Wednesday, 10 June 2020

Making a Stadium Crowd from scratch with Houdini and Character Creator

Creating Stadium Crowds is a fairly routine task for a Crowd FX Artist, but there is scope for some interesting workflow and automation.
I will explain how I have made a basic Stadium Crowd with SideFX Houdini and Reallusion Character Creator. I am using Houdini v18 and Character Creator v3.2. I am also using the Crowd Animation pack from Mocap Online. I find the animation clips are good quality and have plenty of variations. You can also source clips for free from Mixamo.

When planning a Stadium Crowd, there are a few things to consider:
  1. Probably the most important question is "how close to the camera is the crowd?". In most cases, the the crowd will be far away, in the shade and motion blurred. That may not be the best conditions to showcase your work, but it does allow you to work with lower quality assets with faster render times.
  2. Is the crowd system to be customisable for multiple scenarios? I was inspired by the work by Postoffice's Crowd and Stadium Tool to start creating a system that can be used for any team in any stadium.
  3. What assets do you have? Do you have a variety of 3D characters that are rigged? Can you get access to high quality motion capture? Do you have a model of the stadium? Where are you going to get these assets? In my case, I was luck to to have a good model of a stadium (Machester City, Etihad stadium) but there are options out there for free stadium models. You may need to add seating to these models or modify them to suit your needs, but they are a good start.

Break it Down

To create an effect like a stadium crowd, the best strategy is to break the job down into smaller parts while still being concious of the whole pipeline.

First up are the assets. We will need the folowing:
  1. Characters
  2. Animation clips
  3. Geometry for placing the characters
  4. Environment and lighting

There are several sources for gathering character assets. Mixamo has a few that would be suitable for stadium crowd work (Brian, Adam, Liam, Shea, Malcolm, Kate, Suzie, Elizabeth). These are free, rigged and come with animation clips.
If you need higher quality, you may find free models online. Have a look on cgTrader, TurboSquid and Sketchfab.

Another way to get high quality models is to generate them yourself using software, such as Reallusion's Character Creator.
This software can generate character meshes in Obj and Fbx format, posed as you like.
Clothing can be varied using the built-in library but that library is quite limited. However the library can be extended using clothing geometry from other sources.

Here is an example of a character with clothes from the built-in library

Another example using a modified texture and custom decals on a built-in garment

An example of a mesh (hooded sweater) imported into Character Creator

It is also possible to import textures for skin and faces. Here's Pep:

These meshes can be exported from Character Creator as FBX, which will produce a single mesh with primitive groups which will become useful when breaking the mesh in Houdini. The export will also save out texture files for each of the seperate mesh groups. Textures include Diffuse, Normal map, specular, roughness and maybe one or two others, depending on the materials on the clothing. Some of these textures will be too much detail for a Crowd simulation, but they are there if required for close-up shots. I would consider Crowd FX unsuitable for close-up shots, so I only use the Diffuse and Normal maps in most cases.

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