Merge branch 'capabilities' into text-encoding

doc/index.rst

@@ -18,6 +18,7 @@ Content
    user/raspi
    user/todo
    user/usage
+   user/barcode
 
 .. toctree::
    :maxdepth: 1

doc/user/barcode.rst

@@ -0,0 +1,34 @@
+Printing Barcodes
+-----------------
+:Last Reviewed: 2016-07-31
+
+Most ESC/POS-printers implement barcode-printing.
+The barcode-commandset is implemented in the barcode-method.
+For a list of compatible barcodes you should check the manual of your printer.
+As a rule of thumb: even older Epson-models support most 1D-barcodes.
+To be sure just try some implementations and have a look at the notices below.
+
+barcode-method
+~~~~~~~~~~~~~~
+The barcode-method is rather low-level and orients itself on the implementation of ESC/POS.
+In the future this class could be supplemented by a high-level class that helps the user generating the payload.
+
+.. py:currentmodule:: escpos.escpos
+
+.. automethod:: Escpos.barcode
+    :noindex:
+
+CODE128
+~~~~~~~
+Code128 barcodes need a certain format.
+For now the user has to make sure that the payload is correct.
+For alphanumeric CODE128 you have to preface your payload with `{B`.
+
+.. code-block:: Python
+
+   from escpos.printer import Dummy, Serial
+   p = Serial()
+   # print CODE128 012ABCDabcd
+   p.barcode("{B012ABCDabcd", "CODE128", function_type="B")
+
+A very good description on CODE128 is also on `Wikipedia <https://en.wikipedia.org/wiki/Code_128>`_.

doc/user/usage.rst

@@ -218,3 +218,34 @@ Here you can download an example, that will print a set of common barcodes:
 
     * :download:`barcode.bin </download/barcode.bin>` by `@mike42 <https://github.com/mike42>`_
 
+Hint: preprocess printing
+-------------------------
+
+Printing images directly to the printer is rather slow.
+One factor that slows down the process is the transmission over e.g. serial port.
+
+Apart from configuring your printer to use the maximum baudrate (in the case of serial-printers), there is not much
+that you can do.
+However you could use the :py:class:`escpos.printer.Dummy`-printer to preprocess your image.
+This is probably best explained by an example:
+
+.. code-block:: Python
+
+   from escpos.printer import Serial, Dummy
+
+   p = Serial()
+   d = Dummy()
+
+   # create ESC/POS for the print job, this should go really fast
+   d.text("This is my image:\n")
+   d.image("funny_cat.png")
+   d.cut()
+
+   # send code to printer
+   p._raw(d.output)
+
+This way you could also store the code in a file and print later.
+You could then for example print the code from another process than your main-program and thus reduce the waiting time.
+(Of course this will not make the printer print faster.)
+
+