macOS: start on wgpu on Intel Metal by skipping indirect-call validation (#1627)

wgpu validates indirect draw and dispatch arguments with a compute shader it
compiles when the device is created. Metal on an Intel Iris Pro (MacBookPro11,3,
macOS 12.7.6) fails to compile it ("Compiler encountered an internal error" in
MTLCompilerService), the device is lost, and the window falls back to OpenGL.

PdfCraft draws and dispatches nothing indirectly, so leave the check out of the
instance flags. WGPU_VALIDATION_INDIRECT_CALL=1 turns it back on. VectorCraft
does the same (storytold/vectorcraft#651).

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

apps/pdfcraft/src/main.rs

@@ -484,6 +484,11 @@ fn write_control_file(path: &str, port: u16, token: &str) -> std::io::Result<()>
 ///   its window appeared. D3D12 is the native, best-supported backend there.
 fn configure_gpu(native: &mut eframe::NativeOptions) {
     let eframe::egui_wgpu::WgpuSetup::CreateNew(setup) = &mut native.wgpu_options.wgpu_setup else { return };
+    // Nothing draws or dispatches indirectly, so wgpu's check of indirect arguments only costs a
+    // compute shader when the device is created, one that Metal can't compile on an Intel Iris
+    // Pro: the device is lost and the window falls back to OpenGL. `WGPU_VALIDATION_INDIRECT_CALL=1`
+    // turns the check back on.
+    setup.instance_descriptor.flags = setup.instance_descriptor.flags.difference(eframe::wgpu::InstanceFlags::VALIDATION_INDIRECT_CALL).with_env();
     // egui-wgpu requests only 8192 pixels even when the adapter can render larger surfaces.
     // A restored 3440-point window at 250% DPI requests 8600 pixels and otherwise panics in
     // Surface::configure before the app starts. Keep the renderer's other device requirements,
@@ -781,6 +786,10 @@ mod tests {
         if std::env::var_os("WGPU_POWER_PREF").is_none() {
             assert_eq!(setup.power_preference, eframe::wgpu::PowerPreference::LowPower);
         }
+        if std::env::var_os("WGPU_VALIDATION_INDIRECT_CALL").is_none() {
+            let flags = setup.instance_descriptor.flags;
+            assert!(!flags.contains(eframe::wgpu::InstanceFlags::VALIDATION_INDIRECT_CALL), "Intel Metal can't compile its shader: {flags:?}");
+        }
         if cfg!(target_os = "windows") && std::env::var_os("WGPU_BACKEND").is_none() {
             let backends = setup.instance_descriptor.backends;
             assert!(backends.contains(eframe::wgpu::Backends::DX12), "{backends:?}");

docs/development.md

@@ -114,6 +114,7 @@ driver's shader compilation, and explicit `PDFCRAFT_RENDERER=wgpu` still disable
 | `XDG_DATA_HOME` | Linux/FreeBSD: base of the settings folder (`pdfcraft/`), the log folder and crash recovery |
 | `WGPU_POWER_PREF` | GPU choice; by default PdfCraft draws on the GPU the Wayland compositor draws with (it says so through linux-dmabuf feedback), else the GPU that drives the primary display (Windows) or the built-in panel (Linux), else the low-power (integrated) GPU. The log says which one was chosen |
 | `WGPU_BACKEND` | Graphics backend; by default Windows uses Direct3D 12, falling back to OpenGL |
+| `WGPU_VALIDATION_INDIRECT_CALL` | `1` turns wgpu's check of indirect draw arguments back on. PdfCraft draws nothing indirectly and turns it off, since the compute shader the check needs fails to compile on some drivers (Metal on an Intel Iris Pro), which lost the device at start-up |
 | `PDFCRAFT_RENDERER` | `gl` starts with OpenGL (glow) and never loads wgpu; `wgpu` reports a wgpu failure instead of retrying with OpenGL; unset, wgpu is retried with OpenGL when it can't start (see [Renderer fallback](#renderer-fallback)) |
 | `PDFCRAFT_BUILD_LABEL` | Build time: a label for a local or patched build (letters, digits, inner dots), shown after the version in `--version`, About and the log (`0.7.1 (titlebar)`). `packaging/linux/package.sh` also puts it in the file names and the .rpm/.deb release (`1.titlebar`), which upgrades over the release of the same version |
 | `CRAFT_FONTS_DIR` | Build time: a [craft-fonts](https://github.com/storytold/craft-fonts) checkout to embed (Japanese fonts) |