Scripts to use the correct nixGL paths

.profile

function use_nvidia_drivers() {
    export LD_LIBRARY_PATH=/nix/store/xl3cr8kwlpi0j7il0zx4cb6sw05wx40g-libglvnd-1.2.0/lib:/nix/store/lhfyarm78k3lswp6xcvp51s9x4j6baq0-nvidia-440.64/lib:/nix/store/k8x3i9r3lyx4sv0wls45akvkk23bflg7-nvidia-440.64-lib32/lib:/nix/store/aw33ya4m2qmfjhvrxlvlw9gl28ixviya-libglvnd-1.2.0/lib:${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}
}

function use_intel_drivers() {
    export LIBGL_DRIVERS_PATH=/nix/store/vjcmnq73yj45bksaivwkzpzdc1vzf6yd-mesa-20.0.2-drivers/lib/dri:/nix/store/bdyq8k5kyp2lgva9vr03f04b18ys1vbg-mesa-20.0.2-drivers/lib/dri
    export LD_LIBRARY_PATH=/nix/store/vjcmnq73yj45bksaivwkzpzdc1vzf6yd-mesa-20.0.2-drivers/lib:/nix/store/bdyq8k5kyp2lgva9vr03f04b18ys1vbg-mesa-20.0.2-drivers/lib:$LD_LIBRARY_PATH
}

if [ -f "$HOME/bin/is_egpu_connected.sh" ]; then
    . "$HOME/bin/is_egpu_connected.sh"
    is_egpu_connected
    if [ $? -eq 1 ]; then
        use_nvidia_drivers
    else
        use_intel_drivers
    fi
fi

is_egpu_connected.sh

#!/usr/bin/env bash
# inspired by https://github.com/hertg/egpu-switcher

# declare files
declare xdir=/etc/X11
declare xfile=$xdir/xorg.conf
declare xfile_egpu=$xdir/xorg.conf.egpu

function is_egpu_connected() {

	# read pci id from xorg.conf.egpu
	declare egpu_pci_id=$(cat $xfile_egpu | grep -Ei "BusID" | grep -oEi '[0-9]+\:[0-9]+\:[0-9]+')

	# create an array by splitting the BUS-ID on ':'
	declare busArray=(${egpu_pci_id//:/ })
	declare bus1d=${busArray[0]}
	declare bus2d=${busArray[1]}
	declare bus3d=${busArray[2]}

	# convert dec to hex
	declare bus1h=$(printf "%02x" $bus1d)
	declare bus2h=$(printf "%02x" $bus2d)
	declare bus3h=$(printf "%01x" $bus3d)

	if [ $(lspci | grep -iEc "$bus1h:$bus2h.$bus3h") -eq 1 ]; then
        return 1 # connected
    fi
    return 0 # unconnected
}
hash -r

Take this script as an example of how to automatically set up the OpenGL libs for Nixpkgs.
My setup has an external nvidia which is setup by the egpu-switcher utility.

To configure for your system:

• write a check to see if intel or nvidia drivers are required
• check out the contents of your nixGL and nixGLintel scripts,
• paste exports in the driver functions
• Add the contents of .profile to the end of your ~/.profile file.