support --vips-info

now turns on glib g_info() output

TODO

@@ -1,23 +1,3 @@
-- need some simple way to turn on info output from CLI or env var
-
-- switch to glib logging
-
-	vips_error() stuff must stay
-
-	vips_info() and vips_warn() can change 
-
-	- switch to g_warning() and g_info(), have some compat stuff 
-
-	just calls 
-	
-		g_logv (G_LOG_DOMAIN, G_LOG_LEVEL_INFO, format, args);
-
-	also see
-
-	vips_info_set(), --vips-info, VIPS_INFO
-
-
-
 - not sure about utf8 error messages on win
 
 - strange: 

libvips/deprecated/rename.c

@@ -734,6 +734,18 @@ void
 vips_info_set( gboolean info )
 {
 	vips__info = info;
+
+	if( info ) { 
+		const char *old;
+		char *new;
+
+		old = g_getenv( "G_MESSAGES_DEBUG" );
+		if( !old )
+			old = "";
+		new = g_strdup_printf( "%s VIPS", old );
+		g_setenv( "G_MESSAGES_DEBUG", new, TRUE );
+		g_free( new );
+	}
 }
 
 void 

libvips/include/vips/util.h

@@ -135,6 +135,14 @@ G_STMT_START { \
 	} \
 } G_STMT_END
 
+/* The g_info() macro was added in 2.40.
+ */
+#ifndef g_info
+/* Hopefully we have varargs macros. Maybe revisit this. 
+ */
+#define g_info(...) \
+	 g_log( G_LOG_DOMAIN, G_LOG_LEVEL_INFO, __VA_ARGS__ )
+#endif
 
 /* Various integer range clips. Record over/under flows.
  */

libvips/include/vips/vips.h

@@ -82,6 +82,10 @@
 extern "C" {
 #endif /*__cplusplus*/
 
+/* Use glib structured logging,
+ */
+#define G_LOG_USE_STRUCTURED 
+
 #include <glib.h>
 #include <glib/gstdio.h>
 #include <gmodule.h>

libvips/iofuncs/error.c

@@ -103,6 +103,27 @@
  *
  * The domain argument most of these functions take is not localised and is
  * supposed to indicate the component which failed.
+ *
+ * libvips uses g_warning() and g_info() to send warning and information
+ * messages to the user. You can use the usual glib mechanisms to display or
+ * divert these messages. For example, info messages are hidden by default, but
+ * you can see them with: 
+ *
+ * |[
+ * $ G_MESSAGES_DEBUG=VIPS vipsthumbnail k2.jpg 
+ * VIPS-INFO: thumbnailing k2.jpg
+ * VIPS-INFO: selected loader is VipsForeignLoadJpegFile
+ * VIPS-INFO: input size is 1450 x 2048
+ * VIPS-INFO: loading jpeg with factor 8 pre-shrink
+ * VIPS-INFO: converting to processing space srgb
+ * VIPS-INFO: residual reducev by 0.5
+ * VIPS-INFO: 13 point mask
+ * VIPS-INFO: using vector path
+ * VIPS-INFO: residual reduceh by 0.5
+ * VIPS-INFO: 13 point mask
+ * VIPS-INFO: thumbnailing k2.jpg as ./tn_k2.jpg
+ * ]|
+ *
  */
 
 /* Make global array to keep the error message buffer.

libvips/iofuncs/init.c

@@ -343,6 +343,9 @@ vips_init( const char *argv0 )
 
 	/* Deprecated, this is just for compat.
 	 */
+
+	/* If set by --vips-info.
+	 */
 	if( g_getenv( "VIPS_INFO" ) || 
 		g_getenv( "IM_INFO" ) ) 
 		vips_info_set( TRUE );
@@ -579,12 +582,12 @@ vips__ngettext( const char *msgid, const char *plural, unsigned long int n )
 }
 
 static gboolean
-vips_lib_version_cb( const gchar *option_name, const gchar *value, 
+vips_lib_info_cb( const gchar *option_name, const gchar *value, 
 	gpointer data, GError **error )
 {
-	printf( "libvips %s\n", VIPS_VERSION_STRING );
-	vips_shutdown();
-	exit( 0 );
+	vips_info_set( TRUE ); 
+
+	return( TRUE );
 }
 
 static gboolean
@@ -605,9 +608,18 @@ vips_set_fatal_cb( const gchar *option_name, const gchar *value,
 	return( TRUE );
 }
 
+static gboolean
+vips_lib_version_cb( const gchar *option_name, const gchar *value, 
+	gpointer data, GError **error )
+{
+	printf( "libvips %s\n", VIPS_VERSION_STRING );
+	vips_shutdown();
+	exit( 0 );
+}
+
 static GOptionEntry option_entries[] = {
-	{ "vips-info", 0, G_OPTION_FLAG_HIDDEN, 
-		G_OPTION_ARG_NONE, &vips__info, 
+	{ "vips-info", 0, G_OPTION_FLAG_HIDDEN | G_OPTION_FLAG_NO_ARG, 
+		G_OPTION_ARG_CALLBACK, (gpointer) &vips_lib_info_cb,
 		N_( "show informative messages" ), NULL },
 	{ "vips-fatal", 0, G_OPTION_FLAG_HIDDEN | G_OPTION_FLAG_NO_ARG, 
 		G_OPTION_ARG_CALLBACK, (gpointer) &vips_set_fatal_cb,