a simple lua example
Let’s start with a simple example that will print some code on the console. Create a file called luarc in darktable’s configuration directory (usually $HOME/.config/darktable/) and add the following line to it:
print("Hello World !")
Start darktable and you will see the sentence “Hello World !” printed on the console. Nothing fancy but it’s a start.
At this point, there is nothing darktable-specific in the script. We simply use Lua’s standard print function to print a string. That’s nice and all, but we can do better than that. To access the darktable API you first need to require it and save the returned object in a variable. Once this is done you can access the darktable API as subfields of the returned object. All of this is documented in darktable’s Lua API reference manual.
local darktable = require "darktable"
darktable.print_error("Hello World !")
Run the script and … nothing happens. The function darktable.print_error is just like print but will only print the message if you have enabled lua traces by running darktable with “darktable -d lua” on the command line. This is the recommended way to do traces in a darktable lua script.