How to implement custom icons for my script/addon?

Question

Is it possible to use different icons other than the default set and how?

Answer 1

Since 2.75 the python API allows for custom icons.

You can store custom icons and load them with bpy.utils.previews.ImagePreviewCollection class, which works like a dictionary.

First let's create such icon dictionary:

import bpy.utils.previews
icons_dict = bpy.utils.previews.new()

Next, we need to find path to our icons. Its best to put them inside a folder named 'icons' next to the script file:

import os
# this will work for addons 
icons_dir = os.path.join(os.path.dirname(__file__), "icons")
# but it won't give you usefull path when you opened a file in text editor and hit run.
# this will work in that case:
script_path = bpy.context.space_data.text.filepath
icons_dir = os.path.join(os.path.dirname(script_path), "icons")

Finally load icon.png into the dictionary. Blender uses 32x32 icons in UI:

icons_dict.load("custom_icon", os.path.join(icons_dir, "icon.png"), 'IMAGE')

Reference the icon by it's ID, use like this inside UI elements:

icon_value=icons_dict["custom_icon"].icon_id

---

It's best to handle loading of icons in the register function, clearing the icons in unregister function, and storing them in a global variable.

If enabled as an addon the filepath of __init__.py is the module variable __file__ in __init__.py and as shown can be converted to a directory path using os.path.dirname(__file__) to get the path to my_addon

Make an add-on with multiple python files to keep our addon's icons neatly contained in our addon's folder.

my_addon/
    __init__.py
    icons/
        icon.png

To test when running from text editor can add an icons folder to some known path, for example the Desktop folder

Desktop/
    icons/
        icon.png 

and change the code below accordingly to be its absolute path (in this example case /home/user/Desktop/), or the saved path of the text file, or that of the blend file.

bl_info = {
    "name": "Custom Icon Test",
    "author": "Your Name Here",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "View3D > UI > Tools",
    "description": "Test custom icons",
    "warning": "",
    "doc_url": "",
    "category": "Testing",
}

import os
import bpy
import bpy.utils.previews

class CUSTOM_PT_myPanel(bpy.types.Panel):
    bl_label = "My Icon Panel"
    bl_idname = "OBJECT_PT_custom_panel"
    bl_space_type = "VIEW_3D"   
    bl_region_type = "UI"
    bl_category = "Tools"

    def draw(self, context):
        global custom_icons
        self.layout.label(text="Blender SE", icon_value=custom_icons["custom_icon"].icon_id)

# global variable to store icons in
custom_icons = None

def register():
    global custom_icons
    custom_icons = bpy.utils.previews.new()
    addon_path =  os.path.dirname(__file__)
    icons_dir = os.path.join(addon_path, "icons")
    
    custom_icons.load("custom_icon", os.path.join(icons_dir, "icon.png"), 'IMAGE')
    bpy.utils.register_class(CUSTOM_PT_myPanel)

def unregister():
    global custom_icons
    bpy.utils.previews.remove(custom_icons)
    bpy.utils.unregister_class(CUSTOM_PT_myPanel)

if __name__ == "__main__":
    # Test run
    # edit to folder containing your icons folder
    __file__ = "/home/user/Desktop/"
    # The path of this text (if saved)
    #__file__ = bpy.context.space_data.text.filepath
    # The path of this blend file (if saved)
    #__file__ = bpy.data.filepath
    register()

Result: