9

772 Chapter 13: reactor
To highlight multiple non-contiguous list items or
remove highlighting, use
Ctrl +click.
Pick —Lets you add an object to the Fracture
helper. Click this button, and then in the viewport
position the cursor over the object to add to the
helper. If the object can b e used as a fracture piece,
the cursor changes from an arrow to a cross a nd
youcanselecttheobjecttoaddittothehelper.
Add—Lets you add one or more objects from the
scene to the helper. Click the button to open the
Select Rigid Bodies For Fracture dialog. Make a
selectionintheprovidedlist,andthenpressthe
Select button to add the object s to the helper.
Delete—Lets you remove objects from the helper.
In the Pieces l ist, highlight the bodies to remove
from the helper and then click this button.
—
Selected piece
You can assign these properties to pieces
high lighted in t he Pieces list.
Broken—Th is read-only check box shows whether
any of the highlighted pieces have broken off at the
current frame. For example, say you’ve created
an animation from frame 0 to fr ame 50 using
Fracture, where piece A broke off at frame 10.
Highlighting piece A and moving the time slider
to frame 10 or after automatically turns on Brok en.
Movingthetimeslidertoframe9orbeforeturns
off Broken. This is because reactor keeps track
of the times pieces break off. That way, if you
continue the animation at frame 50, reactor knows
itshouldn’taddpieceAtothefractureobject,so
it keeps moving independently. You can restore a
highlighted piece to its "unbroken" state with the
Reset button (see follow ing).
Reset—This button is available if any of the pieces
broke off during a previous animation (reactor
stores the t imes when pieces broke off). C licking
this button tells reactor to ignore the times they
broke off in the previous animation.
Choose the behav ior for highlighted pieces:
•
Nor mal—The default behavior option for a
fracture piece.
•
Unbrea k a ble—The hig h lighted piece never
breaks away from the Fracture object, even if it
experiences an intense collision.
•
Keystone—If this piece breaks, then all pieces
break.
•
Break At Time —The selected piece breaks at
the time you specify. For this kind of piece the
Broken check box reflects the state of the piece
at the current frame. Thus, if you set a piece to
breakatframe5,theBrokencheckboxisonat
frame 5 and later, and off at f r ames before 5.
Use Connectivity —When on, groups of pieces that
are connected to each other move independently
of pieces that they are not connected to. This is like
having multiple fracture objects contained in one
fracture helper. The collision detector determines
that two pieces are connected to each other if their
distance f rom each other is less than the world’s
Collision Tolerance.
Break on
Choose the method by which reactor determines
whether fractur ing should occur:
•
Impulse—Whenapieceofthefractureobject
experiences a collision where the impulse is
greater than the threshold specified, it breaks
off from the fracture object. The impulse of the
collision is proportional to both the relative
velocity of the collision and the mass of the
objects involved in the collision. The higher the
mass of the object that hit the piece, the larger
the i mpulse.
•
Velocity—Whenapieceofthefractureobject
experiences a collision where the relative
velocity is greater than the threshold specified,