Houdini 20.5 Reference Panes

Graph view

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Overview

The graph view lets you view and edit animated parameters (channels) as graphs of their values over time. It is one view of the animation editor. You can also use the dopesheet and table view to edit animation. To switch between these views, use the buttons at the top left corner of the animation editor.

Channels record how the value of a parameter changes over time. You can think of a channel as a parameter animation.

A channel is an extra object associated with a parameter. It stores keyframe information, essentially acting as a keyframe container for the parameter. If you delete all of the keyframes on a parameter, you end up with a parameter with an empty channel (a channel that does not hold any keyframes).

A channel consists of a series of segments. Each segment has two end points, and each end point is at a key and has the following properties - value, slope, and acceleration.

Each segment has a function associated with it that determines the curve’s behaviour between keyframes. Different functions use different end point properties. For example, the constant segment function uses the value property of the first end point only, while the bezier segment function uses all three properties (slope, acceleration, and value) at both end points.

The graph view displays only the selected channels in the channel list. When a channel is displayed in the graph, it is available for viewing and editing in the animation editor’s graph, dopesheet, and table views.

To...Do this

Pan and zoom the view

Drag to pan and to zoom.

Frame the data

To show all the graph data, click Home Channels on the right toolbar, or choose View ▸ Home Channels (All Graphs).

To show all the graph data vertically, click Vertical Adapt on the right toolbar, or choose View ▸ Vertical Adapt.

To show all the graph data horizontally, click Horizontal Adapt on the right toolbar, or choose View ▸ Horizontal Adapt.

Frame part of the data

  1. drag in the graph to select part of the graph.

  2. Click Frame Selection on the right toolbar, or choose View ▸ Frame Selection.

Change the current time

Use any of the following:

  • A tall white vertical line on the graph indicates the current time. Drag the line to change the time.

  • Above the graph, click a location on the timebar or drag the black frame number to move the play position to that point.

  • Use the playbar controls.

Adding and deleting keys

To...Do this

Add a key

Use any of the following:

  • Click the graph with Alt + to create a new keyframe for all curves at that frame. You can also hold Alt + and drag the insertion point along the curves to allow for more accurate positioning. If a key already exists on a selected channel at that frame, a duplicate key will not be created.

  • Click the graph with Alt + ⇧ Shift + to create a new keyframe only on the curve you are hovering over.

  • Hover over the graph and press K to add keyframes at the current frame based on the Global Set Key animation preference.

  • on the graph and select Set Keyframes at Current Time to add a keyframe at the current frame for the selected channels.

  • Hold and drag the white vertical line that runs down the graph indicating the current frame. A small yellow box will appear on the vertical line indicating the parameters values at the point on the curve where you started dragging the line. If you add a key at the new frame, the new key parameters will be set to the values at the yellow box. This essentially copies the parameter values from one point on the curve to another.

  • Hover over the playbar and press K, or click the playbar keyframe button to add keyframes based on the Global Set Key animation preference.

  • In the parameter editor, Alt + on a parameter name or individual component to add a keyframe.

  • In the parameter editor, on a parameter and choose Keyframes ▸ Set Keyframe.

Remove a key

Use any of the following:

  • Select a key on the graph and press ⌦ Del.

  • Select a key on the graph, and choose Delete.

  • In the parameter editor, on a parameter and choose Keyframes ▸ Remove Keyframe.

Editing curves

The following illustration shows the handles at each keyframe. The handles correspond to the text boxes at the bottom of the graph (Frame, Value, Slope, and Accel), which allow you to set the handles to exact values. The buttons on the right toolbar control the display of keyframe handles and values on the graph.

To control how Houdini connects the two ends of a segment, select a segment on the graph and choose a function from the Function menu below the graph. Some common functions:

You can also change the options on the slope, value and acceleration handles at each keyframe, including:

To...Do this

Select a keyframe and its associated handles

  1. For the handles you want to select, turn on their associated display options on the right toolbar (for example, Show Value Handles).

  2. drag the area around the key to select the handles.

Only select handles on a specific channel

If a channel has handles that are already selected, holding S and making a box selection only selects handles on that channel; handles on other channels are not selected. (If S is not held, box selection selects handles on all channels.)

Change the shape of a graph segment

  1. Select the segment you want to change.

    If the segments are drawn as dashed lines, turn on Show Segment Handles on the right display toolbar to make segments selectable.

  2. Choose from the Function menu below the graph, or type a custom expression directly into the Function box.

    You can also change the shape of the segment by clicking the constant and linear function buttons on the top toolbar.

or

Use the handles on the selected keys in the graph to adjust the shape of the curve. You can also type exact values for the selected handle in the Value, Slope, and Accel text boxes on the bottom toolbar.

or

Use curve pulling to edit Bezier and cubic segments. With curve pulling, you can change the shape of the curve by dragging on a segment. This can be easier than interacting directly with slope and acceleration handles, and gives you better control over how the curves behave between keyframes.

Curve pulling

  1. Turn on Curve Pulling on the top toolbar.

  2. Turn on Show Segment Handles on the right toolbar to display the curve segments so they can be selected.

  3. drag on the segment, and the segment shape will change in an attempt to follow the mouse cursor.

    If a segment is monotonic (only increasing or decreasing between keyframes), you can keep the segment monotonic and not overshoot on keyframes by holding ⌃ Ctrl while dragging the curve.

Move the selected keyframe without having the cursor directly over the keyframe

  1. Turn on Show Value Handles on the right toolbar.

  2. Select a keyframe.

    Note

    If Show Value Handles is turned off, you will not be able to box select a value handle.

  3. drag anywhere in the graph to move the selected keyframe along one axis, depending on the direction the keyframe was first moved.

    ⌃ Ctrl + drag anywhere in the graph to move the selected keyframe in X and Y at the same time.

Move a keyframe in time (move in X)

  1. Display the frame handles by turning on Show Time Mark Handles on the right display toolbar. Frame handles, also called time marks, are short vertical lines that runs through the value handle.

  2. Drag the frame handle left or right to move the keyframe.

Time values on the graph have a line under them. When you turn on Settings ▸ Snap Moved Keys to Nearest Frame, the keys will move to the nearest integer frame when you finish dragging. You can also turn on this option by clicking Snap Moved Keys on the top toolbar.

Move a keyframe in Y

Drag the value handle up and down.

Move a keyframe in X or Y

  1. Undisplay the frame handles (time marks) by turning off Show Time Mark Handles on the right display toolbar.

  2. Drag the value handle to move the keyframe along one axis, depending on the direction the keyframe was first moved.

Show Time Mark Handles is turned off by default.

Move a keyframe in X and Y at the same time

Hold ⌃ Ctrl and drag the value handle. This is the same functionality as turning on the Value/Time Handles option (by clicking Value/Time Handles on the top toolbar, or turning on Settings ▸ Value/Time Handles.

Quickly edit curve slopes

Select a keyframe and press 0 to zero the slope, or 9 to make the slope tangent.

Copy a keyframe value

  1. Select a keyframe.

  2. Press ⌃ Ctrl + C or Alt + C to copy the keyframe values.

  3. Move to a different time.

  4. Press ⌃ Ctrl + V or Alt + V to paste the keyframe values at the current frame.

Change a value at a keyframe

Drag the value handle up or down.

or

  1. Click the value handle.

  2. Enter an exact number in the Value field below the graph and press Enter.

Lock the slope orientation and only change the acceleration

Hold ⌃ Ctrl and drag the acceleration handle.

Select all of the same type of handles on a channel

Double-click the handle.

Add all of the same type of handles to the existing selection

⇧ Shift double-click the handle.

⌃ Ctrl + ⇧ Shift double-click removes the same type of handles from the selection.

Select additional handles using a box selection

Hold ⇧ Shift and drag.

⌃ Ctrl + ⇧ Shift and drag removes the handles.

Change multiple values at once

Select multiple handles. Then drag one of the selected handles to move all of them at once.

If you select handles with different values, the Value field will show ---. Edit the Value field to set all the selected values at once.

Edit/Select toolbar

The toolbar above the graph provides several quick access options for editing and changing the functionality of various handles and values. When you hover over a button, a tooltip will display the button name and any associated hotkeys.

Selection Tool

Box Handle

Box Handle with Pivot

Tie Handles

Untie Handles

Constant Function

Linear Function

Tangent (Cubic) Handles

Bezier Handles

Set Selected Slopes To Manual

Set Selected Slopes To Automatic

Tie Values

Untie Values

Swap Active Channels and Snapshots

Clear Channel Snapshots

Value/Time Mark Handles

Snap Moved Keys to Nearest Frame

Keep Acceleration Ratio

Curve Pulling

Display toolbar

The right toolbar provides several quick access options for displaying and framing the selected channels, as well as turning on and off the display of various keyframe handles and values. When you hover over a button, a tooltip will display the button name and any associated hotkeys. Buttons that have an arrow at the bottom right corner (for example, ) have addition options. on the button to view the options.

Home Channels (All Graphs)

Homes all the channels by panning and zooming the main window to show all the keys in the graph or dopesheet.

Vertical Adapt

Automatically pans and zooms the graph to keep all the vertical values visible when selecting different channels.

Horizontal Adapt

Automatically pans and zooms the graph to keep all the horizontal values visible when selecting different channels.

Frame Selection

Pans and zooms the main window to show the area of the graph or dopesheet that is selected.

Toggle Normalized Values Display Mode

Provides options for displaying channels with normalized values.

Note

Toggle Normalized Values Display Mode is deselected by default. When deselected, the graph always displays the Parameter UI Range mode regardless of the mode you select from the options.

this button to display the following options:

Parameter UI Range

The Parameter UI Range mode is the default display mode. It displays the channels at their regular values.

Animation Range

The Animation Range mode normalizes all of the displayed channels so that their values are between 0 and 1. When you have channels that differ widely in their range of values (for example, one channel that varies between 0 and 2, and another that varies between -50 and 50), this option helps to see the relative changes on the different channels.

Animation Range with Offset

The Animation Range with Offset mode normalizes all of the displayed channels so that their values are between 0 and 1 (similar to the Animation Range mode), and stacks the different channels vertically in the graph so that the individual channels are easier to see.

Toggle Multi Graph Display Mode

Provides options for displaying channels in separate graphs within the graph display space.

Note

By default, this option is set to display the selected channels overlapping on one graph. You need to click this button to display the channels separately. When the button is toggled, the icon will change to display the selected number of graphs (for example, for 1 graph, for 6 graphs).

At the default setting, the graph always displays the channels overlapping, regardless of the number of graphs you select from the options.

this button to set the number of graphs displayed from 1 to 6. If you set the graph to display, say, 3 channels, and you select 6 channels in the channel list, then the graph will only display the first 3 channels that are selected.

Channels overlapping on one graph
Channels displayed on 6 graphs

Hide All Handles

Show All Handles

Show Selected Handles - Only show the frame (time mark), value, slope, and acceleration handles of the selected keyframe(s).

Show Value Handles

Show Channel Names

Show Slope and Acceleration Handles

Show Time Mark Handles - Shows the frame handles.

Show Segment Handles - If turned off, the curve segments are shown as dotted lines.

Enable Channel Snapshots

Show Time Group Handles

Show Frame Numbers

Show Value Numbers

Channels menu

Set Keyframes at Current Time

Adds keyframes to the selected channels at the current time.

Sample Values at Current Time

Copies the values of the parameters at the current time to the clipboard. Move to a different time and choose Paste Sampled Values at Current Time to use the same values at another frame.

Paste Sampled Values at Current Time

Pastes the values copied with Sample Values at Current Time.

Import Channels

Opens a dialog to load previously saved animation data from Export Channels into the parameters that are currently displayed.

Export Channels

Opens a dialog that allows you to save the data from the displayed channels.

Edit Channel Properties

Brings up a window that allows you to set various properties of the selected channels, including the channel alias, the channel behavior before the first segment and after the last segment, the auto-key and auto-select flags, and the channel colors displayed in the graph.

Isolate Channels

Displays only the channels with selected keys/handles.

First select any keys/handles in the graph. Then select Isolate Channels or press lowercase I while hovering over the graph to display only the channels with the selected keys/handles. These channels will also show as selected in the channel list (parameters will be highlighted orange).

You can further isolate channels by selecting any keys/handles from the already isolated list of channels, and pressing lowercase I again.

Revert Isolate Channels reverses the actions of Isolate Channels. Selecting and deselecting channels using Isolate Channels and Revert Isolate Channels acts as a stack (see Revert Isolate Channels below).

Revert Isolate Channels

Reverses the actions of Isolate Channels. You can also perform this action by pressing SHIFT + I while hovering over the graph.

Selecting and deselecting channels using Isolate Channels and Revert Isolate Channels acts as a stack. For example:

  1. Start with 9 channels displayed in the graph.

  2. Isolate 4 channels by selecting the keys/handles from 4 channels and pressing I. Only the 4 channels will be displayed.

  3. Further isolate 1 channel by selecting the keys/handles from one of the remaining 4 channels, and pressing I. Only the 1 channel will be displayed.

  4. Revert isolate channels by pressing SHIFT + I. 4 channels will be displayed.

  5. Revert isolate channels again by pressing SHIFT + I. The original 9 channels will be displayed.

The video below shows this example in action:

Isolate and revert isolate channels

Edit menu

Cut/Copy/Paste

Cuts, copies, or pastes all selected handles using the Paste Settings.

Paste Settings

Channel copy and paste works by storing the selected handles in a temporary file. The animated range, channel names, full paths, and row order of the currently displayed channels are also stored in the file. This information can be used to perform a mapping between the copied channel list and the target channel list.

Using Channel Names

Channel mapping is performed based on channel names. This works well for transferring animation between 2 nodes of the same type with the same parameter layout.

Note

Use this with caution when copying multiple transform nodes at the same time, as it will only paste the first occurrence of the channel name.

Using Full Paths

Channel mapping is performed based on full paths. This works well when doing copy/paste to and from the same channels. It will behave correctly even if the list of channels is changing. This mode will not allow copy/paste between different channels.

Using Row Order

Channel mapping is performed using the row order in the displayed channels at the moment of the copy operation and the row order at the moment of the paste operation. It counts parameters without valid channels to make it possible to copy/paste to a node without any channels, or to a node with a different set of channels.

At Current Time

Paste the copied handles at the current time.

At Original Time

Paste the copied handles at their original time.

On Parameters with Existing Channels

Paste only on parameters with existing channels.

On All Parameters

Paste on all the displayed parameters, creating missing channels.

Delete

Deletes the selected channels.

Select All Handles

Selects all the handles on the displayed channels.

Select No Handles

Clears the handle selection.

Invert Handle Selection

Selected handles become unselected. Unselected handles become selected.

Snap Selected Keys to Nearest Frame

Each selected key is rounded in time to the nearest integer frame.

Tie/Untie

Tie locks the left and right slope/value handles together (changing one side changes the other). When the handles are untied, you can alter the left and right handles independently.

To tie/untie the slope handles, select one side of the slope handle and choose this option.

To tie/untie both the slope and value handles, select the slope and value handles together by dragging the area around the key, then choose this option.

You can also tie/untie the slope and value handles by clicking Tie Handles, Untie Handles, Tie Values and Untie Values on the top toolbar.

Note

Tied slope handles are displayed as a solid line. Untied slope handles are displayed as a dotted line.

For a keyframe with its slopes set to automatic (see the Set Selected Slopes to Manual/Automatic option), tied value handles are displayed as one diamond at the keyframe, and untied value handles are displayed as two adjacent diamonds at the keyframe.

Slopes set to automatic - left keyframe slope and value handles are both tied, right keyframe slope and value handles are both untied

For a keyframe with its slopes set to manual, tied value handles are displayed as a square at the keyframe, and untied value handles are displayed as two half diamonds at the keyframe.

Slopes set to manual - left keyframe slope and value handles are both tied, right keyframe slope and value handles are both untied

Note

If one side of a keyframe has a manual slope, and the other side has an automatic slope, the slopes will be untied.

Set Selection to Default Values

Sets the values of the selected keys to their default values (depends on the parameter values).

Set Selected Slopes to Zero

Sets the selected slopes to have a value of 0 (ie. horizontal).

Set Selected Slopes to Manual/Automatic, Toggle Selected Slopes Mode

Sets an auto-slope flag that controls the slope orientation going into and coming out of a keyframe.

When the auto-slope flag is set to automatic, Houdini automatically adjusts the slope orientation of the keyframe depending on its position in relation to its adjacent keyframes, i.e. as you move the keyframe or its adjacent keyframes, the slope orientation changes.

When the auto-slope flag is set to manual, the slope orientation at the keyframe stays the same regardless of how the keyframe is positioned in relation to its adjacent keyframes, i.e. as you move the keyframe or its adjacent keyframes, the slope orientation stays the same.

If the key for a channel is at a local minimum or maximum, the slope at that key will be set to 0.

Select the key handles by dragging the area around the key, or selecting the individual slope handles. Then choose one of Set Selected Slopes to Manual/Automatic to set the auto-slope flag, or toggle the flag (Toggle Selected Slopes Mode).

You can also set the auto-slope flag by clicking Set Selected Slopes To Manual or Set Selected Slopes To Automatic on the top toolbar.

Note

Keyframes with their slopes set to automatic are drawn as diamonds. Keyframes with their slopes set to manual are drawn as squares.

In the below video, the slope of the left keyframe is set to automatic (keyframe is drawn as a diamond), and its slope orientation is automatically adjusted when the right keyframe is moved down.

Orientation of automatic slope is automatically adjusted

In the below video, the slope of the left keyframe is set to manual (keyframe is drawn as a square), and its slope orientation stays the same when the right keyframe is moved down.

Orientation of manual slope is not changed

Smooth Selected Slopes

Sets the value of the selected slopes so that there is no overshoot at the keyframes. If the key for a channel is at a local minimum or maximum, the slope at that key is set to 0. All other slopes are given an approximate value that results in a smooth transition between its adjacent keys. Smoothing also normalizes the acceleration values.

Overshoot at keyframe
After Smooth Selected Slopes

Set Selected Segments to

Allows you to change the segment function. See functions for more information.

Filter Euler Rotations of Selected Channels

The Euler filter fixes bad rotation interpolations that occur when animating rotations using Euler angles over large angles. A common issue is the rotation flipping the wrong way between keyframes.

To apply the filter, select any handle on all 3 rotation channels and apply the filter. The filtering operation is applied to all of the channels that have a selected handle, and it affects the whole channel. The rotation order on the object node affects the filtering operation. (The rotation order is found in the the right drop-down menu of the Transform Order parameter of an object node.)

The filter should only be used on rotation channels. Rotations from multiple objects can be filtered at the same time.

Match Keyframes of Selected Keys

Creates missing keyframes on channels at the selected keys. This ensures that the selected channels have matching keyframes at the same frame.

In the example below, drag to select all of the displayed keyframes on the green and red channels. Then choose Edit ▸ Match Keyframes of Selected Keys.

Original keyframes
Added keyframe on the green curve after match keyframes

Reduce Keyframes of Selected Segments

Opens a window with options to perform a cubic curve refitting on the selected segments after applying a default resampling operation. Refitting reduces the number of keyframes while trying to keep the same curve shape.

Segment expressions and CHOP exports can be baked to keyframes. Keyframes can also be set on animation that is cycled (repeated) if you provide a frame range that is outside the first and last keyframes of the channel.

Refit Segments

Preserve Extremas

When turned on, preserves the local minimas and maximas.

Smooth Slopes After Refit

When turned on, applies auto-slopes to the segments after refitting.

Set Bezier Function on Segments

When turned on, forces the segments to be Bezier segments even if the refitting creates cubic curves.

Resample First

When turned on, performs resampling before refitting. When turned off, does not perform resampling before refitting.

Tolerance

When keyframes are closer than this value in frames, they are merged.

Override Range from Selected Segments

Enable

Turns on/off the explicit range. When turned off, the channel ranges come from the selected segments. When turned on, the channel range is overridden by the start and end values. This is useful for baking channel extrapolation, CHOP exports, and expressions.

Start/End Frames

Defines the start and end frame range to use when Enable is turned on for Override Range from Selected Segments.

Enable Preview

When turned on, shows a preview of the refitting operation in the graph view.

Bake CHOP Exports to Channels

Defines what to do when a parameter is driven by a CHOP export.

Off

Don’t bake CHOP exports.

Bake, Keep Export Flags

Performs the baking but leaves the CHOP export flag in place. The parameter is still driven by the CHOP export, but the baked animation is present on the channel.

Bake, Disable Export Flags

Performs the baking and disables the CHOP export flags on all the CHOP nodes. This does not take into account the possibility that the CHOP nodes can be exporting to other parameters. Use this only when you know that you are baking all the channels exported from a CHOP node.

Bake, Create Delete CHOPs and Move Export Flags

Performs the baking and creates Delete CHOP nodes to disable the exported channels individually.

Bake Keyframes of Selected Segments

Opens a window with options to perform a cubic curve resampling on the selected segments. Resampling adds keyframes without changing the curve’s shape.

Resampling allows segment expressions and CHOP exports to be baked to keyframes. Keyframes can also be set on animation that is cycled (repeated) if you provide a frame range that is outside the first and last keyframes of the channel.

Resample Segments

Rate (at every frame)

Adds keyframes at every n frames or fractional frames.

Tolerance

While resampling, when keyframes are closer than this value in frames, they are merged.

Override Range from Selected Segments

Enable

Turns on/off the explicit range. When turned off, the channel ranges come from the selected segments. When turned on, the channel range is overridden by the start and end values. This is useful for baking channel extrapolation, CHOP exports, and expressions.

Start/End Frames

Defines the start and end frame range to use when Enable is turned on for Override Range from Selected Segments.

Enable Preview

When turned on, shows a preview of the resampling operation in the graph view.

Bake CHOP Exports to Channels

Defines what to do when a parameter is driven by a CHOP export.

Off

Don’t bake CHOP exports.

Bake, Keep Export Flags

Performs the baking but leaves the CHOP export flag in place. The parameter is still driven by the CHOP export, but the baked animation is present on the channel.

Bake, Disable Export Flags

Performs the baking and disables the CHOP export flags on all the CHOP nodes. This does not take into account the possibility that the CHOP nodes can be exporting to other parameters. Use this only when you know that you are baking all the channels exported from a CHOP node.

Bake, Create Delete CHOPs and Move Export Flags

Performs the baking and creates Delete CHOP nodes to disable the exported channels individually.

Smooth Selected Channels

Apply smoothing to selected channels by removing unwanted jitter and noise.

Note

This window’s options provide the same functionality as the SmoothMotion SOP node.

Filter Type

Specifies the type of low-pass filter to smooth the channels with. Currently only the Butterworth Filter is available.

Cutoff Frequency

Sets the cutoff frequency for the filter. Frequencies higher than this value are filtered out/removed on the output.

Filter Order

Sets the order of the filter. This determines how steeply the filter curve rolls off after the cutoff frequency. Higher values correspond to a steeper roll off.

Range

Determines the channel range to apply the smoothing.

Full Channel

Apply the filter to the full channel.

Selection Only

Apply the filter only to the selected portion of the channel.

Playbar Range

Apply the filter only to the range specified in the playbar.

Sampling Rate

Specifies the samples per second. Keys are added to channels at this sampling rate.

Resample Keys

When turned on, resamples the keys when smoothing channels. When turned off, preserves the existing key times.

Snap Keys

When turned on, any keys at fractional frames are moved to integer frame values.

View menu

Home Channels (Current Graph/All Graphs)

Pans and zooms the graph to show all the keys in the current graph or in all the graphs.

Home Playback Range (All Graphs)

Zooms the graphs to the playback range, which is between the start and end frames shown on the playbar.

Home Global Range (All Graphs)

Zooms the graphs to show the .hip file’s global animation range, see playbar.

Frame Selection

Zooms the graphs to show only the selected keys.

Horizontal/Vertical Adapt

When turned on, the graph automatically pans and zooms to keep all horizontal and/or vertical values visible.

Show Box Handle

When turned on, displays handles that allow you to move blocks of keys. You can also turn on this option by selecting a group of keys in the graph and pressing Y, or clicking Box Handle on the top toolbar and selecting a group of keys.

You can drag the edges of the box to translate the group of keyframes from side to side or up and down. The axis is locked, so you can only move the keyframes along one axis at a time. To move along both axes at the same time, hold ⇧ Shift while dragging the edges of the box.

To scale, drag a corner of the box.

Show Box Pivot

When turned on, displays a pivot handle at the center of the box handle. You can also turn on this option by clicking ⇧ Shift + Y in the graph, or clicking Box Handle with Pivot above the graph and selecting a group of keys. Any scaling is done around the pivot location.

To move your pivot, simply drag it to another location. To move it back to the center, click ⇧ Shift + Y + Y. This turns the pivot off and then on again, moving it back to the center.

Show Handles

Choose whether all handles, selected handles or no handles are displayed on the graph. You can also turn on this option by clicking Hide All Handles, Show All Handles or Show Selected Handles on the right toolbar.

Show Values

When turned on, shows the value handles at the keyframes. You can drag the handles to change the parameter value at that keyframe (Value in the toolbar below the graph). If the values at the key are tied together, the value handle is a diamond. If the values at the key are untied, the value handle is two adjacent diamonds. You can also turn on this option by clicking Show Value Handles on the right toolbar.

Show Time Marks

When turned on, shows the short vertical lines (frame handles) indicating the keyframes. You can drag the frame handle left or right to move the keyframe in time. You can also turn on this option by clicking Show Time Mark Handles on the right toolbar.

Show Slopes and Acceleration

When turned on, shows the short lines and round handles indicating the slope and acceleration of segments as they enter and leave a keyframe. You can drag the slope lines and/or acceleration handles to change the shape of the segment (for segments functions that use slopes and/or acceleration). You can also turn on this option by clicking Show Slope and Acceleration Handles on the right toolbar.

When Show Slope and Acceleration Handles is on, and the default segment function is Bezier (default function is set in the animation preferences, Edit ▸ Preferences ▸ Animation ▸ Default Function):

  • Slope and acceleration handles are shown for segments with Bezier, linear, ease, easein, or easeout functions.

  • Only slope handles are shown for cubic segment functions.

  • Dragging the slope/acceleration handles for the linear, ease, easein, and easeout segment functions, or changing their slope/acceleration values on the values toolbar will change the segment into a Bezier function.

When Show Slope and Acceleration Handles is on, and the default segment function is cubic:

  • Only slope handles (no acceleration handles) are shown for segments with cubic, linear, ease, easein, or easeout functions.

  • Slope and acceleration handles are shown for Bezier segment functions.

  • Dragging the slope handles for the linear, ease, easein, and easeout segment functions, or changing their slope on the values toolbar will change the segment into a cubic function.

Note

The default segment function is usually set to Bezier.

See functions for more information on the different types of segment functions.

Tip

If the slope handles are hard to see because they are too short, you can change the length of the slope handles in Settings ▸ Slope Handle Length.

Show Functions

When turned on, allows the selection of segments so that you can change the function that controls their shape. When turned off, the curve segments are shown as dotted lines. You can also turn on this option by clicking Show Segment Handles on the right toolbar.

Show Time Groups

When turned on, shows time groups. A time group is displayed as a vertical yellow line. Keyframes that belong to a time group have a dotted yellow line connecting them to the time group line. Dragging the time group line left or right moves the grouped keyframes in time. You can also turn on this option by clicking Show Time Group Handles on the right toolbar.

Show Time Bar

When turned on, displays a vertical line on the graph that indicates the current frame.

Show Bookmarks

Displays bookmarks as labelled bars in the timebar above the graph, and/or as colored blocks on the graph.

Show Full Channel Names

When turned on, displays the full name of the channel in the graph. For example, box_object1/tx, box_object1/ty, box_object1/tz.

Show Channel Names

When turned on, displays the name of the channel in the graph. For example, tx, ty, tz. You can also turn on this option by clicking Show Channel Names on the right toolbar.

When many channels are displayed, turning off Show Channel Names makes the graph view run significantly faster. Turning off both Show Channel Names and Draw Past Channel Ends further improves performance.

Show Times for Selected Marks

When turned on, displays the frame number for the selected time marks. You can also turn on this option by clicking Show Frame Numbers on the right toolbar.

Show Values for Selected Keys

When turned on, displays the graph value for the selected keys. You can also turn on this option by clicking Show Value Numbers on the right toolbar.

Show Only Attached Time Groups

When turned on, the graph only shows time groups that have visible keyframes attached.

Draw Past Channel Ends

When turned on, draws a horizontal dotted line before the first keyframe and after the last keyframe.

When many channels are displayed, turning off Draw Past Channel Ends makes the graph view run significantly faster. Turning off both Draw Past Channel Ends and Show Channel Names further improves performance.

Draw CHOP exports

When turned on, displays the curves of CHOP exports.

Tools menu

Displays the following sub-panes and toolbars in the graph view:

Left Pane, Channel Groups, Animation Layers, Channel List

Displays/hides the sub-panes to the left of the graph.

Bottom Values Toolbar, Top Timeline, Right Toolbar, Animation Toolbar

Displays/hides the timeline and various toolbars.

Snapshots menu

Snapshots allow you to compare the before and after state of the curve as you make changes to the animation. This can be used to quickly revert a keyframe animation to its previous state.

The current state of the curve is displayed as a solid line. As you make changes to the curve with snapshots turned on, the previous state of the curve (the snapshot) is displayed as a lighter dotted line.

Enable Channel Snapshots

When turned on, creates a temporary copy (snapshot) of the channel every time the keyframe animation changes. You can also turn on this option by clicking Enable Channel Snapshots on the right toolbar.

Persistent Channel Snapshots

When turned on, keeps the snapshot when the channel editor refreshes to show new channels. When turned off, deselecting and reselecting the node clears the snapshot.

Revert Active Channels to Snapshots

Returns the keyframe animation to its snapshot (previous) state.

Swap Active Channels and Snapshots

Switches between the updated channels and the snapshot state. You can also turn on this option by clicking Swap Active Channels and Snapshots on the top toolbar.

Clear Channel Snapshots

Clears the snapshot (accepts the updated curve). You can also turn on this option by clicking Clear Channel Snapshots on the top toolbar.

Time Group menu

A time group is a group of keys that you can easily move through time.

To...Do this

Group keys together in a time group

  1. Select the keys.

  2. Choose Time Group ▸ Create Time Group from Selected Keys.

Make sure you turn on Show Time Group Handles so that the time group line is displayed on the graph.

Add keys to an existing time group

  1. Select the keys.

  2. Hold ⇧ Shift and select the time group line.

  3. Choose Time Group ▸ Attach/Detach Selected Keys to/from Time Group.

Move the keys in a time group together

Drag the yellow time group line left or right.

Move the time group line without moving the keys

Drag the time group line with .

Delete a time group

  1. Click the yellow time group line.

  2. Press ⌦ Del.

Settings menu

Show Audio in Timeline

When turned on, a graphical representation of the currently loaded audio source is shown in the bottom portion of the graph.

Synchronize Group Selection From Channel List

When turned on, adjusts the channel group selection to match the current channels.

Grid Line Density

Choose the density of the grid or turn the grid off.

Slope Handle Length

Allows you to set the length of the slope handles in the graph. The preset lengths are short, medium, and long. You can also set a custom length by choosing Custom.

Curve Quality

Choose the accuracy of the curves. Lower levels of detail can be faster for very complex graphs. The Straight Lines option does not draw curves, just lines connecting keyframes.

Add Keys

Customizes the behavior in the graph when Alt + is used to create keys. If set to At Mouse Click Position, the new key on the channel is created at the value where the mouse is in the graph. If set to At Curve Value, the key is created at the current value of the channel.

Middle Mouse Interaction

Determines how the interacts with the graph. For the default option Move Keys if Selected, Pan Otherwise:

  • If keys are selected, dragging anywhere in the graph moves the selected keys along one axis, depending on the direction the keys were first moved.

  • If no keys are selected, dragging pans the view.

Toggle Auto-Slope Mode Preference

Toggles the auto-slope preference, which determines whether new keys are created with an automatic slope or an existing slope. See the Set Selected Slopes to Manual/Automatic option.

When the auto-slope preference is set to automatic, new keys that are added to the curve will change the shape of the curve (because Houdini automatically calculates the slope of the key based on the location of the adjacent keys). When the auto-slope preference is set to manual, new keys that are added to the curve will not change the shape of the curve (the slopes of the new keys will be tangent to the curve).

Snap Moved Keys to Nearest Frame

When turned on, keys that are moved in the graph are always moved to an integer frame value in time. You can also turn on this option by clicking Snap Moved Keys on the top toolbar.

Snap Scaled Keys to Nearest Frame

When turned on, keys that are translated and scaled in the graph (i.e. using the box handle) are always moved to an integer frame value in time.

Bold Non-Integer Keys

When turned on, keys at non-integer frame values in time are drawn in bold and white.

Keep Acceleration Ratios

When turned on, adjusting the acceleration handle on one end of the key also adjusts the acceleration handle on the other end. You can also turn on this option by clicking Keep Acceleration Ratio on the top toolbar.

Value/Time Handles

When turned on, you can drag and move the key in time and value (X and Y). This is the same functionality as holding ⌃ Ctrl and dragging the key. When turned off, the key can only be moved in Y.

Reset Channels Settings

Resets all channel settings to their factory default settings.

Values toolbar

Frame, key value, slope and acceleration fields

The frame, key value, slope and acceleration fields below the graph display information about the selected keyframe/handle. If more than one key or time group is selected, the field displays ---, and editing the field sets the value for all selected keys/handles.

Frame

The frame number of the selected key or time group.

Value

The numeric representation of the selected key’s in or out value.

Slope

The slope of the selected key’s in or out line. This is only valid for functions that use slope values, such as cubic.

Accel

The acceleration of the selected key’s in or out line. This is only valid for functions that use acceleration values, such as bezier.

To...Do this

Change the values of the fields

  1. Select the handle, or select multiple keyframes/handles by dragging in the graph.

  2. Type the new value directly in the field text box and press ENTER.

    or

    Hover over the field, click to bring up the value ladder, and drag to adjust the field value.

Tip

You can do simple addition (+), multiplication (*), and division (/) on the current value of the field. Replace the current value with, for example:

+ 1.25

…and press Enter.

To subtract, add a negative number, for example:

+ -0.5

Function field

Houdini uses a segment’s function to determine the curve’s behaviour between keyframes. Choose a function from the Function drop-down menu, or type an expression directly in the text box. All of the channels in Houdini are Bezier by default.

Tip

You can set the default curve function for new keyframes in the animation preferences (Edit ▸ Preferences ▸ Animation under Initial Segment).

Function Effect

constant

Uses the in value for the entire segment, and jumps to the out value at the end.

linear

Generates a straight line between the in and out values, animating the value with uniform speed along the segment.

ease

Generates motion that gently accelerates the value at the beginning of the segment and decelerates at the end. The value starts the animation at rest and ends at rest.

easein

Generates motion that gently accelerates the value from rest at the beginning of the segment and continues accelerating until the end.

easeout

Generates motion that gently decelerates the value to rest at the end of the segment.

easep(2) easeinp(2) easeoutp(2)

These are fundamentally the same as the ease functions, but are raised to the power of 2, resulting in steeper slopes.

You can manually change the power in the Function text box (for example, to 3, 4, 5, etc.) to further increase the slope of the curve.

match

Makes the slope of the out curve equal to the slope of the in curve.

For example, if you change a segment to match, the slope at the segment start point is adjusted to be the same as the slope of the previous segment’s end point.

matchin, matchout, vmatch, vmatchin, vmatchout

See the expression reference pages for these functions.

cubic

Gives you control over the in and out slope.

bezier

Gives you control over the in and out slope and acceleration.

spline

Fits a piecewise polynomial function between the keyframes of consecutive selected segments.

qlinear

Generates a spherical linear interpolation in quaternion space between the in and out values. This function is intended for rotation channels and is the default for rotation channels.

Make sure all three rotation channels use qlinear() and all have keys at the same frames.

Segments with quaternion interpolation are displayed as straight lines in the graph, because their intermediate values expressed as Euler angles are mostly meaningless. You can use the expression qlinear() + 0 to fool the graph editor into showing the actual values.

To perform a quaternion-based interpolation between two key frames, the qlinear() function needs to know the three Euler angles. It does this by figuring out what the neighboring channels are, looking for channels ending with x, y, or z, or channels ending with a number. Thus, “rx ry rz” would be one group, and “test0 test1 test2” would be another group.

cycle

Repeats the curve values from the range start_frame to end_frame in the Function text box expression, cycle(start_frame, end_frame).

If the range is longer than the selected segment, only the beginning of the range is used. If the range is shorter than the selected segment, the copied values are repeated throughout the length of the segment.

cycleoffset

Repeats the curve values from the range start_frame to end_frame in the Function text box expression, cycleoffset(start_frame, end_frame), with the selected segment starting at the last value of the previous segment.

If the range is longer than the selected segment, only the beginning of the range is used. If the range is shorter than the selected segment, the copied values are repeated throughout the length of the segment, with each repeated section having its first value set to the last value of the previous section.

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