Changing objects visibility in the viewport and while rendering

The easiest way to hide and show rendering objects is to assign animation keys to them. To do this, move the cursor over the eye icon (visibility in the viewport) or camera (visibility when rendering) in the Outliner window, press the “i” key and then manage the created condition in the Graph Editor like the ordinary animation keys.

But this method is not always available. For example, we cannot assign visibility animation keys for collections, Blender will generate errors like:

“hide_viewport” property cannot be animated

or

“hide_render” property can not be animated

However, using the Blender Python API, we can control the visibility of such objects.

Continue reading “Changing objects visibility in the viewport and while rendering”

Blender autocomplete modules

Nutti, the author of the “fake-bpy-modules” project, has made the installation of the Blender Python API autocomplete modules through the pip platform. Pip installation is faster and easier, but sometimes we just need to copy the autocomplete modules to our project but now they are not included in the Nutti’s GitHub.

Copies of the autocomplete modules for Blender versions 2.79 and 2.80 can be downloaded directly from here: https://github.com/Korchy/blender_autocomplete

 

How to get global vertex coordinates

To get the vertex coordinates in the scene global coordinate system when the object’s scale was not applied, we need to multiply the local vertex coordinates by the object world transformation matrix:

Class naming conventions in Blender 2.8 Python API

In Blender 2.8 API the requirements for the class and their identifiers naming are becoming tougher. The class name must match the following convention:

Where the {SEPARATOR} is two letters denoting the class belonging to a certain type (from which type the class is inherited):

  • HT – Header
  • MT – Menu
  • OT – Operator
  • PT – Panel
  • UL – UI list

The class identifier “bl_idname” mast match the class name.

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Changes in add-ons registration through the API in Blender 2.8

Add-on registration and removing were made with the “Window manager” (wm) in Blender 2.7 Python API:

In Blender 2.8 API add-on operators moved to the “preferences”:

 

3D Cursor location in Blender 2.8 Python API

3D-cursor location property

in Blender 2.8 API moved to “cursor” object

When trying to get the cursor location through the “context.scene.cursor_location” Blender throws an error:

‘Scene’ object has no attribute ‘cursor_location’

Add-on preferences panel

When developing add-ons it is often necessary to give an ability to set a number of parameters that affect the whole add-on work to the user. For example, the user can specify a directory for saving/loading files, set some default variables or switch between add-on modes. Of course, the interface for setting such parameters can be placed in the add-on panel, but it is better to place it in a separate add-on preferences panel, which is located in the “Preferences” window under the add-on installation panel.

The main advantage of the add-on preferences is that they don’t reset when Blender restarts. The user does not need to configure the add-on preferences each time, it’s enough to set the necessary parameters once, personalizing the add-on for convenient work.

Let’s create an add-on and define a parameter, placing it in the add-on preferences panel.

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Matrix, vector and quaternion multiplication in Blender 2.8 Python API

In Blender 2.7 the “*” (star) operator is used in the matrix, vector, and quaternion multiplication. In Blender 2.8 it is replaced with the “@” (at) operator.

If the “*” operator is used in vector, matrix or quaternion multiplication in Blender 2.8 it throws an error:

Element-wise multiplication: not supported between ‘Matrix’ and ‘Matrix’ types

Proper use of the “@” operator:

 

Snapping elements property in Blender 2.8 Python API

The snapping elements property from Blender 2.7

changed in Blender 2.8 API to

 

Accessing the pivot point type in Blender 2.8 Python API

The “pivot_point” property from Blender 2.7

in Blender 2.8 API moved to:

 

use_drag_immediately property in Blender 2.8 Python API

The “use_drag_immediately” property from Blender 2.7

in Blender 2.8 API moved to

 

Changing the current coordinate system in Blender Python API

In Blender 2.7 the current coordinate system could be changed through the

property. In Blender 2.8 coordinate system access moved to the scene collection of “TransformOrientatiosSlots” objects. To get or set the current coordinate system the “transform_orientation_slots” collection is used.

How to set object (mesh) to active in Blender 2.8 Python API

To set mesh (object) as active in Blender 2.8 Python API the “context.view_layer” is used instead of “context.scene”.

When trying to make object active with “bpy.context.scene.objects.active” Blender throws an error:

AttributeError: bpy_prop_collection: attribute “active” not found

To make object active in Blender 2.8 use the following code:

 

Selecting objects (meshes) in Blender 2.8 Python API

According to Blender 2.8 Python API changes mesh (object) can be selected with using getters and setters.

When trying to check the selected status of the mesh through the “bpy.context.active_object.select” property, Blender throws an error:

AttributeError: ‘Object’ object has no attribute ‘select’

To check whether an object is selected in Blender 2.8 use a getter:

To select an object in Blender 2.8 use a setter:

To unselect an object use the same setter:

 

How to check what version of Python interpreter is used in Blender

To find what Python interpreter version is used in current Blender version type the following commands in Python Console window in Blender:

It means that the version of Python used in Blender is 3.7.0.

To make it more readable type the following command:

or with full info:

Porting add-on from Blender 2.7 to Blender 2.8

In the latest version 2.8 of Blender developers have made many changes in API, so all the scripts and add-ons written for earlier Blender versions (2.7 and below) have stopped working. To run your add-ons in the new Blender 2.8, you need to port them – correct their code to work properly with the new Blender API.

To enable your add-on in Blender 2.80 you have to make the following changes in code:

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Using Microsoft Visual Studio Code as external IDE for writing Blender scripts/add-ons

Blender has its own built-in text editor for writing scripts and add-ons, but it’s much convenient to develop them in external IDEs that provide the user with more features such as autocomplete, syntax highlighting, integration with version control systems and other tools that make development faster and easier.

One of these IDEs is Visual Studio Code from Microsoft. This is a free universal environment that supports development with various programming languages, including the Blender API language – Python.

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How to check if Blender object property/attribute is read-only

To check is an attribute/property of any Blender object (mesh, node, modifier, etc.) read-only:

  1. With the is_property_readonly function, execute the following command:

<object> .is_property_readonly (‘<property name>’)

  1. Through the rna structure, execute the following command:

<object> .bl_rna.properties [‘<property name>’]. is_readonly

For example, for the “is_editmode” mesh property (is the mesh in edit mode or not):

How to get the version of the add-on installed in Blender

A complete list of add-ons installed in Blender we can get using the addon_utils:

Having the add-ons list, we can get the version of the desired add-on by its name with the following code:

Where the ADD-ON_NAME is the name of the desired add-on.

If the add-on is missing a version indication, the default result will be returned.

 

How to programmatically switch between vertex, edge and face selection mode

Change the mesh_select_mode property to switch in mesh edit mode between vertex, edge and polygon selection mode in Blender.

For vertex selection mode:

Edge selection mode:

And face selection mode:

The multi-select mode is enabled too. For example for vertex and face selection mode:

In BMesh for vertex, edge and face selection mode:

For multi-select in BMesh:

 

Learning loops

In general, the “loop” is usually a sequential selection of several points, edges or polygons of a mesh.

However, there is an element in the mesh structure, which is also called a “loop”. It is a combination of one vertex with one edge of the mesh. Let’s try to learn what these “loops” are for.

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How to pass command line arguments to a Blender python script or add-on

When starting Blender from the console it processes all parameters passed through the command line. However, some scripts and add-ons for proper work may require specifying their unique command line arguments. If you specify such additional parameters in the command line, Blender will also try to process them, which is likely to result in an error. Blender provides a special way to exclude such arguments from own processing.

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Creating radio buttons in the Blender add-ons interface

State switches so-called “radio buttons” are used in the case to limit the choice by one value from several available ones. There are a lot of such buttons in the Blender interface, for example, switching between RGB and BW rendering modes or setting the texture mapping mode. Such buttons can be created in the Blender add-ons interface too.

Let’s create our own radio button switcher.

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How to programmatically check if the operator is registered in Blender API

Single add-on or script can contain several different operators, and not all of them may be registered in the API by the register() function. To verify that the required operator is registered in the Blender API, run the following command:

Where:

_operator_bl_idname_ – the text value of the bl_idname operator property.

For example for an operator:

the command will look like this:

 

How to programmatically check if the Blender add-on is registered

To start working every Blender add-on must be registered by setting up the checkbox before add-on name in the User Preferences window – Add-ons page.

To programmatically find out if the required add-on is registered, run the following command:

Where:

add-on_name – the name of the add-on file (without the .py extension) or the name of the add-on package, if it was installed from the package.