updated with a compiled version by Guillaume Baratte.
»Delta Mush« is a mesh deformer that fixes/softens the effect of other deformers without affecting high-res details of the mesh. It's been developed in 1997 but was made public only recently in demo videos
of former Rhythm & Hues in-house software »Voodoo« where it was exclusively used. The idea behind Delta Mush is simple but clever:
Local mesh detail (=per point offsets from a smoothed to the original undeformed mesh) is precomputed and stored.
Then the 'to-be-fixed-deformer' is applied, directly after which the mesh is smoothed again with the same smoothing algorithm. This removes newly introduced detail which could potentially include unwanted artefacts
from the deformer. Finally, the stored offsets are applied, restoring the original detail.
This works not only for envelopes, but for all kinds of deformers like cloth sims. On envelopes, it is similar to what weight smoothing does, but (at least in theory) should be able to enhance the envelope effect by adding some sliding movement along the surface of the smoothed mesh. This can't be achieved using enveloping which only does rotations around the joints.
There are two implementations for Softimage. The first one is Miquel's original ICE compounds. The precomputation is done using the »Delta_Mush_dataSet« compound in the modeling stack, with the post effect applied in the animation stack after the envelope using the »Delta_Mush« compound.
local backup: Delta_Mush_dataSet.1.1.xsicompound Delta_Mush.1.1.xsicompound DeltaMush_sample.scn
The following is Guillaume's C++ implementation of Miquel's version, same nodes but performing faster and allowing attenuation of the effect by a weightmap. demo video and author downloads
of the C++ version. Have a look at Guillaume's vimeo page
including his 2014 showreel.
local backup: Delta_Mush.xsiaddon Softimage_DeltaMush_SourceCode.zip