Customize using plugins

The pibooth application is built on the top of pluggy that gives users the ability to extend or modify its behavior thanks to plugins.

Several plugins maintained by the community are available. They add extra features to pibooth. Have a look to the plugins on PyPI.

You can also easily develop your own plugin, and declare it in the [GENERAL][plugins] key of the configuration.

What is a plugin?

A plugin is a set of functions (called hooks) defined in a python module and participating to the pibooth execution when they are invoked.

The list of available hooks are defined on this chapter. A plugin implements a subset of those functions.

There are 2 families of hooks implemented in pibooth:

  • Pibooth state-independent hooks

  • State dependant hooks (see below)

Influencing states

The pibooth application is built on the principle of states. Each state is defined by a specific screen and possible actions available to the user.

The following states are defined:

  • wait : wait for starting a new capture sequence

  • choose : selection of the number of captures

  • chosen : confirm the number of captures

  • preview : show preview and countdown

  • capture : take a capture

  • processing : build the final picture

  • print : show preview and ask for printing

  • finish : thank before going back to wait state

  • failsafe : oops message when an exception occurs

State sequence

There are four hooks defined for each state.

  • state_<name>_enter

    Invoked one time when the state is activating.

  • state_<name>_do

    Invoked in a loop until the state is switching to an other one.

  • state_<name>_validate

    Invoked in a loop, returns the name of the next state if all conditions are met (else return None).

  • state_<name>_exit

    Invoked one time when the state is exiting.

Code skeleton

A plugin is generally a Python module called pibooth_[...].py. For a better configuration management, it should have the constant __version__ set to the plugin version:

__version__ = "1.0.0"

The pibooth_configure hook permits to define some new configuration options. At this step of the starting process, only the pre-loaded configuration is available (application is not created yet).

def pibooth_configure(cfg):
    cfg.add_option('CONTROLS', 'startup_led_pin', 29,
                   "Physical GPIO OUT pin to light a LED at pibooth startup")

The new objects, which should persist between states, can be created and attached to the application instance in the pibooth_startup hook:

def pibooth_startup(cfg, app):
    app.led_startup = LED("BOARD" + cfg.get('CONTROLS', 'startup_led_pin'))

Access to internal variables