SCGetScanLine(3)

NAME
     SCGetScanLine, SCGetFD, SCDataReady - retrieving scan data

SYNOPSIS
     #include <stdio.h>
     #include <scanner.h>

     int SCGetScanLine(SCANNER *s, void *buf, long bytes);

     int SCGetFD(SCANNER *s);

     int SCDataReady(SCANNER *s);

DESCRIPTION
     SCGetScanLine retrieves scan line data.  s specifies a connection to a
     scanner for which SCScan(3) has been called previously.  buf points to
     memory into which the data will be stored, and bytes should be set to the
     number of bytes in a scan line as determined by SCGetScanSize(3).

     For color planar data, SCGetScanLine will need to be called once for each
     line in each plane of data.  For 100 lines of 24 bit planar RGB data,
     SCGetScanLine will be called a total of 300 times, with the first 100
     calls retrieving the red plane, the second 100 calls retrieving the green
     plane, and the third 100 calls retrieving the blue plane.  For other
     types of data, SCGetScanLine will need to be called once for each line of
     data.  The number of lines can be determined by calling SCGetScanSize(3).

     SCGetScanLine cannot be called to retrieve scan data if scanning was
     initiated by a call to SCScanFD(3).

     If scanning was initiated by a call to SCScan(3), SCGetFD returns a file
     descriptor from which scan data can be read.  This file descriptor can be
     used with the select(2) system call to determine when SCGetScanLine(3)
     should be called, or the data can be read directly from the file
     descriptor as an alternative means of retrieving the scan data.

     If scanning was initiated by a call to SCScanFD(3), SCGetFD will return
     the file descriptor that was passed to SCScanFD(3).

     SCDataReady is used to determine whether the scanner driver has prepared
     any data for transfer.  It can be used to determine when SCGetScanLine
     should be called.  It should not be used if scanning was initiated by a
     call to SCScanFD(3).

RETURN VALUE
     SCGetScanLine returns 0 if successful, and -1 if an error occurs.

     SCGetFD returns a file descriptor from which scan data may be read if
     scanning was initiated by a call to SCScan(3).  If scanning was initiated
     by a call to SCScanFD, SCGetFD returns the file descriptor that was
     passed to SCScanFD.  If an error occurs, SCGetFD returns -1.
     SCDataReady returns 1 if data is ready to be retrieved from the scanner.
     0 is returned if data is not ready, and -1 is returned if an error
     occurs.

     If the return value of one of these functions indicates that an error has
     occurred, the cause of the error can be determined by inspecting the
     value of the global variable SCerrno.

EXECUTION ERROR CODES
     SCGetScanLine, SCGetFD, and SCDataReady will fail under the following
     circumstances.

     SCESCANFD                SCGetScanLine called after SCScanFD

     SCECOMM                  Error communicating with scanner driver

SEE ALSO
     libscan(3), SCScan(3), SCScanFD(3).