Blendshape modeling using a copy and an instance?

[stempy]

I have phonemes I must create for a symmetrical face, and I am using blendshapes. For the blendshape objects I wish to work on modeling only on one side of the face and have the other update ie:instances. After creating a blendshape object I am satisfied with I want to delete the instanced half, reduplicate as a copy,combine, merge verts, and create blendshape. This process isn't working. When I move my blendshape slider the points on the base object move to other points locations which they didn't initially correspond to.
Please help. Any advice on modeling blendshapes using only one half of the face (for speed and accuracy reasons) would ease my frustration with this process.

[badcookie]

The reason you can't cut your face in half is because blend shapes depend on point order. In the simplest terms, every point is assigned a number, and your blend shapes deform on a component level. This is why when you duplicate a base object, translate it to the side, and assign a blend shape, your base head will not also move to the side when you dial up your slider. Because object transform information is not a deciding element in how your blend shapes calculate (this includes negative scaling to get mirror copys). However, if you went into component mode, and moved the verts/CVs instead, when you dialed up your slider your base WOULD move to the side. Your blend targets need to have matching vertex order corrosponding to your base shape, because when you dial up your slider, maya thinks " now component number 3 is relocated to this spot, I'll move #3 on the base to match #3 in the target. When you are cutting apart your targets, you are changing the point orders to accomodate the new geometry that has been combined or added. this is why you get spaghetti. #3 used to be in the lip, now its on the eyebrow.

the only way that I know of to get symmetrical blend shapes without modeling both sides is if you are using polys. There is a mirror script on this site in the mel section.

good luck!

[joojaa]

yes well to add a few ponters blend shapes are sensitive to the names of the connections they make. They transform points or whatever (blendshapes do not need to affect components they can affect anything realy like translates and rotates if you so wish). They try to find the corrsponding name in the other hiarachy.

Also this is possible to do if you make two intermediary shapes connected to blends and then combine theese to a new shape. Then the blend would be on each half separetely but the end shape would inherit this. Just one additional solution ive been using lately for generating the blendshapes quickly.

[fongsaiyuk]

apply a cluster to one half of the full model,
move the cluster pivot to the center of the model
and set the scale of the cluster across the symmetry plane to -1.
With the model folded upon itself you can model both sides simultaneously by selecting vertices from both sides of the face at once and moving them. when finished the target shape, delete the cluster. then create 2 new bendshapes and use the mebership tool to remove left side verts from one blend shape and the right side verts from the other.