Expression functions

The old expression language is still available in Houdini for compatibility with older files and scripts. For new animations, we recommend you use the new HOM scripting architecture instead.

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Guide

attributes

  • detail
    Returns the value of a detail attribute.
  • detailattribsize
    Returns the number of components in a detail attribute.
  • details
    Returns the string value of a detail attribute.
  • detailsmap
    Returns a string from a list of strings in a detail attribute.
  • detailsnummap
    Returns the number of unique stings bound to a detail attribute.
  • hasdetailattrib
    Returns 1 if a specified detail attribute exists.
  • haspointattrib
    Returns 1 if a specified point attribute exists.
  • hasprimattrib
    Returns 1 if a specified primtive attribute exists.
  • hasvertexattrib
    Returns 1 if a specified vertex attribute exists.
  • point
    Returns the value of a point attribute.
  • pointattribsize
    Returns the number of components in a point attribute.
  • primattribsize
    Returns the number of components in a primitive attribute.
  • vertexattribsize
    Returns the number of components in a vertex attribute.

channels

  • chexist
    Returns 1 if the specified channel exists, 0 if it doesn’t.
  • chgroup
    return a string containing all of the channels contained in a group.
  • chopcf
    Evaluates a channel within a CHOP at a given time.
  • chopci
    Evaluates a channel within a CHOP at a specified sample point.

character

  • boneangle
    Returns the angle at the joint between two bone objects.
  • objkinoverride
    Returns the current global kinematic override setting for bone objects.

chops

  • chop
    Evaluates a channel within a CHOP at the current time.
  • chopct
    Evaluates a channel within a CHOP at a specified time.
  • chope
    Returns the end index of the channels in a CHOP.
  • chopf
    Evaluates a channel within a CHOP with at a given frame.
  • chopi
    Evaluates a channel within a CHOP at a given sample point.
  • chopl
    Returns the length of the channels in a CHOP, in samples.
  • chopn
    Returns the number of data channels within a CHOP.
  • chopr
    Returns the sample rate of a CHOP.
  • chops
    Returns the start index of a CHOP.
  • chopstr
    Returns the string value of a channel within a CHOP at the current time.
  • chopt
    Returns the value of a channel within a CHOP at a specified time.
  • ic
    Evaluates a CHOP’s input channel at a specific index.
  • ice
    Returns the end index of a CHOP’s input.
  • icl
    Returns the length of a CHOP’s input, in samples.
  • icmax
    Evaluates a CHOP’s input channel’s maximum value.
  • icmin
    Evaluates a CHOP’s input channel’s minimum value.
  • icn
    Returns the number of channels in a CHOP’s input.
  • icr
    Returns the sample rate of a CHOP’s input.
  • ics
    Returns the start index of a CHOP’s input.
  • oc
    Returns the value of a CHOP’s output at a specific sample index.

color

  • hsv
    Converts RGB values to HSV components.
  • rgb
    Converts HSV values to RGB components.

dynamics

  • dopallfields
    Returns a space separated list of all the field names that can be passed to the dopfield function.
  • dopcountslices
    Returns the number of records of a given type in a piece of dynamics data.
  • dopfield
    Returns the value of a field as a float.
  • dopfieldname
    Returns the name of a DOP field.
  • dopfields
    Returns the value of a DOP field as a string.
  • dopfieldtype
    Returns the type of a DOP field.
  • dopframe
    Returns the current frame of the simulation.
  • dopframetost
    Returns the simulation time equivalent of a simulation frame.
  • dopgrouphasobject
    Returns 1 if a specified DOP group contains a specified object.
  • dopgroupismutual
    Returns 1 if a specified DOP group is mutually affecting.
  • dopgrouplist
    returns a string containing a list of all object groups for the current time in a specified DOP Network.
  • dophasfield
    Returns 1 if a specified DOP field exists.
  • dophassubdata
    Returns 1 if a dynamics object has the specified subdata.
  • dopnodeobjs
    Returns the list of objects processed by a DOP in the latest timestep.
  • dopnumfields
    Returns the number of fields in a DOP record type.
  • dopnumobjects
    returns the number of objects in a simulation.
  • dopnumrecords
    Returns the number of records of a given type in a piece of dynamics data.
  • dopnumrecordtypes
    Returns the number of types of record in a piece of dynamics data.
  • dopnumsubdata
    Returns the number of subdata items attached to an object or data.
  • dopobjectlist
    Returns all objects matching the an object specification.
  • dopobjectsareaffectors
    Tests whether a set of objects has an affector relationship with another object.
  • dopobjscreatedby
    Returns the list of objects created by a particular DOP node.
  • dopoption
    Returns the value of a DOP field as a float.
  • dopoptions
    Returns the value of a DOP field as a string.
  • doprecordtypename
    Returns the name of a record in DOPs data given its index.
  • dopsolvedopnet
    Script solver support function.
  • dopsolvenumobjects
    Script solver support function.
  • dopsolveobject
    Script solver support function.
  • dopsolvetimestep
    Script solver support function.
  • dopsttoframe
    returns the simulation frame of a given simulation time.
  • dopsttot
    Returns the global time of a given simulation time.
  • dopsubdataname
    Returns the name of a subdata of a given DOP object.
  • doptime
    Returns the current time of a simulation.
  • doptransform
    Returns a transformation matrix associated with a piece of data.
  • dopttost
    Returns the simulation time equivalent to a given global time.
  • dopvelatpos
    Returns the velocity that a point at a location in simulation space would have if it were attached to a DOP object.
  • seampoints
    Lists all seam points in a surface node.

files

  • findfile
    Searches the Houdini path for a file.
  • findfiles
    Searches the Houdini path for a file or directory.

geometry

  • bbox
    Returns bounding box information for a surface node.
  • centroid
    Returns centroid information for a surface node.
  • curvature
    Returns the curvature of the surface at the given UV coordinates.
  • degree
    Returns the degree a specified face or hull.
  • distance
    Returns the distance between two 3D points.
  • haspoint
    Returns 1 if a specified point is in a specified group.
  • hasprim
    Returns 1 if a specified primitive is in a specified group.
  • isclosed
    Returns 1 if a primitive is closed.
  • iscollided
    Returns 1 if a specified point has collided with something.
  • isspline
    Returns 1 if a specified primitive is a NURBs or Bezier curve or surface.
  • isstuck
    Returns 1 if a specified point is a stuck particle.
  • iswrapu
    Returns 1 if a specified primitive is wrapped in U.
  • iswrapv
    Returns 1 if a specified primitive is wrapped in V.
  • metaweight
    Returns the weight of a metaball at a specific location.
  • mindist
    Finds the smallest distance between a point and a primitive.
  • nearpoint
    Finds the point in a geometry nearest to specific 3D coordinates.
  • normal
    Returns the components of the surface normal specific UV coordinates.
  • npoints
    Returns the number of points in a geometry.
  • nprims
    Returns the number of primitives in a surface node.
  • pointavg
    Returns the average of an attribute across all points in a geometry.
  • pointdist
    Returns the distance between a point and a primitive.
  • pointgrouplist
    Returns the list of point groups in a surface node.
  • pointgroupmask
    Returns the list of point groups matching a pattern in a surface node.
  • pointlist
    Returns a list of all points in a point group.
  • pointneighbours
    Lists points that share a minimum number of primitives with a specified point.
  • pointpattern
    Returns a list of points that match a specified pattern.
  • points
    Returns the string value of a point attribute.
  • pointsmap
    Returns a string from a list of strings in a point attribute.
  • pointsnummap
    Returns the number of unique strings bound to a point attribute.
  • prim
    Returns the value of a primitive attribute.
  • primdist
    Returns the minimum distance and closest points between two primitives.
  • primduv
    Returns the partial derivatives of a primitive attribute.
  • primgrouplist
    Returns the list of primitive groups in a surface node.
  • primgroupmask
    Returns the list of groups matching a pattern in a surface node.
  • primlist
    Returns a list of all primtives in a surface node.
  • primneighbours
    Lists primitives that share a minimum number of points with a specified primitive.
  • prims
    Returns the string value of a primitive attribute.
  • primsmap
    Returns a string from a list of strings in a primitive attribute.
  • primsnummap
    Returns the number of unique strings bound to a primitive attribute.
  • primuv
    Returns the value of a primitive attribute at a certain UV location.
  • realuv
    Converts unit UV to real UV.
  • spknot
    Returns a knot value on a spline curve or surface.
  • surflen
    Returns the length of the 3D curve between two points on a surface.
  • unituv
    Converts real UV to unit UV.
  • uvdist
    Returns the distance between parameteric locations on two primitives.
  • vertex
    Returns the value of a vertex attribute.
  • vertexs
    Returns the string value of a vertex attribute.
  • vertexsmap
    Returns a string from a list of strings in a vertex attribute.
  • vertexsnummap
    Returns the number of unique strings bound to a point attribute.
  • xyzdist
    Returns the distance between a 3D coordinate and a primitive.

images

  • pic
    Returns the color of a pixel in a compositing node.
  • picni
    Returns the non-interpolated color of a pixel in a compositing node.
  • res
    Returns the natural resolution of the image in a compositing node.
  • seqanim
    Returns 1 if a specified compositing node has an animated sequence.
  • seqend
    Returns the end frame of a compositing node’s image sequence.
  • seqlength
    Returns the number of frames in a compositing node’s image sequence.
  • seqstart
    Returns the start frame of a compositing node’s image sequence.
  • tex
    Returns the interpolated color of a point on an on-disk texture map.
  • texni
    Returns the non-interpolated color of a point on an on-disk texture map.

interface

  • mousepane
    Returns the full name of the pane currently under the mouse pointer.
  • mousepath
    Returns the node path of the pane currently under the mouse pointer.
  • vpname
    Takes a viewer name and a viewport number and returns the viewport’s name.

math

  • abs
    Returns the absolute value of the argument.
  • acos
    Returns the arc-cosine of the argument.
  • arclen
    Returns the arc length of a curve between two U positions.
  • asin
    Returns the arc-sine of the argument.
  • atan
    Returns the arc-tangent of the argument.
  • atan2
    Returns the arc-tangent of y/x.
  • ceil
    Returns the smallest integer not less than the value passed in.
  • clamp
    Returns a value clamped between a minimum and maximum.
  • cos
    Returns the cosine of the argument.
  • cosh
    Returns the hyperbolic cosine of the argument.
  • deg
    Converts from radians to degrees.
  • exp
    Returns the logarithmic exponentiation of the argument.
  • fit
    Fits a value from one range to another.
  • fit01
    Fits a value to the 0-1 range.
  • fit10
    Fits a number in the 0-1 range.
  • fit11
    Fits a number to the -1 to 1 range.
  • floor
    Returns the largest integer not greater than a number.
  • frac
    Returns the fractional part of a floating-point number.
  • int
    Converts a number to an integer by truncating any fractional part.
  • log
    Returns the natural logarithm of the argument.
  • log10
    Returns the base 10 logarithm of the argument.
  • max
    Returns the larger of two values.
  • min
    Returns the smaller of two values.
  • modblend
    Blends the two modular values.
  • pow
    Raises a number to an exponent.
  • rad
    Converts from degrees to radians.
  • rint
    Rounds to the nearest integer.
  • round
    Rounds a number to the nearest integer.
  • sign
    Returns -1, 0, or 1 depending on the sign of the argument.
  • sin
    Returns the sine of the argument.
  • sinh
    Returns the hyperbolic sine of the argument.
  • smooth
    Taks a value and range and returns a smooth interpolation between 0 and 1.
  • sqrt
    Returns the square root of the argument.
  • tan
    Returns the tangent of the argument.
  • tanh
    Returns the hyperbolic tangent of the argument.
  • trunc
    Converts a number to an integer by truncating any fractional part, rounding towards 0.
  • wrap
    Wraps a value between a minimum and maximum.

matrices

  • determinant
    Returns the determinant of a matrix.
  • dihedral
    Computes the dihedral matrix between vectors v0 and v1.
  • explodematrix
    Explodes a 3×3 or 4×4 matrix into the euler rotations required to rebuild it.
  • explodematrixp
    Explodes a 3×3 or 4×4 matrix into the euler rotations required to rebuild it.
  • identity
    Creates an identity matrix.
  • invert
    Inverts a matrix.
  • matrix
    Converts a string specification into a matrix.
  • matrixtoquat
    Converts a rotation matrix to a quaternion.
  • mcols
    Returns the number of columns in a matrix.
  • mlookat
    Computes the transformation matrix of a lookat from one vector to another.
  • mlookatup
    Computes the transformation matrix of a lookat from one vector to another, with an up vector.
  • mobjlookat
    Computes the transformation matrix of a lookat from one object to another.
  • morient
    Computes the transformation matrix to orient along specific Z and Y axes.
  • mrows
    Returns the number of rows in a matrix.
  • mzero
    Returns a matrix with all values set to 0.
  • quattomatrix
    Converts quaternion to a 3×3 rotation matrix.
  • rotate
    Returns a 4×4 rotation matrix from an axis and angle.
  • rotaxis
    Returns a 4×4 rotation matrix from an angle and a vector.
  • scale
    Takes three scaling values and returns a scale matrix.
  • translate
    Takes X, Y, and Z translation values and returns a translation matrix.
  • transpose
    Transposes a matrix.

nodes

  • opdigits
    Returns the numeric suffix of a node name.
  • opexist
    Returns 1 if the specified node, group, or bundle exists.
  • opflag
    Returns a list nodes with a particular flag set.
  • opfullpath
    Returns the full path of a node.
  • opfullpathfrom
    Returns the path of a node relative to another node.
  • opid
    Returns the unique ID of a node.
  • opinput
    Returns the name of the node connected to a given input.
  • opinputpath
    Returns the full path of the node connected to a given input.
  • opisloading
    Returns 1 if Houdini is currently loading a scene file.
  • opname
    Returns the name of a node given its path.
  • opnchildren
    Returns the number of nodes inside a container node.
  • opninputs
    Returns the maximum number of connected inputs.
  • opnoutputs
    Returns the number of nodes connected to a node’s output.
  • opoutput
    Returns the name of a node connected a given node’s output.
  • opoutputpath
    Returns the full path of a node connected a given node’s output.
  • oprelativepath
    Returns the relative path from one node to another.
  • opselect
    Returns a list of the selected nodes.
  • opselectrecurse
    Returns a recursive list of the selected nodes.
  • opsubpath
    Returns the full path of a node including any containing subnets.
  • optype
    Returns the type of a node.
  • optypeinfo
    Returns type information about a node.

objects

  • objlightmask
    Returns a list of lights matching an object’s light mask.
  • objlookat
    Computes the rotation vector of a lookat from one object to another.
  • objpretransform
    Returns an object’s pre-transform matrix.
  • opblist
    Returns the full paths of all operators in a bundle.
  • oplightmask
    Returns a list of lights matching an object’s light mask.
  • optransform
    Returns the transformation matrix of an object at the current time.
  • origin
    Returns components of an object’s transforms.
  • originoffset
    Returns components of an object’s offset transforms.

obsolete

  • cucwc
    Deprecated: current working container for custom panels.
  • cudatatype
    Deprecated: data type of a gadget, for custom panels.
  • cumenuadd
    Deprecated: adds a menu entry on a custom panel.
  • cuquery
    Deprecated: returns a value from a custom panel.
  • cutype
    Deprecated: Returns the type of a gadget on a custom panel.
  • oppinput
    Deprecated: replaced by opinput.
  • param
    Deprecated: use stamp instead.

parameters

  • ch
    Returns the value of a parameter.
  • chf
    Evaluates a parameter at a given frame.
  • chramp
    Returns the value of a ramp parameter at a specific position.
  • chrampf
    Returns the value of a ramp parameter at a specific position and frame.
  • chrampt
    Returns the value of a ramp parameter at a specific position and time.
  • chs
    Evaluates the string value of a parameter at the current time.
  • chsop
    Evaluates the parameter at the current time as a node path string.
  • chsraw
    Returns the raw expression value of a parameter as a string.
  • cht
    Returns the value of a parameter at a specified time.
  • instancepoint
    Returns the point number currently being instanced onto.
  • parmisstring
    Returns 1 if a specified parameter is a string.
  • stamp
    Returns a copy stamping floating point value.
  • stamps
    Returns a copy stamping string value.

particles

  • popcontextgeo
    Returns the full path to a particle network context geometry.
  • popevent
    Returns 1 if a particle event is occurring.
  • popeventtime
    Returns the time of a particle event.
  • poppoint
    Returns the value of a particle attribute, by particle number.
  • poppointid
    Returns the value of a particle attribute, by particle ID.
  • poppointnum
    Returns the point number of the particle with the specified ID.

random

  • noise
    Generates 3D noise.
  • oldrand
    Returns a pseudo-random number between 0 and 1.
  • rand
    Returns a pseudo-random number from 0 to 1.
  • snoise
    Generates sparse convolution 3D noise.
  • sturb
    Generates spatially coherent 3D noise based on sparse convolution.
  • turb
    Generates spatially coherent 3D noise.

rendering

  • iprquery
    Queries numeric (floating point) data from an interactive render pane.
  • iprquerys
    Queries textual (string) data from an interactive render pane.
  • shopstring
    Returns the shader string generated by a shader.

segments

  • bezier
    Channel segment function: Bezier interpoloation spline
  • constant
    Channel segment function: constant value.
  • cubic
    Channel segment function: cubic spline.
  • cycle
    Channel segment function: repeats the animation between frames f1 and f2.
  • cyclet
    Channel segment function: repeats the animation between times t1 and t2.
  • ease
    Channel segment function: ease-in and -out.
  • easein
    Channel segment function: ease-in.
  • easeinp
    Channel segment function: ease-in with configurable acceleration.
  • easeout
    Channel segment function: ease-out
  • easeoutp
    Channel segment function: ease-out with configurable acceleration.
  • easep
    Channel segment function: ease-in and -out with configurable acceleration.
  • linear
    Channel segment function: linear interpolation.
  • match
    Channel segment function: matches the incoming and outgoing slopes.
  • matchin
    Channel segment function: matches the incoming slope.
  • matchout
    Channel segment function: matches the outgoing slope.
  • qlinear
    Channel segment function: uses quaternions to interpolate.
  • quintic
    Channel segment function: smoothly interpolates slopes and accelerations.
  • raw
    Channel segment function.
  • repeat
    Channel segment function: repeats animation from previous frames.
  • repeatt
    Channel segment function: repeats animation from previous frames.
  • spline
    Channel segment function: fits a curve to the keyframes.
  • vmatch
    Channel segment function: matches the incoming and outgoing slopes.
  • vmatchin
    Channel segment function: matches the incoming slope.
  • vmatchout
    Channel segment function: matches the outgoing slope.

strings

  • ftoa
    Converts a number to a string.
  • index
    Finds the first occurrence of a pattern in a string.
  • rindex
    Finds the last occurrence of a pattern in a string.
  • strcasecmp
    Compares two strings, ignoring case.
  • strcasematch
    Returns 1 if a string matches a pattern, ignoring case.
  • strcat
    Returns the concatenation of two strings.
  • strcmp
    Compares two strings.
  • strdup
    Duplicates a string.
  • stripmatrix
    Strips non-essential characters from the string representation of a matrix or vector.
  • strlen
    Returns the number of characters in a string.
  • strmatch
    Returns 1 if a string matches a pattern, including case.
  • strreplace
    Replaces substrings with a new string.
  • substr
    Returns a substring of a string.
  • tolower
    Returns the all-lowercase version of a string.
  • toupper
    Returns the all-uppercase version of a string.

utility

  • arg
    Returns an argument from a list of HScript-style arguments.
  • argc
    Returns the number of arguments in an HScript-style list of arguments.
  • atof
    Converts a string to a float.
  • eval
    Evaulates a string as an expression returning a float.
  • evals
    Evaulates a string as an expression returning a string.
  • execute
    Runs a string as an HScript command and returns the command’s output.
  • executeb
    Runs a string as an HScript command and returns the command and error output.
  • executee
    Runs a string as an HScript command and returns any error output.
  • hextoint
    Converts a hexadecimal argument string into an integer.
  • if
    Returns the value of the second or third argument depending on the truth of the first argument.
  • ifs
    Returns the string value of the second or third argument depending on the truth of the first argument.
  • inttohex
    Converts a number into a hexadecimal string.
  • ishvariable
    Returns 1 if a specified Houdini environment variable exists.
  • isvariable
    Returns 1 if a specified Houdini or system environment variable exists.
  • lock
    Returns a value that cannot be changed.
  • opisquitting
    Returns 1 if Houdini is currently shutting down.
  • oppwd
    Returns the path of the current network.
  • oppwf
    Prints the path of the current network.
  • padzero
    Returns a string padding a number to a given length with zeros.
  • print
    Prints a message to the console.
  • pulse
    Returns 1 when a value is within a certain range.
  • pythonexprf
    Evaluates a Python expression, returning a float result.
  • pythonexprs
    Evaluates a Python expression, returning a string result.
  • run
    Runs a string as an HScript command and returns the command’s output.
  • runb
    Runs a string as an HScript command and returns the command and error output.
  • rune
    Runs a string as an HScript command and returns any error output.
  • system
    Runs a system command line and returns the output.
  • systemES
    Runs a system command line and returns the exit status.

vectors

  • angvel
    Returns the angular velocity required to rotate an object from one orientation to another in a certain period of time.
  • clamptosphere
    Clamps a vector to always end between a minimum and maximum sphere.
  • cross
    Computes the cross-product of two vectors.
  • dot
    Computes the dot product of two vectors.
  • length
    Returns the length of a vector.
  • normalize
    Normalizes a vector.
  • vangle
    Returns the angle between two vectors.
  • vector
    Converts a string specification into a vector.
  • vector3
    Converts three values into a 3-component vector.
  • vector4
    Converts four values into a 4-component vector.
  • vlength
    Returns the length of a vector.
  • vlength2
  • vorigin
    Returns a vector of a objects’s transforms.
  • vrorigin
    Returns a vector of an object’s rotations.
  • vscale
    Multiplies a vector by a scaling factor.
  • vset
    Creates a vector with each component set to the same value.
  • vsize
    Returns the number of elements in a vector.
  • vtorigin
    Returns a vector of an object’s translations.

volumes

  • volumeaverage
    Returns the average value of all the voxels in a volume.
  • volumegradient
    Returns the gradient of a volume primitive at a specified location.
  • volumeindex
    Returns the value of a volume primitive at a specified voxel.
  • volumeindextopos
    Converts volume voxel coordinates to world-space coordinates.
  • volumemax
    Returns the maximum value of all voxels in a volume.
  • volumemin
    Returns the minimum value of all voxels in a volume.
  • volumepostoindex
    Converts world space coordinates to volume voxel coordinates.
  • volumeres
    Returns the resolution of a volume.
  • volumesample
    Returns the value of a volume at a specified position.
  • volumevoxeldiameter
    Returns the approximage diameter of a volume voxel in world space.