"I think one of the notable pieces in Shrek 2 was the shampoo hair shot of Prince Charming," Grant recalls.

Clothing too saw a big upgrade in Shrek 2, blending from a procedurally-driven, tight-fitting top to a simulated skirt using the proprietary Emo and Maya. The studio also developed a new fabric shader dealing with threads running in different directions and allowing them to go from cotton to satin to silk.

There was also a noticeable advancement in fluid simulation on Shrek 2 for the From Here to Eternity riff between Shrek and Fiona. Whereas Shrek merely offered a glass of milk, the sequel offered dozens of layers of water elements by animating particles for the waves as well as various splash layers on top of them.

But the crowning achievement of Shrek 2 was the introduction of global illumination. The studio developed a bounce light technique that, given a key light, automatically computes the correct bounce light off of the other objects in the scene. They would then add additional fill light and tweak it from there.

Yet overcast lighting was hard on Shrek 2, so there were additions to the global illumination pipeline for Shrek the Third. Other improvements in Shrek the Third included new character rigs with improved facial animation for better performances; more tactile clothing and fabrics with multiple areas for simulating movement; long and bouncy hair for all of the princesses that didn't take months to render; more effective fire and water engines; more controllable crowds; and greater and more beautiful environments.

"In Shrek 3 we used global illumination except for those sequences with high complexity because it was too time intensive," Grant adds. "But on Shrek 4, we were able to use global illumination to its fullest extent throughout the forest and throughout all those ogre battles and then also through all the hair styles. We have this technique similar to point-based color bleeding called point-based global illumination and it was first introduced on How to Train Your Dragon. But now you got to see that technique applied to all of the Shrek environments in Shrek 4. It's given us the ability to be less limited by what our renderer is capable of and be more focused on trying to put the best image quality out there.

Hair simulation has continued to improve in the Forever After. For instance, there's a key shot of Fiona as the warrior princess where you see her hair flowing in the wind. "Actually, her hair flows and cascades throughout, so the main thing there was it became less of a one-off and more of a standard process," Grant continues. "The other nice thing is that the process before for setting up the hair required a lot of different departments: modeling, surfacing, character effects all working together. But for Fiona, her hair set up was done by one group, which allowed the process to be optimized and work across many, many shots.