cleanup demo build script

build.sh

 #! /bin/bash
 
+CACHE=/tmp/fggl/
+LOG=$CACHE/demo.log
+EXE="../build/demo/FgglDemo"
+
 if [[ ! -d "build/" ]]
 then
 	mkdir build
@@ -10,13 +14,30 @@ sudo dnf install -y wayland-devel libxkbcommon-devel wayland-protocols-devel ext
 sudo dnf install -y glew-devel glm-devel
 
 # if doing shader development, disable the cache to make sure changes take affect
-rm -rf /tmp/fggl/
+rm -rf $CACHE
 
+#
+# build step
+#
 pushd build
 cmake ..
 make
 popd
 
+#
+# additional stuff
+#
+
+# gamemoderun
+if [ -x "$(command -v gamemoderun)" ]; then
+	EXE="gamemoderun $EXE"
+fi
+
+# mangohud
+if [ -x "$(command -v mangohud)" ]; then
+	EXE="mangohud --dlsym $EXE"
+fi
+
 pushd demo
-../build/demo/FgglDemo > /tmp/fggl.log 2>&1 &
+$EXE ../build/demo/FgglDemo > /tmp/fggl.log 2>&1 &
 popd