Part
Two: Transferring Attributes from a Metaball
Another use of the Attribute
Transfer tool is the ability to pass any attribute from one model
to another. An artist may want to use this ability to help generate
a visual effect.
The following
lesson file includes a metaball is moving through the monkey's chest
where a bulge SOP causes a slight deformation of the surface. You
will add some arbitrary attributes to the metaball then pass them
to the monkey using Attribute Transfer.
1.
Preview the Metaball Animation
Scrub back and
forth in the timeline. You will see the monkey's chest bulge slightly
as a metaball passes through it. In the Network pane, select the
monkey object and press i
to go to the geometry level. Now as you scrub, you can see the metaball
passing through the monkey.

2.
Add Attributes to the Metaball
In the Network
pane, MMB-click on
metaball SOP's output. From the pop-up menu select
Convert Meta
and place this operator's tile. This converts the metaball into
geometry with point information.

Next, RMB-click
on the convertMeta SOP's output and from the pop-up
menu select Point.
Select this operator and in the Parameter pane, change Keep
Color to Add
Color then change the XYZ expressions to $BBX
$BBY $BBZ. This expression uses the point's position in
relation to the bounding box to add point values. These attributes
have no purpose at this time but they provide a way of previewing
how arbitrary attributes can be transferred to another model
3.
Set the Display and Footprint flags
In
the Network pane, set the display
flag for the bulge SOP and the footprint
flag for the new point SOP. Scrub in the timeline
until the metaball is just starting to penetrate the monkey's chest.

4.
Apply the Attribute Transfer SOP
In the Viewer
pane, press tab > AttribTransfer.
Press 7 to choose
Connected Primitive selection.
Click on the metaball then RMB-click to accept. Next,
click on the monkey then RMB-click
to accept. The monkey is shown highlighted in yellow and you cannot
see the effect of the transfer. RMB-click
on geometry and select Highlight
to turn it off. Now you can see the monkey affected by the transfer
but the results are not very subtle.

5.
Adjust the Parameters
In the Parameter
pane, go to the Conditions
tab and set the Distance Threshold
to around 1.0.
Now you can see the effect of the metaball on the monkey. You can
further adjust the Distance Threshold
to control the area being effected. You can also set the Set
Blend Width to soften or blur the effect. Scrub
in the timeline or generate a flipbook
animation to watch the results in motion.

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