koreader/doc/Hacking.md

Hacking

How to Debug

We have a helper function called logger.dbg to help with debugging. You can use that function to print string and tables:

local logger = require("logger")
a = {"1", "2", "3"}
logger.dbg("table a: ", a)

Anything printed by logger.dbg starts with DEBUG.

04/06/17-21:44:53 DEBUG foo

Bug hunting in kpv

A real example for hunting bug in KPV's cache system: https://github.com/koreader/kindlepdfviewer/pull/475

Developing UI widgets

tools/wbuilder.lua is your friend, if you need to create new UI widgets. It sets up a minimal environment to bootstrap KOReader's UI framework to avoid starting the whole reader. This gives you quick feedback loop while iterating through your widget changes. It's also a handy tool for debugging widget issues.

To get a taste of how it works, try running this command at the root of KOReader's source tree:

./kodev wbuilder

It will spawn up an emulator window with a grid and simple timer widget for demonstration.

You can add more UIManager:show call at the end of tools/wbuilder.lua to test your new widgets.