User:Sybren/SfA/addon

Scripting for Artists: Creating your own Add-ons

• So far: code in blend file
• Absolutely fine if the code should be there. For example one-off things for that particular blender scene. Rigify also uses this.
• Hard to reuse.
• Hard to distribute.

• Solution: add-ons.

What is an add-on?

• Python code in file on disk, rather than buried inside a blend file.
• Just a text file, you can open it with any text editor.
• Blender's text editor works too, but I always get confused like that. Are you editing a text file on disk, or a text datablock in the blend file? Saving with Ctrl+S or Alt+S.
• Use a free text editor, like Visual Studio Code, Atom, Notepad++.
• On Windows, avoid Notepad. Even though Python is text, Notepad doesn't support files from Linux and thus you can have trouble reading code from Blender itself, or other people's add-ons.
• PyCharm works for bigger projects, but the smarter your editor the more work you need to do to remove all the error markers.
• Naming: recommended lower case, letters without accents, numbers, and underscores only. And end in .py.

Location of add-ons:

 
import addon_utils
print(addon_utils.paths())

• More info:
  • Help
  • Manual
  • Advanced
  • Scripting & Extending Blender
  • Lots of info there, including Add-on Tutorial

Ingredients of a simple Add-on

• Starts with some metadata in bl_info, like name of the add-on, the version number, version of Blender that's compatible with it, authors, etc.
• register and unregister functions.
• Then code just like we're used to.
• Can be enabled & disabled in user preferences.

Minimal add-on:

bl_info = {
    "name": "My Test Add-on",
    "blender": (2, 83, 0),
    "category": "Object",
}
def register():
    print("Hello World")
def unregister():
    print("Goodbye World")

Dictionary: already seen in chapter 5. Basically a lookup table, bl_info["name"] gives "My Test Add-on".

• Save in random directory, name my_first_addon.py.
• Start Blender, user prefs, install, enable & disable add-on and check console.
• Now you know why in the previous chapter we had an unregister() function, even though it wasn't used yet.
• Was saved by Blender in $HOME/.config/2.83/scripts/addons/my_first_addon.py, Blender made the right directories for us.
• Now open the installed file in your editor so you can keep editing and reloading. (what happens on reload we'll cover in a few minutes)

Monkey Grid Add-on

• Add bl_info
• Copy code from previous chapter
• Save & reload scripts
• Done!

Accessing add-on from within Blender

import my_first_addon
print(my_first_addon.__file__)
my_first_addon.register()

# change the print statements for both register & unregister.

my_first_addon.unregister()

import importlib
my_first_addon = importlib.reload(my_first_addon)

my_first_addon.register()

Making code usable by others (maybe skip this part)

• Operators are glue between menus, buttons, and the code to run.
• Avoid calling operators from Python code. Sometimes unavoidable, and that's fine.
• Put monkey grid generation code into a function.
• Call that function from the operator.
• Call that function from the console.

Conclusion

• Code is just text in files.
• Single-file add-on. Multi-file is not much different, but won't cover here. Requires trick with reloading; look at how other add-ons are doing it.
• Add-on requires bl_info and register/unregister functions.
• Put one or more operators there.
• Later video: making a user interface