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Flags. Python
examples.
dynExpression( selectionItem , [creation=boolean], [runtimeAfterDynamics=boolean],
[runtimeBeforeDynamics=boolean],
[string=string])
Note: Strings representing object names and
arguments must be separated by commas. This is not depicted in the
synopsis.
dynExpression is undoable, queryable, and editable.
This command describes an expression that belongs to the specified
particle shape. The expression is a block of code of unlimited
length with a C-like syntax that can perform conversions,
mathematical operations, and logical decision making on any numeric
attribute(s) or per-particle attribute(s) in the scene. One
expression can read and alter any number of these attributes. Every
particle shape in your scene has three expressions, one for the
runtimeBeforeDynamics, one for the runtimeAfterDynamics and one for
creation time. The create expression gets executed for every
particle in the object whose age is 0.0. The runtime expression
gets executed for each particle with an age greater then 0.0.
Unlike expressions created with the expression command,
particle expressions always exist and are a part of the owning
particle object's shape. They default to empty strings, but they
are always there. Because of this, there is no need to use the '-e'
flag. Every call to the dynExpression command is considered an edit
by default. Per-particle attributes are those attributes of a
particle shape that have a potentially different value for each
particle in the object. Examples of these include position
and velocity. If this command is being sent by the command
line or in a script, then the user should be sure to embed escaped
newlines (\n), tabs (\t) for clarity when reading them in the
expression editor. Also, quotes in an expression must be escaped
(\") so that they are not confused by the system as the end of your
string. When using the expression editor, these characters are
escaped for you unless they are already within quotes. This type of
expression is executed during the evaluation of the dynamics. If an
output of the expression is requested before that, then the
dynamics will be force to compute at that time. If dynamics is
disabled, then these expressions will have no effect.
| string |
The particle shape which this expression belongs to |
In query mode, return type is based on queried flag.
particle
creation, runtimeAfterDynamics, runtimeBeforeDynamics, string
| Long name (short name) |
Argument types |
Properties |
string(s) |
string |
  |
|
Set the expression string. This is queriable with the -q/query
flag and the -rbd/runtimeBeforeDynamics, the
-rab/runtimeAfterDynamics or the -c/creation flag. |
|
creation(c) |
boolean |
 |
|
Tells the command that the string passed will be a creation
expression for the particle shape. This means that this expression
will be executed when a particle is emitted or at the beginning of
the scene for existing particles. |
|
runtimeBeforeDynamics(rbd) |
boolean |
|
|
Tells the command that the string passed will be a runtime
expression for the particle shape. This expression will be executed
before dynamics whenever a particle's age is greater then zero
(0). |
|
runtimeAfterDynamics(rad) |
boolean |
|
|
Tells the command that the string passed will be a runtime
expression for the particle shape. This expression will be executed
after dynamics whenever a particle's age is greater then zero
(0). |
|
| Flag can appear in Create mode of
command |
Flag can appear in Edit mode of command |
| Flag can appear in Query mode of command |
 Flag can have multiple arguments, passed
either as a tuple or a list. |
import maya.cmds as cmds
cmds.dynExpression( 'particleShape1', s='rgbPP = << 1, 0, 0 >>', c=1 )
# This expression tells particleShape1 that whenever new particles are
# created for this object, then their color should start out as << 1, 0, 0 >>,
# which is red.
cmds.dynExpression( 'particleShape1', s='rgbPP = rgbPP * .9;', rbd=1 )
# This sets the runtime before dynamics expression for rgbPP. When a particle is
# first "born", its color will be red from the previous example. Every other frame after
# that, its color is reduced by 10 percent each time the expression is executed.
cmds.dynExpression( 'particleShape1', s='rgbPP = rgbPP * .9;', rad=1 )
# This sets the runtime after dynamics expression for rgbPP. When a particle is
# first "born", its color will be red from the previous example. Every other frame after
# that, its color is reduced by 10 percent each time the expression is executed.