mirror of https://github.com/GNOME/gimp.git
149 lines
6.1 KiB
Plaintext
149 lines
6.1 KiB
Plaintext
=============================================================
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How does resource tagging in Gimp work?
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=============================================================
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GimpTagged
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Tagging is not limited to a concrete class hierarchy, but any class
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implementing the GimpTagged interface can be tagged. In addition to
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methods for adding/removing/enumerating tags it also requires
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GimpTagged objects to identify themselves:
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* gimp_tagged_get_identifier: used to get a unique identifier of a
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GimpTagged object. For objects which are stored in a file it will
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usually be a filename.
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* gimp_tagged_get_checksum: the identifier mentioned above has the problem
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that it can change during sessions (for example, user moves or renames
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a resource file). Therefore, there needs to be a way to get another
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identifier from the data of the tagged object, so that tags stored between
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session can be remapped properly.
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GimpTag
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Tags are represented by a GimpTag object. There are no limitations for
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tag names except that they cannot contain a selected set of terminal
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punctuation characters (used to separate tags), leading or trailing
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whitespace and cannot begin with a reserved prefix for internal tags
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('gimp:'). These conditions are enforced when creating a tag object from a
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tag string. The only reason for tag creation to fail is if there are
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no characters left after trying to fix a tag according to the
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rules above. Tag names are displayed as the user typed them (case
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sensitive), but tag comparison is done case-insensitively.
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Tags are immutable, i.e. when a tag is created with one name string, it
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cannot be changed, but a new tag has to be created instead.
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There are methods provided for convenient use with glib, a comparison
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function which can be used to sort tag lists and functions for storing
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tags in a GHashTable.
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GimpTagCache
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Between sessions, tags assigned to objects are stored in a cache
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file. The cache file is a simple XML file, which lists all resources and
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tags which are added to them. Resources which have no tags assigned
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are listed here too, so that when we check the cache we know that they
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have no tags assigned instead of trying to find out if the resource file
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has been renamed.
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When the session ends, a list of all resources and their tags
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is constructed. Resources which were not loaded during this session,
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but had tags assigned are also added to the list (they are saved
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because they could be useful in the next session, for example, when
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a temporarily disconnected network directory is reconnected). The list
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is then written to a tag cache file in the user's home directory.
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When the session starts, the previously saved resource and tag mapping has to
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be loaded and assigned to GimpTagged objects. First the tag cache is
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loaded from file, and then containers are added (GimpContainer objects
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which contain items implementing the GimpTagged interface). After that,
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loaded resources are assigned tags:
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If a resource identifier matches an identifier in the cache,
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corresponding tags are assigned to the GimpTagged object.
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Else, if the identifier is not found in the tag cache,
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an attempt is made to check if the resource file has been
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moved/renamed. In such case the checksum is used to match the
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GimpTagged object with all of the records in the tag cache.
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If a match is found,
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the identifier is updated in the tag cache.
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Otherwise,
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the loaded GimpTagged object is considered to be a newly
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added resource.
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GimpFilteredContainer
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A GimpFilteredContainer is a "view" (representation) of a
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GimpContainer. It is related to tagging in that it can be used to
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filter a GimpContainer to contain only GimpTagged objects which have
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certain tags assigned. It is automatically updated with any changes in
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the GimpContainer it wraps. However, items should not be added or removed
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from this container manually as changes do not affect the original
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container and would be lost when the GimpFilteredContainer is
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updated. Instead, the contents should be changed by setting a tag list
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which would be used to filter GimpTagged objects containing all of the
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given GimpTags.
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GimpFilteredContainer can use any GimpContainer as a source
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container. Therefore, it is possible to use the decorator design pattern
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to implement additional container views, such as a view combining items
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from multiple containers.
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GimpTagEntry widget
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The GimpTagEntry widget extends GtkEntry and is used to either assign or
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query tags depending on the selected mode. The widget support various
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usability features:
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* Jellybeans: When a tag is entered and confirmed by either separator,
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pressing return or otherwise, it becomes a jellybean, i.e. a single
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unit, not a bunch of characters. Navigating in a GimpTagEntry,
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deleting tags, etc. can be performed much faster. However, while a tag
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is just being entered (not yet confirmed), all actions operate on
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characters as usual.
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* Custom auto completion is implemented in the GimpTagEntry widget which
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allows to complete tags in the middle of a tag list, doesn't offer
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already completed tags, tab cycles all possible completions, etc.
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* If the GimpTagEntry is empty and unused it displays a description for
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the user regarding its purpose.
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When operating in tag assignment mode, tags are assigned only when
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the user hits the return key.
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When operating in tag query mode, the given GimpFilteredContainer is
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filtered as the user types. The GimpTagEntry also remembers recently used
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configurations, which can be cycled using up and down arrow keys.
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GimpComboTagEntry widget
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The GimpComboTagEntry widget extends GimpTagEntry and adds the ability to pick
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tags from a menu-like list (using the GimpTagPopup widget).
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GimpTagPopup widget
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The GimpTagPopup widget is used as a tag list menu from the GimpComboTagEntry
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widget. It is not designed to be used with any other widget.
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GimpTagPopup has many visual and behavioral similarities to GtkMenu.
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In particular, it uses menu-like scrolling.
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GimpTagPopup implements various usability features, some of which are:
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* Tags which would result in an empty selection of resources are made
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insensitive.
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* Closing either with the keyboard or by clicking outside the popup area.
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* Underlining of highlighted (hovered) tags.
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