Show "No Available Printers" Instead of an Empty Printer Dropdown

A ComboBox with no items opened a one-row-high popup that DropDown never
paints, leaving a blank strip with stale pixels under the box. Don't open
the list when it is empty, and label the printer box in the print and
send-to-printer dialogs when no printer is available.

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

@@ -574,7 +574,8 @@ DMABUF workaround and then branches on `GDK_BACKEND` (an `x11` prefix means the
 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`
+DMABUF renderer. On a hypervisor guest (`/proc/cpuinfo` `hypervisor` flag) and WebKitGTK >= 2.44 it sets
+`WEBKIT_DMABUF_RENDERER_FORCE_SHM=1` alone, since virtual GPUs cannot back the hardware path either. On the default path it forces `GDK_BACKEND=x11` when wx lacks EGL and `WAYLAND_DISPLAY`
 is set, and sets `WEBKIT_DISABLE_COMPOSITING_MODE=1` (non-replacing) inside that branch when the linked
 WebKitGTK is older than 2.42: a forced X11 backend in a Wayland session is the only default-path case
 that runs through XWayland, which `DISPLAY` and `WAYLAND_DISPLAY` alone do not tell you (a native

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

@@ -568,13 +568,18 @@ 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)
-sets the NVIDIA DMABUF workaround and then branches on `GDK_BACKEND`:
+sets the DMABUF workarounds 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
   accelerated compositing instead of dropping it; `WEBKIT_FORCE_DMABUF_RENDERER` clears the
   Debian/Ubuntu/openSUSE `isNVIDIA()` early return, which otherwise returns before the FORCE_SHM check.
+- **Hypervisor guests**, same position: when `is_hypervisor_guest()` (the `hypervisor` flag in
+  `/proc/cpuinfo`) and WebKitGTK >= 2.44, it sets `WEBKIT_DMABUF_RENDERER_FORCE_SHM=1` non-replacing.
+  Virtual GPUs (VirtualBox VMSVGA, VMware, QEMU) cannot back the hardware DMABUF path either, and
+  FORCE_SHM alone was confirmed to fix web views in VirtualBox; the `WEBKIT_FORCE_DMABUF_RENDERER` pair
+  is not needed without the Debian `isNVIDIA()` patch. The flag is x86-only, so ARM guests are not covered.
 - **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`, and in that same branch it sets
   `WEBKIT_DISABLE_COMPOSITING_MODE=1` non-replacing when the linked WebKitGTK predates 2.42
@@ -590,9 +595,9 @@ Runtime backend detection elsewhere uses Orca's `is_running_on_wayland()` / `is_
 (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 accelerated compositing and only
+- **Rule:** On NVIDIA and hypervisor guests reach for `WEBKIT_DMABUF_RENDERER_FORCE_SHM` before
+  `WEBKIT_DISABLE_COMPOSITING_MODE`. **Why:** the proprietary driver and virtual GPUs cannot back WebKit's
+  hardware DMABUF renderer, leaving web views blank or slow; FORCE_SHM keeps accelerated compositing and only
   skips the hardware path, while disabling compositing drops it. Threaded scrolling is a separate,
   release-dependent default (off in 2.44/2.45, on from 2.46). `WEBKIT_DISABLE_DMABUF_RENDERER` is not a
   substitute — it is read first, leaves the transport set empty (no compositing from 2.44 on, where the

src/OrcaSlicer.cpp

@@ -1126,6 +1126,19 @@ static void load_downward_settings_list_from_config(std::string config_file, std
     }
 }
 
+#ifdef __WXGTK__
+// Virtual GPUs (VirtualBox, VMware, QEMU) cannot back WebKit's hardware DMABUF renderer.
+static bool is_hypervisor_guest()
+{
+    std::ifstream cpuinfo("/proc/cpuinfo");
+    std::string line;
+    while (std::getline(cpuinfo, line))
+        if (boost::starts_with(line, "flags"))
+            return line.find(" hypervisor") != std::string::npos;
+    return false;
+}
+#endif
+
 int CLI::run(int argc, char **argv)
 {
     // Mark the main thread for the debugger and for runtime checks.
@@ -1176,6 +1189,9 @@ int CLI::run(int argc, char **argv)
             ::setenv("WEBKIT_FORCE_DMABUF_RENDERER", "1", /* replace */ false);
         }
 
+        if (is_hypervisor_guest() && WebView::SupportsForceSharedMemory())
+            ::setenv("WEBKIT_DMABUF_RENDERER_FORCE_SHM", "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/libvgcode/src/Layers.cpp

@@ -75,7 +75,7 @@ std::vector<float> Layers::get_zs() const
 
 size_t Layers::get_layer_id_at(float z) const
 {
-    auto iter = std::upper_bound(m_items.begin(), m_items.end(), z, [](float z, const Item& item) { return item.z < z; });
+    auto iter = std::upper_bound(m_items.begin(), m_items.end(), z, [](float z, const Item& item) { return item.z > z; });
     return std::distance(m_items.begin(), iter);
 }
 

src/slic3r/GUI/Plater.cpp

@@ -21178,7 +21178,12 @@ void Plater::print_job_finished(wxCommandEvent &evt)
     Slic3r::DeviceManager* dev = Slic3r::GUI::wxGetApp().getDeviceManager();
     if (!dev) return;
 
-    dev->set_selected_machine(evt.GetString().ToStdString());
+    const std::string dev_id = evt.GetString().ToStdString();
+    MachineObject* selected = dev->get_selected_machine();
+    // After a LAN print, the completion event reselects the same printer.
+    // Keep the active session while asynchronous status traffic may still be in flight.
+    if (!selected || selected->get_dev_id() != dev_id || selected->connection_type() != "lan")
+        dev->set_selected_machine(dev_id);
     p->main_frame->request_select_tab(TAB_ID_MONITOR);
     // Selects the status page on a built Device tab; one built by the switch starts there.
     MonitorPanel* curr_monitor = MonitorPanel::if_built();

src/slic3r/GUI/SelectMachine.cpp

@@ -4087,7 +4087,7 @@ void SelectMachineDialog::update_user_printer()
     {
         m_printer_last_select = "";
         update_select_layout(nullptr);
-        m_printer_box->GetPrinterComboBox()->SetTextLabel("");
+        m_printer_box->GetPrinterComboBox()->SetValue(_L("No available printers"));
     }
 
     BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << "for send task, current printer id =  " << m_printer_last_select << std::endl;

src/slic3r/GUI/SendToPrinter.cpp

@@ -1229,7 +1229,7 @@ void SendToPrinterDialog::update_user_printer()
     }
     else {
         m_printer_last_select = "";
-        m_comboBox_printer->SetTextLabel("");
+        m_comboBox_printer->SetValue(_L("No available printers"));
     }
 
     BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << "for send task, current printer id =  " << m_printer_last_select << std::endl;

src/slic3r/GUI/Widgets/ComboBox.cpp

@@ -287,7 +287,7 @@ void ComboBox::DoDeleteOneItem(unsigned int pos)
 
 void ComboBox::ForceDropdownOpen()
 {
-    if (!IsEnabled())
+    if (!IsEnabled() || items.empty())
         return;
 
     if (!drop_down) {
@@ -398,7 +398,7 @@ void ComboBox::mouseDown(wxMouseEvent &event)
     SetFocus();
     if (drop_down) {
         drop.Hide();
-    } else if (drop.HasDismissLongTime()) {
+    } else if (!items.empty() && drop.HasDismissLongTime()) { // DropDown paints nothing for an empty list
         drop.autoPosition();
         drop_down = true;
         drop.Popup(&drop);
@@ -426,7 +426,7 @@ void ComboBox::keyDown(wxKeyEvent& event)
         case WXK_SPACE:
             if (drop_down) {
                 drop.DismissAndNotify();
-            } else if (drop.HasDismissLongTime()) {
+            } else if (!items.empty() && drop.HasDismissLongTime()) {
                 drop.autoPosition();
                 drop_down = true;
                 drop.Popup();