HOUDINI_DISABLE_CONSOLE

    If set, disables creation of floating consoles on Windows
    machines.

HOUDINI_TEXT_CONSOLE

    If set, instead of creating a floating console, a normal window
    shell will be created on NT machines.

HOUDINI_WINDOW_CONSOLE

    On the Windows operating system, the setting of this environment variable
    will force the creation of a floating console regardless of whether its
    output is redirected. This is only necessary for broken shells that 
    incorrectly start up Houdini window applications with redirected output.
    At the time of this writing, only cygwin-compiled shells require this.

HOUDINI_VERBOSE_ERROR

    Print out unexpected file save errors to the console as well as
    displaying them in error boxes.

HOUDINI_OLD_SPINNER

    If set, the old style interrupt dialog graphic will be used (i.e.
    the spinning pie).

HOUDINI_OLD_CONST_BEHAVIOUR

    If set, the old behaviour dealing with constant() expression segments 
    is used instead. The old behaviour allows changing the value of a
    constant() expression channel segment at any given frame within it, not
    just at its boundaries.

HOUDINI_DISABLE_CPUID

    If set, Houdini will not try to detect the CPU type of the
    machine.  Attempts to detect the CPU type will cause I386 and
    earlier machines to crash.

HOUDINI_DISABLE_XMMX

    If set, disable MMX support for VEX.

HOUDINI_COREDUMP

    If set, on Unix systems, Houdini will attempt to dump a core
    file instead of simply exiting on signals SIGILL, SIGEMT, SIGBUS
    or SIGSEGV.  Please see signal(5) for more information.

HOUDINI_DSO_ERROR

    Cause DSO/DLL errors on plug-ins to be printed out to the console.
    This can help in debugging custom operators.

HOUDINI_TIFF_BOTTOMLEFT

    Older versions of Houdini generated TIFF files with the first
    scanline of data representing the bottom of the image.  This
    control can be turned on to replicate the behaviour of older
    versions of Houdini.

HOUDINI_TIFF_SAMPLEFORMAT

    If set, the TIFF SAMPLEFORMAT tag will be output in all cases.
    This may cause older versions of the TIFF library to print
    warnings/errors about unknown tags.

HOUDINI_DISABLE_IMAGE_DSO

    formats will be installed.

HOUDINI_THREAD_IMAGE

    If set, some old-style compositing operations will be
    multi-threaded.  On some platforms, this can provide a performance
    boost.  However, on other platforms, this can cause a performance
    hit.  This also affects Houdini applications like ipaint.

HOUDINI_LMINFO_VERBOSE

    Typically, Houdini will print out warnings at start-up time if
    licenses are due to expire shortly.  If this control is set to 0,
    then no warnings will be printed out when applications start.

HOUDINI_NOHKEY

    Setting this environment variable will no longer cause the license
    manager to start when a license check fails.

HOUDINI_JITTERY_CAMERA

    Setting this environment variable will prevent the direct
    assignment of the camera transform to the GL view transform.  This
    will cause the camera to jitter in some cases.  It, however, fixes
    reversed-perspective problems with the ES Tornado 3000 video card.

HOUDINI_VEX_OLD_DERIV

    If set, VEX will compute non-centered derivatives.  This provides
    backward compatibility with pre-4.1 versions of mantra.

HOUDINI_DISABLE_UNSAFE_VEX

    There are some optimizations made in the VEX engine which were
    deemed to be potentially unsafe when they were implemented.  These
    optimizations should work properly, but this environment variable
    provides a mechanism for turning these optimizations off.  The
    optimizations are typically non-critical optimizations.  As a
    note, any VEX code which is fixed by setting this variable should
    be sent to the Side Effects Software support team.

HOUDINI_OGL_ALPHA_PIXMAP

    If set to 1 on Linux, this will allow the OpenGL ROP to render alpha
    planes.

HOUDINI_OGL_SOFTWARE

    Force Houdini to use software OpenGL rendering.

HOUDINI_OGL_HARDWARE

    Force Houdini to use hardware OpenGL rendering.

HOUDINI_OGL_FAST_ORDER2

    NURBS and Bezier surfaces which have an order 2 basis (linear) in
    each dimension will be rendered with a lower level of detail if
    this control is set.

HOUDINI_OGL_TEXT_SPACE_FIX

    Fix display of text for some graphics boards

HOUDINI_OGL_DISABLE_SMOOTH_STIPPLED_LINES

    This disables rendering of stippled lines using anti-aliasing. Notably,
    Oxygen GVX1 Pro video cards can have trouble doing this.

HOUDINI_OGL_ENABLE_PBUFFER

    Enable OpenGL p-buffer support.  This accelerates off-screen
    rendering on some IRIX platforms.  However, it may also cause
    errors on Octanes.

HOUDINI_OGL_OVERLAY_SUPPORT

    Force Houdini to use overlay support on Windows machines

HOUDINI_OGL_DISABLE_RASTER_IN_OVERLAY

    Skip rendering raster icons in overlay planes.  This can
    significantly speed up the drawing of op menus containing
    bitmap icons on some platforms.

HOUDINI_OGL_INT_RASTER_ZOOM_ONLY

    Used for troubleshooting image zooming problems, particularly in
    MPlay and COPs. Set to 0, 1 or 2.
    0   If non-integer zooms are supported by the video hardware,
        non-integer zooms are used (default). If non-integer zooms
        are not supported, the result is exactly the same as if this
        variable was set to 1.
    1   Forces Houdini to use only integer zooming, even if supported
        by the hardware. Software zooming is used in combination with
        integer zooming to produce non-integer zooms, at a slight
        performance hit.
    2   Never use hardware zooming. Software zooming only. Incurs a
        substantial performance hit, but may be necessary on some
        video cards that do not do zooming properly.

HOUDINI_OGL_MARQUEE_FIX

    When set this will change the order the lines are drawn for the
    picking marquee (ie, the box drawn during box pics).  On some
    systems, such as SGI Octanes with V6 graphics, this may prevent
    the pick box from leaving garbage on the screen.

HOUDINI_HIP_FROM_PATH

    When loading .hip files, force the Houdini HIP variable to the
    path of the HIP file specified rather than the HIP variable set

HOUDINI_VIEW_RMAN

    This variable specifies the command to run when "View: RMan" is
    chosen from the viewport rendering menu.

HOUDINI_THUMB_RENDER

    This provides a default value for the -r option of the thumbrender
    application.  This application is used to render thumb-nails for
    the SHOP palette.

HOUDINI_VIEW_MANTRA

    This variable specifies the command to run when "View: Mantra" is
    chosen from the viewport rendering menu.

HOUDINI_DISABLE_EXPORT_RENAME

    This variable disables the immediate recooking of exported CHOPs whenever
    a new node is created or when an existing node is renamed. For example,
    if you have a chop that is exporting to /obj/geo*, then it requires 
    recooking if an object is renamed from /obj/foo to /obj/geo1. To disable
    this behaviour, set this environment variable to 1.

MANTRA_FORCE_RAY

    Force mantra to use ray-tracing (same as -r option)

MANTRA_DISABLE_FOGBOX

    When rendering fog, mantra will create a matte shaded
    object automatically so the fog will be picked up in the
    background.  Setting this variable disables this feature.

MANTRA_CULL_0AREA

    Obsolete control

MANTRA_RAYDUMP

    Obsolete control

HOUDINI_HSVCOP_COMPAT

    Obsolete control

HOUDINI_COP_FAKE_MOVIEREAD

    Obsolete control

HOUDINI_RMAN_INCLUDE_FIX

    Setting this variable will cause the order of pre/post includes to
    be different when generating RIB.  This allows for proper motion
    blur of RiReadArchive geometry read using the include files.

HOUDINI_MI_DISABLE_FLIP_RMAP

    When auto-generating reflection maps for MentalRay, one of the
    images is flipped by default.  Setting this variable will turn the
    flipping off.

HOUDINI_DISABLE_SAVE_THUMB

    Disable saving of thumb-nails in .hip files.  This makes .hip
    files smaller and faster to save/load.

HOUDINI_UI_COREDUMP

    Prevent Houdini from trying to saving a .hip file when a crash is
    detected.  Instead, Houdini will simply crash.

HOUDINI_ENABLE_FPS_SCALE

    If enabled, it will stretch all keys in your animation so that the time
    at the start of the last keyframe is the total animation length when you
    change the frame rate of your animation. Usually, when you change your
    animation frame rate, the last keyframe will end up at a fractional
    keyframe of your new frame rate because each frame in Houdini is actually
    a (1/FPS) seconds in length. Note that when you do this, the actual timing
    of your animation will be changed when you modify your frame rate.

HOUDINI_X11_SYNCHRONOUS

    Force Unix X11 servers to be synchronous.  This may affect
    performance.

HOUDINI_IPLAY_FLIP

    Causes iplay to flip all images vertically

HOUDINI_VIEW_METACAM

    Specifies operator types that contain a camera or light and that need to be 
    locked to the view in a special way. When a camera is inside an OTL and it
    is locked to the view, the view attempts to modify the camera parameters
    to align the camera view to itself. However, if a camera is inside an OTL,
    its parameters are locked and cannot be changed and the camera view will not
    be aligned with the viewport.
    To allow alignment of cameras and lights with the view when they are inside
    an OTL, we can modify the OTL transform parameters such that the camera
    or light inside it is aligned with the viewport (when the camera is
    locked to a viewport).  The locked viewport will modify the camera's parent 
    (OTL) transform parameters, instead of trying to change (usually locked)
    transform parameters of the  camera object (which lives within the OTL). 
    Such OTLs are specified in the HOUDINI_VIEW_METACAM
    variable. The variable contains a list of space delimeted words and if the 
    operator type name contains any of them as a substring then the OTL parameters
    are modified (instead of the camera parameters) to orient the camera
    such that its view is the same as the viewport.
    An OTL can register itself when loading or when first instance is created by 
    appending its name to this variable in the appropriate script:
    setenv HOUDINI_VIEW_METACAM = "$HOUDINI_VIEW_METACAM my_magic_otl_substring"

HOUDINI_SKIP_NAME

    Avoid printing viewport name in Houdini

HOUDINI_DISABLE_DISPLAYLIST

    Disable optimized rendering of geometry.  This will cause Houdini
    to use less memory at the expense of OpenGL rendering speed.

HOUDINI_DISPLAYLIST_DELAY

    How many redraws must occur with static geometry before it is
    cached inside a display list.  The default value is 2.

HOUDINI_DISABLE_POLYTESS_CACHE

    This disables the caching of the tesselation for shaded polygons.
    Setting this will decrease memory usage at the cost of degraded
    performance.

HOUDINI_TOP_POS_SINGLE_PASS

    Set this environment variable to force only a single pass for
    drawing the wireframe outside of stamped projections in the
    TOP texture positioner view.  Otherwise multiple passes are used
    to only draw the frame outside of the stamped projection.

HOUDINI_IPLAY_IP

    Force "ip" image device to use iplay instead of mplay.  This
    behaviour can be overridden using the HOUDINI_IP_COMMAND and
    HOUDINI_IP_COMMAND_FLIP controls.

HOUDINI_CONSOLE_LINES

    Number of lines to store in the Windows console

HOUDINI_INTERRUPT_THRESH

    Timeout before the interrupt dialog appears to interrupt long
    operations.

HOUDINI_TEX3D_USAGE

    Amount of memory used by 3D texture maps in VEX.

HOUDINI_RAT_USAGE

    Amount of memory used by RAT textures in Houdini and renders.
    This amount is specified in mega-bytes.  For example, setting the
    control to 32 will limit Houdini/Mantra to use 32 Mb of RAM for
    RAT file texturing.

HOUDINI_MDISPLAY_WAIT_TIME

    Number of seconds to wait before deciding that iplay could not be
    started.

HOUDINI_OVERRIDE_XRES

    Specifies the horizontal resolution of your monitor in pixels.
    Houdini will not create any windows wider than the value specified
    here. You can use this value to force Houdini to only use a
    portion of your screen.

HOUDINI_OVERRIDE_YRES

    Specifies the vertical resolution of your monitor in pixels.
    Houdini will not create any windows taller than the value specified
    here. You can use this value to force Houdini to only use a
    portion of your screen.

HOUDINI_OVERRIDE_WIDTH

    Specifies the width of your monitor in millimetres. You can use this
    value to modify the pixels-per-inch value calculated by Houdini.
    Setting this value to be larger than your actual monitor size will
    cause Houdini to display smaller fonts. You can also use this value
    if the value calculated by Houdini seems to be incorrect.

HOUDINI_OVERRIDE_HEIGHT

    Specifies the height of your monitor in millimetres. You can use this
    value to modify the pixels-per-inch value calculated by Houdini.
    Setting this value to be larger than your actual monitor size will
    cause Houdini to display smaller fonts. You can also use this value
    if the value calculated by Houdini seems to be incorrect.

HOUDINI_UISCALE

    This specifies a fixed scale factor to adjust the dots-per-inch
    Houdini uses for displaying ui.  A value of 100 will provide the
    default of 85 dpi.  A value of 200 will have all fonts and icons
    twice that size, and 50 will make them half that size.  A value of
    -1 will cause the dpi to be calculated from the monitor's
    dimensions and resolution, or by HOUDINI_OVERRIDE_*.
    By default the value is 100.

HOUDINI_SCRIPT_DEBUG

    If set, errors will be printed when loading dialog scripts and
    scripted operators.

HOUDINI_RMAN_CURVE_STEP

    Overrides the step size when writing RiCurve primitives for RIB

MANTRA_COLOR_CACHE

    Specifies the storage for color caching when rendering.

MANTRA_GRID_CACHE

    Specifies the number of micro-polygon grids stored in RAM.

MANTRA_PSOUP

    Specifies the number of primitives in a single object before the
    object is considered to be polygon soup and memory optimizations
    are invoked.

MANTRA_RAY_CACHE

    Specifies the storage size for caching of ray tracing geometry
    when rendering.

HOUDINI_MANTRA3_CACHE

    Obsolete control

HOUDINI_UI_QUEUE_SIZE

    Specifies the size of the UI event queue.  Increasing this can
    help prevent queue overflows.

FPS

    This variable is used by iplay to set the default frames per
    second.  It is automatically set by the OpenGL output driver.

HOUDINI_PERFORMANCE_SIZE

    Specifies the number of lines that the performance monitor keeps.

HOUDINI_ABEKAS_PAL_XRES

    Overrides the default resolution of the abekas image device.

HOUDINI_ABEKAS_PAL_YRES

    Overrides the default resolution of the abekas image device.

HOUDINI_GAUSS_EXP

    Specifies the exponent for the Gaussian filter kernel.  This
    affects any Gaussian filtering (image scaling, rendering, etc.)

HOUDINI_MITCHELL_B

    Specified the B parameter of the Mitchell filter kernel.  This 
    affects any Mitchell filtering (image scaling, rendering, etc.)

HOUDINI_MITCHELL_C

    Specified the C parameter of the Mitchell filter kernel.  This 
    affects any Mitchell filtering (image scaling, rendering, etc.)

HOUDINI_CHOP_OLDNOISE

    The noise CHOP in Houdini5 and greater has a new method for
    computing random values.  This produces different results than
    Houdini4, but is more consistent on different hardware
    platforms.  If this variable is set, the noise CHOP in Houdini5
    will generate same values as Houdini4.

HOUDINI_CHOP_LINEWIDTH

    This variable controls the line thickness in the CHOP viewer.

HOUDINI_CHOP_UNITS

    This sets the default parameter for the Units parameter of CHOPs.

HOUDINI_CHOP_IMAGE

    This variable can be set to point to an image file which is
    displayed when the CHOP viewer is disabled.

HOUDINI_CINEON_WHITE_POINT

    Defines the white point for reading and writing cineon files.
    This value is not used if a LUT file is used.

HOUDINI_CINEON_FILM_GAMMA

    Defines the film gamma for reading and writing cineon files.
    This value is not used if a LUT file is used.

HOUDINI_CINEON_FULL_RANGE

    If set, the generated LUT from the CINEON_WHITE_POINT and
    CINEON_FILM_GAMMA is not clipped above the white point; the
    full range of the cineon data is preserved. Only used by the 
    Houdini 4.0 Compositor.

HOUDINI_CINEON_RENDER_LUT

    Defines the default render LUT filename for reading and writing 
    cineon files.

HOUDINI_CINEON_PREVIEW_LUT

    Defines the default preview LUT filename for reading and writing
    cineon files. Only used by the Houdini 4.0 Compositor.

HOUDINI_IMAGE_DISPLAY_LUT

    Defines the default display LUT filename for displaying images in
    the compositor's viewer and mplay.

HOUDINI_IMAGE_INSPECT_LUT

    Defines the default inspect LUT filename for inspecting images in
    the compositor's viewer and mplay.

HOUDINI_LOD

    This is an Level of Detail number, such as 0.01 or 1.0.  It becomes 
    the default LOD for new windows.  Higher LODs will result in more 
    accurate drawing of curves and surfaces, however at a corresponding 
    cost in display speed.  By default, it is set to 1.0.  If you find
    yourself having to constantly change the View Parameter:Viewer:LOD
    setting, you might save some work by just making your default a
    better value.

HOUDINI_WF_GAMMA

    Specifies the gamma value written out to Wavefront .rla files.

EDITOR

    Houdini will use this variable to determine which external graphical
    editor to invoke when editing text.  The editor should run in the
    foreground.
    If the VISUAL environment variable is set, then it is used instead of
    EDITOR and started as a graphical process. In other words, the VISUAL
    environment variable will override this and thus have no effect if VISUAL
    is also set. If both the VISUAL and EDITOR variables are _not_ set, then
    the following command lines are used:
	Windows:    notepad
	Solaris:    dtpad
	Linux:	    /usr/bin/gedit
	Irix:	    jot -f
    This environment variable may be used by applications other than Houdini.

VISUAL

    Houdini will use this variable to determine which external editor
    to invoke when editing text.
    If this environment variable is not set, then the EDITOR environment
    variable is used. See the help for the EDITOR environment variable to see
    what are the defaults if both are not set.
    This environment variable may be used by applications other than Houdini.

HFS

    The path where Houdini is installed.
    Houdini reads the configuration information from $HFS/houdini.

SHELL

    When Houdini starts external applications, it uses the SHELL
    variable to determine how to start them.
    This may be used by applications other than Houdini.

HOME

    This variable determines your "home" directory.
    This may be used by applications other than Houdini.
    Houdini mostly uses files in $HOME/houdiniVERSION, where VERSION i
    the current version number (ie: $HOME/houdini6 or
    $HOME/houdini6.1)

HSITE

    The HSITE variable is a path to the site-specific Houdini
    conifguration information.  This allows a site to have a common
    set of defaults and files.  It is, by default, in the HOUDINI_PATH
    between HOME and HFS.  To change global configuration information,
    you should use this rather than editting the contents of
    $HFS/houdini.
    Like HOME, Houdini uses $HSITE/houdiniVERSION, where version is
    the current version number (ie: $HSITE/houdini6 or
    $HSITE/houdini6.1)

JOB

    This variable is often used as a path to the current job.  It is
    not used by any of the default Houdini paths.

HOUDINI_TEMP_DIR

    Specifies a directory where Houdini will generate temporary files.

HOUDINI_UNDO_DIR

    Specifies a directory where Houdini will store undo information.
    If not specified, the temporary directory will be used.

HOUDINI_CONDENSE_HIP

    If this variable is set Houdini will attempt to make paths entered
    "friendly" by replacing portions of filename paths with $HIP if
    it's appropriate.  This behaviour is off by default.

HOUDINI_MESSAGE_COMMAND

    An external program which Houdini uses to display graphical
    messages.

HOUDINI_CONFIRM_COMMAND

    An external program which Houdini uses to display confirmation
    boxes.

HOUDINI_ERRORLOG_FILENAME

    If set to a valid file name, Houdini will log all errors of severity 
    above HOUDINI_ERRORLOG_LEVEL to this file.

HOUDINI_ERRORLOG_LEVEL

    The minimum error level that Houdini will write to the error log file
    specified by HOUDINI_ERRORLOG_FILENAME.  Valid values are integers 
    between 0 (all errors will be logged) and 6 (nothing will be logged)
    inclusive.  Default value is 3.  
    Error levels are defined as follows: 1, message; 2, prompt; 3, warning;
    4, abort operation; 5, fatal error.

HOUDINI_DEFAULT_TEXTURE_COLOR

    Specifies the default color to use when texture maps cannot be
    found while rendering.  This can be specified as a single string
    containing four floating point numbers representing the red,
    green, blue and alpha components of the default color.  For
    example:
       setenv HOUDINI_DEFAULT_TEXTURE_COLOR "0 0 0 0"
    to set it to zero black.

HOUDINI_VEX_DEFAULT_AMBIENT

    The default VEX ambient light shader.  If no shader can be found
    for an ambient light source, this shader will be applied at render
    time.

HOUDINI_VEX_DEFAULT_LIGHT

    The default VEX light shader.  If no shader can be found for a
    light source, this shader will be applied at render time.

HOUDINI_VEX_DEFAULT_MATTE

    The default VEX matte surface shader.  This shader is used at render
    time to provide a background surface if there is fog applied to a scene.

HOUDINI_VEX_DEFAULT_OGLSURF

    The default VEX surface shader for displaying objects in VEX shaded
    mode in the object viewport.

HOUDINI_VEX_DEFAULT_OGLSEL

    The default VEX surface shader for displaying selected geometry in
    VEX shaded mode in the object viewport.

HOUDINI_VEX_DEFAULT_PHOTON

    The default VEX photon shader.  If no photon shader can be found,
    this shader will be applied at render time.

HOUDINI_VEX_DEFAULT_SHADOW

    The default VEX shadow shader.  If a light source is casting shadows,
    but no shadow shader is found, this shader is applied at render time.

HOUDINI_VEX_DEFAULT_SURFACE

    The default VEX surface shader.  If no surface shader can be
    found, this shader will be applied at render time.

HOUDINI_OGL_DBL_BUFFER_FIX

    Some graphics boards (notably quadro and geforce) boards have
    problems writing simultaneously to the front and back buffers.  By
    setting this variable to 1, Houdini will only write to one buffer
    at a time.

HOUDINI_COPY_SUFFIX

    When copy/pasting, this variable can be used to create
    user-specific temporary files.

HOUDINI_RMAN_CURVE_BASIS

    Specify the curve basis when generating RiCurve primitives in a
    RIB stream.  This should be one of "linear" or "cubic".

HOUDINI_COP_DISK_DEFAULTNAME

    Obsolete control

HOUDINI_MANTRA3_SHADOW

    Obsolete control

HOUDINI_MANTRA3_REFLECT

    Obsolete control

HOUDINI_RI_SHADERPATH

    When the shader path is not specified in the RIB output driver,
    this environment variable is checked.  If this variable exists,
    it's value will be output to the RIB stream.  If the variable
    doesn't exist, then no shader path will be output to the RIB file.

HOUDINI_RI_TEXTUREPATH

    When the texture path is not specified in the RIB output driver,
    this environment variable is checked.  If this variable exists,
    it's value will be output to the RIB stream.  If the variable
    doesn't exist, then no texture path will be output to the RIB file.

HOUDINI_RI_EYESPLITS

    When the eye splits are not specified in the RIB output driver,
    this environment variable is checked.  If this variable exists,
    it's value will be output to the RIB stream.  If the variable
    doesn't exist, then no eye-split information will be output to the
    RIB file.

HOUDINI_FILE_VIEWER

    Specify an external application to view files.

HOUDINI_CHECK_XFORM

    When generating scripts for renderers, if this variable is set,
    the transforms on objects will be tested to see if they are
    singular (i.e. whether there are zero scales).  If the transform
    is singular, the object will not be output.
    The value of this variable is the threshold at which the transform
    is considered zero.  Thus, the variable should be set to some very
    small floating point number.

HOUDINI_STPATH

    Specify a path to search for the source to a shader when editing
    shader code from pop-up dialog scripts.

HOUDINI_STEDIT

    Specify an external application to edit shaders with.

HOUDINI_DOUBLEBUFFER

    This variable can be set to either ON or OFF.  It will force
    houdini to run in either single or double buffer mode.

HOUDINI_WORKSHEET_BOXPICK

    This environment variable is used to override using the left mouse
    button for box picking in the network worksheet.  Can be set to
    either "middle" or "right".

HOUDINI_DEFOPTYPEPREFIX

    When you convert a subnet into a new operator type, this prefix,
    if present, will be used for guessing what the basename of the new
    operator should be.  If not present, the username is used.
    For example, setting this to "foobar_" will ensure all operators
    created will have their basename type prefixed by foobar_.  This
    can be used to ensure conflicts don't occur with other projects
    operators.

HOUDINI_VRML_CONVERT

    External application to convert Inventor format to VRML format.

HOUDINI_VRML_CONVERT2

    External application to convert Inventor format to VRML 2 format.

HOUDINI_ABEKAS_LOGNAME

    Specify the user name for logging into an abekas frame recorder.

HOUDINI_ABEKAS_LOGPASSWD

    Specify the password for logging into an abekas frame recorder.

HOUDINI_MD_COMMAND

    Specify the external application used by the md image device to
    read images from stdin and display them in a persistent frame
    buffer device (i.e. mplay).

HOUDINI_MD_COMMAND_FLIP

    Specify the external application used by the md image device to
    read images from stdin and display them upside down in a
    persistent frame buffer device (i.e.

HOUDINI_MPLAY_LOCKPATH

    Specify a directory to create the mplay lockfiles.  These files
    will normally be created in the user's HOME directory.  The value
    of this variable should point to a directory where lockfiles can
    be created (i.e. /tmp or c:/temp).

HOUDINI_IP_COMMAND

    Specify the external application used by the ip image device to
    read images from stdin and display them in a viewer (i.e. iplay).

HOUDINI_IP_COMMAND_FLIP

    Specify the external application used by the ip image device to
    read images from stdin and display them upside down in a viewer
    (i.e. iplay).

USER

    information from the login session.  This variable represents the
    name of the user logged in.

HOUDINI_OS

    The OS that Houdini believes it's running on.  Possible values of
    this variable are currently defined as "Windows", "Linux",
    "Solaris", or "IRIX".

HOUDINI_PATH

    The path of directories where Houdini looks for configuration
    files.

HOUDINI_OTL_PATH

    The path of directories where Houdini looks for OPlibraries files
    for loading OTL files at startup.  Note that the OTL files themselves
    can be anywhere.  Houdini only does a directory search for OPlibraries
    files, which just contain a list of OTL file names.

HOUDINI_SCRIPT_PATH

    The path of directories where Houdini searches for scripts.  This
    includes .cmd files for hscript, .class files for the java command,
    .tcl and .tk files for the tcl and tk commands, and command scripts
    for the Alfred Output Driver.

HOUDINI_CLIP_PATH

    The path of directories where Houdini looks for .clip and .bclip
    channel files

HOUDINI_CUSTOM_PATH

    The path of directories where Houdini looks for custom panel
    information.

HOUDINI_DESK_PATH

    The path of directories where Houdini looks for desktops

HOUDINI_DSO_PATH

    The search path for loading custom plug-ins (Dynamic Shared
    Objects or Dynamic Link Libraries).

HOUDINI_GEOMETRY_PATH

    The search path for geometry files.

HOUDINI_MACRO_PATH

    The search path for toolbar macro files.

HOUDINI_STOOLBAR_PATH

    The search path for factory and custom toolbars used in the viewports.
    This path may be different from the one defined for the network pane.
    (see HOUDINI_TOOLBAR_PATH). If you think you have set the path correctly
    and the toolbar menu does not list any toolbars, ensure that "Show custom
    toolbars" is enabled in Houdini's Preferences dialog.

HOUDINI_TEXTURE_PATH

    The search path for loading images.  This includes .rat files and
    other 2D formats as well as .i3d 3D texture files.

HOUDINI_TOOLBAR_PATH

    The search path for factory and custom toolbars used in the network
    pane. This path may be different from the one defined for interactive states
    (see HOUDINI_STOOLBAR_PATH). If you think you have set the path correctly
    and the toolbar menu does not list any toolbars, ensure that "Show custom
    toolbars" is enabled in Houdini's Preferences dialog.

HOUDINI_VEX_PATH

    The search path for VEX code.  Setting this path will override the
    default path of $HOUDINI_PATH/vex/.  Searching for the dialog
    scripts is independent of VEX searching and is controlled by the
    HOUDINI_PATH.

HOUDINI_OUTLINEFONT_PATH

    This is the path searched for Adobe Type 1 or True Type fonts used
    in the font SOP, font COP 

HOUDINI_BACKUP_DIR

    This is the directory used to store the backed-up hip files when the 
    "Numbered Backup" save option is set.

HOUDINI_BACKUP_FILENAME

    A template for the filename used for file backups when the
    "Numbered Backup" save option is set.  Two variables are required:
    $BASENAME, which will be replaced by the name of the file being saved
    without its extension; and $N, which is replaced by the backup number.
    $N can be followed by a single digit which is interpreted as the number
    of digits to be used in the backup number; numbers with fewer digits than
    this will be padded with zeroes.  Default value is '$BASENAME_bak$N'.

HOUDINI_AUTOSAVE_FILENAME

    A template for the filename used for auto save file backups when the
    "Numbered Backup" auto save option is set.  Two variables are required:
    $BASENAME, which will be replaced by the name of the file being saved
    without its extension; and $N, which is replaced by the backup number.
    $N can be followed by a single digit which is interpreted as the number
    of digits to be used in the backup number; numbers with fewer digits than
    this will be padded with zeroes.  Default value is '$BASENAME_auto$N'.

HOUDINI_MAX_BACKUP_FILES

    Setting this environment variable will limit the number of backup files
    Houdini creates when the "Numbered Backup" save option is set.  Setting
    this environment variable to 0 will disable the limit and Houdini will
    write as many backup files as resources permit (default).

HOUDINI_NO_SPLASH

    Setting this environment variable will disable the Houdini splash screen
    from being displayed.

HOUDINI_BUFFEREDSAVE

    When enabled .hip files are first saved to a memory buffer and
    then written to disk.  This is useful when saving over the network
    from Windows 2000 machines, or other places where seeking to the
    network is expensive.

HOUDINI_UI_SATURATION

    Reduces or increases the color saturation of Houdini's user interface.
    The default is 1 (as is), values less than one reduce the coloring of the 
    UI, 0 produces monochrome UI and values greater than 1 super-saturate
    Houdini.

HOUDINI_UI_BRIGHTNESS

    Defines the brightness factor of the houdini UI (default 1).
    First the HOUDINI_UI_GAMMA (default 1) is applied, followed by the
    HOUDINI_UI_CONTRAST (default 1) and finally and finally the brightness.

HOUDINI_UI_CONTRAST

    Defines the color contrast of the houdini UI (default 1).
    First the HOUDINI_UI_GAMMA (default 1) is applied, followed by the
    contrast and finally HOUDINI_UI_BRIGHTNESS (default 1).

HOUDINI_UI_GAMMA

    Defines the gamma factor applied to the houdini UI (default 1).
    First the gamma is applied, followed by HOUDINI_UI_CONTRAST (default 1) 
    and finally HOUDINI_UI_BRIGHTNESS (default 1).

HOUDINI4_COMPATIBILITY

    When this is enabled, some of the quirks of Houdini 4 are turned
    on.  This is designed to be used to allow old hip files to be
    loaded.  Support for these inconsistencies is not guaranteed in
    future versions of Houdini.  Currently, this will:
	- Change the order of points in Spheres, Tubes, Torii, and
	  Circles under certain orientations.
	- Reverse the direction of the Clip SOP's "distance"
	  parameter.
	- Revert to the old capture region weighting method 

HOUDINI55_COMPATIBILITY

    When this is enabled, some of the quirks of Houdini 5.5 (and earlier) are
    turned on.  This is designed to be used to allow old hip files to be
    loaded identically.  Support for these inconsistencies are not guaranteed
    in future versions of Houdini.  Currently, this will:
	- Not always use the shortest path rotation blending the PolyWire
	  SOP and Composite CHOP
	- Revert to the old boneangle() behaviour of calculating the angle
	  between the two negative z axes of the given bones
	  (Note that usually this expression would have been used as
	  (180-boneangle(...)) which can easily be converted into the new
	  behaviour by no longer subtracting from 180)
	- The Switch Operators in POPs, SOPs, COP2s and SHOPs will not
	  consolidate null inputs.
	- When globbing channel patterns, the order will be reverted back to 
	  reverse creation order. This affects the Fetch CHOP, and the
	  following hscript commands: chls, chread, chwrite
	- The "tmgls -l" hscript command will revert to showing paths that
	  start with /Director.
	- Revert to the old behaviour where when Houdini is told to look at
	  something with an up vector that is parallel to the target
	  direction, we do nothing.  This affects all of Houdini. This includes
	  (but not limited to) the Look At parameter in all operators,
	  the mlookat() expression function, and the lookat() VEX function.

HOUDINI6_COMPATIBILITY

    When this is enabled, some of the quirks of Houdini 6.0 (and earlier) are
    turned on.  This is designed to be used to allow old hip files to be
    loaded identically.  Support for these inconsistencies are not guaranteed
    in future versions of Houdini.  Currently, this will:
	- With soft transforms (SoftPeak, SoftTransform, and Soft
	  Options in the Edit SOP that are not applied) and Ignore
	  Connectivity Off, connectivity does not respect the soft
	  radius.  In Houdini 6.1 and later, two points are connected
	  only if there is a sequence of edges within the soft radius
	  that connects them.  In 6.0 and earlier, or with this flag
	  on, they are connected if there is any sequence of edges
	  that connects them.
	- The Fetch CHOP will create the order of its fetched tracks in the
	  following order:
	  - animated channels (in the parmeter order of fetched operator)
          - chop data tracks
	  - non-animated parameters (again in parameter order)

HOUDINI6_FILTER_COMPATIBILITY

    There was a large bug found in the low level filtering code in
    Houdini6.1.  Fixing this bug caused the results of filtering to
    change quite dramatically from previous versions.  To maintain
    previous behaviour, this control can be set.  However, use of this
    control is discouraged since the filtering was incorrect before
    the fix.  This control may be removed in future versions of
    Houdini.

HOUDINI_SAVE_EXTRAINPUTS

    This option is only required if you wish to load hip files in versions of
    Houdini prior to 5.1 with pre-generated naming dependencies. Naming
    dependencies are always regenerated when an operator cooks.
    When this is enabled, extra inputs of operators are saved. In versions
    prior to Houdini 5.1, these were saved and reloaded so that naming
    dependencies could be maintained without cooking. eg. Renaming an 
    operator will also rename all channel references to it. This was because
    naming dependencies would only be generated when an operator cooked and
    loading a hip file does not necessarily cook the operators. This is
    especially true if loading a file in hscript.
    Starting with Houdini 5.1, naming dependencies are generated regardless of
    whether an operator is cooked and so saving extra inputs are not needed. 
    Furthermore, when loading hip files, extra inputs are now silently ignored
    if they happen to exist.

HOUDINI_HIPEXT

    When this variable is set, Houdini will no longer add the ".hip" extension
    from the Save dialog.

HOUDINI_ACCESS_METHOD

    This value can be 0 (the default), 1, or 2. It selects the method used
    by Houdini to check file and directory permissions under Windows. 0 checks
    the permissions of the current user against the Windows user and group
    permissions set for the file in question. This method may be slow on
    machines that use a network login server. 1 uses a different method for
    checking the Windows user and group permissions, but relies on
    functionality that is broken in Windows 200 Service Pack 2. Method 2 simply
    checks the file attributes. This method is fast, but ignores the user
    and group permissions, and so may report that some files or directories
    can be written to when actually they cannot.

HSCRIPT_SAFEQUIT

    If this variable is set, the quit command in hscript will prompt
    the user to verify that they want to quit.

HOUDINI_IRIX_OSTRSTREAM_MAX_SIZE

    This variable is used to specify the maximum size when using a "dynamic"
    ostrstream.  It is only used when running on an IRIX machine and is 
    necessary to work around a bug which prevents these streams from growing.
    The default value is 5242880 (5M), and the minimum acceptable value is
    8192 (8K).  Try increasing this variable when saving, such as writing
    OTLs, is failing on an IRIX machine.

PathExpansionHelp

    Special characters in path definition are:
	@  - Typically expands to the HOUDINI_PATH.  Thus, if the
	     HOUDINI_PATH was set to:
	        $HIP
		$HFS/houdini
		$HOME/houdini
	     a path defined as "@/vex" would expand to the paths
	        $HIP/vex
		$HFS/houdini/vex
		$HOME/houdini/vex
	=  - This expands to the $HIP variable.  This path will always
	     point to where the currently loaded hip resides.
	&  - The ampersand character expands to the "default" path.
	     For example, to add a directory to the a path without
	     worrying about what the default path should actually be,
	     simply set the path to: "/mypath;&".  This will search
	     the "/mypath" path first, then search the default path.
	^  - Some paths are used for multiple directories.  For
	     example, the HOUDINI_VEX_PATH is used to define the
	     search path for Surface, Displacement, Sop, etc. VEX
	     shaders.  For VEX, the ^ symbol expands to the shader
	     type.  Thus, if the HOUDINI_VEX_PATH variable is set to
	     something like "/usr/local/vex;$HOME/vex/^", when
	     loading Surface shaders, the following directories will
	     be scanned:
		/usr/local/vex
		$HOME/vex/Surface
	     and if Sop shaders are being searched for, the
	     following paths will be searched:
		/usr/local/vex
		$HOME/vex/Sop