From da4a717ddcd6ba5b5b0819aabbe49fcd5f77ae4d Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Sat, 2 May 2015 10:09:28 +0200 Subject: remove unused sources --- tiff/html/addingtags.html | 292 ---------------------------------------------- 1 file changed, 292 deletions(-) delete mode 100644 tiff/html/addingtags.html (limited to 'tiff/html/addingtags.html') diff --git a/tiff/html/addingtags.html b/tiff/html/addingtags.html deleted file mode 100644 index 452821c..0000000 --- a/tiff/html/addingtags.html +++ /dev/null @@ -1,292 +0,0 @@ - - - -Modifying The TIFF Library - - - - - -

-Defining New TIFF Tags -

- -Libtiff has built-in knowledge of all the standard TIFF tags, as -well as extentions. The following describes how to add knowledge of -new tags as builtins to libtiff, or how to application specific tags can -be used by applications without modifying libtiff. -

- -

TIFFFieldInfo

- -How libtiff manages specific tags is primarily controlled by the -definition for that tag value stored internally as a TIFFFieldInfo structure. -This structure looks like this: -

- -

-typedef	struct {
-  ttag_t    field_tag;          /* field's tag */
-  short	    field_readcount;    /* read count/TIFF_VARIABLE/TIFF_SPP */
-  short	    field_writecount;   /* write count/TIFF_VARIABLE */
-  TIFFDataType field_type;      /* type of associated data */
-  unsigned short field_bit;     /* bit in fieldsset bit vector */
-  unsigned char field_oktochange;/* if true, can change while writing */
-  unsigned char field_passcount;/* if true, pass dir count on set */
-  char	*field_name;		/* ASCII name */
-} TIFFFieldInfo;
-
- - - -A TIFFFieldInfo definition exists for each built-in tag in the tif_dirinfo.c -file. Some tags which support multiple data types have more than one -definition, one per data type supported.

- -Various functions exist for getting the internal TIFFFieldInfo definitions, -including _TIFFFindFieldInfo(), and _TIFFFindFieldInfoByName(). See -tif_dirinfo.c for details. There must be some mechanism to get the whole -list, though I don't see it off hand.

- -

Default Tag Auto-registration

- -In libtiff 3.6.0 a new mechanism was introduced allowing libtiff to -read unrecognised tags automatically. When an unknown tags is encountered, -it is automatically internally defined with a default name and a type -derived from the tag value in the file. Applications only need to predefine -application specific tags if they need to be able to set them in a file, or -if particular calling conventions are desired for TIFFSetField() and -TIFFGetField().

- -When tags are autodefined like this the field_readcount and -field_writecount values are always TIFF_VARIABLE. The -field_passcount is always TRUE, and the field_bit is -FIELD_CUSTOM. The field name will be "Tag %d" where the %d is the tag -number.

- -

Defining Application Tags

- -For various reasons, it is common for applications to want to define -their own tags to store information outside the core TIFF specification. -This is done by calling TIFFMergeFieldInfo() with one or more TIFFFieldInfos. -

- -The libgeotiff library provides geospatial information extentions within -a TIFF file. First, a set of TIFFFieldInfo's is prepared with information -on the new tags:

- -

-static const TIFFFieldInfo xtiffFieldInfo[] = {
-  
-  /* XXX Insert Your tags here */
-    { TIFFTAG_GEOPIXELSCALE,	-1,-1, TIFF_DOUBLE,	FIELD_CUSTOM,
-      TRUE,	TRUE,	"GeoPixelScale" },
-    { TIFFTAG_GEOTRANSMATRIX,	-1,-1, TIFF_DOUBLE,	FIELD_CUSTOM,
-      TRUE,	TRUE,	"GeoTransformationMatrix" },
-    { TIFFTAG_GEOTIEPOINTS,	-1,-1, TIFF_DOUBLE,	FIELD_CUSTOM,
-      TRUE,	TRUE,	"GeoTiePoints" },
-    { TIFFTAG_GEOKEYDIRECTORY, -1,-1, TIFF_SHORT,	FIELD_CUSTOM,
-      TRUE,	TRUE,	"GeoKeyDirectory" },
-    { TIFFTAG_GEODOUBLEPARAMS,	-1,-1, TIFF_DOUBLE,	FIELD_CUSTOM,
-      TRUE,	TRUE,	"GeoDoubleParams" },
-    { TIFFTAG_GEOASCIIPARAMS,	-1,-1, TIFF_ASCII,	FIELD_CUSTOM,
-      TRUE,	FALSE,	"GeoASCIIParams" }
-};
-
- -In order to define the tags, we call TIFFMergeFieldInfo() on the -desired TIFF handle with the list of TIFFFieldInfos.

- -

-#define	N(a)	(sizeof (a) / sizeof (a[0]))
-
-    /* Install the extended Tag field info */
-    TIFFMergeFieldInfo(tif, xtiffFieldInfo, N(xtiffFieldInfo));
-
- -The tags need to be defined for each TIFF file opened - and when reading -they should be defined before the tags of the file are read, yet a valid -TIFF * is needed to merge the tags against. In order to get them -registered at the appropriate part of the setup process, it is necessary -to register our merge function as an extender callback with libtiff. -This is done with TIFFSetTagExtender(). We also keep track of the -previous tag extender (if any) so that we can call it from our extender -allowing a chain of customizations to take effect.

- -

-static TIFFExtendProc _ParentExtender = NULL;
-
-static
-void _XTIFFInitialize(void)
-{
-    static int first_time=1;
-	
-    if (! first_time) return; /* Been there. Done that. */
-    first_time = 0;
-	
-    /* Grab the inherited method and install */
-    _ParentExtender = TIFFSetTagExtender(_XTIFFDefaultDirectory);
-}
-
- -The extender callback is looks like this. It merges in our new fields -and then calls the next extender if there is one in effect.

- -

-static void
-_XTIFFDefaultDirectory(TIFF *tif)
-{
-    /* Install the extended Tag field info */
-    TIFFMergeFieldInfo(tif, xtiffFieldInfo, N(xtiffFieldInfo));
-
-    /* Since an XTIFF client module may have overridden
-     * the default directory method, we call it now to
-     * allow it to set up the rest of its own methods.
-     */
-
-    if (_ParentExtender) 
-        (*_ParentExtender)(tif);
-}
-
- -The above approach ensures that our new definitions are used when reading -or writing any TIFF file. However, since on reading we already have -default definitions for tags, it is usually not critical to pre-define them. -If tag definitions are only required for writing custom tags, you can just -call TIFFMergeFieldInfo() before setting new tags. The whole extender -architecture can then be avoided.

- -

Adding New Builtin Tags

- -A similar approach is taken to the above. However, the TIFFFieldInfo -should be added to the tiffFieldInfo[] list in tif_dirinfo.c. Ensure that -new tags are added in sorted order by the tag number.

- -Normally new built-in tags should be defined with FIELD_CUSTOM; however, if -it is desirable for the tag value to have it's own field in the TIFFDirectory -structure, then you will need to #define a new FIELD_ value for it, and -add appropriate handling as follows: - - -

    -
  1. Define the tag in tiff.h. -
  2. Add a field to the directory structure in tif_dir.h - and define a FIELD_* bit (also update the definition of - FIELD_CODEC to reflect your addition). -
  3. Add an entry in the TIFFFieldInfo array defined at the top of - tif_dirinfo.c. - Note that you must keep this array sorted by tag - number and that the widest variant entry for a tag should come - first (e.g. LONG before SHORT). -
  4. Add entries in _TIFFVSetField() and _TIFFVGetField() - for the new tag. -
  5. (optional) If the value associated with the tag is not a scalar value - (e.g. the array for TransferFunction) and requires - special processing, - then add the appropriate code to TIFFReadDirectory() and - TIFFWriteDirectory(). You're best off finding a similar tag and - cribbing code. -
  6. Add support to TIFFPrintDirectory() in tif_print.c - to print the tag's value. -
- -

-If you want to maintain portability, beware of making assumptions -about data types. Use the typedefs (uint16, etc. when dealing with -data on disk and t*_t when stuff is in memory) and be careful about -passing items through printf or similar vararg interfaces. - -

Adding New Codec-private Tags

- -To add tags that are meaningful only when a particular compression -algorithm is used follow these steps: - -
    -
  1. Define the tag in tiff.h. -
  2. Allocate storage for the tag values in the private state block of - the codec. -
  3. Insure the state block is created when the codec is initialized. -
  4. At TIFFInitfoo time override the method pointers in the - TIFF structure - for getting, setting and printing tag values. For example, -
    -    sp->vgetparent = tif->tif_vgetfield;
-    tif->tif_vgetfield = fooVGetField;	/* hook for codec tags */
-    sp->vsetparent = tif->tif_vsetfield;
-    tif->tif_vsetfield = fooVSetField;	/* hook for codec tags */
-    tif->tif_printdir = fooPrintDir;	/* hook for codec tags */
-
    - (Actually you may decide not to override the - tif_printdir method, but rather just specify it). -
  5. Create a private TIFFFieldInfo array for your tags and - merge them into the core tags at initialization time using - _TIFFMergeFieldInfo; e.g. -
    -    _TIFFMergeFieldInfo(tif, fooFieldInfo, N(fooFieldInfo));
-
    - (where N is a macro used liberaly throughout the distributed code). -
  6. Fill in the get and set routines. Be sure to call the parent method - for tags that you are not handled directly. Also be sure to set the - FIELD_* bits for tags that are to be written to the file. Note that - you can create ``pseudo-tags'' by defining tags that are processed - exclusively in the get/set routines and never written to file (see - the handling of TIFFTAG_FAXMODE in tif_fax3.c - for an example of this). -
  7. Fill in the print routine, if appropriate. -
- -Note that space has been allocated in the FIELD_* bit space for -codec-private tags. Define your bits as FIELD_CODEC+<offset> to -keep them away from the core tags. If you need more tags than there -is room for, just increase FIELD_SETLONGS at the top of -tiffiop.h. - -
- -Last updated: $Date: 2004/09/10 14:43:18 $ - - - - -- cgit v1.2.3