Expression functions Global expression variables

Playbar variables

$FPS

Playback speed in frames per second (as set with the Playbar controls).

$FSTART

Frame number of the first frame of animation (as set with the Playbar controls). $NFRAMES (the number of frames in the animation) = $FEND - $FSTART + 1. See also $RFSTART below.

$FEND

Frame number of the last frame of animation (as set with the Playbar controls). See also $RFEND below.

$F

The current frame, (as set with the Playbar controls). This is a very useful variable, especially for rendered picture filename numbering.

$FF

Floating point frame number.

$NFRAMES

Number of frames in the animation. $NFRAMES = $FEND (the last frame of animation) - $FSTART (the first frame of animation) + 1.

$RFSTART

Frame number of the first frame shown in the playbar. The playbar can show a subset of the total number of frames, allowing you to focus on a particular section of a long animation. $RFSTART and $RFEND control the subset of frames shown in the playbar.

$RFEND

Frame number of the last frame shown in the playbar.

$T

Current time in seconds. Equals ($F-1)/$FPS

$TLENGTH

Total length of animation in seconds.

$TSTART

Start time of animation in seconds.

$TEND

End time of animation in seconds.

Global Variables

$PI

The mathematical constant pi (3.1415926…). You can use it to calculate the lengths of arcs. 2*$PI*r (radius of circle) equals the circumference. Also, pi = 180˚ expressed in radians.

$E

The mathematical constant e (2.71828…).

$HIP

Job directory. This defaults to the directory where you started Houdini. You can set it through the Textport.

$HIPNAME

The name of the current .hip file.

$ACTIVETAKE

Contains the name of the current take.

Channel Variables

$OS

Operator String. Contains the current OP’s name.

$CH

Current channel name.

$IV

In value (value at start of segment).

$OV

Out value.

$IM

In slope

$OM

Out slope

$IA

In acceleration

$OA

Out acceleration

$LT

Local time - not including stretch or offset

$IT

Start time of segment

$OT

End time of segment

$LIT

Local start time of segment

$LOT

Local end time of segment

$PREV_IT

Previous segment start time

$NEXT_OT

Next segment end time

COP-specific variables

$CSTART

Start frame of the current COP.

$CEND

End frame of the current COP.

$CFRAMES

Number of frames for the current COP.

$CFRAMES_IN

Number of frames available from the first input COP.

$CINC

Gets the global frame increment value.

$W

Current image width.

$H

Current image height

Output Driver Specific Variables

$N

Current frame being rendered.

$NRENDER

Number of frames being rendered.