How to create hundreds of fire with Maya Fluid and Python

Remember the last episode of Game of Thrones? By the last, I meant not the 6th episode which made no sense and nearly destroyed the story of the whole show, but 3rd episode – The Long Night. Surely, most of us were absolutely hyped for the Long night episode. For me, I was mostly looking for a battle between a dead dragon and two other dragons also how the Dothraki army would fight against the dead.

The Dothraki was so fearsome and terrorized everyone throughout 8 seasons. They were living legends and were so famous that someone tells stories about them to scare people. Also, their army was the biggest ever Dothraki army. Then the dead came and massacred them with a blink of an eye. (Talk about a disappointment!)

Anyhow, there was one shot that was appealing to me. The shot was, you know, a witch came to the army and ignite a fire on their blade. At that moment, I thought it would be painful to create such fire effects for a whole army. There are hundreds of them and each of them potentially moves slightly, because they were sitting on a horse, and, of course, it is fire simulation. How would you create and simulate hundreds of fire blade efficiently? I decided to give a try. Here is my process from a TD view.

Firstly, I created a fire simulation on Maya Fluid. That hero fire fx would be sent to a lighting and rendering artist while I figure out how to simulate hundreds of them. Obviously, I would not want to manually work on them and would assume a fire emitter object and fluid fx will change when feedback comes. With those assumptions, I started coding in Python.

The first issue is creating clones of hero fx. Here I assumed that I would have animated objects from layout and animation artists that could be emitters. That could be anything – mesh, curve, and shape etc. Because of this, I abstracted a type of the object and wrote a function to create a clone of hero fx for each animated objects.

def duplicate_fluids(fluid, obj):
    Create fluid containers
    :param fluid:  a source fluid name
    :param obj: an emitter object type
    # Duplicate a fluild container
    for obj in

Then those fluid containers need to be transformed and linked to emitters. MatchTransform method and a translation were used for this task. Once each fluid containers moved to a position I wanted, an emitter created and linked to it.

def create_fluid_on_emitters(emit_objects, fluids, obj, y_offset, rate=100, her=1, der=1):
    Create fluid containers on an emitter and move container. Also, set some attributes of an emitter

    :param emit_objects: objects emit from
    :param fluids: fluid containers
    :param obj: emit object type
    :param y_offset: move y of a container
    :param rate: emitter rate
    :param her: heatEmissionRate
    :param der: densityEmissionRate
    for i in range(len(
        # Moving up a fluid container
        cmds.matchTransform(fluids[i], emit_objects[i])[i])
        cmds.move(y_offset, y=True)
        # Create an emitter and connect it to fluid container
        emitter = cmds.fluidEmitter(emit_objects[i], type='surface', rate=rate, her=her, der=der)
        cmds.connectDynamic(fluids[i], em=emitter[i])

Now I am ready to cache them. However, I still need to select them. Instead of selecting them from a maya outline, I wrote a function to accomplish it. The function simply checks all ‘transform’ nodes whether their name has ‘fluid’ and a substring from a start is shorter than a given number. Since there are so many other unnecessary nodes with ‘fluid’ in it, I needed to find nodes like ‘fluid1’, ‘fluid12’, and ‘fluid3433’.

def select_fluid_containers(count):
    Select all fluid containers

    :param count: a number of digits (fluidXXX)
    :return: fluid containers
    # Select fuild containers
    return[f for f in'transform') if (('fluid' in f) and (len(f) <= len('fluid') + count))])

With those functions, I can create any number of fire fx and cache them without touching anything. Lastly, on the original shot, there was a slight offset for fire ignition. With a camera pan, it did add suspension to the screen. To assist this, I wrote a function to change a start frame of fluid fx. Now I simply need to use the function in a loop to set a slight offset. It changes start frame of all fluid containers one by one, 5 by 5, or any number in a loop.

def set_animation_start(fluid, start):
    Set startFrame of a given fuild
    :param fluid: fluid container
    :param start: startFrame
    cmds.setAttr(cmds.listRelatives()[0] + '.startFrame', start)

Finally, I can package those functions in a python script, add some animation or write a guide creating an offset animation, and send it along with hero fx to an animation team.

In the future, I could have a different fire fluid fx to choose from. For this case, I will send a list of fire fx to the ‘duplicate_fluids’ function and randomly select from them for each animated objects. And, offset may need other work such as adding a bit randomness. That will be adding a random number on the start frame when using the ‘set_animation_start’ function. Furthermore, when feedback comes or hero fire fx is changed, I could pass a dictionary with necessary attributes to the functions.

Thanks to Python and Maya. Creating hundreds of fire turned out to be not so hard.

Setting Maya for development

During the last weekend, I had tried to set up maya python environment. You know, developing python scripts using IDE and testing it with maya script editor is a bit painful. Ideally, you would need to have IDE that supports auto-complete and maya introspection.

After googling a bit, I found out that Autodesk provides python interpreter for maya. It is located in ~/usr/autodesk/maya2018/bin/mayapy, for my case. This python interpreter loads all maya modules automatically, which is what I want. Now I just need to use this interpreter for my IDE. As for IDE, I typically use PyCharm for any CG scripts development. It lets you set its python interpreter. Using this feature, we can choose mayapy as a python interpreter.

To do this, firstly, I created a PyCharm project for Maya python script development. When you create a new project, PyCharm asks you to choose a python interpreter. You would need to choose mayapy for it. Here you can create a new interpreter or choose an existing one. Either way, you need to set it as a system interpreter. So select a system interpreter and locate your mayapy. Since we are using a system interpreter, you need to authorise it. That is it. You are ready to develop maya python scripts with PyCharm.

Once the project was set up, PyCharm may complain about “python packaging tools not found”. It did for my case. It is not something you need to worry about. Because, autodesk did not include some libraries that python environment needs i.e as pip, PyCharm is notifying it. It is also the reason you need to set your python interpreter as a system interpreter. If you choose it as either virtualenv or conda, PyCharm would fail to set a python interpreter for the project since virtualenv and conda are not included in a python interpreter that autodesk provided.

However, I think that it would not be an issue for us. Now you can import maya and pymel modules. See codes below.

import sys
import maya.cmds as cmds
import pymel.core as pmc
print sys.modules.keys()

It shows modules imported. From there, we can see maya and pymel are loaded. You can also initialise maya and run it. To do that, we need to import maya and initialise it.

import maya.standalone

It may take a while since it is loading maya. But when you do import it, you can see all other modules that maya need are imported.

Now let us get auto-completion working. Note that I am using PyCharm 2019.1 Community Edition and Maya 2018. Firstly, get DevKit from here: Then install it on your maya root. For my case, my maya root is /usr/autodesk/maya2018. To install devkit, extract the zip you downloaded then copy devkit and mkspecs folders to you maya root. Leave lib and include folders as it is. If you copy those folders to your maya root, you will get some symbol look up errors and your maya won’t run. Believe me I did copy those and got those errors :)) .

Once you copied those folders, run your Pycharm and open its settings. Under your project interpreter settings, look for a gear icon next to your project interpreter location. Click into that and click Show all. See a picture below:

Select your mayapy and click at an icon at the bottom of the right-side panel. You will see all python modules loaded for you there. You need to add another library from devkit here and remove one path. Click add button and point to your maya root/devkit/other/pymel/extras/completion/py directory. Then remove your maya bin/lib/python2.7/site-packages directory. If in doubt, see a picture below.

As a cherry on the cake, it would be nice if maya knows the directory of scripts that I am developing. There are two ways to accomplish it: import it in or set environment variable. Or you can edit system environment variable if you want to go extreme.

In my case, I chose to use Since I am using Linux, I needed to create inside ~/maya/2018/scripts. A content of is simply:

import sys

Here I chose my a cloud sync directory as I want to use those scripts from different machines. Lastly, let’s quickly test what I have achieved.

>>> import pymel.core as pmc
>>> for n in type(pmc.joint()).__mro__:
...     print n
<class 'pymel.core.nodetypes.Joint'>
<class 'pymel.core.nodetypes.Transform'>
<class 'pymel.core.nodetypes.DagNode'>
<class 'pymel.core.nodetypes.Entity'>
<class 'pymel.core.nodetypes.ContainerBase'>
<class 'pymel.core.nodetypes.DependNode'>
<class 'pymel.core.general.PyNode'>
<class 'pymel.util.utilitytypes.ProxyUnicode'>
<type 'object'>

There it printed an object hierarchy of a joint correctly.

How to setup Nuke Python scripting environment

A while ago I had spent a couple of hours to set up my Nuke scripting environment. There were only a few things that need to be taken care of. Namely, those were setting up python environment, setting PySide2 working (no kidding), and using Nuke as a module. Yeah, it seems easy; however, it managed to waste a good amount of my time. So here I will share how I set up Nuke scripting environment.

Firstly, I always create a new virtual environment whenever I work on a new project. So I created a python2 virtual environment dedicated to Nuke, Maya and Houdini scripting. I found it helpful and dependable when some random incompatibility error occurs I know where to look and how to fix them. Then I installed PySide2. According to VFXPlatform, PySide2 started being industry standard from 2016. Since then, I believe that the visual effects industry completely shifted to it. However, some old tutorials on the internet use PySide and give an error regarding QtWidget. In PySide, QtWidget can be imported from QtGui class. But that is not the case for PySide2. Here you need to import PySide2.QtWidgets.

Another issue related to PySide2 was rather funny. Somehow VSCode was not recognising PySide2 objects in its editor. It imported a whole PySide2 module and run a code successfully. Unfortunately, it was saying PySide2 objects are not imported and showed undefined-variable error everywhere. Well, no one likes to see red underlines below their code. Do they?

As I could not think of any solution since the code works and PySide2 installed correctly, I switched to PyCharm community edition. I think it is only for python2 and hope VSCode will be fixed after a few updates. For now, I use whatever gets a job done.

Next fun task was using Nuke as a module. We need auto-complete and function annotations when we develop a script for Nuke. There comes a very helpful script: Nuke-Stubs-Generator.

It simply generates stubs for us to use as file. Place it in your home/.nuke directory and run Nuke. Then run this command from Nuke script editor to generate

import nukeStubs

Now I can put it anywhere you need. Realistically, I would have a bunch of scripts and tools that I am working on. But that implies that I would end up putting it in multiple places in order to use external IDE for writing scripts for Nuke. You know that it is bad practice.

To solve it, I put inside site-packages of my virtual environment. Since I was using virtualenvwrapper, I put it here:

That way I do not have to copy it in a few places and can import nuke globally anywhere I would like to use. Of course, I have to activate the virtual environment in order to import it.

So that basically wraps up how I set up Nuke scripting environment. Now it is time to write cool GUIs and pipeline scripts.

Developing Python application: Virtual environment

Nowadays Python is everywhere – academics, data science, machine learning, enterprise application, web application, scripting you name it python is everywhere. Whatever you do, python is there to help you or give you a headache. Let us say, you have learnt python programming and ready to use to develop applications that wow your future employers and make your future glorious. Surely, as that is great, you jump into coding python scrips and eventually start installing python packages. From there one follows a dangerous path into developer’s nightmare.

Package installation may lead to having incompatibility issues or make other application unworkable. And you may discover that your code does not work on some machines, while your code just works flawlessly on your local machine. Even though it gives a classic excuse for not writing good code, we, as developers, should make sure our code works everywhere. So what is a problem here? Python environment.

So, not to have a daily nightmare about incompatibility issues, individual python environment needs to be created for a project. A virtual environment is a bunch of scripts and directories that can run python isolated. By using a virtual environment, each python projects can have its own dependencies regardless of other project and system python environment. Here I will write about how to create and use virtual environment in python2 and python3. I will use virualenv for python2 and venv, virtualenvwrapper, and conda for python3.

Starting with python2, you need to install virtualenv package.

See, I already have installed it. After installing it, you can see its commands by:


We do not need to use most of those. To create a virtual environment, we use virtualenv [options] destination. Specifically, call

virtualenv –python=python2 path/to/virtual/environment/dir

Obviously, we can create a python3 virtual environment by –python=python3 assuming you have python3 installed on your machine. This command creates an isolated virtual environment as same as a given python path. Instead of using python2 and python3, we can give a direct path.

Once a virtual environment is created, we can use it by calling:

source path/to/virtual/environment/bin/activate

And calling deactivate when a virtual environment is activated, leaves the virtual environment. On python3, it has venv package as default for a virtual environment. To use it, we just need to call

python3 -m venv path/to/virtual/environment 

Everything else is same. What we have done is that we created a fresh python environment and copied dependencies to a specified directory. There we can install any packages without affecting other environment and local python by activating this environment. That is an absolute breeze.

However, we do not want to push it git repository but we do need to have a way of knowing required dependencies since some of us work on a project from different machines. I, for one, work from three different machines with windows and linux system.

One way to solve this problem is to create a folder for the virtual environment and ignore it for git. That way we can work on a project from different machines and on different os. We just have to keep a track of required dependencies. Using pip, we can save information of installed dependencies into a file and install those dependencies on a different environment when need to. Pip freeze command shows packages installed on the python environment. We need to save it to a file. It is a good practice to save it as ‘requirement.txt’. Later, on a different machine, we install required dependencies by using

pip install -r requirement.txt

Now we are in a very convenient position where we can work on a python project with any machines in any os. But what is the .env on my terminal and what about the occupied disk space of virtual environment? Obviously, those virtual environment files are necessary. However, when you have a number of completed python project and you want to release some spaces for some reason, would you check each projects and delete those files manually? Or wouldn’t it be easier if all virtual environment files are in one directory? And .env is a directory name where virtual environment is created. Ok, cool. But wouldn’t it be more convenient to see an actual python project name when the virtual environment is being used?

Virtual environment wrapper

To solve those minor inconveniences, we can use virtualenvwrapper package. Install this package with:

pip install virtualenvwrapper

after installing it, we need to activate its shell functions and create an environment variable that indicates a location of virtual environments. By running which, we get a path of its shell functions. We need to add it to shell startup. Since I am using ubuntu, I added it to ~/.bashrc. I also created environment variable for a location where I save virtual environments. So far, I added those lines to .bashrc:

export WORKON=$HOME/.virtualenvs 
source /usr/local/bin/

So now, you can create a virtual environment with:

mkvirtualenv -p python3 name/of/virtual/env

And activate it and use it. Also, virtualenvwrapper provides a few useful shell functions. One of those is workon. See, it makes life easier. To see a complete guide, visit this page.

p3venv is a name of env

Because it saves all files of every virtual environment created, it is easy to delete those if need to. And seeing the project name on terminal is pretty cool actually. That is it for creating and managing virtual environments using pip.

Using Conda

Now let’s see how to do it with conda. Conda is a package management system for Python, R, Lua, Scala, Java, JavaScript, and Fortran. Widely used in academic fields, we may know it by Anaconda. And people claim that conda is better tool for data science projects (I don’t know why. Read it here). Anaconda distribution is used by universities and it has its own GUI environment management tool with its navigator. However, not every developer loves to use gui-based tools, right?

Assuming conda is installed (if not install it from here), to create a conda environment

conda create --name name/of/env python=3.x 

and activate the created environment with

conda activate name/of/env

Conda creates virtual environment and stores all related files to its installation location. Which makes it easy to manage. To see all conda environments, we can call:

conda info --envs 

To remove particular environment, we call

conda remove -- name name/of/env -- all

Conda stores all environment names inside environment.txt in home directory/.conda folder. A content of it is same as conda info –envs command. On the other hand, all executables and packages are stored inside anaconda installation directory/envs folder. It is useful to know it since anaconda stores GBs of files (unbelievable, right?).

It is not the only way to create a conda virtual environment. We can save required information inside a yml file and use it to create conda environment. Generally, people create environment.yml and put python info, environment name, and dependencies there. With that yml file, we can create a virtual environment easier by calling

conda env create -f environment.yml

Updating environment.yml is easy, just need to write what needs to put there and call

conda env update -f environment.yml 

You can confirm it by conda list command. I know it prints a tremendous amount of packages. For love of the god, I hope conda does use all of them effectively. To distribute our project, we need to save dependencies information. Calling conda env export shows you all required information to save. We need to copy and paste it into requirement.yml (for ubuntu, simply run conda env export > environment.yml).

So that is it. Now I hope it becomes easier to manage python virtual environment. From here, we can write our application with ease and eventually package it and distribute it. That is another story to tell some other time.