Making gifs with Blender

Blender is a great 3D creation tool with many features. Modelling, sculpting, animation, compositing, scripting… It’s like a treasure chest with many toys in it.

Blender can be scripted with Python via its API. This makes it an interesting tool for making gifs or Twitter bots!

I used it recently to create Clitoris Vulgaris a Twitter bot that promotes cliteracy! This write up lets me share my notes and learnings I made during the project.

Set up your scene

We will use the default Blender scene: it has a camera, a cube and a light. Open Blender and save the default scene to scene.blend in a folder named myblendergif. In the next section we are going to use Python to tweak and render images.

Launching Blender with a Python script

If you are on macOS you should alias Blender so you can use it from the terminal.

If not there already add the following line in your .bashrc or .zshrc. It will make it easier to call Blender from the terminal. Here is a one liner to execute in the terminal to do it:

echo 'alias blender="/Applications/blender.app/Contents/MacOS/blender"' >> .bashrc

Blender has a lot of options available when running it from the terminal. Have a look at the options by typing:

blender --help

What we want to do is run a Python script when the scene.blend has been loaded. To do so create a Python script file scene.py and save it in the same folder as your scene.blend. We will start with the following code:

import bpy

def update_scene(scene):
    print("Hello!")

if __name__ == "__main__":
    update_scene(bpy.data.scenes[0])

Save it. We will now open Blender from the terminal, run the Python script and render 1 frame. Point your terminal to folder with your scene.blend and scene.py.

cd myblendergif
blender --background scene.blend --python scene.py --render-output botimage --render-frame 1

You should see the Hello! message in the terminal and have a botimage0001.png in the folder.

Interacting with the scene

Have a look at Blender’s Python API documentation.

You have two ways to interact with Blender: via the bpy.data or bpy.ops. bpy.data lets you access everything in the scene. bpy.ops lets you trigger any action you can do in the Blender UI like clicking a button.

Today we will only use bpy.data.

Every object has a name that you can change in the UI. Our cube is by default called “Cube”! Let’s access our cube and move it on the x axis by 2 unit. Edit your scene.py to look like this:

import bpy

def update_scene(scene):
    print("Hello!")

    cube = scene.objects["Cube"]

    # Position
    cube.location.x = cube.location.x + 2

if __name__ == "__main__":
    update_scene(bpy.data.scenes[0])

Similarly you could change the scale of the object on the y axis with cube.scale or the rotation with cube.rotation_euler.rotate. Before we continue we need to add some helper tools like Euler and to_radians in the import section.

import bpy
from math import radians as to_radians
from mathutils import Euler

def update_scene(scene):
    print("Hello!")

    cube = scene.objects["Cube"]

    # Position
    cube.location.x = cube.location.x + 2

    # Scale
    cube.scale.y = 2

    # Rotation use radians angles!
    rotate_by = Euler((to_radians(45), 0, 0), "XYZ")
    cube.rotation_euler.rotate(rotate_by)

if __name__ == "__main__":
    update_scene(bpy.data.scenes[0])

Let’s now change the colour of the cube. Objects have a default material that has a diffuse colour. We will need to import the Colour object in order to manipulate it. Colours are expressed in RGB with 3 values between 0 and 1. For example (0.0, 0.0, 0.0) is pure black, (0.8, 0.0, 0.0) is a red and (1.0, 1.0, 1.0) is pure white.

import bpy
from math import radians as to_radians
from mathutils import Euler
from mathutils import Color

def update_scene(scene):
    print("Hello!")

    cube = scene.objects["Cube"]

    # Position
    cube.location.x = cube.location.x + 2

    # Scale
    cube.scale.y = 2

    # Rotation use radians angles!
    rotate_by = Euler((to_radians(45), 0, 0), "XYZ")
    cube.rotation_euler.rotate(rotate_by)

    # Colors
    cube.active_material.diffuse_color = Color((0.8, 0.0, 0.0))

if __name__ == "__main__":
    update_scene(bpy.data.scenes[0])

After doing a render you should see a red cube!

Creating an animation

To create an animation we need to render more than one frame and execute the script for each frame.

Blender has an event system that lets us call a function before rendering a new frame. Let’s use it to call our update_scene function!

import bpy
from math import radians as to_radians
from mathutils import Euler
from mathutils import Color

def update_scene(scene):
    print("Hello!")

    cube = scene.objects["Cube"]

    # Position
    cube.location.x = cube.location.x + 2

    # Scale
    cube.scale.y = 2

    # Rotation use radians angles!
    rotate_by = Euler((to_radians(45), 0, 0), "XYZ")
    cube.rotation_euler.rotate(rotate_by)

    # Colors
    cube.active_material.diffuse_color = Color((0.8, 0.0, 0.0))

if __name__ == "__main__":
    bpy.app.handlers.frame_change_pre.append(update_scene)

Now we can use the --frame-start and --frame-end with the --render-anim option when using Blender via the terminal:

blender --background scene.blend --python scene.py --render-output botimage --frame-start 1 --frame-end 12 --render-anim

We will get 12 images in total! But they are all the same!

Random!

We are now going to change our script to use random values instead of predefined values. Python has a handy function called uniform(min, max). It returns a random value between min and max!

For example if we want to move our cube on the x axis randomly between -10 and 10 units we can use uniform(-10, 10). Similarly we will do the same for the scale, rotation and colour.

import bpy
from math import radians as to_radians
from mathutils import Euler
from mathutils import Color
from random import uniform

def update_scene(scene):
    print("Hello!")

    cube = scene.objects["Cube"]

    # Position
    cube.location.x = uniform(-5, 5)

    # Scale
    cube.scale.y = uniform(1, 4)

    # Rotation use radians angles!
    rotate_by = Euler((to_radians(uniform(0, 360)),
                       to_radians(uniform(0, 360)),
                       to_radians(uniform(0, 360))),
                       "XYZ")

    cube.rotation_euler.rotate(rotate_by)

    # Colors
    color_values = (uniform(0, 1), uniform(0, 1), uniform(0, 1))
    cube.active_material.diffuse_color = Color(color_values)

if __name__ == "__main__":
    bpy.app.handlers.frame_change_pre.append(update_scene)

Let’s render 12 frames and see what happens!

Making a gif

We are going to use GraphicsMagick to create a gif from all our images. How to install it on macOS? First install Homebrew then in the terminal run brew install graphicsmagick.

We want to use all the botimageXXXX.png and convert them to a looping gif with a frame rate of 20 fps.

gm convert -delay 20 -loop 0 botimage*.png animation.gif

Open and enjoy your animation.gif!

Have a look at my final version of the code! Hope it will inspire you to make some nice gifs! Don’t forget to tweet them at me 😎!

Optional: How can I use Python modules in Blender?

Blender comes with its own Python binary and modules. I recommend using virtualenv to create an environment with the same Python version as the one used by Blender.

How to set up a virtualenv and install requests:

virtualenv -p python3 .pyenv source .pyenv/bin/activate pip install requests

In your scene.py you can then manually update the import path to let Python find your virtualenv libraries.

import sys
sys.path.append(os.path.dirname(__file__))