Fix #545: Windows renders through DX12 before Vulkan

Windows lists each GPU under both backends, and Vulkan came first. On an
Intel GPU its driver made the whole window flicker black while the
pointer moved; the same machine was fine with WGPU_BACKEND=dx12 or gl.
adapter_order now ranks a GPU's DX12 adapter before its Vulkan one, after
the power preference, so the GPU chosen doesn't change, only how it is
driven. Vulkan stays the fallback (a failed DX12 start restarts on it)
and WGPU_BACKEND=vulkan still picks it. Elsewhere there is no DX12
adapter, so nothing changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ROADMAP.md

@@ -4,7 +4,7 @@ VectorCraft is a clean-room, open-source, pure-Rust reimplementation of the Adob
 
 This file tracks **how far we are and what's left**. Time estimates are wall-clock hours of continuous Claude Opus 5.5 agent work (including builds and the CI gate), given both for **one agent** and for **4–6 parallel agents** on disjoint crates. They are counted from the remaining work (see [Parity estimate](#parity-estimate)), calibrated against measured throughput, and updated as work lands.
 
-_Last updated: 2026-10-08 (after M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG window (#493), panels, panel groups and the Tools panel undocking into flLine truncated
+_Last updated: 2026-10-08 (after M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG window (#493), panels, panel groups and the Tools panel undocking into flLine truncated
 
 ## Where we are
 
@@ -42,7 +42,7 @@ since 2026-10-01.
 | **Bundled content:** brush, symbol, style and swatch libraries | ~30% | Ours are original and generated in code, and far fewer than Illustrator ships; brush and symbol libraries are still missing |
 | **Performance** | unverified | Multithreaded, off-thread rendering and caches are in place. The last budget run (2026-10-01, loaded machine) measured 290 ms for a 50k-path fit against a 16 ms budget. Re-run `vectorcraft-cli perf` on an idle machine |
 | **Robustness** | good, new | ~2,840 tests, property tests, no panics in shipped code (lints, the `guard` safety net, import fuzzing), Data Recovery. Missing: a corpus of real-world files, Windows/Linux/browser QA |
-| **Platforms and 1.0 polish** | ~60% | The macOS app and the web build work, and Finder opens every readable format with the macOS app (#295, #354); on macOS the menus are in the system menu bar, laid out as a Mac app's, with the in-window menus as a fallback (`--in-window-menus`; verified on Windows and by cross-compilation, not yet by hand on a Mac); hybrid-graphics laptops render on the power-saving GPU by default on Windows and macOS (#306), and Linux on the GPU the desktop runs on, since a Wayland compositor may refuse frames from the other one; a window that fails on its GPU while starting up starts again on the next one instead of crashing (#502; the dual-GPU Wayland case is verified by unit tests and cross-compilation, not on such hardware); web drops land in the document they were dropped on (#359); desktop drops carry no pointer position (winit 0.30), so a dropped document opens as a tab of its own and a picture or text is placed in the middle of the view, while the web places anything dropped on the canvas and opens what is dropped off it, as Illustrator does (#472); a web page that loses its WebGPU device or WebGL context restarts its graphics with the same documents (#369); on Linux/Wayland the clipboard reads the compositor's own (data-control) and copied image files paste, but files can't be dropped on the window under Wayland until eframe moves to winit 0.31 (#398; the Wayland side is verified by compilation only); on Linux the Paste menu checks the system clipboard on a background thread, so a clipboard owner that never answers no longer freezes the window, while Windows and macOS keep their quick in-line check (#510; the X11 hang verified by the contributor, here by headless tests); on KDE Plasma 6.3+ under Wayland, pens and pen displays reach the app only under XWayland (`WAYLAND_DISPLAY=`) or with KWin's `KWIN_WAYLAND_EMULATE_TABLET=1`, since winit 0.30 has no Wayland tablet input (#491, not verified on hardware); Windows/Linux packaging and accessibility are pending; an experimental, unsupported Windows 7 x64 OpenGL build exists (community-contributed, not verified by maintainers) |
+| **Platforms and 1.0 polish** | ~60% | The macOS app and the web build work, and Finder opens every readable format with the macOS app (#295, #354); on macOS the menus are in the system menu bar, laid out as a Mac app's, with the in-window menus as a fallback (`--in-window-menus`; verified on Windows and by cross-compilation, not yet by hand on a Mac); hybrid-graphics laptops render on the power-saving GPU by default on Windows and macOS (#306), and Windows renders through DX12 before Vulkan (#545: Vulkan flickered black on an Intel GPU, DX12 and OpenGL didn't; verified by unit tests and the reporter's runs with `WGPU_BACKEND`), and Linux on the GPU the desktop runs on, since a Wayland compositor may refuse frames from the other one; a window that fails on its GPU while starting up starts again on the next one instead of crashing (#502; the dual-GPU Wayland case is verified by unit tests and cross-compilation, not on such hardware); web drops land in the document they were dropped on (#359); desktop drops carry no pointer position (winit 0.30), so a dropped document opens as a tab of its own and a picture or text is placed in the middle of the view, while the web places anything dropped on the canvas and opens what is dropped off it, as Illustrator does (#472); a web page that loses its WebGPU device or WebGL context restarts its graphics with the same documents (#369); on Linux/Wayland the clipboard reads the compositor's own (data-control) and copied image files paste, but files can't be dropped on the window under Wayland until eframe moves to winit 0.31 (#398; the Wayland side is verified by compilation only); on Linux the Paste menu checks the system clipboard on a background thread, so a clipboard owner that never answers no longer freezes the window, while Windows and macOS keep their quick in-line check (#510; the X11 hang verified by the contributor, here by headless tests); on KDE Plasma 6.3+ under Wayland, pens and pen displays reach the app only under XWayland (`WAYLAND_DISPLAY=`) or with KWin's `KWIN_WAYLAND_EMULATE_TABLET=1`, since winit 0.30 has no Wayland tablet input (#491, not verified on hardware); Windows/Linux packaging and accessibility are pending; an experimental, unsupported Windows 7 x64 OpenGL build exists (community-contributed, not verified by maintainers) |
 | **Agent automation** | beyond Illustrator | Every command, gesture and dialog is drivable over MCP, the CLI and the control channel |
 | **Scrubby numeric fields** | beyond Illustrator | As in Photoshop, dragging a numeric field's label (`W:`, `Opacity:`, the Character panel's icons) left or right steps its value live; one undo step per drag, Escape cancels (#400) |
 
@@ -159,7 +159,7 @@ grade by behaviour against `plan/illustrator/`, not by whether a menu item exist
   - EPS and DXF in and out, EMF/WMF in and out; PNG (with PNG-8), JPEG, WebP, GIF, TIFF, BMP, Targa and layered PSD export. EPS import runs a PostScript Level 3 interpreter written from the PostScript Language Reference: resource categories and `resourceforall`, local and global VM (`currentglobal`/`setglobal`/`gcheck`), `clipsave`/`cliprestore`, subarrays and substrings that share storage, the standard dictionaries in `systemdict`, `dictstack`, `internaldict`, executable filters and strings, `load` by any key, `//name` immediate names, `token`, `execform`, user paths, `cshow`, `rootfont`, `cachestatus`, colour rendering and halftone queries, file `status` and data read with `flushfile`, and `pdfmark` marks dropped (Discord feedback, #466, #469, #474). Masked images (`ImageType 3` in its three interleavings) and reusable streams are read, and an image's several data sources are read in turn, as the reference defines (procedures that read one file get their own rows: such images came in banded, #498). `restore` puts dictionaries back as they were at the `save`, so programs that count their saves in a dictionary read to their end (part of #505). Tiling patterns come in as pattern swatches, uncoloured ones too; Type 3 fonts' glyphs as their outlines, spaced by `ashow`/`widthshow`/`xshow`/`kshow`; mesh and function-based shadings (types 1, 4–7) as gradient meshes; sampled functions (type 0) and Flate/LZW predictors are read. It is tested with programs written from the specification in the ways common generators use these features; Inkscape/cairo EPS files open as vectors. When a file's PostScript still can't be read, it opens as its TIFF preview, its Windows metafile preview (as vectors) or its EPSI preview, and the warning (in the status bar, `document.open`/`app.open`/MCP `open_file` replies and `vectorcraft-cli info`) names the error, the operator that raised it and the procedures it ran in. Legacy PostScript `.ai` files (Illustrator 3–8, written with the prolog that defines their operators) keep their groups and nested groups (`u` … `U`), between and inside clipping groups; EPS and EMF/WMF import nest clips (and groups) at most 128 deep, so a hostile file can't exhaust the stack. DXF TEXT justified Fit or Aligned spans its two points (stretched, or scaled as a whole).
   - Place and the Links panel, Package, File Info, Print with print presets, PostScript output and print tiling, slices and Save for Web, Export for Screens and Asset Export, CSS Properties, PNG/PDF/SVG/text clipboard flavours; files copied in a file manager paste as art (SVG, PDF, EMF/WMF, bitmaps) on every desktop platform, and Linux/Wayland reads the compositor's clipboard (#398); on Linux the Paste menu checks the clipboard off the UI thread, so an X11 owner that never answers can't freeze the window (#510); screenshots and other copied pictures paste as embedded images at the view centre everywhere, the web included (#457).
 - **Performance:** 20k shapes + 1k texts render in 27 ms per full-retina frame (7.8 ms zoomed), 7× faster than the first version. The UI thread never blocks. The web build is 7.1 MB gzipped.
-- **Graphics processor:** the canvas is rasterized on the CPU and the GPU only composites it, so any GPU that can show the window will do. Preferences › Performance › Graphics Processor (`gpuPreference`) is Automatic by default: the power-saving GPU on Windows and macOS (the integrated one on hybrid-graphics laptops, where presenting from the discrete GPU made the window flicker, #306), and the GPU the desktop runs on under Linux, where KWin on an NVIDIA GPU refused frames from a Ryzen's integrated GPU and 0.5.0 crashed at startup (#502). Power Saving and High Performance pick a kind of GPU; `WGPU_POWER_PREF`, `WGPU_ADAPTER_NAME` and `WGPU_BACKEND` override them. The app picks among the adapters that can present to the window (native backends before OpenGL, hardware before software), and if the window fails on one while starting up it starts again without it instead of crashing; Help › About, `ui.inspect` and the log name the adapter in use. When the browser drops the page's WebGPU device or WebGL context, the web build writes recovery copies, starts again on new graphics with the same app and uploads its textures again; if it can't, it removes the stale canvas and says to reload, which offers the copies back. The desktop app writes the copies and says to restart (#369). On Windows and Linux the tools' cursors are OS cursors (bitmaps rasterized once per display scale), which the system moves itself: painted into the window, they trailed the pointer by the frames waiting to be shown, and the window now queues one frame instead of two (#444). macOS and the web still paint them (macOS sizes cursor bitmaps in points, eframe has no bitmap cursors on the web). Pens and touch drive the tools as the mouse does, and a tap pressed and lifted within one frame clicks where it tapped (#491); pen pressure reaches the Liquify tools' Use Pressure Pen on Windows, while winit 0.30 reports none on macOS or Linux and egui none on the web. On Linux, see `docs/development.md` for pens under Wayland.
+- **Graphics processor:** the canvas is rasterized on the CPU and the GPU only composites it, so any GPU that can show the window will do. Preferences › Performance › Graphics Processor (`gpuPreference`) is Automatic by default: the power-saving GPU on Windows and macOS (the integrated one on hybrid-graphics laptops, where presenting from the discrete GPU made the window flicker, #306), and the GPU the desktop runs on under Linux, where KWin on an NVIDIA GPU refused frames from a Ryzen's integrated GPU and 0.5.0 crashed at startup (#502). Power Saving and High Performance pick a kind of GPU; `WGPU_POWER_PREF`, `WGPU_ADAPTER_NAME` and `WGPU_BACKEND` override them. The app picks among the adapters that can present to the window (native backends before OpenGL, hardware before software, and on Windows a GPU's DX12 adapter before its Vulkan one: Intel's Vulkan driver made the whole window flicker black, #545), and if the window fails on one while starting up it starts again without it instead of crashing; Help › About, `ui.inspect` and the log name the adapter in use. When the browser drops the page's WebGPU device or WebGL context, the web build writes recovery copies, starts again on new graphics with the same app and uploads its textures again; if it can't, it removes the stale canvas and says to reload, which offers the copies back. The desktop app writes the copies and says to restart (#369). On Windows and Linux the tools' cursors are OS cursors (bitmaps rasterized once per display scale), which the system moves itself: painted into the window, they trailed the pointer by the frames waiting to be shown, and the window now queues one frame instead of two (#444). macOS and the web still paint them (macOS sizes cursor bitmaps in points, eframe has no bitmap cursors on the web). Pens and touch drive the tools as the mouse does, and a tap pressed and lifted within one frame clicks where it tapped (#491); pen pressure reaches the Liquify tools' Use Pressure Pen on Windows, while winit 0.30 reports none on macOS or Linux and egui none on the web. On Linux, see `docs/development.md` for pens under Wayland.
 - **Tests and robustness:** ~2,840 automated tests: model-based property tests, a junk-parameter sweep over every command, import fuzzing (SVG, PDF, libraries), golden renders, and MCP end-to-end tests over stdio. Shipped code never panics (workspace lints and a rollback safety net; see `docs/development.md`).
 
 ## Milestones and estimates

apps/vectorcraft/src/gpu.rs

@@ -4,9 +4,9 @@
 //! 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, and the power
-//! preference ([`power_preference`]) among the rest. eframe is handed [`selector`], which takes
-//! the first of that order.
+//! before software, the native backends (Vulkan, Metal, DX12) before OpenGL, 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.
 //!
 //! 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
@@ -89,15 +89,17 @@ fn key(backend: Backend, vendor: u32, device: u32) -> 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`, keeping the system's order among
-/// equals (all of it for [`PowerPreference::None`]).
+/// 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> {
     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))
+        (unnamed, c.device_type == DeviceType::Cpu, c.backend == Backend::Gl, power_rank(c.device_type, power), c.backend == Backend::Vulkan)
     });
     order.into_iter().map(|(i, _)| i).collect()
 }
@@ -361,7 +363,7 @@ mod tests {
     }
 
     /// A Windows machine lists every GPU twice (Vulkan and DX12): power saving still takes the
-    /// integrated GPU first, as wgpu's own choice did (#306).
+    /// integrated GPU first, as wgpu's own choice did (#306), each GPU through DX12 first (#545).
     #[test]
     fn hybrid_laptop_on_windows_renders_on_the_integrated_gpu_with_power_saving() {
         let c = vec![
@@ -372,8 +374,25 @@ mod tests {
             gpu("Microsoft Basic Render Driver", Backend::Dx12, DeviceType::Cpu),
         ];
         let order = adapter_order(&c, PowerPreference::LowPower, None, &[]);
-        assert_eq!(order, [1, 3, 0, 2, 4]);
-        assert_eq!(adapter_order(&c, PowerPreference::HighPerformance, None, &[]), [0, 2, 1, 3, 4]);
+        assert_eq!(order, [3, 1, 2, 0, 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.
+    /// DX12 comes first whatever the preference; Vulkan stays a fallback, and `WGPU_ADAPTER_NAME`
+    /// or a restart leaving DX12 out still reach it.
+    #[test]
+    fn a_windows_gpu_renders_through_dx12_before_vulkan() {
+        let c = vec![
+            gpu("Intel(R) Graphics", Backend::Vulkan, DeviceType::IntegratedGpu),
+            gpu("Intel(R) Graphics", Backend::Dx12, DeviceType::IntegratedGpu),
+            gpu("Microsoft Basic Render Driver", Backend::Dx12, DeviceType::Cpu),
+            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, PowerPreference::LowPower, None, &[c[1].key.clone()]), [0, 3, 2], "DX12 failed: Vulkan next");
     }
 
     #[test]

docs/development.md

@@ -38,7 +38,7 @@ 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, keeping the system's order among equals.
+- **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).