add support for PNG output (default)

regularize include guards

Change-Id: Ia1d0fa49c8c98e2c11f775b839d04a24e5450170

configure.ac

@@ -1,6 +1,41 @@
 AC_INIT([webpdecode], [0.1])
 AM_INIT_AUTOMAKE
 AC_PROG_LIBTOOL
+AM_PROG_CC_C_O
+
+dnl === check for PNG support ===
+
+PNG_INCLUDES=""
+PNG_LIBS=""
+AC_PATH_PROG(LIBPNG_CONFIG, libpng-config)
+if test -n "$LIBPNG_CONFIG"; then
+  PNG_INCLUDES=`$LIBPNG_CONFIG --cflags`
+  PNG_PREFIX=`$LIBPNG_CONFIG --prefix`
+  if test "${PNG_PREFIX}/lib" != "/usr/lib" ; then
+    PNG_LIBS="-L${PNG_PREFIX}/lib"
+  fi
+fi
+
+AC_ARG_WITH(pngincludedir,
+            [--with-pngincludedir=DIR use PNG includes from DIR],
+            PNG_INCLUDES="-I$withval")
+AC_ARG_WITH(pnglibdir,
+            [--with-pnglibdir=DIR    use PNG libraries from DIR],
+            [PNG_LIBS="-L$withval"])
+
+AC_CHECK_HEADER(png.h,
+  AC_CHECK_LIB(png, main,
+               [PNG_LIBS="$PNG_LIBS -lpng"
+                PNG_INCLUDES="$PNG_INCLUDES -DWEBP_HAVE_PNG"
+                AC_DEFINE(WEBP_HAVE_PNG, [1], [Set to 1 if PNG library is installed])
+               ],
+               AC_MSG_WARN(Optional png library not found),
+               [$MATH_LIBS]),
+  AC_MSG_WARN(png library not available - no png.h)
+)
+AC_SUBST(PNG_LIBS)
+AC_SUBST(PNG_INCLUDES)
+
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_FILES([Makefile examples/Makefile src/dec/Makefile])