in configure/CMakeList.txt :
- TIFF_INT8_T/TIFF_UINT8_T is signed/unsigned char
sizeof(char)==1 in C standard
- TIFF_INT16_T/TIFF_UINT16_T is signed/unsigned short
sizeof(short)>=2 in C standard
- TIFF_INT32_T/TIFF_UINT32_T is defined so its sizeof() is 4
- TIFF_INT64_T/TIFF_UINT64_T is defined so its sizeof() is 8
- TIFF_SIZE_T is defined so it has same sizeof() than size_t
- TIFF_SSIZE_T is defined so it has same sizeof() than unsigned char *
Those advanced writing functions must be used in a particular sequence
to make their intended effect. Their aim is to control when/where
the [Strip/Tile][Offsets/ByteCounts] arrays are written into the file.
The purpose of this is to generate 'cloud-optimized geotiff' files where
the first KB of the file only contain the IFD entries without the potentially
large strile arrays. Those are written afterwards.
The typical sequence of calls is:
TIFFOpen()
[ TIFFCreateDirectory(tif) ]
Set fields with calls to TIFFSetField(tif, ...)
TIFFDeferStrileArrayWriting(tif)
TIFFWriteCheck(tif, ...)
TIFFWriteDirectory(tif)
... potentially create other directories and come back to the above directory
TIFFForceStrileArrayWriting(tif): emit the arrays at the end of file
See test/defer_strile_writing.c for a practical example.
... and add per-strile offset/bytecount loading capabilities.
Part of this commit makes the behaviour that was previously met when
libtiff was compiled with -DDEFER_STRILE_LOAD available for default builds
when specifying the new 'D' (Deferred) TIFFOpen() flag. In that mode, the [Tile/Strip][ByteCounts/Offsets]
arrays are only loaded when first accessed. This can speed-up the opening
of files stored on the network when just metadata retrieval is needed.
This mode has been used for years by the GDAL library when compiled with
its embeded libtiff copy.
To avoid potential out-of-tree code (typically codecs) that would use
the td_stripbytecount and td_stripoffset array inconditionnaly assuming they
have been loaded, those have been suffixed with _p (for protected). The
use of the new functions mentionned below is then recommended.
Another addition of this commit is the capability of loading only the
values of the offset/bytecount of the strile of interest instead of the
whole array. This is enabled with the new 'O' (Ondemand) flag of TIFFOpen()
(which implies 'D'). That behaviour has also been used by GDAL, which hacked
into the td_stripoffset/td_stripbytecount arrays directly. The new code
added in the _TIFFFetchStrileValue() and _TIFFPartialReadStripArray() internal
functions is mostly a port of what was in GDAL GTiff driver previously.
Related to that, the public TIFFGetStrileOffset[WithErr]() and TIFFGetStrileByteCount[WithErr]()
functions have been added to API. They are of particular interest when
using sparse files (with offset == bytecount == 0) and you want to detect
if a strile is present or not without decompressing the data, or updating
an existing sparse file.
They will also be used to enable a future enhancement where client code can entirely
skip bytecount loading in some situtations
A new test/defer_strile_loading.c test has been added to test the above
capabilities.
