Houdini 20.5 Import and export

Reading and writing Filmbox (FBX) files

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Overview

Filmbox (usually called FBX) is an interchange format for entire scenes. It stores a large scope of 3D animation software information, including multiple objects, bones, skinning, lights, and cameras.

Because an FBX file contains an entire scene, it usually maps to multiple objects and File nodes in the Houdini scene, unlike a pure-geometry format such as .geo, where one File node handles the geometry.

Because FBX encompasses many different types of scene data, it can be slightly difficult to import procedurally. However, you can use the File node to import individual object geometry from an FBX file procedurally, and you can use the fbximport command to incorporate FBX loading into a scripted workflow.

Importing FBX

  • Use File ▸ Import ▸ Filmbox (FBX) to import data from an FBX file into the current scene.

    This command will potentially create multiple light objects, camera objects, Geometry container objects containing File nodes, and so on, corresponding to objects in the FBX file.

    See the Import FBX window for the import options.

  • Inside an object, a File node can import a single object from an FBX file. Use filename#‹object_name› to specify the object to import.

  • The fbximport HScript command lets you script the equivalent of the File ▸ Import ▸ Filmbox (FBX) menu item.

Note

For animated characters, the easiest way to export deforming skin to Houdini is a vertex cache. If you save skinned bones, Maya writes out separate weighting data, which Houdini translates into an Capture Override surface node that sets the weights. However, because Houdini must fill in the Override node directly (rather than referencing the source file), it will not pick up changes to the source file.

Exporting FBX

  • Use File ▸ Export ▸ Filmbox (FBX) to export the current scene to an FBX file.

    The export dialog includes an option to only export a branch of the scene tree, for example /obj/subnet1.

    See the Export FBX window for the export options.

  • To export FBX procedurally, use the FBX render driver node.

  • The FBX exporter only exports textures if they are visible in the viewport.

Capabilities

Geometry

Import Export

  • Polygons

  • Triangulated NURBS and Patches

  • Geometry transformations

  • Visibility flag

  • Native NURBS curves and surfaces, including trimmed

  • Patches (converted to NURBS)

  • Polylines and Bezier curves

  • Markers

  • Polygons

  • Triangulated NURBS and all other primitives

  • Geometry transformations

  • Visibility flag

  • Instances

  • Nurbs and trimmed NURBS

  • Open, closed, and periodic NURBS and Bezier curves, polylines

Attributes

Import Export

  • Normals

  • Normal map UVs

  • Bump map UVs

  • Diffuse & diffuse factor UVs

  • Emissive & emissive factor UVs

  • Ambient & ambient factor UVs

  • Specular & specular factor UVs

  • Shininess & shininess factor UVs

  • Transparency & transparency factor UVs

  • Reflection & reflection factor UVs

  • Vertex colours

  • User layer data attributes

  • User object parameters

  • Soft and hard edges

  • Per-vertex and per-point normals

  • UVs

  • Vertex colours

  • User layer data attributes

Lights

Import Export

  • Type (spot, directional, point)

  • Position

  • Rotation

  • Intensity

  • Color

  • Attenuation and its parameters

  • Cone angle (for spot lights)

  • Enable/disable switch

  • Global ambient light

  • Type (spot, directional, point)

  • Position

  • Rotation

  • Intensity

  • Color

  • Attenuation and its parameters

  • Cone angle (for spot lights)

  • Enable/disable switch

  • Ambient lights

Cameras

Import Export

  • Near/far clip planes

  • Pixel aspect ratios

  • Position

  • Rotations

  • Window size

  • Aperture

  • Focal length

  • Focus distance

  • Projection type

  • Orthogonal zoom

  • Near/far clip planes

  • Pixel aspect ratios

  • Position

  • Rotations

  • Aperture

  • Focal length

  • Focus distance

  • Projection type

  • Orthogonal zoom

General

Import Export

  • Node look-at targets

  • Pivots (converted)

  • Node look-at targets

Materials

The FBX importer creates either VOP networks or pre-built VEX FBX shader nodes. It supports basic material properties (such as color and textures) for things like specular, diffuse, ambient, emissive, etc., but nothing complex.

Import Export

  • Diffuse and diffuse factor textures

  • Opacity and opacity factor textures

  • Reflection and reflection factor textures

  • Ambient and ambient factor textures

  • Emissive and emissive factor textures

  • Shininess textures

  • Specular and specular factor textures

  • Normal map textures

  • Texture wrapping mode

  • Texture translations, rotations, and scaling

  • Textures swap U and V flag

  • Texture blending for all four FBX compositing methods

  • Material diffuse, ambient, emissive, refection, specular, shininess and opacity factors and colors

  • Material instancing

  • Materials, textures, and all their properties supported as both a special VEX FBX Surface Shader and as a VOP Surface network of nodes

  • Multiple materials per object

  • Diffuse, ambient, emissive, and specular colors

  • Shininess

  • Transparency

  • Diffuse layered textures

  • Per-object or per-polygon materials

Hierarchy

Import Export

  • Basic Shapes

  • Joint-based skeletons

  • Bone-based skeletons

  • Basic Shapes

  • Skeletons and joints

Animation

Import Export

  • Translations

  • Euler rotations

  • Scaling

  • Takes

  • Curve resampling

  • Constant segments

  • Linear segments

  • Bezier and cubic segments

  • Light color

  • Light intensity

  • Light cone angle

  • Camera focal length

  • Joint animation (resampled)

  • Maya-style vertex caches

  • MAX-style vertex caches

  • Visibility

  • Translations

  • Euler rotations

  • Scaling

  • Takes

  • Curve resampling

  • Constant segments

  • Linear segments

  • Bezier and cubic segments

  • Maya-style vertex caches

  • MAX-style vertex caches

  • Partial curve resampling

  • Joint animation (resampled)

  • Light color

  • Light intensity

  • Light cone angle

  • Camera focal length

  • Camera FOV

  • Visibility

Dynamics

Import Export

Specific settings cannot be imported; however, the baked results can be.

  • Particle systems

  • RBD, cloth, and fluid simulations

Skinning and Deformations

Houdini supports importing characters as both pre-backed vertex caches, as well as skinned meshes. However, FBX is only really good for relatively simple rigs and IK is not supported.

Import Export

  • Joints and bones skinning

  • Blend deformers

  • Blend deformers using a Blend SOP

  • Cluster deformers

  • Skinning

Geometry Path Options

When an FBX file is loaded as generic geometry, such as the File SOP, some options are available by appending #node_name,option1,option2,... to the path. The first token after the # is a node_name that specifies a specific FBX node’s geometry to load. The node name can be empty (eg. #,option1,option2,...) to specify loading all FBX node geometries.

The following options are currently available:

  • converton - Convert NURBS/Patches to polygons

  • convertoff - Do NOT convert NURBS/Patches to polygons

  • convertunits - Only valid when loading all FBX node geometries. When specified, units conversion will be performed to match the current Houdini units preference.

  • frame=X.Y - Only valid when loading all FBX node geometries. If specified, the geometry is transformed by evaluating it at frame X.Y.

The default behaviour (when there is no # option string) is to load all FBX nodes, with no conversion to polygons, and with their transforms evaluated without animation.

Limitations

Import

  • FBX SDK has a bug in it where vertex caches created in Maya as float-type (and not double-type) will be read incorrectly by the SDK. Currently there is a workaround UI option for this issue in Houdini’s import dialog.

  • Maya doesn’t export vertex caches to FBX unless “Export Quick Selection Set as Geometry Cache File(s)” is checked.

  • Softimage XSI seems to put picture width and height as horizontal and vertical aspect ratios. This not only gives an incorrect result for window sizes, but also derails the focal length computation badly.

  • FBX has a cubic light attenuation fall-off, whereas Houdini does not.

  • FBX has a “visibility” flag, whereas Houdini has separate flags for visible in the viewer and visible in the render.

  • Cameras and objects with pre-transforms with non xyz-rotation orders may have kinks in their animation curves when imported into Houdini.

  • Skinning import is ignored on a Mac because of a bug in the FBX SDK.

The following data is not imported from FBX yet.

Category Not imported
Attributes

  • Polygon groups
Lights

  • Global fog settings
Cameras

  • Global cameras

  • Render settings (such as anti-aliasing)
General

  • Node up targets
Hierarchy

  • Euler rotation order

  • Instancing
Animation

  • Camera FOV

  • Partial curve resampling
Skinning and deformations

  • Cluster deformers with an associated shape

Export

  • To properly import anything that uses variable-vertex animated geometry (such as our particle fluids), you have to turn on the Use FBX framerate in Maya checkbox in Maya’s FBX importer.

  • On FBX import, FBX joints are represented as null nodes with fake bones between them; each bone has an expression for the length and look-at target, so that it always spans the two joints it is related to. On export, our code tries to detect these situations, and if found, converts them to proper joint hierarchies without fake bones.

  • Houdini bones are converted to joints on export, since most applications seem to export/import just joints, and not bones, from FBX (it can represent both).

The following data is not exported to FBX yet.

Category Not exported
Attributes

  • Spare object parameters

  • Polygon groups
General

  • Pivots

  • Node up targets
Dynamics

  • Smoke and fire

Import and export