Blendshape causing double transform on another blendshape?

Rigging
#1

Hi!
I have a couple of blendshapes going into a bridge shape.
When I drive up the value of one of my eyelid tweak targets, it seems to cause a double transform on my brow targets, causing them to go either up 200% or down 200% depending if they were already up or down. Then if I also trigger the same eyelid tweak target on the left side, they go up to 300%.

Eyelid Tweak = 1 + Eyebrow = 0 = Normal/No Unusual Effect
Eyelid Tweak = 0 + Eyebrow = 1 = Normal/No Unusual Effect
Eyelid Tweak = 1 + Eyebrow = 1 = Double Transform on Eyebrows
L_Eyelid tweak = 1 + R_Eyelid tweak = 1 + Eyebrow = Triple Transform on Eyebrows

Not sure exactly where I am going wrong here. I have plenty of other shapes going on and these are the only ones where I am seeing double transforms.

#2

Update:
I think I figured it out.
I was unable to easily use the GUI to add targets to a blendshape, so I created a second blendshape under my bridge shape to pipe things into.

I then had some weird messy problems setting up my blendshapes and seeing them invert when I set up SDK’s to drive them with CTRLS…So I figured…what if I just switch the envelope to -1 for one of my blendshapes.

I think the issue arose when I had targets under one blendshape set to +1 envelope mixing with targets from another set to -1.

I sorta hacked it all to work now and I am not getting double transforms anymore.
Hopefully I am not causing myself any more problems down the line.

Are there resources out there for best practices for blendshape workflows?
Is it bad to use multiple blendshapes to house targets on a bridge shape?
Is it bad to set envelopes to -1?

#3

There’s nothing wrong with setting deformer envelopes or blendshape weights to negative values, but some game engines won’t support it, if you are exporting to a game.

You’ve mentioned “a bridge shape” before. So just to be clear, it means you are feeding the output of one blendshape into another blendshape, right?

From what I understand from this article on parallel eval, and my own tests speeding up rigs, chaining blendshapes into other blendshapes is not GPU-friendly. (But I was testing that in Maya 2016. Also the speed loss might not be that big of a deal, depending on your rig and mesh. It is definitely a common way to organize deformations.)

#4

Hey again!
Great, thanks. What I have seems to be working. Just get worried that I did something wrong up the chain and that just hacking it together to compensate will cause further issues somewhere down the line.
Great, luckily I am just planning on rendering this guy out of Maya.

Yes, I duplicated and separated the head off of my character to create a bridge that I am blendshaping back into my global rig. I then duplicated that bridge head shape off for other shapes/local rigs that feed into my bridge and then down into my global rig.

Thanks for the article on parallel eval. It looks like an interesting workflow. Looking forward to trying it out and seeing how it works for me!