Package gl was not found in the pkg-config search path on WSL2

When you got following error to run the program that depends gl package on WSL2 Ubuntu environment.

% go run main.go
# pkg-config --cflags  -- gl gl
Package gl was not found in the pkg-config search path.
Perhaps you should add the directory containing `gl.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gl' found
Package gl was not found in the pkg-config search path.
Perhaps you should add the directory containing `gl.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gl' found
pkg-config: exit status 1

Try this to resolve problems.

% sudo apt install libgl1-mesa-dev
% export PKG_CONFIG_PATH=/usr/lib/x86_64-linux-gnu/pkgconfig
% export DISPLAY=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}'):0

# run powershell as administrator
> New-NetFirewallRule -DisplayName "WSL" -Direction Inbound  -InterfaceAlias "vEthernet (WSL)"  -Action Allow

install vcxsrv and run on Windows.
https://sourceforge.net/projects/vcxsrv/

And try it again.