Make QGL optional.

m4/check-qt.m4

+dnl
+dnl $1 == required: bail out on error
+dnl $1 == optional: just issue a warning.
+dnl
 AC_DEFUN([ALBERT_CHECK_QT],
 [AC_ARG_WITH([qtdir],
 [  --with-qtdir=QTDIR     Attempt to use the QT toolkit located in QTDIR.
@@ -6,7 +10,7 @@ AC_DEFUN([ALBERT_CHECK_QT],
 	yes)
 		;;
 	no)
-		AC_MSG_ERROR([Nope, we _need_ QT])
+		test "$1" = required && AC_MSG_ERROR([Nope, we _need_ QT])
 		;;
 	*)
 		QTDIR=${withval}
@@ -21,7 +25,7 @@ done
 ])
 AC_LANG_PUSH([C++])
 ALBERT_CHECK_PACKAGE(Qt, qt-mt, ${QTDIR}/lib, ${X_LIBS} -lX11,
-                     qgl.h, ${QTDIR}/include, required)
+                     qgl.h, ${QTDIR}/include, $1)
 AC_LANG_POP
 dnl
 dnl check for QGLWidget
@@ -37,7 +41,11 @@ AC_CACHE_CHECK([whether class QGLWidget compiles and links],
 #endif]],
                                     [[QGLWidget qgl;]])],
                     [ac_cv_qglwidget_links=yes],
-                    [AC_MSG_FAILURE([Unable to compile and link a "QGLWidget"])
+                    [if test "$1" = required; then
+                       AC_MSG_FAILURE([Unable to compile and link a "QGLWidget"])
+                     else
+                       AC_MSG_RESULT([Unable to compile and link a "QGLWidget"])
+                     fi
                    ])
     AC_LANG_POP
     LDFLAGS="${ac_save_LDFLAGS}"
@@ -51,13 +59,19 @@ AC_ARG_WITH([moc],
 	yes)
 		;;
 	no)
-		AC_MSG_ERROR([Nope, we need moc])
+		test "$1" = required && AC_MSG_ERROR([Nope, we need moc])
 		;;
 	*)
 		MOCPATH=${withval}
 		;;
 esac],
 [MOCPATH=${QTDIR}/bin])
-AC_PATH_PROG([MOC], moc, , [$MOCPATH:$QTDIR/bin:$PATH])
+AC_PATH_PROG([MOC], moc,
+  [test "$1" == required && AC_MSG_ERROR(["moc" not found])],
+  [$MOCPATH:$QTDIR/bin:$PATH])
 
+if test -n "$Qt_LIB" -a -n "$MOC" -a "$ac_cv_qglwidget_links" = yes; then
+	AC_DEFINE([HAVE_QGL_WIDGET], 1,
+		  [Define to "1" if Qt's QGLWidget is present and compiles])
+fi
 ])