WSLg GUI: force Mesa d3d12 + GTK4 GL renderer for system apps

System-installed GUI apps (nautilus, gnome-software, epiphany when
run as RPM not flatpak) fail to render content on WSLg because:

- Mesa 25 defaults to Zink (GL-on-Vulkan) for the GL stack
- Zink requires Vulkan features (nullDescriptor, robustness2)
- WSLg's only Vulkan ICD is dzn (DirectX-to-Vulkan bridge), which
  is non-conformant and missing those features
- Result: window registers with weston RDP rail (taskbar icon
  appears) but the frame buffer can never initialize -> nothing
  ever renders inside the window

Operator 2026-05-10: "the windows never render though--there's an
icon on the windows taskbar but no actual window EVER rendered."

Fix: /etc/profile.d/mios-wslg-gpu.sh exports:
  GALLIUM_DRIVER=d3d12               -> Mesa GL via Direct3D 12
  MESA_LOADER_DRIVER_OVERRIDE=d3d12  -> override DRI auto-detection
  LIBGL_KOPPER_DISABLE=1             -> skip Mesa-25 Kopper-on-Zink
  GSK_RENDERER=gl                    -> GTK4 OpenGL renderer (not Vulkan)
  WEBKIT_DISABLE_COMPOSITING_MODE=1  -> WebKitGTK avoids Vulkan path
  WAYLAND_DISPLAY=wayland-0          -> WSLg Wayland default
  DISPLAY=:0                         -> XWayland fallback

Gated on /mnt/wslg presence (ConditionPath equiv) -- inert outside
WSLg, so bare-metal / Hyper-V / QEMU / OCI deployments keep their
canonical Mesa path.

Verified: weston.log RDP-rail shows windows registering at proper
sizes once the env is loaded by an interactive shell (apps run from
the user's bash prompt source /etc/profile.d/* via /etc/profile).

Note: this gets system apps to register windows but content
rendering is still gated on the underlying d3d12-driver path. For
GTK4 apps that still hit dzn-unsupported features, GSK_RENDERER
can be flipped to "cairo" via per-app override or operator-level
~/.config/environment.d/. Follow-up: evaluate adding NVIDIA Vulkan
ICD when host has NVIDIA GPU (RTX 4090 in the operator's case).

Author: Kabuki94

etc/profile.d/mios-wslg-gpu.sh

@@ -0,0 +1,71 @@
+# /etc/profile.d/mios-wslg-gpu.sh
+#
+# WSLg GUI rendering env. Without this, GTK4 + Mesa default to
+# Vulkan-via-Zink-via-dzn (DirectX-to-Vulkan bridge on WSLg) --
+# but dzn is non-conformant and missing features Zink requires
+# (nullDescriptor, robustness2, descriptor pool memory). Result:
+# the app's Wayland surface registers with weston RDP rail (the
+# Windows taskbar shows the icon), but the frame buffer can never
+# initialize. Operator-visible failure mode 2026-05-10: "the
+# windows never render though--there's an icon on the windows
+# taskbar but no actual window EVER rendered."
+#
+# Solution: force Mesa onto the d3d12 Gallium driver (translates
+# OpenGL calls to Direct3D 12 -> goes through /dev/dxg -> real GPU
+# acceleration on the Windows host), and tell GTK4's GSK to use
+# its GL renderer instead of the Vulkan one. dzn stays available
+# for apps that explicitly want it, but isn't the default.
+#
+# Gated on /mnt/wslg presence -- inert outside WSLg (bare-metal /
+# Hyper-V / QEMU / OCI keep their canonical Mesa+Vulkan path).
+#
+# Compatible with bash, sh, zsh, dash login shells -- no bashisms.
+
+[ -d /mnt/wslg ] || return 0
+
+# ── Mesa / GL ────────────────────────────────────────────────────
+# d3d12 = the Mesa Gallium driver that targets WSLg's WDDM via
+# /dev/dxg. Far more reliable than dzn (Vulkan) for typical GTK
+# workloads. The MESA_LOADER override forces Mesa's loader to
+# pick the d3d12 driver even when its auto-detection fails (which
+# it does on WSLg because /dev/dri/* devices don't exist).
+export GALLIUM_DRIVER="${GALLIUM_DRIVER:-d3d12}"
+export MESA_LOADER_DRIVER_OVERRIDE="${MESA_LOADER_DRIVER_OVERRIDE:-d3d12}"
+# Mesa-25+ replaced the old DRI2 path with Kopper for X-on-Vulkan;
+# Kopper on WSLg goes through Zink which goes through dzn -- so
+# disable Kopper to keep GL apps on the d3d12 path.
+export LIBGL_KOPPER_DISABLE="${LIBGL_KOPPER_DISABLE:-1}"
+
+# ── GTK4 ─────────────────────────────────────────────────────────
+# GTK4's default GSK_RENDERER on >= 4.14 is "ngl" (preferring
+# Vulkan). On WSLg with dzn broken that renders to a 0x0 surface.
+# Force "gl" (the OpenGL renderer that uses GALLIUM_DRIVER=d3d12
+# above). "cairo" is the software fallback if d3d12 also fails.
+export GSK_RENDERER="${GSK_RENDERER:-gl}"
+
+# ── WebKit (Epiphany / GNOME-Web) ───────────────────────────────
+# WebKit's accelerated compositing path tries Vulkan first too.
+# Disabling AC mode keeps WebKit on the GL path which honors
+# GALLIUM_DRIVER=d3d12.
+export WEBKIT_DISABLE_COMPOSITING_MODE="${WEBKIT_DISABLE_COMPOSITING_MODE:-1}"
+
+# ── Wayland defaults ─────────────────────────────────────────────
+# WSLg sets WAYLAND_DISPLAY=wayland-0 and stages the socket at
+# /mnt/wslg/runtime-dir/wayland-0 (symlinked into $XDG_RUNTIME_DIR).
+# These are usually already exported by WSL's init -- export them
+# defensively so apps launched from non-login shells (cron, dbus
+# activation) still find them.
+export WAYLAND_DISPLAY="${WAYLAND_DISPLAY:-wayland-0}"
+[ -n "${XDG_RUNTIME_DIR:-}" ] || export XDG_RUNTIME_DIR="/run/user/$(id -u 2>/dev/null || echo 1000)"
+
+# ── X11 fallback (XWayland) ──────────────────────────────────────
+# Some apps (older Qt5 utilities) still want X11. WSLg provides
+# XWayland at /tmp/.X11-unix/X0 -- ensure DISPLAY points there.
+export DISPLAY="${DISPLAY:-:0}"
+
+# ── Vulkan ICD ──────────────────────────────────────────────────
+# WSLg ships dzn at /usr/share/vulkan/icd.d/dzn_icd.x86_64.json.
+# We don't unset it -- apps that explicitly request Vulkan can
+# still use it (and may work for compute / non-graphical workloads).
+# But we don't make it the GTK / GL default.
+: