How do I create an add-on in Blender?

To create an add-on in Blender, you generally follow a process that involves writing Python code to define your add-on's functionality and then packaging it correctly for distribution and installation. The core steps focus on organizing your code, defining essential metadata, and building a distributable file.

How Do I Create an Add-on in Blender?

Creating an add-on in Blender involves writing Python scripts that extend Blender's capabilities, from new tools and panels to custom operators and modifiers. Once your code is developed, the crucial next step is to package it into a distributable format.

1. The Foundation: Coding Your Blender Add-on

Before packaging, you need to write the Python code that defines your add-on's functionality. Blender add-ons leverage the bpy module, which provides access to Blender's data, functions, and user interface elements.

Key Elements of an Add-on Script:

bl_info Dictionary: A required dictionary at the top of your main add-on file, containing essential metadata like name, author, version, and Blender compatibility.
register() Function: Called when the add-on is enabled. This is where you register classes (operators, panels, etc.) with Blender.
unregister() Function: Called when the add-on is disabled. This is where you unregister classes to clean up resources.
Add-on Structure: For simple add-ons, a single .py file is sufficient. For more complex add-ons, you'll create a Python package (a directory containing an __init__.py file and other Python modules).

Example of a basic add-on structure:

# my_simple_addon.py
bl_info = {
    "name": "My Simple Add-on",
    "author": "Your Name",
    "version": (1, 0, 0),
    "blender": (3, 6, 0),
    "location": "View3D > Sidebar > My Panel",
    "description": "A simple Blender add-on example.",
    "category": "Development",
}

import bpy

class MY_PT_SimplePanel(bpy.types.Panel):
    bl_label = "My Simple Panel"
    bl_idname = "MY_PT_SimplePanel"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = 'My Panel'

    def draw(self, context):
        layout = self.layout
        layout.label(text="Hello from My Add-on!")
        # Add buttons, properties, etc. here

def register():
    bpy.utils.register_class(MY_PT_SimplePanel)
    print("My Simple Add-on Registered")

def unregister():
    bpy.utils.unregister_class(MY_PT_SimplePanel)
    print("My Simple Add-on Unregistered")

if __name__ == "__main__":
    register()

2. Packaging Your Blender Add-on for Distribution

Once your add-on's code is ready, you need to prepare it for easy installation by other users. This involves organizing your files and creating a distributable package.

Step-by-Step Packaging Process:

The following steps are essential for formalizing your add-on for distribution, particularly when building an extension .zip file for Blender's robust extension system.

Open the Directory Containing the Add-on Code or Theme File:
- Begin by ensuring all your add-on's Python files (e.g., your main *.py script, or a directory acting as a Python package containing an __init__.py file) are organized within a dedicated folder. This folder will be the root of your add-on package.
- Tip: Name this directory something concise and descriptive, as this will often be the name users see in their add-ons list.

Add a blender_manifest.toml File with All the Required Meta-data:

Inside the root directory of your add-on, create a file named blender_manifest.toml. This file serves as a modern metadata descriptor for your add-on, providing crucial information that Blender uses for identification, display, and management.
The .toml (Tom's Obvious, Minimal Language) format is used for configuration files.
Required Meta-data: The reference specifically mentions name and maintainer. Other common fields include version, description, tags, blender_version, and homepage.

Example blender_manifest.toml:

# blender_manifest.toml
name = "My Awesome Add-on"
maintainer = "Jane Doe <[email protected]>"
version = "1.0.0"
description = "A powerful tool to automate mundane tasks in Blender."
blender_version = "4.0.0" # Minimum Blender version required
tags = ["modeling", "utility"]
homepage = "https://yourwebsite.com/my_addon"

Table: Common blender_manifest.toml Fields

Field	Type	Description	Example
`name`	String	The display name of your add-on.	`"My Awesome Add-on"`
`maintainer`	String	Your name and contact information.	`"John Doe <[email protected]>"`
`version`	String	The version of your add-on (e.g., "1.0.0").	`"1.0.0"`
`description`	String	A brief explanation of what your add-on does.	`"A tool for fast modeling."`
`blender_version`	String	The minimum Blender version required for your add-on to function.	`"4.0.0"`
`tags`	Array	Keywords for categorization and search.	`["modeling", "animation"]`
`homepage`	String	A URL to your add-on's website or repository.	`"https://github.com/my/addon"`

Use the Blender Command-Line Tool to Build the Extension .zip File:
- With your add-on code in its directory and the blender_manifest.toml file correctly configured, you can now generate a distributable .zip file. This is typically done using Blender's command-line interface (CLI).
- Blender provides tools to package extensions into a .zip archive, which makes installation seamless for users (they can just use Blender's "Install Add-on..." button).
- The specific command may vary slightly with Blender versions and the exact tooling provided, but it generally involves running Blender in "background" mode with an argument to build the extension.
- Example (conceptual command, actual command might vary slightly based on Blender's exact packaging tools):
```
blender --background --python-expr "import bpy; bpy.ops.wm.extension_build(directory='path/to/your/addon/folder', output_path='path/to/output/my_awesome_addon.zip')"
```
  (Note: The exact bpy.ops.wm.extension_build or similar command might need to be verified with the latest Blender documentation for precise usage.)

3. Testing and Distribution

Once you have your .zip file:

Installation: In Blender, go to Edit > Preferences > Add-ons, click "Install...", navigate to your .zip file, and select it. Then, enable the add-on by checking its box.
Testing: Thoroughly test your add-on's functionality in various scenarios to catch any bugs or edge cases.
Distribution: Share your .zip file through your website, GitHub, or Blender community platforms.

By following these steps, especially integrating the blender_manifest.toml and utilizing Blender's command-line tools for packaging, you ensure your add-on is well-structured, discoverable, and easily installable by other Blender users.