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We need to adapt to both the change in the name of the project, and to the name change in the pkg-config file.
164 lines
4.2 KiB
Plaintext
164 lines
4.2 KiB
Plaintext
Information about the icon theme cache format used by GTK
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for more information, see the mailing list threads at
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http://mail.gnome.org/archives/gtk-devel-list/2004-April/msg00065.html
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http://lists.freedesktop.org/archives/xdg/2004-October/005140.html
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Back in May, Owen Taylor proposed [1] caching scheme for icon theme
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information, to reduce the amount of stating and disk seeking at
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application startup, and to reduce the memory overhead if each app
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allocates all the icon theme data separately.
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The proposal is to keep the information about the icons in the
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directory tree below each icon theme directory in an mmap()able
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cache file (There is basically one cache file per index.theme file).
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The cache doesn't try to hold all information from the index.theme files
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that you would need to do lookups; it turns out that with the icon theme
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specification, this isn't even sensible - you can install a
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$HOME/.local/share/icons/Bluecurve/index.theme
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That overrides
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/usr/share/icons/Bluecurve/index.theme
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and chances how lookup happens for icons in /usr/share/icons/Bluecurve.
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We would like to propose the cache file format as an appendix to the
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icon theme specification. One thing which still needs to be investigated
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is caching of the actual image data; the file format is has an
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IMAGE_DATA_OFFSET member to allow adding that compatibly. An
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implementation of the caching scheme for GTK can be found at [2]. The
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cache generator which is included in the patch depends only on glib, and
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it may be a good idea to move it to freedesktop.org as well.
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Regards, Matthias Clasen
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The cache file format:
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Header:
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2 CARD16 MAJOR_VERSION 1
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2 CARD16 MINOR_VERSION 0
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4 CARD32 HASH_OFFSET
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4 CARD32 DIRECTORY_LIST_OFFSET
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DirectoryList:
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4 CARD32 N_DIRECTORIES
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4*N_DIRECTORIES CARD32 DIRECTORY_OFFSET
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Hash:
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4 CARD32 N_BUCKETS
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4*N_BUCKETS CARD32 ICON_OFFSET
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Icon:
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4 CARD32 CHAIN_OFFSET
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4 CARD32 NAME_OFFSET
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4 CARD32 IMAGE_LIST_OFFSET
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ImageList:
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4 CARD32 N_IMAGES
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8*N_IMAGES Image IMAGES
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Image:
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2 CARD16 DIRECTORY_INDEX
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2 ICON_FLAGS FLAGS
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4 CARD32 IMAGE_DATA_OFFSET
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ICON_FLAGS
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HAS_SUFFIX_PNG 1
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HAS_SUFFIX_XPM 2
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HAS_SUFFIX_SVG 4
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HAS_ICON_FILE 8
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ImageData:
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4 CARD32 IMAGE_PIXEL_DATA_OFFSET
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4 CARD32 IMAGE_META_DATA_OFFSET
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4 CARD32 IMAGE_PIXEL_DATA_TYPE
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4 CARD32 IMAGE_PIXEL_DATA_LENGTH
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N/A N/A PIXEL_DATA
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IMAGE_PIXEL_DATA_TYPE
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0 GdkPixdata format
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MetaData:
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4 CARD32 EMBEDDED_RECT_OFFSET
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4 CARD32 ATTACH_POINT_LIST_OFFSET
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4 CARD32 DISPLAY_NAME_LIST_OFFSET
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EmbeddedRect:
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2 CARD16 X0
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2 CARD16 Y0
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2 CARD16 X1
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2 CARD16 Y1
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AttachPointList:
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4 CARD32 N_ATTACH_POINTS
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4*N_ATTACH_POINTS AttachPoint
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AttachPoint:
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2 CARD16 X
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2 CARD16 Y
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DisplayNameList:
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4 CARD32 N_DISPLAY_NAMES
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4*N_DISPLAY_NAMES DisplayName
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DisplayName:
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4 CARD32 DISPLAY_LANG_OFFSET
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4 CARD32 DISPLAY_NAME_OFFSET
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Notes:
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* All offsets are from in bytes from the beginning of the file
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* Strings are zero-terminated
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* Directories are stored as relative paths.
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* All numbers are in network (big-endian) order. This is
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necessary because the data will be stored in arch-independent
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directories like /usr/share/icons or even in user's
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home directories.
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* The hash function is that used by g_str_hash()
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unsigned int
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icon_str_hash (gconstpointer key)
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{
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const char *p = key;
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unsigned int h = *p;
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if (h)
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for (p += 1; *p != '\0'; p++)
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h = (h << 5) - h + *p;
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return h;
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}
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This should not be implemented by calling g_str_hash(). For
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optimal results, N_BUCKETS should be typically be prime.
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* The same file format is used for icon themes (e.g.,
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/usr/share/icons/Bluecurve) and for unthemed icon directories
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(e.g., /usr/share/pixmaps)
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For an unthemed directory, N_DIRECTORIES==0 and each
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image has a DIRECTORY_INDEX field of 0xFFFF.
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* Up-to-dateness of a cache file is determined simply:
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If the mod-time on the directory where the cache file
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lives is newer than the mod-time of the cache file,
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the cache file is out of date.
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* Cache files have to be written atomically - write to a
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temporary name, then move over the old file - so that
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clients that have the old cache file open and mmap'ed
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won't get corrupt data.
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