$Header: /a/cvs/386BSD/ports/xv/tiff/README,v 1.1.1.1 1993/08/18 21:10:20 smace Exp $ Configuration Comments: ---------------------- Aside from the compression algorithm support, there are configuration-related defines that you can override in the Makefile or in the default configuration file tiffconf.h: COLORIMETRY_SUPPORT if this is defined, support for the colorimetry tags will be compiled in. JPEG_SUPPORT if this is defined, support for the JPEG-related tags will be compiled in. Note that at the present time the JPEG compression support is not included. YCBCR_SUPPORT if this is defined, support for the YCbCr-related tags will be compiled in. Note that you'll want YCBCR support for JPEG compression+decompression. CMYK_SUPPORT if this is defined, support for the CMYK-related tags will be compiled in. MMAP_SUPPORT if this is set, and OS support exists for memory mapping files, then the library will try to map a file if it is opened for reading. If mmap does not exist on your system, or the mmap call fails on the file, then the normal read system calls are used. It is not clear how useful this facility is. By default tiffconf.h defines COLORIMETRY_SUPPORT, JPEG_SUPPORT, YCBCR_SUPPORT, CMYK_SUPPORT. MMAP_SUPPORT is not defined. Portability Comments: -------------------- I run this code on SGI machines (big-endian, MIPS CPU, 32-bit ints, IEEE floating point). Makefiles exist for other platforms that the code runs on -- this work has mostly been done by other people. I've also been told that the code runs on Macintosh and PC-based systems, although I don't know the particulars. In general, I promise only that the code runs on SGI machines. I will, however, gladly take back fixes to make it work on other systems -- when the changes are reasonable unobtrusive. I've tried to isolate as many of the OS-dependencies as possible in two files: tiffcomp.h and tif_.c. The latter file contains OS-specific routines to do I/O and I/O-related operations. The UNIX (tif_unix.c), Macintosh (tif_apple.c), and VMS (tif_vms.c) code has had the most use; the MS/DOS support (tif_msdos.c) assumes some level of UNIX system call emulation (i.e. open, read, write, fstat, malloc, free). Machine dependencies such as byte order are determined on the fly and do not need to be specified. Five general portability-related defines are: USE_VARARGS define as 0 or 1 to select between the use of varargs.h and stdarg.h; i.e. -DUSE_VARARGS=0 means use stdarg.h USE_PROTOTYPES define as 0 or 1 to select function declarations and definitions with parameter types USE_CONST if your compiler defines __STDC__ or __EXTENSIONS__, but does not support const, define this as 0, otherwise leave it alone BSDTYPES define this if your system does NOT define the usual 4BSD typedefs HAVE_IEEEFP define as 0 or 1 according to the floating point format suported by the machine If you compile the code with prototypes (USE_PROTOTYPES=1), then you must have USE_VARARGS=0. Note that tiffcomp.h defines: USE_PROTOTYPES 1 USE_VARARGS 0 USE_CONST 1 HAVE_IEEEFP 1 (BSDTYPES is not defined). General Comments: ---------------- The library is designed to hide as much of the details of TIFF as possible. In particular, TIFF directories are read in their entirety into an internal format. Only the tags known by the library are available to a user and certain tag data may be maintained that a user doesn't care about (e.g. transfer function tables). To add support for a new directory tag the following mods are needed: 1. Define the tag in tiff.h. 2. Add a field to the directory structure in tiffioP.h and define a FIELD_* bit. 3. Add an entry in the FieldInfo array defined at the top of tiff_dirinfo.c. 4. Add entries in TIFFSetField1() and TIFFGetField1() for the new tag. 5. (optional) If the value associated with the tag is not a scalar value (e.g. the array for TransferFunction), 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 tiff_print.c to print the tag's value. To add support for a compression algorithm: 1. Define the tag value in tiff.h. 2. Edit the file tiff_compress.c to add an entry to the CompressionSchemes[] array. 3. Create a file with the compression scheme code, by convention files are named tif_*.c (except perhaps on some systems where the tif_ prefix pushes some filenames over 14 chars. 4. Edit the Makefiles to include the new source file. A compression scheme, say foo, can have up to 10 entry points: TIFFfoo(tif) /* initialize scheme and setup entry points in tif */ fooPreDecode(tif) /* called once per strip, after data is read, but before the first row in a strip is decoded */ fooDecode*(tif, bp, cc, sample)/* decode cc bytes of data into the buffer */ fooDecodeRow(...) /* called to decode a single scanline */ fooDecodeStrip(...) /* called to decode an entire strip */ fooDecodeTile(...) /* called to decode an entire tile */ fooPreEncode(tif) /* called once per strip/tile, before the first row in a strip is encoded */ fooEncode*(tif, bp, cc, sample)/* encode cc bytes of user data (bp) */ fooEncodeRow(...) /* called to decode a single scanline */ fooEncodeStrip(...) /* called to decode an entire strip */ fooEncodeTile(...) /* called to decode an entire tile */ fooPostEncode(tif) /* called once per strip/tile, just before data is written */ fooSeek(tif, row) /* seek forwards row scanlines from the beginning of a strip (row will always be >0 and