Printing Graphics

1
Printing Graphics

• An introduction to capabilities of the HP Printer
  Control Language

2
Escape-sequences

• The PCL language employs some special sequences
  of ASCII control-codes, known as escape
  sequences (since they begin with the code for the
  escape-key 0x1B)
• The character-sequence \e may be used to
  generate this special non-printable byte
• The punctuation-symbols, numerals, and alphabetic
  characters that follow specify a specific command
  to the HP laser printer

3
Printer Communication

• An application that wishes to do printing can
  create a textfile containing a mixture of
  document text and PCL commands
• This text file is then submitted to the printer
  using a Linux command (e.g., lpr)
• The printer recognizes commands by the occurrence
  of an escape code

4
Initilization

• Printer initialization command has format
• ESC E
• Example fprintf( prn, \eE )
• // This statement writes the initialization
• // command to a file whose file-pointer is
• // the prn variable

5
Dots-per-inch

• Setting print resolution for raster graphics is
  done with the following command
• ESC t R
• Here the symbol denotes a numeric parameter
  that specifies the number of dots-per-inch (i.e.,
  the pixel resolution)
• Possible choices are 75, 100, 150, 300

6
Set the Cursor Position

• Set the cursors Y-coordinate
• ESC p Y
• Set the cursors X-coordinate
• ESC p X
• Example If dots-per-inch equals 300, then
• fprintf( prn, \epdY\epdX, 150, 150 )
• places the cursor a half-inch from margins

7
Set the Compression Mode

• Here is the command that specifies the type of
  raster data-compression used
• ESC b M
• The possible numeric parameters are
• 0 unencoded (no compression)
• 1 run-length encoding
• 2 tagged image file format (TIFF)
• 3 delta row compression

8
Enter Raster Graphics Mode

• The printers default mode is text mode
• To switch into raster graphics mode, the
  following command is issued
• ESC r A
• Here the symbol specifies the type of
  cursor-positioning that is used
• 1 means use current cursor position
• 0 means use the printers left margin

9
Sending Raster Data

• Here is the command for sending raster graphics
  data to the printer
• ESC b W
• Here the symbol stands for a numeric
  parameter that specifies the number of bytes of
  raster data that follows the W
• Then the cursor moves to the next row

10
Leaving Raster Graphics Mode

• To exit from raster graphics mode, the following
  command is used
• ESC r B
• This command switches the printer back to its
  normal text mode, and it is issued after the
  final row of raster graphics data is sent

11
End-of-Page

• The PCL language is page oriented, and once a
  pages description is complete, the printer
  should eject that page
• The form-feed command \f can be sent to the
  printer to eject the completed page
• fprintf( prn, \f )

12
Our wavprint.cpp demo

• We have posted an application program that prints
  certain Waveform Audio files, using the printers
  PCL raster graphics commands
• So far it only works with 8-bit non-stereo
  data-format
• To avoid wasting paper and toner, it only prints
  the first page of the waveform