# pcb-rnd modularization

## Why bother...

I believe good software should be modular. This is especially important in the context of large software, such as CAD applications. There should be a thin core that can model the world and provide the basic operations defined on it but anything else should go in separate modules.

Fortunately PCB already had a strong infrastructure supporting this idea. It has dynamic loadable plugins and the GUI and exporters are in separate HID modules. While working on pcb-gpmi and later pcb-rnd, I added the gpmi module as a separate plugin.

In version 1.0.8 to 1.1.0 a considerable chunk of core code has been moved into core plugins. A core plugin is just a plugin that is maintained together with the core, in the same repository, still the code is somewhat detached from the core. More importantly, the user can choose, for each plugin, separately:

- to compile it as a buildin (static-link it into the pcb executable)
- to compile it as a plugin (dynamic-link it runtime, if the .so is installed in the plugins/ directory)
- to disable the plugin, so it is not compiled at all

I believe such modularization has benefits on multiple levels:

- it is possible to compile smaller, potentially faster executables by omitting features the specific user would never use anyway
- in a distribution dynamic-link plugins can be distributed as separate packages providing the user with the option to decide what features to install
- such plugins have to have some sort of APIs if they want to reference each other or if the code needs to reference them; such an API may not (and often did not) exist when the code is part of the core

## Progress in charts

### Before-after

All numbers are in SLOC and are acquired running sloccount on the given directory. While lines of code alone is not a true measure of complexity, it's a good estimation. The slices of pie charts are the major components of the pcb-rnd executable.

Before modularization: pcb-rnd version 1.0.7 Note: gpmi was already a plugin |  | After modularization: current pcb-rnd Note: gpmi is part of the "plugins" slice

### Zooming on to the plugins

total size per class
IO plugins

feature plugins
export plugins

HID plugins
import plugins

library plugins
footprint plugins

(Red means the plugin doesn't really work).

## Progress in numbers

Below is a table with the summary of core plugins.

module | size [sloc] | status | configure default | class | description
--- | --- | --- | --- | --- | ---