View Click Group Selection in an event or add
a Group Selection operator to the particle system and then click
The Group Selection
operator extends Particle Flow's ability to select particles. Originally
in Particle Flow, you select a single group of particles explicitly
that remains selected throughout the entire flow. With Group Selection,
however, you can specify any number of groups according to various
criteria: location, particle properties, at random, and more.
You can divert selected
particle groups to another event with the
or indicate an outside event to affect particles with the
The Group Selection icon can be scaled and transformed to change
the particle selection dynamically over the course of the particle
You can instance the
Group Selection operator in different events to define the same
selection subset. If the particles converge into another event, the
selection subsets are united, and a Group Operator works with the
combined selection subset.
The Group Selection operator
doesn't change particle properties. It adds a data channel that
indicates the selection status of a particle corresponding to the
selection operator. To modify particles based on their selection
status, use a Group Operator or Split Group test.
Group Selection icon
Adding a Group Selection
operator to a Particle Flow system creates a 3D icon, or helper,
that you can select in viewports. The icon is placed at the world
origin (0,0,0). When you select this icon, the Parameters rollout opens
on the Modify panel that provides the controls described in the
following section. The position of the icon is used by Particle
Flow when you choose the
Inside Icon Volume option.
Group Selection icon
- Selection Update
Choose how to calculate the
- OnceThe operator
determines the selection status only once, at the time a particle
enters the event.
the selection status anew at every frame.
Depending on other options,
the Group Selection operator may detect the selection status change
in between frames, on sub-frame sampling basis.
- Reverse Selection
Inverts the particle selection.
- Selection Condition
Determines the method the
operator uses to select particles. The choices are as follows:
- Entire Particle StreamSelects
all particles in the event. Use this option if particle selections
are merging in the current event, and in a later event you plan
to separate particles with an instanced Group Selection operator.
- By SnapshotSelects
particles based on those currently selected in the PF Source sub-object
level, or all particles present in the event at the current frame.
The number of selected particles appears next to By Snapshot.
To select the particles,
choose one of the following sources from the dropdown menu and then
click Generate Snapshot:
- Selected in PF SourceSelects the
particles currently selected at the Particle sub-object level of
the PF Source. Before using this option, make sure both of the PF
Source object's Quantity Multiplier settings (Viewport % and Render
%) are the same.
- All in Current EventSelects
all particles in the event at the current frame.
- Generate SnapshotClick
to select the particles as specified by the choice in the drop-down
list. The number of selected particles appears next to By Snapshot.
Once you have generated
a snapshot, you can change the frame or sub-object particle selection
without affecting the selection in this Group Selection operator.
Keep in mind that the selection is based on the particle IDs. Therefore,
if the number of particles in the viewport and the rendering are
different, the overall effect can differ drastically. To use this type
of selection effectively, synchronize the percentage of particles
in the viewport and renderer.
- Inside Icon Volume Displays
the Group Selection icon in the viewports, and selects all particles within
the icon. If Selection Update (see preceding) is set to Once, only
particles that are inside the icon at the start of the event are selected.
If Selection Update is set to Continuous, particles are members
of the group only when present inside the icon volume; thus, the
selection can change throughout the animation.
- Icon TypeSets
the overall shape of the icon: Box, Cylinder, or Sphere. The initial
size of the icon is set by the Icon Size parameter, near the bottom
of the rollout. To change the icon size and shape, change this parameter
or use either uniform and non-uniform scaling . You can also move,
rotate, and animate the icon to change the selection area.
- Subframe SamplingWhen
off, the motion of the icon or the reference object is considered
to be linear between frames. If the icon or the object has fast,
complex motion, turn on this option for greater precision in the
calculation of the icon/object location.
NoteThis setting also
applies to the Inside Object option (see following).
- Inside ObjectLets
you designate an arbitrary object as the volume for selecting particles
for the group. After choosing this option, click the “None” button
and then select a reference object to use as a selection bounding
area. All particles inside the reference object are selected. If
the object doesn't define a closed space, the resulting selection
might not be consistent.
NoteThe Subframe Sampling
option (see preceding) applies to Inside Object as well as Inside
- Animated ShapeIf
the reference object is animated in a way that changes its shape
or volume, turn on this option.
- Select By Particle PropertyUses
particle properties to define the selection set. This choice appears
in parentheses in the event, after the operator name. From the Property
list, choose one of the following:
- AgeUses particle
age to define the subset. All particles with ages in the From/To
range become selected. Use the Variation parameter to vary the selection
- Birth IDUses
a unique particle ID is used to define the subset. All particles
with IDs in the From/To range become selected. Use the Variation
parameter to vary the selection status.
NoteThe Birth ID property
is not scalable in reference to the Quantity Multiplier parameters
of the PF Source object.
the particle speed vector and the icon direction vector to determine
the selection subset. Particles are selected if their speed vectors
are close in direction to the icon vector. When this option is selected,
the icon shows an arrow with a surrounding cone to show the effects
of the Divergence parameter. All particles with a speed vector within
the cone become selected. The Divergence and Variation parameters
are expressed in degrees.
particle scale value to define the selection subset. Since the scale
value is a vector, and From and To values are scalar, the maximum
value of the scale components is used to define the range inclusion.
- Script FloatUses
a particle float data channel to define the selection subset. The
Float data channel is usually controlled by a Script operator.
particle size to define the selection subset. Particle size is controlled
by Shape and Scale operator parameters. As with the Scale option,
the operator uses the maximum value of the size vectors components
to define the range inclusion.
particle speed to define the selection subset. The From, To, and
Variation parameters are defined in units per second.
- Uniform IndexA
scalable particle ID parameter. If the Quantity Multiplier is set
to 100%, then the Uniform Index is the same as the Birth ID index.
If the Uniform Index parameter is used, then the area with selected
particles is consistent regardless of the Quantity Multiplier parameters.
- Randomly SelectedSelects
particles at random. The Chance % parameter defines how many particles
will be selected. 100% means that all particles are selected; 50% means
that roughly half of the particles are selected.
- Combine GroupsSelects
particles using a combination of the selection subsets defined by
other Group Selection operators. Buttons A and B define the other
Group Selection operators. The available combinations are:
- A and BA
particle is selected if it is selected by both operators A and B.
- A or BA particle
is selected if it is selected by operator A or operator B.
- A or B not bothA
particle is selected if it is selected by operator A but not by
operator B, or vice-versa.
- A and not Ba
particle is selected if it is selected by operator A but not by
- Icon Size
Sets the size of the
3D icon. Available only for the selection conditions Inside Icon
Volume and Select By Particle Property: Direction.
- Logo Size
Sets the logo size, which has
no effect on particles.
- Color Coordinated
When on, the color of the
3D icon is synchronized with the Display operator in the current
event. When off, the icon has a standard Particle Flow operator
These controls set randomization
for the Randomly Selected and Select By Particle Property selection
Specifies a randomization
Calculates a new seed using
a randomization formula.