[gimp] libgimp: gimp_image_metadata_save_prepare() uses metadata preferences.

[Jehan Pagès <jehanp src gnome org>]

commit 3061268e25785f858d6679b37685818af9d91f4f
Author: Jehan <jehan girinstud io>
Date:   Thu Jan 11 05:17:59 2018 +0100

    libgimp: gimp_image_metadata_save_prepare() uses metadata preferences.
    
    gimp_image_metadata_save_prepare() now back to suggesting metadata
    flags, but this time with reasonnable base. It indeed uses the presence
    of particular metadata, but also whether the preferences asks for this
    metadata to be exported by default or not.

 libgimp/gimpimagemetadata.c |   29 ++++++++++++++++++-----------
 1 files changed, 18 insertions(+), 11 deletions(-)
---
diff --git a/libgimp/gimpimagemetadata.c b/libgimp/gimpimagemetadata.c
index 1c62e94..53a2fb4 100644
--- a/libgimp/gimpimagemetadata.c
+++ b/libgimp/gimpimagemetadata.c
@@ -202,19 +202,23 @@ gimp_image_metadata_load_finish (gint32                 image_ID,
  * gimp_image_metadata_save_prepare:
  * @image_ID:        The image
  * @mime_type:       The saved file's mime-type
- * @available_flags: Value of @flags which would save all available
- *                   metadata in @image_ID when passed to
+ * @suggested_flags: Suggested default values for the @flags passed to
  *                   gimp_image_metadata_save_finish()
  *
  * Gets the image metadata for saving it using
  * gimp_image_metadata_save_finish().
  *
- * The @available_flags are determined from what kind of metadata
- * (Exif, XMP, ...) is actually present in the image. The suggested
- * value for GIMP_METADATA_SAVE_THUMBNAIL is determined by whether
- * there was a thumbnail in the previously imported image.
- * It is up to the calling application to update @available_flags in
- * order to remove any unwanted metadata before exporting.
+ * The @suggested_flags are determined from what kind of metadata
+ * (Exif, XMP, ...) is actually present in the image and the preferences
+ * for metadata exporting.
+ * The calling application may still update @available_flags, for
+ * instance to follow the settings from a previous export in the same
+ * session, or a previous export of the same image. But it should not
+ * override the preferences without a good reason since it is a data
+ * leak.
+ *
+ * The suggested value for GIMP_METADATA_SAVE_THUMBNAIL is determined by
+ * whether there was a thumbnail in the previously imported image.
  *
  * Returns: The image's metadata, prepared for saving.
  *
@@ -258,7 +262,8 @@ gimp_image_metadata_save_prepare (gint32                 image_ID,
 
       /* Exif */
 
-      if (! gexiv2_metadata_has_exif (g2metadata))
+      if (! gimp_export_exif () ||
+          ! gexiv2_metadata_has_exif (g2metadata))
         *suggested_flags &= ~GIMP_METADATA_SAVE_EXIF;
 
       if (comment)
@@ -296,7 +301,8 @@ gimp_image_metadata_save_prepare (gint32                 image_ID,
 
       /* XMP */
 
-      if (! gexiv2_metadata_has_xmp (g2metadata))
+      if (! gimp_export_xmp () ||
+          ! gexiv2_metadata_has_xmp (g2metadata))
         *suggested_flags &= ~GIMP_METADATA_SAVE_XMP;
 
       gexiv2_metadata_set_tag_string (g2metadata,
@@ -332,7 +338,8 @@ gimp_image_metadata_save_prepare (gint32                 image_ID,
 
       /* IPTC */
 
-      if (! gexiv2_metadata_has_iptc (g2metadata))
+      if (! gimp_export_xmp () ||
+          ! gexiv2_metadata_has_iptc (g2metadata))
         *suggested_flags &= ~GIMP_METADATA_SAVE_IPTC;
 
       g_snprintf (buffer, sizeof (buffer),