feat(quickemu): prefer GTK display backend and add GTK->SDL fallback

- Set default --display to 'gtk' instead of 'sdl'
- Add runtime check to fall back to 'sdl' when QEMU lacks GTK support
  and print a note to the user
- Update usage text to show 'gtk' as the default display option

Signed-off-by: Martin Wimpress <martin@wimpress.org>

Author: flexiondotorg

quickemu

@@ -2295,7 +2295,7 @@ function usage() {
     echo "  --cpu-pinning                     : Choose which host cores correspond to which guest cores."
     echo "  --delete-disk                     : Delete the disk image and EFI variables"
     echo "  --delete-vm                       : Delete the entire VM and its configuration"
-    echo "  --display                         : Select display backend. 'sdl' (default), 'cocoa', 'gtk', 'none', 'spice' or 'spice-app'"
+    echo "  --display                         : Select display backend. 'gtk' (default), 'sdl', 'cocoa', 'none', 'spice' or 'spice-app'"
     echo "  --fullscreen                      : Starts VM in full screen mode (Ctl+Alt+f to exit)"
     echo "  --ignore-msrs-always              : Configure KVM to always ignore unhandled machine-specific registers"
     echo "  --ignore-tsc-warning              : Skip TSC stability warning for macOS VMs on AMD"
@@ -2338,6 +2338,14 @@ function display_param_check() {
         usb_controller="xhci"
     fi
 
+    # Fallback to SDL if GTK display is not available
+    if [ "${display}" == "gtk" ]; then
+        if ! "${QEMU}" -display help 2>&1 | grep -q "^gtk$"; then
+            echo " - NOTE: GTK display not available, falling back to SDL"
+            display="sdl"
+        fi
+    fi
+
     if [ "${OS_KERNEL}" == "Darwin" ]; then
         if [ "${display}" != "cocoa" ] && [ "${display}" != "none" ]; then
           echo "ERROR! Requested output '${display}' but only 'cocoa' and 'none' are avalible on macOS."
@@ -2525,7 +2533,7 @@ cpu_cores=""
 disk_format="${disk_format:-qcow2}"
 disk_img="${disk_img:-}"
 disk_size="${disk_size:-16G}"
-display="${display:-sdl}"
+display="${display:-gtk}"
 extra_args="${extra_args:-}"
 fixed_iso=""
 floppy=""