Additive Blendshapes 2003-11-26 - By Kevin Chu
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Hi Eric,
Thanks for the help, but keying at the sides counter clockwise didn't work.
In the end it had to be an additive expression.
-- -- Original Message -- --
From: "Eric Kunzendorf" <kunzendorf@(protected)>
To: <maya@(protected)>
Sent: Monday, November 24, 2003 5:30 AM
Subject: Re: Additive Blendshapes
> Hi Kevin!
>
> What is happening is that you are keying the sdk with the sphere in the
center, let's say at x0,y0 and moving the sphere to the upper right corner
at x1,y1, correct? The four corners from upper left moving counter
clockwise would be: x1,y1; x-1, y1; x-1,y-1; and x1,y-1. Correct also? The
problem is that you should only use one attribute to drive an SDK control.
>
> So let's say you assign the upper right hand corner x1,y1 to smile and the
upper left hand corner x-1,y1 to frown. Trying to have both x and y drive
the blendshape is a mistake; it will cause problems because you have the
same blendshape assigned to different values at different times. But if you
use just x, then you will be okay with this instance, but the shape will mix
with whatever shape you assign to y. If you try this with y, you won't get
any good results because you will be assigning both smile and frown to y1,
that won't work. I believe I am correct here, but jump in anyone if I am not
describing this clearly.
>
> Two suggestions: first, try assigning the blendshapes to the middle of the
sides, rather than the corners. These coordinates will be from the right
hand side moving counter clockwise: x1, y0; y1,x0; x-1,y0; and x0,y-1. That
might get you what you want. Keep in mind that the blendshapes will mix at
the corners. Or...
>
> Jason Osipa's Stop Staring book covers exactly how to do what you are
trying to do with this type of interface. But he doesn't use SDK, he uses
expressions very elegantly. While I don't agree with doing EVERYTHING with
blendshapes, as he does; he very clearly explains how to use expressions
with blendshapes to create slider based interfaces. He also explains how to
convert a range of coordinate values to -1,0,1 for use in driving
blendshapes. Also, check out his use of the clamp function(procedure?) to
clamp values to a particular range. I found it to be clearly explained even
to a math dunderhead such as myself! I hope this helps, and good luck!
>
> Excelsior!
> Eric Kunzendorf
> Computer Chair and Animation Instructor
> The Atlanta College of Art
>
> Kevin Chu wrote:
>
> > Hi All,
> > I have an interesting problem with some blendshapes. I'm trying to set
up an interface using set driven keys and blendshapes. I have an interface
in the shape of a square and a sphere in the middle of the square which I am
using as the driver in my set driven keys, to drive a series of blendshapes.
Each of the four corners of the squares represents a blendshape, and the
center of the square represents the starting shape.
> >
> > So here's what I did. First I made four blendshape targets, and ended
up with 4 blendshape sliders. Then I started making a driven key, setting
up my sphere in the center of the square as the driver, I then keyed all of
the blendshapes at zero when the sphere was at the center of the square.
Then I proceeded to move my sphere to the top right hand corner, and this
time I changed one blendshape slider to 1 and kept the other 3 at zero. I
continued this process for the other three corners. So theoretically, when
I move my sphere to the far corners of the square, I should have three of my
four blendshape sliders at zero and one of the sliders at 1. However, this
is not so, in fact, my results are quite strange, and I'm not sure how to
solve this problem. What I do know, is that I need to set this up so that
the blendshapes are some how additive to one another. Does anyone have any
ideas?
> >
> > Thanks
> >
> > -Kevin
> >
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