Linux: use WebKit's shared-memory transport for the NVIDIA DMABUF renderer

The Device tab web view is slow on NVIDIA proprietary drivers even with
accelerated compositing left on: since the DMABUF renderer became the
default in WebKitGTK 2.42, the driver cannot back it, and web views fall
back to a slow path. Gating the old WEBKIT_DISABLE_COMPOSITING_MODE
fallback on WebKit < 2.42 is the wrong axis, because the failure is
version-independent from 2.42 on.

Force the shared-memory transport with WEBKIT_DMABUF_RENDERER_FORCE_SHM=1.
That keeps compositing and threaded scrolling and skips only the hardware
path. Also set WEBKIT_FORCE_DMABUF_RENDERER=1, which clears the isNVIDIA()
early return that Debian/Ubuntu/openSUSE patch into
rendererBufferTransportMode() and which otherwise returns before the
FORCE_SHM check is reached.

Both are set before the X11-vs-Wayland split so the workaround also covers
XWayland, and only when WebKitGTK is new enough to honour FORCE_SHM
(>= 2.44, WebView::SupportsForceSharedMemory()).

The AppImage launcher exported the superseded
WEBKIT_DISABLE_DMABUF_RENDERER=1, which is read first, leaves the transport
set empty and so disables compositing outright; replace it with the same
pair. The wxWidgets skill reference is updated to match.

.claude/skills/orca-wxwidgets/references/platforms.md

@@ -569,13 +569,16 @@ on the **first** call. So:
 #endif
 ```
 
-**Before GTK starts**, only the environment exists. `CLI::run` (`src/OrcaSlicer.cpp`) branches on
-`GDK_BACKEND` (an `x11` prefix means the X11 opt-in). On the default path it forces `GDK_BACKEND=x11`
-when wx lacks EGL and `WAYLAND_DISPLAY` is set. It sets `WEBKIT_DISABLE_COMPOSITING_MODE=1`
-(non-replacing) only when both `DISPLAY` and `WAYLAND_DISPLAY` are set and the linked WebKitGTK is
-older than 2.42, and calls `XInitThreads()`
+**Before GTK starts**, only the environment exists. `CLI::run` (`src/OrcaSlicer.cpp`) sets the NVIDIA
+DMABUF workaround and then branches on `GDK_BACKEND` (an `x11` prefix means the X11 opt-in). On both
+paths, when `/proc/driver/nvidia/version` exists and the linked WebKitGTK honours the switch (>= 2.44,
+`WebView::SupportsForceSharedMemory()`), it sets `WEBKIT_DMABUF_RENDERER_FORCE_SHM=1` and
+`WEBKIT_FORCE_DMABUF_RENDERER=1` (non-replacing): the proprietary driver cannot back WebKit's hardware
+DMABUF renderer. On the default path it forces `GDK_BACKEND=x11` when wx lacks EGL and `WAYLAND_DISPLAY`
+is set. It sets `WEBKIT_DISABLE_COMPOSITING_MODE=1` (non-replacing) only when both `DISPLAY` and
+`WAYLAND_DISPLAY` are set and the linked WebKitGTK is older than 2.42, and calls `XInitThreads()`
 only when `DISPLAY` is set. With neither variable set, the GUI refuses to start ("Neither DISPLAY nor
-WAYLAND_DISPLAY set"). The details and the WebKit rule (c12912e0df) are in
+WAYLAND_DISPLAY set"). The details and the WebKit rules (c12912e0df) are in
 `references/webview-gl-aui-media.md` §WebKitGTK on Linux sessions.
 
 **wx's own detectors**, for reference:

.claude/skills/orca-wxwidgets/references/webview-gl-aui-media.md

@@ -568,7 +568,13 @@ vue-resize workaround script and sets a persistent SQLite cookie store on the vi
 ## WebKitGTK on Linux sessions
 
 **Mechanism.** `CLI::run` (`src/OrcaSlicer.cpp`, under `#ifdef __WXGTK__`, before GTK initialises)
-branches on `GDK_BACKEND`:
+sets the NVIDIA DMABUF workaround and then branches on `GDK_BACKEND`:
+- **Both paths**, before the split: when `/proc/driver/nvidia/version` exists and the linked WebKitGTK
+  honours the switch (>= 2.44, `WebView::SupportsForceSharedMemory()`), it sets
+  `WEBKIT_DMABUF_RENDERER_FORCE_SHM=1` and `WEBKIT_FORCE_DMABUF_RENDERER=1` non-replacing. The
+  proprietary driver cannot back WebKit's hardware DMABUF renderer, so the shared-memory transport keeps
+  compositing and threaded scrolling; `WEBKIT_FORCE_DMABUF_RENDERER` clears the Debian/Ubuntu/openSUSE
+  `isNVIDIA()` early return, which otherwise returns before the FORCE_SHM check.
 - **Default path** (`GDK_BACKEND` unset or not starting with `x11`): if wx lacks EGL (`!wxHAS_EGL`) and
   `WAYLAND_DISPLAY` is set, it forces `GDK_BACKEND=x11`; it sets `WEBKIT_DISABLE_COMPOSITING_MODE=1`
   non-replacing **only** when the linked WebKitGTK predates 2.42 (`WebView::NeedsCompositingWorkaround()`)
@@ -577,13 +583,31 @@ branches on `GDK_BACKEND`:
   `DISPLAY` is set.
 - **`GDK_BACKEND=x11…` opt-in path**: sets `DRI_PRIME=1` (and the NVIDIA PRIME variables when
   `/proc/driver/nvidia/version` exists), calls `XInitThreads()`, and deliberately does **not** disable
-  compositing (the comment: the WebKit2GTK XWayland bug appears fixed in WebKit2GTK ≥ 2.42, and leaving
-  compositing on keeps hardware acceleration for Device / Setup Wizard / login pages).
+  compositing, which keeps hardware acceleration for Device / Setup Wizard / login pages.
 
 Runtime backend detection elsewhere uses Orca's `is_running_on_wayland()` / `is_running_on_x11()`
 (see `references/platforms.md`), not these environment variables.
 
 **Pitfall.**
+- **Rule:** On NVIDIA reach for `WEBKIT_DMABUF_RENDERER_FORCE_SHM` before
+  `WEBKIT_DISABLE_COMPOSITING_MODE`. **Why:** the proprietary driver cannot back WebKit's hardware
+  DMABUF renderer, leaving web views blank or slow; FORCE_SHM keeps compositing and threaded scrolling
+  and only skips the hardware path, while disabling compositing also turns threaded scrolling off.
+  `WEBKIT_DISABLE_DMABUF_RENDERER` is not a substitute — it is read first, leaves the transport set
+  empty (no compositing) and has a reported crash path. On Debian/Ubuntu and openSUSE the `isNVIDIA()`
+  patch returns before the FORCE_SHM check, so `WEBKIT_FORCE_DMABUF_RENDERER=1` must clear it first.
+  WebKit reads all of these once per process, before the first WebView.
+  ```cpp
+  // Wrong: kills compositing and threaded scrolling (and can crash on modern WebKit)
+  ::setenv("WEBKIT_DISABLE_DMABUF_RENDERER", "1", false);
+  // Right: keep compositing, skip only the hardware DMABUF path
+  if (::access("/proc/driver/nvidia/version", F_OK) == 0 && WebView::SupportsForceSharedMemory()) {
+      ::setenv("WEBKIT_DMABUF_RENDERER_FORCE_SHM", "1", /*replace*/ false);
+      ::setenv("WEBKIT_FORCE_DMABUF_RENDERER", "1", /*replace*/ false);
+  }
+  ```
+  Cite: WebKit 2.52.6 `Source/WebKit/UIProcess/gtk/AcceleratedBackingStore.cpp`
+  (`rendererBufferTransportMode()`), Debian `disable-nvidia-dmabuf.patch`, WebKit bug 262607.
 - **Rule:** Set `WEBKIT_DISABLE_COMPOSITING_MODE` only on the default path in Wayland sessions,
   non-replacing (`setenv(..., false)`, so a value the user already exported wins), before GTK
   initialises; never unconditionally, and only for the WebKitGTK releases that need it (older than

src/OrcaSlicer.cpp

@@ -1164,6 +1164,14 @@ int CLI::run(int argc, char **argv)
         // honours the first backend in the comma-separated list).
         const bool x11_opt_in = gdk_backend && boost::starts_with(gdk_backend, "x11");
 
+        // NVIDIA's proprietary driver cannot back WebKitGTK's DMABUF renderer.
+        // Force the shared-memory transport, which keeps compositing and threaded
+        // scrolling; the second variable clears Debian/Ubuntu/openSUSE's isNVIDIA().
+        if (::access("/proc/driver/nvidia/version", F_OK) == 0 && WebView::SupportsForceSharedMemory()) {
+            ::setenv("WEBKIT_DMABUF_RENDERER_FORCE_SHM", "1", /* replace */ false);
+            ::setenv("WEBKIT_FORCE_DMABUF_RENDERER", "1", /* replace */ false);
+        }
+
         if (x11_opt_in) {
             // ===== X11 / XWayland (opted in via GDK_BACKEND=x11) =====
             BOOST_LOG_TRIVIAL(info) << "GDK_BACKEND=x11 detected; applying v2.3.2 X11/XWayland workarounds.";

src/dev-utils/platform/unix/build_linux_image.sh.in

@@ -429,7 +429,8 @@ if [ "\$XDG_SESSION_TYPE" = "wayland" ] && [ "\$ZINK_DISABLE_OVERRIDE" != "1" ];
                 export __EGL_VENDOR_LIBRARY_FILENAMES=/usr/share/glvnd/egl_vendor.d/50_mesa.json
                 export MESA_LOADER_DRIVER_OVERRIDE=zink
                 export GALLIUM_DRIVER=zink
-                export WEBKIT_DISABLE_DMABUF_RENDERER=1
+                export WEBKIT_DMABUF_RENDERER_FORCE_SHM=1
+                export WEBKIT_FORCE_DMABUF_RENDERER=1
             fi
         fi
     fi

src/slic3r/GUI/Widgets/WebView.cpp

@@ -417,6 +417,17 @@ bool WebView::NeedsCompositingWorkaround()
 #endif
 }
 
+bool WebView::SupportsForceSharedMemory()
+{
+#ifdef __linux__
+    const guint major = webkit_get_major_version();
+    const guint minor = webkit_get_minor_version();
+    return major > 2 || (major == 2 && minor >= 44);
+#else
+    return false;
+#endif
+}
+
 #if wxUSE_WEBVIEW_EDGE
 bool WebView::CheckWebViewRuntime()
 {

src/slic3r/GUI/Widgets/WebView.hpp

@@ -30,11 +30,16 @@ public:
     // ignoring every navigation. A panel that gets true here recreates its view on first Show().
     static bool NeedsRecreateOnShow();
 
-    // True when the linked WebKitGTK predates the fix for the XWayland accelerated
-    // compositing bug (< 2.42), so accelerated compositing must be forced off. False
-    // on every other platform. Safe to call before GTK initialises.
+    // True when the linked WebKitGTK predates 2.42, where accelerated compositing
+    // could fail silently on XWayland sessions, so it is forced off as a fallback.
+    // False on every other platform. Safe to call before GTK initialises.
     static bool NeedsCompositingWorkaround();
 
+    // True when the linked WebKitGTK is new enough (>= 2.44) to honour
+    // WEBKIT_DMABUF_RENDERER_FORCE_SHM, the shared-memory transport switch.
+    // False on every other platform. Safe to call before GTK initialises.
+    static bool SupportsForceSharedMemory();
+
     static void RecreateAll();
 };