update Nix shell function for 3D graphics applications

1 files changed, 9 insertions, 16 deletions

diff --git a/INSTALL.md b/INSTALL.md
index d268dc1..f0c3f25 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -98,24 +98,17 @@ install the *TWEED* packages, use the following command:
 
 	$ nix-env -f tweed.nix -i
 
-Nix applications that use 3D graphics acceleration need help in finding the
-system libraries and drivers.  The paths vary according to operating system and
-graphics card.  For a CentOS 6 system, for example, with an Intel graphics card
-six extra paths need to be defined.  This can be accomplished with an alias or
-a shell function.  Using the shell function approach for the CentOS example,
-the following lines added to the .bashrc file provide a function that sets the
-necessary environment variables and runs the FreeCAD application:
+It is necessary to set an extra environment variable for Nix applications that
+use 3D graphics acceleration.  The extra variable defines the path to the
+directory in the Nix store that contains the graphics drivers.  This can
+conveniently be accomplished with an alias or a shell function.  Using the
+shell function approach, for the FreeCAD application, the following lines added
+to the ~/.bashrc file provide a function that sets the necessary environment
+variable and runs the application:
 	
 	freecad () {
-		FONTCONFIG_PATH="$HOME/.nix-profile/etc/fonts/fonts.conf" \
-		LIBGL_DRIVERS_PATH="/usr/lib64/dri" \
-		LIB1="/lib64/libselinux.so.1" \
-		LIB2="$HOME/.nix-profile/lib/libdrm.so" \
-		LIB3="$HOME/.nix-profile/lib/libdrm_intel.so" \
-		LIB4="$HOME/.nix-profile/lib/libdrm_radeon.so" \
-		LIB5="$HOME/.nix-profile/lib/libpciaccess.so.0" \
-		LD_PRELOAD=$LIB1:$LIB2:$LIB3:$LIB4:$LIB5 \
-		FreeCAD
+                LIBGL_DRIVERS_PATH=$(nix-build --no-out-link -A mesa_drivers $HOME/.nix-defexpr/channels/nixpkgs)/lib/dri \
+		$HOME/.nix-profile/bin/FreeCAD
 	}