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180 Chapter 11: Space Warps and Particle Systems
Inter face
Particle Geo m et ry group
Use this control for defining the object to be used
as the particle geometry. This object is known as
the reference object.
[button]—Click this button, and then select a
geometry object in the scene to b e used as the
particle shape. The mouse cursor changes to a
cross shape when positioned over an object that’s
valid for use as a reference object. Valid objects
include multi-shape objectssuchasgroupsand
hierarchies; see Separate Particles For g roup (page
2–181).
After picking a reference object, its name appears
on the button.
You can use a lmost any geometry object as
a reference object. By default, the operator
automatically converts closed splines to rendering
geometry by “filling in” the area defined by the
shapeoutline. Tousetheshapeoutlineinstead,
select the original shape and, on the Modify p anel
> Rendering rollout, tur n on Display Render Mesh.
You needn’t tur n on Renderable, but changes to al l
other Rendering rollout settings, such Thickness
and Sides, are reflected in the rendered particles.
Particle Flow does not automatically “fill in” open
shapes such as Line (non-closed) and Arc. To
render these sh apes w hen using them a s particles,
turn on Modify panel > Rendering rollout >
Display Render Mesh.
If a Shape Instance operator is in effect for which
the geometry object is not defined, and the
viewport display ty pe is set to Geometry, then the
particlesappearintheviewportsasXcharacters.
Note: If a multi-shape object used as a reference
object comprises objects both w ith and without
materialsapplied,andAcquireMaterialison,
P article Flo w will apply the first available material
to any objects without materials applied.
Note: You can use a NU RBS surface as a reference
object, but not a NURBS curve. To use a NURBS
curve as particle geometry, first convert it to a
surface using a method such as t he Cap function.
Tip: For b est results, w hen using an animated
reference object, it’s highly recommended that
you hide t he original object before rendering, or
use Object Proper ties to turn off its Renderable
check box.
Note: If using a group as a reference object,
make sure the group is closed before selecting it.