fix oxygen

see https://github.com/libvips/libvips/issues/2650#issuecomment-1050142161

configure.ac

@@ -228,6 +228,13 @@ VIPS_LIBDIR=$expanded_value
 VIPS_EXEEXT=$EXEEXT
 AC_SUBST(VIPS_EXEEXT)
 
+# cplusplus/Doxyfile.in needs an input and output directory ... they are the
+# same for copnfigure, but meson has separate source and build areas
+DOXY_INPUT_DIRECTORY=$ac_pwd/$srcdir/cplusplus
+DOXY_OUTPUT_DIRECTORY=$ac_pwd/$srcdir/cplusplus
+AC_SUBST(DOXY_INPUT_DIRECTORY)
+AC_SUBST(DOXY_OUTPUT_DIRECTORY)
+
 # vips.c/im_guess_prefix.c need to know the exe suffix and (as a fallback)
 # the configure-time install prefix
 AC_DEFINE_UNQUOTED(VIPS_PREFIX,"$prefix",[configure-time install prefix])

cplusplus/Doxyfile.in

@@ -58,7 +58,7 @@ PROJECT_LOGO           =
 # entered, it will be relative to the location where doxygen was started. If
 # left blank the current directory will be used.
 
-OUTPUT_DIRECTORY       = @OUTPUT_DIRECTORY@
+OUTPUT_DIRECTORY       = @DOXY_OUTPUT_DIRECTORY@
 
 # If the CREATE_SUBDIRS tag is set to YES then doxygen will create 4096 sub-
 # directories (in 2 levels) under the output directory of each output format and
@@ -756,7 +756,7 @@ CITE_BIB_FILES         =
 # messages are off.
 # The default value is: NO.
 
-QUIET                  = NO
+QUIET                  = YES
 
 # The WARNINGS tag can be used to turn on/off the warning messages that are
 # generated to standard error (stderr) by doxygen. If WARNINGS is set to YES
@@ -824,17 +824,17 @@ WARN_LOGFILE           =
 # Note: If this tag is empty the current directory is searched.
 
 INPUT                  = \
-  README.md \
-	VConnection.cpp \
-	VError.cpp \
-	VImage.cpp \
-	VInterpolate.cpp \
-	vips-operators.cpp \
-	include/vips/VConnection8.h \
-	include/vips/VError8.h \
-	include/vips/VImage8.h \
-	include/vips/VInterpolate8.h \
-	include/vips/vips8
+	@DOXY_INPUT_DIRECTORY@/README.md \
+	@DOXY_INPUT_DIRECTORY@/VConnection.cpp \
+	@DOXY_INPUT_DIRECTORY@/VError.cpp \
+	@DOXY_INPUT_DIRECTORY@/VImage.cpp \
+	@DOXY_INPUT_DIRECTORY@/VInterpolate.cpp \
+	@DOXY_INPUT_DIRECTORY@/vips-operators.cpp \
+	@DOXY_INPUT_DIRECTORY@/include/vips/VConnection8.h \
+	@DOXY_INPUT_DIRECTORY@/include/vips/VError8.h \
+	@DOXY_INPUT_DIRECTORY@/include/vips/VImage8.h \
+	@DOXY_INPUT_DIRECTORY@/include/vips/VInterpolate8.h \
+	@DOXY_INPUT_DIRECTORY@/include/vips/vips8
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses

cplusplus/meson.build

@@ -41,7 +41,9 @@ if get_option('doxygen')
     doxygen_data = configuration_data()
     doxygen_data.set('VIPS_MAJOR_VERSION', version_major)
     doxygen_data.set('VIPS_MINOR_VERSION', version_minor)
-    doxygen_data.set('OUTPUT_DIRECTORY', 'cplusplus')
+    doxygen_data.set('DOXY_INPUT_DIRECTORY', 
+      join_paths(meson.source_root(), meson.current_source_dir()))
+    doxygen_data.set('DOXY_OUTPUT_DIRECTORY', 'cplusplus')
 
     doxyfile = configure_file(
         input: 'Doxyfile.in',