Printing Graphics An introduction to capabilities of the HP Printer Control Language 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 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 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 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 Set the Cursor Position Set the cursor s Y coordinate ESC p Y Set the cursor s X coordinate ESC p X Example If dots per inch equals 300 then fprintf prn e p dY e p dX 150 150 places the cursor a half inch from margins 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 Enter Raster Graphics Mode The printer s 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 printer s left margin 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 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 End of Page The PCL language is page oriented and once a page s 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 Our wavprint cpp demo We have posted an application program that prints certain Waveform Audio files using the printer s 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
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