A Look at OpenSubdiv

BACKGROUND

OpenSubdiv is an open source tool that quickly and easily subdivides and smoothes a 3D model through the process of interpolation. It utilises the Catmull-Clark method of subdivision and has been widely adopted by the industry due to its efficiency (Pixar, 2016). 

opensubdiv

A simple tube with and without OpenSubdiv

Originally developed by Pixar, it was released to the public as an open source library and, since then, has been incorporated into software such as Autodesk’s 3DsMax and Maya and Blender (FX Guide, 2015).

geris-game1

Geri’s Game (1996)

The first instance of OpenSubdiv was developed by Tony DeRose and Tien Truong for the Pixar short Geri’s Game (Pixar, 2016). Pixar released it as open source in the hopes that it would be adopted by the industry and thus gain hardware support, as well as to increase efficiency throughout the industry (FX Guide, 2015).

APPLICATIONS

As OpenSubdiv was originally developed for character modelling, and because it smoothes and interpolates the mesh, it is most commonly used for organic modelling (FX Guide, 2015). It has been used for many Pixar characters such as Woody from Toystory.

woody

Woody with OpenSubdiv

More interestingly, OpenSubdiv has been used on non-organic characters, such as Steve McQueen from Cars and WALL-E, to achieve a high-poly look while still being manageable to animate (FX Guide, 2015). 

wally

WALL-E with OpenSubdiv and CreaseSet

WALL-E’s many details were achieved through subdivision in combination with creasing.

IN PRACTICE (3DsMAX)

Using OpenSubdiv in 3DsMax is very simple. OpenSubdiv is a modifier that can be applied to a model via the modify tab.

modifier

The model may lose some of its original volume but can still be changed without having to collapse the modifier (and therefore add all those extra polys). This was one of the major advancements of OpenSubdiv and is one of the reasons it is so efficient as it allows the model’s current topology to be edited while also being able to see how it will look once it is subdivided.

Volume

The bulkness of the hands is reduced and smoothed with OpenSubdiv

One of the quickest and easiest ones to gain back some of the volume is to add an additional loop to the model.

EdgeLoop

Using additional edge loops on a tree trunk

However, this may not be what is needed. The creasing of the model can be adjusted in the Edges mode of the Editable Poly modifier. This is done by selecting the edges that require more creasing (i.e. they need to be less smoothed) and adjusting the “Crease” value (Autodesk, 2014).

ModifierCrease

CreasedEdges

Uncreased Vs. Creased edges

Alternatively, a CreaseSet modifier can be used to a similar result. The benefit of the CreaseSet modifier is that it allows multiple sets of creases with different values to be managed in all one place (Autodesk, 2014).

MY PROJECT

I have been using OpenSubdiv while modelling my character and her accessories.

Render

As demonstrated in the pictures earlier in this post, I have been using both creasing and additional edge loops. I have also found that I am using OpenSubdiv on the non-organic elements of the model.

shoulderpads

Overall, using OpenSubdiv has allowed me to quickly add detail and give my model a smooth look.

REFERENCES

Autodesk. (2014). 3ds Max 2015 Extension 1 – Working with OpenSubdiv. Retrieved 4th of May, 2016 from
https://www.youtube.com/watch?v=1Cy3niOZ7nA

Autodesk. (2014), To Work with OpenSubdiv.  Retrieved 4th of May, 2016 from
https://knowledge.autodesk.com/support/3ds-max/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/3DSMax/files/GUID-EEF18A3F-DE80-4BBE-8811-48B89FF0AC97-htm.html

FX Guide. (2015). Pixar’s OpenSubdiv V2: A detailed look. Retrieved 4th of May, 2016 from
https://www.fxguide.com/featured/pixars-opensubdiv-v2-a-detailed-look/

Pixar. (2016). OpenSubDiv. Retrieved 4th of May, 2016 from
http://graphics.pixar.com/opensubdiv/docs/intro.html

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