detail available environmental variables

pages/Configuring/Environmental-variables.md

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+# Environmental Variables
+
+We have [previously mentioned] using a wrapper to launch Hyprland. Whether you
+start Hyprland through TTY or a Display Manager, it is recommended to use a wrapper.
+As such, you can pass certain environmental variables to improve Wayland compatibility, or
+simply change certain aspects of your desktop.
+
+Please avoid putting those environmental variables in /etc/environment. That will cause all
+sessions (including Xorg ones) to pick up your wayland-specific environmental on traditional
+Linux distros.
+
+## XDG Specifications
+
+- XDG_CURRENT_DESKTOP=Hyprland
+- XDG_SESSION_TYPE=wayland
+- XDG_SESSION_DESKTOP=Hyprland
+
+XDG specific environmental variables are often detected through portals and applications that may
+set those for you, however it is a good idea to provide them in your wrapper script as a fail-safe.
+
+## QT Variables
+
+- QT_AUTO_SCREEN_SCALE_FACTOR=1 - [(From the QT documentation)](https://doc.qt.io/qt-5/highdpi.html)
+  enables automatic scaling, based on the monitor's pixel density
+- QT_QPA_PLATFORM="wayland;xcb" - Tell QT applications to use the Wayland backend, and fall back to x11 if Wayland is unavailable
+- QT_WAYLAND_DISABLE_WINDOWDECORATION=1 - Disables window decorations on QT applications
+- QT_QPA_PLATFORMTHEME=qt5ct - Tells QT based applications to pick your theme from qt5ct, use with Kvantum.
+
+## NVIDIA Specific
+
+To force GBM as a backend, set the following environment variables:
+
+- GBM_BACKEND=nvidia-drm
+- \_\_GLX_VENDOR_LIBRARY_NAME=nvidia
+
+> See [Archwiki Wayland Page](https://wiki.archlinux.org/title/Wayland#Requirements) for more details on those variables.
+
+- LIBVA_DRIVER_NAME=nvidia - Hardware acceleration on NVIDIA GPUs
+
+> See [Archwiki Hardware Acecleration Page](https://wiki.archlinux.org/title/Hardware_video_acceleration)
+> for details and necessary values before setting this variable.
+
+- \_\_GLX_GSYNC_ALLOWED - Controls if G-Sync capable monitors should use Variable Refresh Rate (VRR)
+
+> See [Nvidia Documentation](https://download.nvidia.com/XFree86/Linux-32bit-ARM/375.26/README/openglenvvariables.html) for details.
+
+- \_\_GL_VRR_ALLOWED - Controls if Adaptive Sync should be used. Recommended to set as "0" to avoid having problems on some games.
+
+- WLR_DRM_NO_ATOMIC=1 - use legacy DRM interface instead of atomic mode setting. Might fix flickering issues.
+
+## Toolkit Backend Variables
+
+- SDL_VIDEODRIVER=wayland - Run SDL2 applications on Wayland. Remove or set to x11 if games that provide older versions of SDL cause
+  compatibility issues
+- \_JAVA_AWT_WM_NONEREPARENTING=1 - Fix possibly broken Java applications. Set to 1 until Wakefield is available.
+- CLUTTER_BACKEND="wayland" - Clutter package already has wayland enabled, this variable will force Clutter applications
+  to try and use the Wayland backend
+
+- GDK_BACKEND - Force backend for wayland-enabled GTK3 and GTK4 backends. Available options are "wayland" or "x11". If GTK XWayland
+  applications cause issues when set to "wayland", try "wayland,x11"
+
+## Theming Related Variables
+
+- GTK_THEME - Set a GTK theme manually, for those who want to avoid appearance tools lxappearance or nwg-look
+- XCURSOR_THEME - Set your cursor theme. The theme needs to be installed and readable by your user.
+- XCURSOR_SIZE - Set cursor size. See [here](../FAQ/) for why you might want this variable set.