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= 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 ==

`$ACTIVETAKE`:

Contains the name of the current take.

`$E`:

The mathematical constant e (2.71828...).

`$HFS`:

The directory where Houdini is installed.

`$HH`:

`$HFS/houdini`.

`$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.

`$HOME`:

Your home directory.

`$JOB`:

A custom variable that determines where your jobs are located.

`$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藲 expressed in radians.

`$WEDGE`:

Contains the wedge name when using the Wedge ROP.

== 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.

= Standard Variables =

NOTE:

Variable names ending with `2` refer to the geometry from the second input, if applicable. For example, `PT2` is the current point number from the second input.

TX, TY, TZ:

Point position.

TW:

See WEIGHT.

CEX, CEY, CEZ:

The centroid of the geometry.

XMIN, XMAX:

The X extents of the bounding box of the geometry.

YMIN, YMAX:

The Y extents of the bounding box of the geometry.

ZMIN, ZMAX:

The Z extents of the bounding box of the geometry

SIZEX, SIZEY, SIZEZ:

The size of the bounding box.

BBX, BBY, BBZ:

The point鈥檚 relative position in the bounding box.

WEIGHT:

Point spline weight.

PT:

The point number of the currently processed point.

PR, NPR:

Primitive number & total number of primitives.

VTX, NVTX:

Vertex number & total number of vertices.

NPT:

The total number of points in the template geometry.

LIFE:

Percent of total life used (from 0 to 1).

NX, NY, NZ:

Normal vector.

MAPU, MAPV, MAPW:

Point or vertex texture coordinates.

VX, VY, VZ:

Velocity direction.

MAT:

Material name specification.

CR, CG, CB:

Diffuse point or vertex color.

CA:

Point or vertex alpha value.

COMX, COMY, COMZ:

Center of mass.

LOD:

Level of detail.

RESTX, RESTY, RESTZ:

The rest position.

DIST:

Distance from particle to last collision.

MASS:

Point mass.

DRAG:

Point drag.

TENSION:

Spring tension of an edge.

SPRINGK:

Elasticity of a point.

PSCALE:

Particle Scale.

AGE:

The seconds a particle in the template has been alive.

CREASE:

Point or vertex crease weight value.

AREA:

The surface area of the primitive (created by the [Measure SOP|Node:sop/measure]).

PERIMETER:

The perimeter of the primitive (created by the [Measure SOP|Node:sop/measure]).

ID:

The ID of the particle in the input.

UPX, UPY, UPZ:

The vector pointed in the up direction.

WIDTH:

The width of the curve. Used by [mantra|Node:out/ifd] for rendering curves & polywire for generating trees.

SEGS:

Number of segments to divide a curve up into in Polywire (created by [L-systems|Node:sop/lsystem]).

DIV:

Number of divisions to build the circle swept with Polywire (created by [L-systems|Node:sop/lsystem]).

LAGE:

The age of the point in the [L-system|Node:sop/lsystem] computation.

ARC:

Arc length distance from root in the [L-systems|Node:sop/lsystem].

GEN:

Generation in the [L-systems|Node:sop/lsystem].

CURLAYER:

Stores the currently processed layer for texture/materials (set by the [Layer SOP|Node:sop/layer]).

MAXLAYER:

The number of layers that are considered active for display.

这些都是平常没事时总结下来的