How To Make My Addon Support “Undo” In Blender

GOAL

Today’s goal is to implement “Undo” in my Blender addon.

Environment

Blender 2.83
Windows10

Method

Add bl_options “UNDO” or “UNDO_GROUPED” into the your custom operator. It’s easy.

UNDO Undo: Push an undo event (needed for operator redo).
UNDO_GROUPED: Grouped Undo, Push a single undo event for repeated instances of this operator.

from Blender2.93.2 Python API Documentation

The following is an example.

class ADDMATRIX_add_cube(bpy.types.Operator):
    bl_idname = 'add_matrix_obj.add_cube'
    bl_label = "Add matrix cube"
    bl_options = {'REGISTER', "UNDO"} # Add "UNDO" option here

    input1: bpy.props.IntProperty()
    input2: bpy.props.IntProperty()

    def execute(self, context):
        for xi in range(self.input1):
            x = xi*1.2
            for yi in range(self.input2):
                y = yi*1.2
                bpy.ops.mesh.primitive_cube_add(size=0.5, enter_editmode=False, align='WORLD', location=(x, y, 0))
        return {'FINISHED'}

Postscript

be aware of the error where Blender crashed when undo after executing script in python console. (Reference: Fix T86293: crash undoing after executing the python console in certain)

That was fixed in Blender 2.93, the latest version. And You can fix the error by adding bl_options “UNDO_GROUPED” into the ConsoleExec operation in C:/Program Files/Blender Foundation/Blender 2.83/2.83/scripts/startup/bl_operators/console.py.

class ConsoleExec(Operator):
    """Execute the current console line as a python expression"""
    bl_idname = "console.execute"
    bl_label = "Console Execute"
    bl_options = {"UNDO_GROUPED"} # add undo here

    interactive: BoolProperty(
        options={'SKIP_SAVE'},
    )

    @classmethod
    def poll(cls, context):
        return (context.area and context.area.type == 'CONSOLE')

How To Get Icon List In Blender

GOAL

Today’s goal is to show Icon Viewer that shows the list of icon we can use in Blender and use it.

Environment

Blender2.83(LTS)
Windows10

Method

1. Activate addon “Development Icon Viewer”

2. Open Icon Viewer

Open text Editor and click “Dev” tab.

Click on any icon you like and it’s name will be copied to the clipboard. Then paste it into your editor.

Examples

1. Operator button

def draw(self, context):
    layout = self.layout
    col = layout.column(align=True)
    col.operator("mesh.primitive_monkey_add", icon="MONKEY")

2. EnumProperty

class MyProp(bpy.types.PropertyGroup):
    items = [("id1", "name1", "description 1", "HELP", 0),
             ("id2", "name2", "description 2", "GHOST_ENABLED", 1),
             ("id3", "mame3", "description 3", "FUND", 2),]
    enum: bpy.props.EnumProperty(items=items)

def draw(self, context):
    layout = self.layout
    col = layout.column(align=True)
    col.prop(context.scene.MyProp, "enum")

How To Pass Arguments To Custom Operator In Blender Python

GOAL

Today’s goal is to create operator that takes arguments in Blender Python.

The following is a custom operator that takes 2 argument “count_x” and “count_y”, and add cube object in the form of count_x rows and count_y columns.

Environment

Blender 2.83(LTS)
Windows10

Method

1. Create operator with properties

Pass the argument values through the properties to custom operator. Use “:” to add property in Blender custom operator as below. Check “Operator Example” in Blender manual for details.

class ADDMATRIX_add_cube(bpy.types.Operator):
    bl_idname = 'add_matrix_obj.add_cube'
    bl_label = "Add matrix cube"
    bl_options = {'REGISTER', "UNDO"}

    input1: bpy.props.IntProperty() # add argument1 as property "input1"
    input2: bpy.props.IntProperty() # add argument2 as property "input2"

    def execute(self, context):
        for xi in range(self.input1):
            x = xi*1.2
            for yi in range(self.input2):
                y = yi*1.2
                bpy.ops.mesh.primitive_cube_add(size=0.5, enter_editmode=False, align='WORLD', location=(x, y, 0))
        return {'FINISHED'}

You can execute operator with passing values of arguments “input1” and “input2” as below.