Slim Look-Dev


The goal of this project is to create and shade a cupcake, using RenderMan and techniques such as Physically Plausible Shading, PTEX Vector Displacement, Sub-surface Scattering, etc.



Below are the cupcakes used as reference. They taste awful.

 MG 4753
 MG 4776

Modeling & Texturing

Cream modeling was done in Houdini using a spiral curve. However. At first, the paper cup was model as a high polygon count geometry, but then was replaced by a much lower polygon count geometry because of a new solution using a custom SLIM shader. 

The next step is to bring these low-detail model into Autodesk Mudbox, by increasing the mesh density, we’ll have the ability to add details using basic sculpturing tools.

The sculpture details were then exported using Mudbox as a Vector Displacement Map (VDM) in PTEX format.


(*no higher resolution available) 

The most challenge task is to correctly transfer the vector displacement from Mudbox to Maya, while maintain to use PTEX map and RenderMan shader. As shown in the renders below, different displacement settings in both Mudbox and SLIM editor can lead to various result.

Another issue while using PTEX Vector Displacement Map is the lost of detail. The amount of sculpture detail in Mudbox is very difficult to be transfer to Maya completely. After lots of try and error tests, it looks like using “object space” can preserve most of the details, although the quality is still not acceptable.

Lighting & Shading

Lighting is done using an HDR image I took.


It’s quite difficult to get a good result from subsurface shader. There’s useful information on Pixar’s website giving some reference value of common materials.

proj1 cupcake renderman v3.0045


In general, subsurface is very useful when doing look development for edible objects, but is difficult to control. Vector Displacement has the potential to be a very helpful tool in terms of modeling, but also requires a lot of work to gain the ideal result. 

© Ziye Liu 2014