+# Check for gtk 3
+AC_ARG_ENABLE([gtk3],
+ AS_HELP_STRING([--enable-gtk3], [Build with gtk3 support]))
+AS_IF([test "$enable_gtk3" = "yes"],
+ [PKG_CHECK_MODULES(GTK, gtk+-3.0 >= 3.0)],
+ [PKG_CHECK_MODULES(GTK, gtk+-2.0 >= 2.18)])
+AS_IF([test "$enable_gtk3" = "yes"],
+ [GTK_VERSION=gtk+-3.0],
+ [GTK_VERSION=gtk+-2.0])
+AC_SUBST(GTK_VERSION)
+
+# Check for glut for example plugin
+AC_CHECK_LIB(glut, glutSolidTeapot, GLUT_LIBS="-lglut")
+AM_CONDITIONAL(HAVE_GLUT, test "$GLUT_LIBS" != "")
+AC_SUBST(GLUT_LIBS)
+
+# Test for windowing system