Can you Change Orginal Character Model and Blendshapes at the same time?

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  03 March 2011
Can you Change Orginal Character Model and Blendshapes at the same time?

Hey Everyone,

So i've hit a big snag in production, and desperately need to change my main character's head model. However my friend had already made blendshapes for my main character. Is there a tool or anyway in Maya to edit the original model and the blendshapes at the same time (so as that I can continue to use said blendshapes)?

Thanks for reading

  03 March 2011
This depends on what changes you have to do to the model. Unfortunately I don't know about Maya, in XSI it is only possible to edit the base geometry to a limited extent (inserting edge loops, move vertices around) without destroying the blendshapes. In any case the blend shapes will most likely have to be readjusted manually. I have never heard of a function that does those adjustments automatically.

What you could do is to not change the original head model, but duplicate it first. Do the modelling changes to the new head, then use a cage deformer (shrink wrap) to transfer the deformations of the blendshapes from the old head model to the new one.
  03 March 2011
As far as I know, there is no such tool, and I've done quite a bit of messing around with blendshapes in Maya.
It also depends on what changes you want to make. I'm pretty sure you can extrude, add edge loops and move vertices around after applying the blendshapes, and your main geometry will deform accordingly. The only issue is that any additional loops/extrusions you add may not deform exactly as you like(I might have a way to fix this, which I'll explain later)

To test out what I'm saying, create a new file(just to be safe) with your character and its blendshapes, apply all the blendshapes to your base geometry and make whatever changes you like to the base mesh. Delete all your blendshape geometry and check all the blendshape sliders to see if everything deforms in a way that you're okay with, and if it does, move ahead.

Now you might have issues with UVs here, so there's one more thing I'll suggest you do if my previous suggestion works for you.
If all the blendshapes are working well for you, here's what you can do do clean up your history, fix deformations of added loops/extrusions and fix your UVs.
First off, save another copy of the file(yes, I'm very particular about file management, haha)
Next, unwrap your mesh again if necessary, or make whatever little UV changes you want to.
One by one, move the blendshape sliders up to 1 weight, duplicate your base mesh and move the duplicated mesh away from the base mesh. When you've done this for each and every blendshape, you'll basically have the deformation your friend worked on creating, but with all the topology changes you've made.
Make sure you're happy with your UVs, and all the blendshape sliders on your base mesh are turned down to zero, and then delete the history on your base mesh. Re-apply each blendshape from the objects you duplicated earlier, and check them again.
Lastly, if certain topological changes you've made aren't deforming evenly or properly, you can manually edit them on the duplicated geometry.

Of course, all this information is assumption because I don't really know what you're planning on doing.
Strange things often happen to me......
  06 June 2011
Incidentally, I ran into this issue while working on something for a friend, and in my experience, the only tool that has given trouble when modifying topology on the base mesh with all the blend shapes applied is the Fill Hole tool.

Hope this helps someone.
Strange things often happen to me......
  06 June 2011
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