candidate], order: &[usize]) -> Vec<String> {
         order.iter().map(|&i| c[i].name.clone()).collect()
     }
 
+    const NVIDIA_3090: (u32, u32) = (0x10de, 0x2204);
+    const AMD_IGPU: (u32, u32) = (0x1002, 0x164e);
+    const INTEL_IGPU: (u32, u32) = (0x8086, 0xa780);
+    const WARP: (u32, u32) = (0x1414, 0x008c);
+
+    fn pci_gpu(name: &str, backend: Backend, device_type: DeviceType, pci: (u32, u32)) -> Candidate {
+        Candidate { key: key(backend, pci.0, pci.1, name), name: name.into(), backend, device_type, pci, presents: true }
+    }
+
+    fn monitor(pci: (u32, u32)) -> DisplayGpu {
+        DisplayGpu { pci, primary: false }
+    }
+
+    fn primary(pci: (u32, u32)) -> DisplayGpu {
+        DisplayGpu { pci, primary: true }
+    }
+
+    /// The desktop of pdfcraft#378 as wgpu lists it on Windows: a Ryzen's integrated GPU without a
+    /// monitor and an RTX 3090 driving both monitors, each under Vulkan and DX12, then WARP and
+    /// OpenGL (which reports no device id).
+    fn ryzen_desktop() -> Vec<Candidate> {
+        vec![
+            pci_gpu("NVIDIA GeForce RTX 3090", Backend::Vulkan, DeviceType::DiscreteGpu, NVIDIA_3090),
+            pci_gpu("AMD Radeon(TM) Graphics", Backend::Vulkan, DeviceType::IntegratedGpu, AMD_IGPU),
+            pci_gpu("NVIDIA GeForce RTX 3090", Backend::Dx12, DeviceType::DiscreteGpu, NVIDIA_3090),
+            pci_gpu("AMD Radeon(TM) Graphics", Backend::Dx12, DeviceType::IntegratedGpu, AMD_IGPU),
+            pci_gpu("Microsoft Basic Render Driver", Backend::Dx12, DeviceType::Cpu, WARP),
+            pci_gpu("NVIDIA GeForce RTX 3090/PCIe/SSE2", Backend::Gl, DeviceType::Other, (NVIDIA_3090.0, 0)),
+        ]
+    }
+
+    /// pdfcraft#378: power saving picked the integrated GPU, whose driver reset when Windows had to
+    /// present its frames on the monitors of the NVIDIA card. The GPU that drives the displays now
+    /// comes first, through DX12 (#545); the integrated GPU stays the fallback a restart reaches.
+    #[test]
+    fn a_desktop_draws_on_the_gpu_that_drives_its_monitors() {
+        let c = ryzen_desktop();
+        for displays in [vec![primary(NVIDIA_3090)], vec![monitor(NVIDIA_3090)]] {
+            assert_eq!(adapter_order(&c, PowerPreference::LowPower, &displays, None, &[]), [2, 0, 3, 1, 5, 4], "{displays:?}");
+            assert_eq!(adapter_order(&c, PowerPreference::None, &displays, None, &[]), [2, 0, 3, 1, 5, 4], "{displays:?}");
+        }
+        // Without the display information the order is power saving's, as before.
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[], None, &[]), [3, 1, 2, 0, 5, 4]);
+        // After the NVIDIA adapters failed, the integrated GPU is next.
+        let skip = vec![c[2].key.clone(), c[0].key.clone()];
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[primary(NVIDIA_3090)], None, &skip), [3, 1, 5, 4]);
+    }
+
+    /// A hybrid laptop: the panel (primary) on the integrated GPU, an external monitor on the
+    /// discrete one. Power saving and the display agree, in either enumeration order.
+    #[test]
+    fn a_hybrid_laptop_draws_on_the_integrated_gpu_that_drives_its_panel() {
+        let c = ryzen_desktop();
+        for displays in [vec![primary(AMD_IGPU), monitor(NVIDIA_3090)], vec![monitor(NVIDIA_3090), primary(AMD_IGPU)], vec![primary(AMD_IGPU)]] {
+            assert_eq!(adapter_order(&c, PowerPreference::LowPower, &displays, None, &[]), [3, 1, 2, 0, 5, 4], "{displays:?}");
+        }
+        // Linux names no primary unless there is a built-in panel: a monitor on each GPU keeps the
+        // system's order among them (Mesa puts the compositor's GPU first), and a GPU without one
+        // comes after both.
+        let linux = vec![
+            pci_gpu("AMD Radeon Graphics (RADV RAPHAEL_MENDOCINO)", Backend::Vulkan, DeviceType::IntegratedGpu, AMD_IGPU),
+            pci_gpu("NVIDIA GeForce RTX 3090", Backend::Vulkan, DeviceType::DiscreteGpu, NVIDIA_3090),
+            pci_gpu("Intel(R) Arc(TM) A380", Backend::Vulkan, DeviceType::DiscreteGpu, INTEL_IGPU),
+            pci_gpu("llvmpipe (LLVM 20.1.8, 256 bits)", Backend::Vulkan, DeviceType::Cpu, (0x10005, 0)),
+        ];
+        let both = [monitor(AMD_IGPU), monitor(NVIDIA_3090)];
+        assert_eq!(adapter_order(&linux, PowerPreference::None, &both, None, &[]), [0, 1, 2, 3]);
+        assert_eq!(adapter_order(&linux, PowerPreference::None, &[monitor(INTEL_IGPU)], None, &[]), [2, 0, 1, 3]);
+        assert_eq!(adapter_order(&linux, PowerPreference::None, &[monitor(NVIDIA_3090), primary(AMD_IGPU)], None, &[]), [0, 1, 2, 3]);
+    }
+
+    /// A Windows desktop with a monitor on each GPU: the window opens on the primary display, so
+    /// its GPU draws, whichever kind it is.
+    #[test]
+    fn the_primary_display_decides_between_gpus_that_both_drive_a_monitor() {
+        let c = ryzen_desktop();
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[monitor(AMD_IGPU), primary(NVIDIA_3090)], None, &[]), [2, 0, 3, 1, 5, 4]);
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[primary(AMD_IGPU), monitor(NVIDIA_3090)], None, &[]), [3, 1, 2, 0, 5, 4]);
+        // The displays only matter among adapters that can show the window; a GPU driving no
+        // display still loses to one that does.
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[monitor(AMD_IGPU), monitor(INTEL_IGPU)], None, &[]), [3, 1, 2, 0, 5, 4]);
+    }
+
+    /// Display GPUs none of the adapters match (another driver's ids, OpenGL's missing device id,
+    /// Metal's zeros) change nothing: power saving's order, the old behaviour.
+    #[test]
+    fn displays_no_adapter_matches_leave_the_power_preference_in_charge() {
+        let c = ryzen_desktop();
+        let low = adapter_order(&c, PowerPreference::LowPower, &[], None, &[]);
+        for displays in [vec![monitor(INTEL_IGPU)], vec![primary((0x8086, 0x1234)), monitor((0x8086, 0x5678))], vec![primary((0, 0))]] {
+            assert_eq!(adapter_order(&c, PowerPreference::LowPower, &displays, None, &[]), low, "{displays:?}");
+        }
+        assert_eq!(names(&c, &adapter_order(&c, PowerPreference::HighPerformance, &[monitor(INTEL_IGPU)], None, &[]))[0], "NVIDIA GeForce RTX 3090");
+        // The #502 machine's adapters report no ids in these tests: the primary display never matches.
+        let c = issue_502();
+        assert_eq!(
+            adapter_order(&c, PowerPreference::None, &[primary(NVIDIA_3090)], None, &[]),
+            adapter_order(&c, PowerPreference::None, &[], None, &[])
+        );
+        assert!(adapter_order(&[], PowerPreference::LowPower, &[primary(NVIDIA_3090)], None, &[]).is_empty());
+    }
+
+    /// `WGPU_ADAPTER_NAME` and "can't present" still come before the displays.
+    #[test]
+    fn a_named_adapter_comes_before_the_one_driving_the_display() {
+        let mut c = ryzen_desktop();
+        let displays = [primary(NVIDIA_3090)];
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &displays, Some("radeon"), &[]), [3, 1, 2, 0, 5, 4]);
+        c[2].presents = false;
+        c[0].presents = false;
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &displays, None, &[]), [3, 1, 5, 4]);
+    }
+
+    /// A user's own choice (Preferences or `WGPU_POWER_PREF`) is kept as it is; only Automatic
+    /// looks at the displays.
+    #[test]
+    fn only_automatic_considers_which_gpu_drives_the_display() {
+        assert!(automatic(None, None));
+        assert!(automatic(Some("automatic"), None));
+        assert!(automatic(Some("powerSaving"), None));
+        assert!(!automatic(Some("lowPower"), None));
+        assert!(!automatic(Some("highPerformance"), None));
+        assert!(!automatic(None, Some(PowerPreference::None)));
+        assert!(!automatic(Some("automatic"), Some(PowerPreference::LowPower)));
+        assert!(preferred_displays(Some("lowPower"), None).is_empty());
+        assert!(preferred_displays(None, Some(PowerPreference::HighPerformance)).is_empty());
+        // Automatic reports whatever this machine has (nothing on macOS, in CI, or under Remote Desktop).
+        assert_eq!(preferred_displays(None, None), display_gpus());
+    }
+
+    #[test]
+    fn pci_ids_come_from_windows_device_ids() {
+        assert_eq!(pci_ids("PCI\\VEN_10DE&DEV_2204&SUBSYS_40421458&REV_A1"), Some(NVIDIA_3090));
+        assert_eq!(pci_ids("PCI\\VEN_1002&DEV_164E&SUBSYS_88771043&REV_C1"), Some(AMD_IGPU));
+        assert_eq!(pci_ids("pci\\ven_1002&dev_164e"), Some(AMD_IGPU));
+        // Remote Desktop and other non-PCI display devices, and malformed ids.
+        assert_eq!(pci_ids("ROOT\\BasicDisplay\\0000"), None);
+        assert_eq!(pci_ids("PCI\\VEN_10DE&SUBSYS_40421458"), None);
+        assert_eq!(pci_ids("PCI\\VEN_10DE&DEV_ZZZZ"), None);
+        assert_eq!(pci_ids("VEN_&DEV_"), None);
+        assert_eq!(pci_ids(""), None);
+    }
+
+    /// Whatever this machine has: every GPU listed is a PCI device, at most one drives the primary
+    /// display, and none is listed twice. (A headless CI runner may list none.)
+    #[cfg(windows)]
+    #[test]
+    fn windows_lists_each_gpu_with_a_monitor_once() {
+        let gpus = windows_display_gpus();
+        assert!(gpus.iter().filter(|g| g.primary).count() <= 1, "{gpus:?}");
+        for (i, g) in gpus.iter().enumerate() {
+            assert_ne!(g.pci.0, 0, "{gpus:?}");
+            assert!(!gpus[..i].iter().any(|h| h.pci == g.pci), "{gpus:?}");
+        }
+    }
+
+    #[test]
+    fn internal_panels_are_edp_lvds_and_dsi_connectors() {
+        for name in ["eDP-1", "LVDS-1", "DSI-1"] {
+            assert!(is_internal_panel(name), "{name}");
+        }
+        for name in ["DP-3", "HDMI-A-1", "DVI-D-1", "VGA-1", "Writeback-1", ""] {
+            assert!(!is_internal_panel(name), "{name}");
+        }
+    }
+
+    /// A sysfs like a hybrid laptop's with an external monitor: the panel and a disconnected port
+    /// on the integrated GPU (card0), the monitor on the discrete one (card1), and a card without
+    /// PCI ids. Each GPU is listed once, the one with the panel as primary.
+    #[test]
+    fn linux_display_gpus_come_from_the_connected_connectors() -> std::io::Result<()> {
+        let dir = std::env::temp_dir().join(format!("vectorcraft-drm-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let card = |name: &str, (vendor, device): (u32, u32)| -> std::io::Result<()> {
+            std::fs::create_dir_all(dir.join(name).join("device"))?;
+            std::fs::write(dir.join(name).join("device/vendor"), format!("{vendor:#06x}\n"))?;
+            std::fs::write(dir.join(name).join("device/device"), format!("{device:#06x}\n"))
+        };
+        let connector = |name: &str, status: &str| -> std::io::Result<()> {
+            std::fs::create_dir_all(dir.join(name))?;
+            std::fs::write(dir.join(name).join("status"), format!("{status}\n"))
+        };
+        card("card0", AMD_IGPU)?;
+        card("card1", NVIDIA_3090)?;
+        std::fs::create_dir_all(dir.join("card2"))?;
+        connector("card0-eDP-1", "connected")?;
+        connector("card0-HDMI-A-1", "disconnected")?;
+        connector("card1-DP-1", "connected")?;
+        connector("card1-DP-2", "connected")?;
+        connector("card2-Virtual-1", "connected")?;
+        std::fs::write(dir.join("renderD128"), "")?;
+        let mut gpus = linux_display_gpus(&dir);
+        gpus.sort_by_key(|g| g.pci);
+        assert_eq!(gpus, [primary(AMD_IGPU), monitor(NVIDIA_3090)]);
+        assert!(linux_display_gpus(&dir.join("no such dir")).is_empty());
+        std::fs::remove_dir_all(&dir)
+    }
+
+    #[test]
+    fn display_gpus_are_logged_as_pci_ids() {
+        assert_eq!(primary(NVIDIA_3090).to_string(), "10de:2204 (primary)");
+        assert_eq!(monitor(AMD_IGPU).to_string(), "1002:164e");
+        let mut gpus = vec![];
+        add_display_gpu(&mut gpus, NVIDIA_3090, false);
+        add_display_gpu(&mut gpus, NVIDIA_3090, true);
+        add_display_gpu(&mut gpus, AMD_IGPU, false);
+        assert_eq!(gpus, [primary(NVIDIA_3090), monitor(AMD_IGPU)]);
+    }
+
     /// The machine of #502 as Vulkan lists it with Mesa's device-select layer: the GPU KDE's
     /// compositor runs on (NVIDIA) first, then the Ryzen's integrated GPU, Mesa's software
     /// renderer, and OpenGL.
@@ -270,7 +651,7 @@ mod tests {
     #[test]
     fn automatic_keeps_the_systems_order_on_linux_and_saves_power_elsewhere() {
         let c = issue_502();
-        let order = adapter_order(&c, power_preference(None, None), None, &[]);
+        let order = adapter_order(&c, power_preference(None, None), &[], None, &[]);
         let first = &c[order[0]].name;
         if cfg!(any(windows, target_os = "macos")) {
             assert_eq!(first, "AMD Ryzen 9 7900X (RADV RAPHAEL_MENDOCINO)");
@@ -283,7 +664,7 @@ mod tests {
     #[test]
     fn each_preference_orders_the_adapters_then_falls_back_to_opengl_and_software() {
         let c = issue_502();
-        let order = |power| names(&c, &adapter_order(&c, power, None, &[]));
+        let order = |power| names(&c, &adapter_order(&c, power, &[], None, &[]));
         assert_eq!(
             order(PowerPreference::None),
             [
@@ -324,14 +705,15 @@ mod tests {
             name: name.into(),
             backend: Backend::Metal,
             device_type,
+            pci: (0, 0),
             presents: true,
         };
         let c = vec![mac("NVIDIA GeForce GT 750M", DeviceType::DiscreteGpu), mac("Intel Iris Pro Graphics", DeviceType::IntegratedGpu)];
         assert_eq!((c[0].key.as_str(), c[1].key.as_str()), ("Metal:NVIDIA GeForce GT 750M", "Metal:Intel Iris Pro Graphics"));
-        let first = adapter_order(&c, PowerPreference::LowPower, None, &[]);
+        let first = adapter_order(&c, PowerPreference::LowPower, &[], None, &[]);
         assert_eq!(names(&c, &first)[0], "Intel Iris Pro Graphics");
         let skip = parse_skip(&c[first[0]].key);
-        assert_eq!(names(&c, &adapter_order(&c, PowerPreference::LowPower, None, &skip)), ["NVIDIA GeForce GT 750M"]);
+        assert_eq!(names(&c, &adapter_order(&c, PowerPreference::LowPower, &[], None, &skip)), ["NVIDIA GeForce GT 750M"]);
         // A comma in a name can't split the list.
         assert_eq!(parse_skip(&key(Backend::Gl, 0, 0, "Mesa, llvmpipe")), ["Gl:Mesa  llvmpipe"]);
     }
@@ -341,7 +723,7 @@ mod tests {
         let c = issue_502();
         let mut skip = vec![];
         let mut tried = vec![];
-        while let Some(&i) = adapter_order(&c, PowerPreference::LowPower, None, &skip).first() {
+        while let Some(&i) = adapter_order(&c, PowerPreference::LowPower, &[], None, &skip).first() {
             tried.push(c[i].name.clone());
             skip.push(c[i].key.clone());
         }
@@ -362,33 +744,36 @@ mod tests {
         c[0].presents = false;
         c[3].presents = false;
         for power in [PowerPreference::None, PowerPreference::LowPower, PowerPreference::HighPerformance] {
-            let order = adapter_order(&c, power, None, &[]);
+            let order = adapter_order(&c, power, &[], None, &[]);
             assert!(!order.contains(&0) && !order.contains(&3), "{power:?}: {order:?}");
             assert_eq!(order.len(), 2);
         }
         for p in &mut c {
             p.presents = false;
         }
-        assert!(adapter_order(&c, PowerPreference::None, None, &[]).is_empty());
-        assert!(adapter_order(&[], PowerPreference::HighPerformance, None, &[]).is_empty());
+        assert!(adapter_order(&c, PowerPreference::None, &[], None, &[]).is_empty());
+        assert!(adapter_order(&[], PowerPreference::HighPerformance, &[], None, &[]).is_empty());
     }
 
     #[test]
     fn wgpu_adapter_name_picks_an_adapter_first_and_the_rest_stay_as_fallbacks() {
         let c = issue_502();
-        let order = adapter_order(&c, PowerPreference::HighPerformance, Some("radv"), &[]);
+        let order = adapter_order(&c, PowerPreference::HighPerformance, &[], Some("radv"), &[]);
         assert_eq!(c[order[0]].name, "AMD Ryzen 9 7900X (RADV RAPHAEL_MENDOCINO)");
         assert_eq!(order.len(), 4);
         // Any case; every match comes before the rest, natively first.
-        let order = adapter_order(&c, PowerPreference::LowPower, Some("GeForce"), &[]);
+        let order = adapter_order(&c, PowerPreference::LowPower, &[], Some("GeForce"), &[]);
         assert_eq!(names(&c, &order[..2]), ["NVIDIA GeForce RTX 5070", "NVIDIA GeForce RTX 5070/PCIe/SSE2"]);
         // An empty name or one nothing matches changes nothing.
         for named in ["", "no such gpu"] {
-            assert_eq!(adapter_order(&c, PowerPreference::LowPower, Some(named), &[]), adapter_order(&c, PowerPreference::LowPower, None, &[]));
+            assert_eq!(
+                adapter_order(&c, PowerPreference::LowPower, &[], Some(named), &[]),
+                adapter_order(&c, PowerPreference::LowPower, &[], None, &[])
+            );
         }
         // A named adapter that failed is left out like any other.
         let skip = vec![c[1].key.clone()];
-        assert_eq!(adapter_order(&c, PowerPreference::None, Some("radv"), &skip)[0], 0);
+        assert_eq!(adapter_order(&c, PowerPreference::None, &[], Some("radv"), &skip)[0], 0);
     }
 
     /// A Windows machine lists every GPU twice (Vulkan and DX12): power saving still takes the
@@ -402,9 +787,9 @@ mod tests {
             gpu("Intel(R) Iris(R) Xe Graphics", Backend::Dx12, DeviceType::IntegratedGpu),
             gpu("Microsoft Basic Render Driver", Backend::Dx12, DeviceType::Cpu),
         ];
-        let order = adapter_order(&c, PowerPreference::LowPower, None, &[]);
+        let order = adapter_order(&c, PowerPreference::LowPower, &[], None, &[]);
         assert_eq!(order, [3, 1, 2, 0, 4]);
-        assert_eq!(adapter_order(&c, PowerPreference::HighPerformance, None, &[]), [2, 0, 3, 1, 4]);
+        assert_eq!(adapter_order(&c, PowerPreference::HighPerformance, &[], None, &[]), [2, 0, 3, 1, 4]);
     }
 
     /// The machine of #545: one Intel GPU, whose Vulkan driver made the window flicker black.
@@ -419,9 +804,9 @@ mod tests {
             gpu("Intel(R) Graphics", Backend::Gl, DeviceType::Other),
         ];
         for power in [PowerPreference::LowPower, PowerPreference::HighPerformance, PowerPreference::None] {
-            assert_eq!(adapter_order(&c, power, None, &[]), [1, 0, 3, 2], "{power:?}");
+            assert_eq!(adapter_order(&c, power, &[], None, &[]), [1, 0, 3, 2], "{power:?}");
         }
-        assert_eq!(adapter_order(&c, PowerPreference::LowPower, None, &[c[1].key.clone()]), [0, 3, 2], "DX12 failed: Vulkan next");
+        assert_eq!(adapter_order(&c, PowerPreference::LowPower, &[], None, &[c[1].key.clone()]), [0, 3, 2], "DX12 failed: Vulkan next");
     }
 
     #[test]

apps/vectorcraft/src/main.rs

@@ -431,7 +431,21 @@ fn main() -> std::process::ExitCode {
     #[cfg(feature = "wgpu")]
     let gpu_pref = saved.as_ref().and_then(|ui| ui.engine_prefs.get("gpuPreference")).and_then(serde_json::Value::as_str);
     #[cfg(feature = "wgpu")]
-    let power = gpu::power_preference(gpu_pref, eframe::wgpu::PowerPreference::from_env());
+    let power_env = eframe::wgpu::PowerPreference::from_env();
+    #[cfg(feature = "wgpu")]
+    let power = gpu::power_preference(gpu_pref, power_env);
+    // Automatic draws on the GPU that drives the (primary) display: a GPU without a monitor reset
+    // its driver and took every monitor down (pdfcraft#378). Logged first: the first question in
+    // every black-window report.
+    #[cfg(feature = "wgpu")]
+    let displays = gpu::preferred_displays(gpu_pref, power_env);
+    #[cfg(feature = "wgpu")]
+    if gpu::automatic(gpu_pref, power_env) {
+        let listed: Vec<String> = displays.iter().map(ToString::to_string).collect();
+        log::info!("display GPUs (PCI vendor:device): {}", if listed.is_empty() { "unknown".to_string() } else { listed.join(", ") });
+    } else {
+        log::info!("graphics processor chosen by the user ({power:?}): which GPU drives the display isn't considered");
+    }
     #[cfg(feature = "wgpu")]
     let startup = std::sync::Arc::new(gpu::Startup::default());
     let options = eframe::NativeOptions {
@@ -458,7 +472,7 @@ fn main() -> std::process::ExitCode {
         options.wgpu_options.surface = eframe::egui_wgpu::SurfaceConfig::LOW_LATENCY;
         // Only adapters that can show the window, in the order `gpu` gives (#306, #502).
         if let eframe::egui_wgpu::WgpuSetup::CreateNew(create) = &mut options.wgpu_options.wgpu_setup {
-            create.native_adapter_selector = Some(gpu::selector(power, startup.clone()));
+            create.native_adapter_selector = Some(gpu::selector(power, displays, startup.clone()));
             // Nothing draws or dispatches indirectly, so wgpu's check of indirect arguments only
             // costs a compute shader at start-up, one some drivers can't compile (OCLP-patched
             // Metal on an Iris Pro, #651). `WGPU_VALIDATION_INDIRECT_CALL=1` turns it back on.

docs/development.md

@@ -45,10 +45,15 @@ How the web shell (`apps/vectorcraft-web/src/web.rs`) differs from desktop:
 
 The canvas is rasterized on the CPU (`vectorcraft-render`, vello_cpu); the GPU (wgpu, through eframe) only composites the canvas texture and draws the UI, so any GPU that can show the window will do. The desktop app picks the window's adapter itself (`apps/vectorcraft/src/gpu.rs`, eframe's `native_adapter_selector`) and logs every adapter it found and the one it uses.
 
-- **Order:** adapters that report they can't present to the window are never tried; then the one `WGPU_ADAPTER_NAME` names; hardware before software (llvmpipe, WARP); the native backends (Vulkan, Metal, DX12) before OpenGL; then the power preference; then, on Windows, where each GPU is listed under both, a GPU's DX12 adapter before its Vulkan one (Intel's Vulkan driver made the whole window flicker black, #545), keeping the system's order among equals. `WGPU_BACKEND=vulkan` still picks Vulkan.
-- **Preferences › Performance › Graphics Processor** (`gpuPreference`): `automatic` (the default), `lowPower` (Power Saving, the integrated GPU) or `highPerformance` (the discrete GPU). The adapter is chosen when the window opens, so a change applies after a restart.
-  - **Automatic on Windows and macOS** is power saving: the system shows frames from any GPU, and presenting frames rendered on a discrete GPU through the integrated one made the window flicker on some hybrid laptops (#306).
-  - **Automatic on Linux and the BSDs** keeps the system's order: Mesa's Vulkan device-select layer puts the GPU the desktop runs on first (the integrated one on hybrid laptops; `DRI_PRIME` and `MESA_VK_DEVICE_SELECT` steer it). A Wayland compositor may not accept frames from another GPU: on a desktop whose compositor ran on an NVIDIA GPU, rendering on the Ryzen's integrated GPU made KWin end the window's connection ("importing the supplied dmabufs failed") and 0.5.0 crashed at startup (#502).
+- **Order:** adapters that report they can't present to the window are never tried; then the one `WGPU_ADAPTER_NAME` names; hardware before software (llvmpipe, WARP); the native backends (Vulkan, Metal, DX12) before OpenGL; with Automatic, the GPU that drives a display, and among those the one that drives the primary display; then the power preference; then, on Windows, where each GPU is listed under both, a GPU's DX12 adapter before its Vulkan one (Intel's Vulkan driver made the whole window flicker black, #545), keeping the system's order among equals. `WGPU_BACKEND=vulkan` still picks Vulkan.
+- **The GPU that drives the display.** A GPU without a monitor is the wrong one even when it says it can show the window: on a desktop with a Ryzen's integrated GPU (no monitor) and an NVIDIA card driving both monitors, power saving picked the integrated GPU, Windows had to present every frame across adapters, and the integrated GPU's driver reset under that: the graphics device was lost, or the desktop's compositor went down and every monitor stayed black for minutes (pdfcraft#378). So Automatic asks the system which GPU drives which display and puts that GPU first; the power preference only orders the rest, and decides alone where the system can't say.
+  - **Windows:** `EnumDisplayDevices` (the display devices attached to the desktop, and the primary one), through the `winsafe` crate; the PCI ids in each device id are matched against wgpu's adapters. The registry doesn't tell a user which adapter drives a display, and WMI reports a resolution for a GPU without a monitor, so neither is used.
+  - **Linux:** the connected connectors in `/sys/class/drm` and their cards' PCI ids; a built-in panel (`eDP`, `LVDS`, `DSI`) counts as the primary display.
+  - **macOS**, OpenGL adapters (no device id) and Metal (no ids at all): no match, so the power preference decides as before.
+  - The log's first lines list the display GPUs (`display GPUs (PCI vendor:device): 10de:2204 (primary)`), every adapter with whether it drives a display, and the one drawn on and why (`drawing on NVIDIA GeForce RTX 3090 (Dx12, DiscreteGpu): it drives the primary display`). That is the first thing to look for in a black-window report.
+- **Preferences › Performance › Graphics Processor** (`gpuPreference`): `automatic` (the default), `lowPower` (Power Saving, the integrated GPU) or `highPerformance` (the discrete GPU). The adapter is chosen when the window opens, so a change applies after a restart. Power Saving and High Performance are the user's own choice and order by kind alone, without looking at the displays; so does `WGPU_POWER_PREF`.
+  - **Automatic on Windows and macOS** is the GPU that drives the primary display, then power saving: the system shows frames from any GPU, and presenting frames rendered on a discrete GPU through the integrated one made the window flicker on some hybrid laptops (#306). On a hybrid laptop the integrated GPU drives the panel, so both rules agree.
+  - **Automatic on Linux and the BSDs** is the GPU that drives the panel or a monitor, then the system's order: Mesa's Vulkan device-select layer puts the GPU the desktop runs on first (the integrated one on hybrid laptops; `DRI_PRIME` and `MESA_VK_DEVICE_SELECT` steer it). A Wayland compositor may not accept frames from another GPU: on a desktop whose compositor ran on an NVIDIA GPU, rendering on the Ryzen's integrated GPU made KWin end the window's connection ("importing the supplied dmabufs failed") and 0.5.0 crashed at startup (#502).
   - 0.5.0 saved `powerSaving`, its default, for everyone; it reads as `automatic`.
 - **If the window fails on its adapter while starting up** (an error from wgpu, or a panic inside wgpu or egui-wgpu during the first frames), the app starts again without that adapter and tries the next one, telling which in the status bar; the run that failed keeps its log as `vectorcraft.1.log`. On Unix the new app replaces the process (an AppImage stays mounted); on Windows it starts beside it. Adapters are told apart by backend and PCI ids, or by name where the backend reports no ids (Metal lists every GPU of a dual-GPU Mac as `0000:0000`, #651). The adapters left out travel in `VECTORCRAFT_GPU_SKIP` (`backend:vendor:device`, such as `Vulkan:1002:164e`), one more on each restart, so the restarts end. When no adapter is left, the app logs why and exits with an error instead of panicking.
 - **Environment variables** for when the choice still goes wrong, all read at startup and stronger than the preference: