Graphics Reference
In-Depth Information
two. At this point, it doesn't matter what the property value
itself is, so just leave it at 1.0.
Select one of the primary arm bones in Pose mode so that
its Copy Rotation or Copy Location constraints show in a
Bone Constraint context. RMB over the Influence slider and
choose
Create Driver
from the menu that pops up. Most
of the options in this pop-up menu (shown in
Figure 9.29
)
deal with keyframing, which we'll address in Chapter 11.
When you create a driver for a control or property, it turns
purple. Any changes you make directly to that control's value
while an active driver is attached will be ignored.
Now we're going to venture into the Graph Editor. There's
a lot here, so don't freak out. We're pretty far into the guts
of rigging now, and it's not the time to faint. Most of the
stuff in the Graph Editor can be happily ignored for the
time being. This is a targeted mission: Get in. Tweak a
setting or two. Get out.
Figure 9.29
Adding a driver to the constraint's Influ-
ence control.
Temporarily switch your 3D view to show a Graph Editor instead. You could create a whole new screen
for working with Drivers if you'll be doing a lot of it, but for our purposes, reusing our existing screen
is fine. On the Graph Editor header, change the visualization from
F-curve Editor
to
Drivers.
When
you do, you'll see something like the mini-nightmare in
Figure 9.30
. Press the N key to bring up the
Graph Editor properties on the right. In the upper left of the window you'll see your armature listed, with
the driver you just created underneath it. LMB click on the driver name, which will be called something
like “Influence (arm_lower: Copy Location),” to make sure it is activated.
What we're really concerned with here is the
Drivers
panel on the right. Change the
Type
control to
Averaged Value
. The type control tells the driver how to deal with incoming information, which is
called
targets
. You can actually have a driver that is influenced by several targets at once, using the Aver-
aged or Sum types. You could also just enter certain mathematical expressions with the Scripted Expression
type. However, we're just going to point the driver at the object property we created a few minutes ago,
so either Averaged or Sum will work fine.
Below the Averaged value selector, LMB click the
Add Variable
button. This is where we define the
actual target.
Figure 9.31
shows the new panel that is created. In the
Value
field, select the armature object
from the pop-up menu. When you do, a weird field called
Path
appears with what looks like a strand of
DNA in it. This is where the magic happens. Make sure that you have the Object properties context
showing, along with the custom property we already created, the one called “IK Switch Left Arm”. Hover
the mouse over the property value itself, click with the RMB, and choose
Copy Data Path
from the
pop-up menu. You've just copied to the clipboard Blender's internal reference for that particular property.
LMB in the
Path
field over in the Driver panel in the Graph Editor and press
Ctrl-V
to paste that data
path. Press
Enter
to confirm it.
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