Introduction

I decided to recreate this short tutorial from YouTube to practice using the Blender Python API. This post goes through the code I came up with to replicate the tutorial plus some small additions.

shape_key_mg

Import Dependencies

The only dependencies strictly required for this tutorial are bpy and bmesh. The bpy package is the base API for Blender and the bmesh module provides access to Blender’s internal mesh editing API. I also used the math module from the Python Standard Library for one of my helper functions.

import-dependencies

Define Helper Functions

I made some wrapper functions for the standard location, rotation, and scale transformations as well as getting the name of the active object.

You can get the name of the active object with bpy.context.active_object.name.

The three standard transformations can be accessed for individual objects with the following:

  • bpy.data.objects["object_name"].location
  • bpy.data.objects["object_name"].rotation_euler
  • bpy.data.objects["object_name"].scale

I also made a function to empty the default collection so that nothing gets duplicated. Collections can be accessed with bpy.data.collections["collection_name"] or bpy.data.collections[index].

Lastly, I made a function to easily add sequences of keyframes to a given object. The function uses the built-in setattr() method to set the desired value for the target object and uses the object.keyframe_insert() method to add the keyframe.

define-helper-functions

Set up Scene

The first thing I do is set the Color Management property, View Transform, from the default value of Filmic to Standard. This setting can be accessed at bpy.data.scenes["Scene"].view_settings.view_transform.

Next, I set the background to the desired color. In my case, it’s pure black. The background color is stored in bpy.data.worlds['World'].node_tree.nodes["Background"].inputs[0].default_value.

The last setup step is to clear any objects added from the last time the script was run with the clear_collection() function.

set-up-scene

Create and Position Camera

Cameras can be added using the bpy.ops.object.camera_add() method. I then positioned the camera using the wrapper functions I defined earlier.

create-camera

Create Material With Emission Shader

I decided to add some color to the motion graphic so I needed to create a new material. It is recommended to check if the material exists before trying to create it. This can be done in one line as shown below.

material = bpy.data.materials.get(material_name) or bpy.data.materials.new(material_name)

Since there’s is no light, I’ll add an Emission shader. This requires enabling nodes for the material with material.use_nodes = True.

Next, I remove the default Principled_BSDF node as well as any Emission nodes from earlier runs. Nodes can be removed using the material.node_tree.nodes.remove() method.

The Emission node needs to be linked to the first slot in the Material Output node. Nodes are linked using the material.node_tree.links.new() method.

create-emission-material

Create a Plane With the Material

The object in the above motion graphic is a plain. Plains can be added using the bpy.ops.mesh.primitive_plane_add() method.

I then assign the previously created material to the plane. Materials can be added to an object with object.data.materials.append(material).

create-plane

Cut Out Center From Plane

The next step is to make a square hole in the plane like in the above Gif. This requires modifying the mesh for the plane.

Mesh data for the currently selected object is stored at bpy.context.object.data.

To edit the mesh, we need to get a BMesh representation. We first create an empty BMesh with bm = bmesh.new() and then fill it with the mesh using bm.from_mesh(mesh).

We can make the square by adding a new inset to the plane using the bmesh.ops.inset_individual() method. Then, we delete the new face that gets created with bmesh.ops.delete().

The mesh then needs to be updated with these alterations using bm.to_mesh(mesh). Finally, we need to free the BMesh representation we created with bm.free().

cut-out-center-square

Add Shape Keys

We can add shape keys with the bpy.ops.object.shape_key_add() method. To deform the plane, we need to access its vertices. We can do this in edit mode with the bmesh module.

We first enter edit mode for the plane with bpy.ops.object.mode_set(mode="EDIT"). We can then create a new BMesh representation for the current mesh in edit mode using bm = bmesh.from_edit_mesh(mesh).

The vertices are stored in bm.verts, but we need to create our own list since we can’t index it directly.

Unlike the tutorial video, I just set the positions for the inner vertices directly. It took some trial and error to determine the correct indices for the inner vertices.

After freeing the BMesh representation, we can enter object mode with bpy.ops.object.mode_set(mode="OBJECT").

First Shape Key

add-shape-keys

Second Shape Key

The process for the second shape key is identical except it only moves two of the inner vertices.

add-shape-key-2

Add Keyframes

Before adding the keyframes, I set the render frame rate as well the start and end frames for the scene. The frame rate is stored at bpy.context.scene.render.fps.

The start and end frames are stored in bpy.data.scenes['Scene'].frame_start and bpy.data.scenes['Scene'].frame_end respectively.

set-up-animation

Shape Keys

The shape keys for the plane are stored in bpy.context.selected_objects[0].data.shape_keys. Individual shape keys can be accessed with bpy.context.selected_objects[0].data.shape_keys.key_blocks[index].

First Shape Key

add-keyframes-first-shape-key

Second Shape Key

add-keyframes-second-shape-key

Plane Rotation

add-keyframes-plane

Material Color

The color for the Emision shader can be accessed at material.node_tree.nodes["Emission"].inputs["Color"].default_value.

add-keyframes-color

Conclusion

I feel like this exercise was worthwhile as it forced me to learn about multiple parts of the API. Although, it took quite a bit longer than the nine minute length of the tutorial video to track down all the required parts of the API. Finding out how to properly add the Emission shader was particularly time consuming. I did not realize that the name used to create the Emission shader was different than the name used to reference it. Fortunately, Blender has been around for a while and someone on the internet had already asked how to do most of the individual steps.