**CIGAL Reference Manual, Chapter 4 (Variables): dflags**
===== Dflags -- Integer variable controlling disk I/O options =====
**usage: dflags = value**

DFLAGS is an internally defined integer variable controlling options
related to reading and writing disk files.  The value of the DFLAGS
parameter can be changed at any time and remains set until it is
explicitly modified again.  The meaning of the various flag bits are:

    Value (octal)    Meaning
      1       1o     Compress data when writing -- Runcode compression
      2       2o     Compress data when writing -- Packbits compression
      4       4o     Compress data when writing -- LZW compression
      8      10o     Use TIFF format when writing -- standard header (default)
     16      20o     Use TIFF format when writing -- short header
     32      40o     Use TIFF format when writing -- reverse byte order
     64     100o     Don't read/write header record
    512    1000o     Don't advance disks on read error (see [DISKHI][4])
   1024    2000o     Do advance disk on write error
   2048    4000o     Do advance disk on delete error
   4096   10000o     Change DATADIR to new disk on read jump
   8192   20000o     Change DATADIR to new disk on write jump
  16384   40000o     When writing SOLID, store as multiple 2-D matrices

Notes:

1. By default CIGAL uses the TIFF (Tagged Image File Format, Aldus Corp.)
format when writing binary data files (DFLAGS = 10o).  For most CIGAL data
variables this results in a standard TIFF file, readable by any software
that recognizes the TIFF format (for exceptions see Note 3).  Setting bit
20o lets you specify that an abbreviated, fixed length TIFF header should
be used.  Fixed length headers are generally easier to transfer to non-TIFF
applications.  The TIFF flags do not affect file reading; CIGAL
automatically recognizes which file format is being used when reading
input.  See [[jvs:cigal:manual:chapter1:tiff|TIFF(1)]] for more on CIGAL's data file formats.

2. Bit values 512 to 8192 are used on systems with multiple disk drives to
allow CIGAL to automatically make use of the extra disk space provided by
multiple disks.  These flags are used in conjunction with the variables
DATADIR, DISKHI and DISKLO.  See help for [[jvs:cigal:manual:chapter4:diskhi|DISKHI(4)]] for more information
about how to specify which disks are available for data files.

3. Graphics files containing vector data (such as created by the SKETCH
command) are written in the TIFF format but are not likely to make sense to
any other software because CIGAL vectors are not a standard TIFF format.
Similarly, variables containing REAL (non-integer) data can be read but
will probably not make sense to other software that uses the TIFF format.
Because TIFF does not recognize 3-dimensional data formats, a SOLID
variable written by CIGAL will be interpreted as a 2-dimensional matrix by
other TIFF readers; this can be partially avoided by setting the 40000o bit
in DFLAGS which causes solid variables to be written as a succesion of 2-d
matrices.  See [[jvs:cigal:manual:chapter1:tiff|TIFF(1)]] for more details of CIGAL's nonstandard TIFF usage.

4. [obsolete] Flag bit 10o is used when transferring data between a file and
the graphics display screen (@0) in 16 color VGA mode.  Data transfer is
much faster if different bitplanes are written separately, compared to
writing pixel by pixel.  However, separating bitplanes means the data file
will only make sense if it is read back to the same type of graphics
display device.  Usually you can avoid using this flag by selecting which
of the different screen display identifiers to use because each name is
associated with a different data format (see [[jvs:cigal:manual:chapter1:vga|VGA(1)]] and 
[[jvs:cigal:manual:chapter2:read|READ(2)]]):
          @0      4 bit pixels in interleaved bitplanes
         @@0      8 bit bitplanes separated as 4 layers
          @1      8 bit file pixels converted to/from 4 bit screen pixels

**See Also:**\\
[[jvs:cigal:manual:chapter4:diskhi|DISKHI(4)]], 
[[jvs:cigal:manual:chapter2:read|READ(2)]], 
[[jvs:cigal:manual:chapter1:tiff|TIFF(1)]], 
[[jvs:cigal:manual:chapter1:vga|VGA(1)]]

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