Blend over Blend

Ever since I first started tackling Maya, and the subject of blend shape deformers, I wondered if there was a way around the most common way of using them; namely, the duplication of the original shape and the push-pull tweaking of the original shape .  I’m not going to complain that said method is ineffective or inefficient, because if you’re using it to do what it’s most commonly tasked with, that of creating facial expressions on characters, then it’s certainly the best way to go about using them.
However, what if you wanted to have one shape completely change into another specific shape?  Well, if you can visualize comparatively what the parts of those shape are that will become the parts of the new shape, then what I’ve learned is that indeed, you can do this.

The trick is, how to build two sets of objects side by side not only with the same number of vertices, but so that the vertices are ordered identically.

Fortunately, I covered a way to do this several weeks ago.

What follows is how to take that knowledge and applying it across several parts intended to be merged into one object without losing that ordering of vertices, or the intended effect of either blend-shape, independently able to be controlled.

To that end, I’ve created for this demonstration, what will end up being a single object with two blend shapes attached.  For now though, that object takes the form of two separate objects one on top of the other, and their corresponding two blend-shape targets, all created independently of one another (not duplicated and modified) but tested to ensure that they have the same number and order of verts as the first using the methods already outlined previously.

From here, we simply create two blend shape nodes, one for the two top halves and one for the two bottom halves.

The rest of the process is relatively straightforward.  After merging the objects, the surface can be made seamless again without re-ordering the verts by simply selecting and deleting one row and one row only of polygons from around the circumference of the morphing object.  The reason this is, is because eliminating one row of faces along the seam line only eliminates the faces while leaving the verts and their ordering in place, and it’s the vertices that matter most when doing this.  Now all that is left is to either use the bridge tool, or the append polygon tool to make the surface continuous.  The final result is a morphing object that has two independently created targets applied to it, and with independent control, as you can see by the varied rate of morphing in the following clip:

Now, this method is not without it’s drawbacks.  Primary among them is the fact that we are still left with multiple blend shape nodes, which bogs things down the more you have of them.  Have not yet figured out whether or not it can ever be done so that both blend shape controls occupy the same node by modifying the steps shown here, but if I do, I’ll be sure to make an update about it.

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