The Stretchy Eye Balls

According to the finalized model, the eye balls of the character are not exact spheres; the eyes movement will be a problem as the pivot point is not located exactly at the center of the eye balls. Some studios would use texture project to make the pupils, but the pupils will be distorted and the projected image may not be stable after the geometry of the eye ball are stretched with the head. Jared Lindquist tried using rivet script and “Freeze Geometry’” of lattice to keep the pupils remains circular and attaching on the eye, and I had modified this method to make the eye stretch with the head properly.

1. Create a nurbs sphere for eye model; rename it to eye _geo and a polygon sphere roughly the same size; rename it to eye_rivet_base_geo. ( it’s good habit which rename all new nodes to some meaningful names after create, it will help to trace and solve problem)

The polygon sphere can be created by duplicate the nurbs sphere and convert into polygon.

Figure2 - a nurbs sphere for eye model and a polygon sphere

2. Use rivet script which was created by technical director Michael Bazhutkin, On the eye_rivet_base_geo, select two parallel edges in front of the location of pupil, and create a rivet. The locater will stick on the polygon face even thought the face has been translated or deformed. Rename locator to eye_rivet_loc.

Figure 3 - select two parallel edges in front of the eye_rivet_base_geo and create rivet

Figure 4 – a locator (rivet) is created accordingly and stick to that polygon

3. Position the eye _geo and eye_rivet_base_geo with rivet on same location, we can use point constrain to position two geometries on the exact same location:

• Select the eye _geo then shift select eye_rivet_base_geo with rivet

• Choose Constrain > Point to assign point constrain

Figure 5 –eye _geo and eye_rivet_base_geo snaped together

• Delete the point constrain node under eye_rivet_base_geo.

Figure 6 – delete point constrain node under eye_rivet_base_geo in outliner

4. In the original idea of Jared Lindquist’s, the eyes are deformed and stretched by lattice, but it the lattice could not be deformed with and driven by the head rig. Instead of the lattice, I use wrap deformer as a main deformer for the eyes.

Create wrap deformer for eye_geo

• Duplicate eye_geo and rename eye_wrap_base_geo

• Scale eye_wrap_base_geo a bit, slightly larger than eye_geo and eye_rivet_base_geo, and wrap around them.

• Select eye_geo first, and then shift select eye_wrap_base_geo,

• Choose Create Deformers > Wrap, to create wrap deformer.

• Select eye_geo, rename the wrap input node to eye_geo_wrap.

• Set the Max Distance of eye_geo_wrap to 50.

Figure 7 –Set the Max Distance of eye_geo_wrap up to 50.

Create wrap deformer for eye_rivet_base_geo as well

• Select eye_rivet_base_geo first, and then shift select eye_wrap_base_geo,

• Choose Create Deformers > Wrap, to create wrap deformer.

• Select eye_rivet_base_geo, rename the wrap input node to eye_rivet_base_geo _wrap.

• Set the Max Distance of eye_rivet_base_geo _wrap to 50.

Figure 8 –Set the Max Distance of eye_rivet_base_geo _wrap up to 50.

5. eye_geo and eye_rivet_base_geo are deformed according to the shape of eye_wrap_base_geo and eye_wrap_base_geo can be bound on the head rig, so the eye can be stretch with head. But the CV for pupils could not remain in circular. Now we use the rivet and lattice to remain the shape of pupils.

Figure 9 - eye_geo and eye_rivet_base_geo are deformed according to the shape of eye_wrap_base_geo.

• Reset the shape of eye_wrap_base_geo

• Select the CV for pupils on eye_geo

Figure 10 - the CV for the pupils on eye_geo

• Choose Create Deformers > Lattice, rename the ffdLattice to pupils_ffd_Lattice and ffdBase to pupils_ffd_Base. Select eye_geo and rename the ffd input node to pupils_ffd.

Figure 11 – create Lattice on the CV for pupils and rename properly

• Set the division of S, T, U, for the pupils_ffd_shape to 2, and check the ‘Freeze Geometry’ option of pupils_ffd in the attributes editor

• Parent pupils_ffd_Lattice under eye_rivet_loc

Figure 12 – the setting for pupils_Lattices

Now select both eye_geo and eye_rivet_base_geo, the CVs for pupils are remaining circular as the shape is frozen by the pupils_ffd. We can assign ramp texture and shader eye_geo. The shape of eye is driven by the eye_wrap_base_geo, deform the eye_wrap_base_geo to fit in the eye socket of the character and bind to head joint later on.

As the eye_geo and eye_rivet_base_geo have to rotate together, we can use orient constrains to make eye_rivet_base_geo following to eye_geo.

Figure 13 –pupils are remaining circular no meter how the eye had been stretched

Now the eye movement can been created by rotate the eye_geo, the pupils are remained circular no meter what shape of the eye ball. Group all the elements for eye into one group in order to clarify the scene and ready for next step.

Figure 14 – the move and deform the eye_wrap_base_geo to fit the eye into the eye socket.

The eye movement can been created by rotate the eye_geo.

References for marking stretchy eye ball

Lindquist, J. (2007). Nyeng! Stretchy eyes in Maya. Retrieved March 18, 2008 from http://www.nyeng.com/?page_id=345

Bazhutkin, M. (2007). Bazhutkin Software. Retrieved March 18, 2008 from http://www.geocities.com/bazhutkin/