Houdini 22.0 Nodes Copernicus nodes

Curve Animate 3D 1.0 Copernicus node

Lets you interactively draw and animate Bézier curves using tools similar to 2D illustration programs, as well as polylines and NURBS.

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Since 22.0

Overview

This node’s interactive state lets you draw and edit cubic Bézier curves using tools similar to 2D illustration programs like Illustrator, Sketch, and InkScape. This is useful for drawing artistic curves by hand. For example, tracing images, drawing logos, drawing profile curves to extrude, and revolve.

This node also includes an Auto-Bézier point type, similar to Illustrator’s Curvature tool, which lets you guide a curve by placing edit points without having to worry about tangents.

You can also draw polylines, non-cubic orders of Bézier curves, and NURBS. However, when you are drawing these other types, you click to place each point and Houdini interprets the point according to the curve type, without the special support for drawing tangents you get when drawing cubic Bézier curves.

Terms

Edit points

Also called on-curve points or anchor points. In a Bézier curve, the curve passes through these points.

Tangent handles

Also called control points. In a cubic Bézier curve, these control the direction of the curve going into and coming out of an edit point.

Corner point

An edit point where the tangents have zero length or point in different directions, causing a sharp corner. This is sometimes called having broken tangents.

Smooth point

An edit point where the node keeps the tangents together in a line, so the curve has smooth tangent continuity as it goes through the point.

Balanced point

An edit point where the node keeps the tangents together in a line and also enforces that the tangent points are equal distance from the edit point. This makes the curve have smooth curvature continuity as it goes through the point.

Auto Point

An edit point where the tangents are automatically computed based on the positions of surrounding points and tangents to create a smooth curve. Specifically, the control vertices are computed such that the curve is continuous in both its first and second derivatives (direction and curvature) through these points.

Branch point

An edit point containing multiple vertices.

End Point

An edit point at either end of an open curve.

Tools

While the Curve tool’s state is active, you can be in one of four tools: the Edit tool, the Draw tool, the Orient tool, or the Scale tool. The buttons for these tools are in the operation toolbar across the top of the viewer when the node’s state is active, or you may cycle through them with the F/Shift+F hotkeys.

Using the interactive state

  • With the Curve node selected, click the Handles tool (to the left of the viewer), or move the mouse over the viewer and press Enter.

Note

In Houdini, pressing ⎋ Esc will switch from the active viewer state to the View tool. This can be confusing if you meant to cancel drawing. To get back to the Handles tool (and the curve animate node’s state), make sure the Curve Animate node is still selected, move the mouse over the viewer, and press Enter.

  • The handle in the Curve Animate state is automatically shown or hidden based on the current tool and the selection. By default the handle is turned off. To enable the handle, enable Show Handle in the settings HUD or the parameter pane.

Drawing Bézier curves

In Draw tool, click or drag in empty space to start a new curve, or click/drag the start or end point of an existing curve to continue drawing the curve. Choose the type of anchors to place with the Draw Type parameter in the Draw tab of the settings HUD or the equivalent parameter in the parameter pane.

To...Do this

Place a retracted corner point

  • Click to place a corner point.

Place a smooth point

  • Press to place the point and without releasing the mouse button, move to drag out tangent handles.

Create a straight segment

  • Hold ⌃ Ctrl + ⇧ Shift to straighten the current segment.

Switch from a straight line to a smooth curve

  • Hold ⌃ Ctrl and press to place a point, then drag out the outgoing tangent handle.

Draw two curve segments connected by a corner (broken tangents)

  1. Press to place the point, and without releasing the mouse button, move to drag out tangent handles.

  2. With the mouse button still down, press ⌃ Ctrl to freeze the incoming tangent, so you are now only dragging the outgoing tangent.

    (You can release ⌃ Ctrl to go back to dragging the tangents together.)

  3. Drag the outgoing tangent to where you want, then release the mouse button.

Edit points while drawing

  • Press ⌦ Del to delete the previous point.

  • Click to pick points and select them, then perform an option on the selected point from the operation toolbar.

  • Drag anchor points to move them.

Begin drawing from branch point

  • Click an existing mid point of a curve to create a branch point and begin drawing a new curve from it.

    or

  • CTRL + Click on a curve segment to insert a point into the curve. Then to create a branch point at the inserted point and begin drawing from it.

Finish the curve

  • Click the start point to close the curve. You can also drag to edit the tangents on the point.

    or

  • Click Close Curve on the toolbar to automatically connect the previous point to the first point.

    or

  • Press Enter to finish drawing the (open) curve.

    or

  • Press ⇧ Shift + Enter to finish drawing the curve and close it.

    or

  • Switch to the Edit tool.

Draw on a surface geometry

  1. Template the surface geometry.

    To visualize the templated surface while snapping, change the Draw tool for Template Model Geometry to Hidden Line Invisible.

    This option is in the Display Options dialog, Markers tab, then set Set display options for to Template Model Geometry.

  2. Turn on Primitive Snapping on the left side of the viewport.

    Optionally, turn off the Current Geometry to prevent snapping to the curve itself.

  3. Draw points on the surface of the templated geometry.

Drawing with Auto-Bézier points

When drawing Auto-Bézier points, you can only click to place points (there are no tangent handles). The relative placement of the points controls the direction and curvature of the curve. The preview shows the new shape of the curve if you add a point at the current pointer location.

With some practice, you can learn how to place points (closer together or farther apart) to control the curve’s turning speed and its shape.

To...Do this

Add a point

  • Click to add a smooth point.

  • Hold Ctrl+Shift to place a straight line segment and convert the previous auto point into a corner.

  • Hold ⌃ Ctrl and drag to place a corner and drag the outgoing tangent before beginning the next segment.

Finish the curve

  • Click the start point to close the curve. (You can also drag to edit the tangents on the point.)

    or

  • Click Close Curve on the toolbar to automatically connect the previous point to the first point.

    or

  • Press Enter to finish drawing the (open) curve.

    or

  • Switch to the Edit tool.

Editing curves

To...Do this

Select a point or points using the Edit tool

  • Click a point to select it.

  • Drag a selection box around multiple points to select them.

  • Click a curve segment to select the edit points at the start and end of the segment.

  • Hold ⇧ Shift and click a point to add it to the selection.

Make a smooth point into a corner (break tangents)

  • Click a point to show its tangent handles.

  • Hold ⌃ Ctrl and drag one of the tangent handles to move it independently of the other.

Change points from corner to smooth to balanced

  1. Click a point to select it.

  2. Do one of the following:

    • Click Make Corner in the toolbar, or press 1.

    • Click Make Smooth in the toolbar, or press 2.

    • Click Make Balanced in the toolbar, or press 3

Reshape a Bézier curve

Do any of the following:

  • Select a point to show its tangent handles. Drag a tangent handle to change the direction and speed of the curve going into or out of the point.

  • Press on a curve segment (between edit points) and drag. The node will manipulate the tangents to shape the curve interactively as you drag it.

  • Drag the line connecting the tangent handles to rotate the tangents without affecting their distances from the point.

  • Select a curve segment and click the Make Straight button in the toolbar.

Move a point

  • Select a point and drag it to move it.

Move a point in 3D space

  1. Select the point.

  2. Press T, R, or E or enable Show Handle in the settings HUD G to show the transform handle.

  3. Use the handle to move the point in 3D space.

Move an entire curve

  • Hold ⇧ Shift and drag the curve.

Insert a point in the curve

  • Hold ⌃ Ctrl and click the curve where you want to insert the new point.

Cut a curve at a point

  1. Select the point you want to cut at the curve.

  2. In the toolbar, click Cut Curves at Selected Points.

Join two open endpoints

  1. Select two endpoints.

  2. In the toolbar, click Join Selected Points

Join two open endpoints with a line

  1. Select two endpoints.

  2. In the toolbar, click Add Segment Between Endpoints.

Fuse two points into a branch point

  1. Select two points.

  2. In the toolbar, click Fuse Branch.

Split a branch point into independent points for each vertex.

  1. Select a branch point.

  2. In the toolbar, click Split Branch.

Delete a point

  1. Select the point.

  2. Click Delete Point in the toolbar, or press ⌦ Del.

    If Approximate Bezier Shape on Delete is enabled, the node reshapes the curve to try to approximate its previous shape without the deleted point.

Delete a curve segment

  1. Select a segment in the curve.

  2. In the toolbar, click Delete Segment.

Reverse a curve

  1. Select one or more points on the curve.

  2. Click the Reverse button in the tooblar.

Convert a curve to a different type

  1. Select one or more points on the curve.

  • In the toolbar or right click menu, click To Polygon Hull to convert a NURBs Curve or Bezier Curve to a polygon by reinterpreting the control vertices.

  • In the toolbar or right click menu, click To Resampled Polygon to convert a NURBs Curve or Bezier Curve to a polygon by resampling the curves. The number of divisions per span is specified by Resample Divs.

  • In the toolbar or right click menu, click To Bezier to convert a NURBs Curve or a Polygon to a Bezier Curve. When converting from Polygon, if Match Polygon Shape when Converting is enabled, the resulting Bezier will match the polygon shape by inserting extra control vertices, otherwise it will reinterpret the polygon as a Bezier curve.

  • In the toolbar or right click menu, click To NURBS to convert a Bezier Curve or a Polygon to a NURBs Curve. When converting from Polygon, if Match Polygon Shape when Converting is enabled, the resulting NURBs Curve will match the polygon shape by inserting extra control vertices, otherwise it will reinterpret the polygon as a Bezier curve.

Clear all curves

  • In the parameter editor, click Reset All Changes.

    or

  • Click the Edit tool, select all points, then press ⌦ Del.

Set colors on curves

  • Select one or more points on each curve you want to change the color of.

  • In the toolbar click or in the right click menu click Set Curve Color under Utility.

  • In the color selection dialog choose the color you wish to apply and press OK.

Set names on curves

  • Select one or more points on each curve you want to name.

  • In the right click menu click Set Selected Curve Names under Naming.

  • In the shown naming dialog, click into the string field beside each numbered primitive to begin editing its name.

    If the curve already had a name, the value in the field will be set to the current name when the dialog is opened.

  • Press OK to apply the new names after editing.

Copy and paste curves

  • Select one or more points on each curve you want to copy.

  • Press Ctrl+C to copy the curves.

  • Press Ctrl+V to paste the copied curves.

    Pasted curves will be centered on the position on the Edit Plane under the cursor in the viewport.

    If any pasted curves have animated points, the offset when pasting will also be applied to any affected position channels.

Creating an Orient Attribute

In the Orient tool, you can specify target orientation on anchor points by specifying a target Up vector. Attributes for the orientations are then created to smoothly transition in and out of the specified orientations. The resulting attributes use a parallel transport along the curve to determine the orientation for all other points.

To output the orient or axis attributes, turn on Output Quaternion, Output X Axis, Output Y Axis, or Output Z Axis. When any orientation have been created, guide geometry is drawn on curves in the viewport to visualize the attribute. The guide geometry can be shown or hidden with the Show Guide parameter, you can decide which components to show with Guide Components, and the scale of the swept Gnomons for the guides can be customized with Guide Scale.

When in the orient tool, interactive gadgets are available on each of the selected points with a target orientation. By dragging these gadgets, you can rotate the frame around the curve tangent at the point.

To...Do this

Add a target orientation point

  • Select one or more anchor points and press A or Create Up Point in the right click menu.

Remove a target orientation point

  • Select one or more target orientation points and press ⌦ Del or Remove Up Point in the right click menu.

Change all selected orientation points

  • Select one or more orientation points.

  • Enable Change all Selected in the Orient and Scale HUD settings and drag the rotation handles in the viewport.

Creating a Radius Attribute

In the Scale tool, you can specify target scales on anchor points by specifying target Scale values. A pscale attribute is then created to smoothly transition in and out of the specified target scales. The resulting attribute is then interpolated between target scales to determine the values for all other points. To output the scale attribute, enable Radius Attribute.

When any scales have been created, guide geometry can also be drawn on the curve in the viewport to visualize the attribute. The guide is shared between the orientation and scale tools, showing the orientations and scale factors along the curves. The guide geometry can be shown or hidden with the Show Guide parameter, you can decide which components to show with Guide Components, and the scale of the swept Gnomons for the guides can be customized with Guide Scale.

When in the scale tool, interactive gadgets are available on each of the selected points with a target scale. By dragging these gadgets you can increase or decrease the scale value at a particular point.

To...Do this

Add a target scale point

  • Select one or more anchor points and press A or Create Scale Point in the right click menu.

Remove a target scale point

  • Select one or more target up points and press ⌦ Del or Remove Scale Point in the right click menu.

Change all selected scale points

  • Select one or more scale points.

  • Press [ or ] to increase or decrease the scales by a fixed amount set by the Handle Scale Step in the extra state parameters P.

    or

  • Enable Change all Selected in the Orient and Scale HUD settings and drag the scale handles in the viewport.

Animating a Curve

To...Do this

Keying a point on a curve

  • Disable Synchronize Keys per Curve if you do not want all points on the curve to be keyed.

  • Press K or click Set Keyframe in the right click menu.

Keying all points on a curve

  • Select all points on the curve, then press K

    or

  • Enable Synchronize Keys per Curve, select any number of points on the curve, then press K

Create animation on a point

  • With the point selected, press K if the point does not yet have channels.

  • Move the playbar to a different time.

  • Press K to insert a new keyframe, then edit the curves in the Animation Editor panel.

    or

  • Drag the point in the viewport to automatically create a new keyframe.

Animating the orientation or scale

  • With an orient or scale point selected, press K to create channels if they do not yet exist.

  • Move the playbar to a different time.

  • Press K to insert a new keyframe, then edit the upx/upy/upz/pscale channels in the Animation Editor panel.

    or

  • Drag the orientation/scale gadgets in the viewport to automatically create a new keyframe with the adjusted values.

Remove a keyframe from the selected points

  • Click the keyframe in the playbar and press ⌦ Del.

    or

  • Select the keyframe in the Animation Editor and press ⌦ Del.

    or

  • Click Remove keyframe in the right click menu of the viewer state.

Remove channels from the selected points.

  • Click Remove All Keys in the right click menu of the viewer state.

  • Click Ok on the pop up to confirm that you want to remove the channels from the selected points.

Change channel names on the selected points

  • In the right click menu of the viewer state, click Set Selected Point Channel Names under Naming.

  • In the shown naming dialog, click into the string field beside each numbered point to begin editing its name.

    The value in the field will be set to the current channel name when the dialog is opened.

  • Press OK to apply the new names after editing.

    Note that spaces are not allowed in channel names and will be automatically replaced with underscores when renaming.

Operation toolbar

Tools

F/Shift+F

The top level tools available in the state.

Edit Tool

Edit curves, drag points and drag tangents.

Draw Tool

Create new curves or extend existing curves.

Orient Tool

Create orientation attributes on the curves.

Scale Tool

Create pscale attributes on the curves.

Delete Points

⌦ Del

Remove selected points from curves.

Join Points

Join two selected end vertices into a single vertex.

Cut Points

Split one vertex into two end vertices.

Fuse Branch

Fuse two or more points into a single branch point.

Split Branch

Split a branch point into multiple points.

Delete Segment

Remove a segment from a curve, leaving two open end vertices.

Join Segment

Join two open end vertices by adding a new curve segment between them.

Close Curves

Close curves by inserting new curve segments between their open end vertices.

Reverse Curves

Reverse the vertices in the selected curves.

Corner

1

Convert the selected bezier points into corner points where the tangents are untied.

Smooth

2

Convert the selected bezier points into smooth points where the tangents are colinear.

Balance

3

Convert the selected bezier points into balanced points where the tangents are symmetric.

Auto

4

Convert the selected bezier points into auto points where the tangents are automatically computed to provide continuity in the first and second derivatives through the point.

Retract Points

Make the tangents attached to the selected points zero length.

Expand Points

Expand out any retracted tangents on the selected points.

Straigthen Segment

Move the tangents on the selected segments to make them straight lines.

Flatten to Edit Plane

Flatten the selected points and tangents to the current edit plane.

Space on Circle

Space all the points on the selected curves around circles.

Evenly Space

Evenly space the selected points.

Relax

Relax the selected points.

Straighten

Project the current selection along a straight line.

Set Curve Color

Change the colors on selected curves.

To Polygon Hull

Convert the selected Bezier and NURBs curves to their polygon hull.

To Resampled Polygon

Convert the selected Bezier and NURBs curves to resampled polygons. The number of divisions is controlled by Resample Divs.

To Bezier

Convert the selected curves to Bezier curves.

To NURBs

Convert the selected curves to NURBs curves.

Shortcut reference

C

Show a radial menu with the commonly used tools and actions.

K

Key selected points and create channels if they do not yet exist. If Synchronize Keys per Curve is enabled, all points on the curves with selected points will be keyed.

F/Shift+F

Cycle forward or backward through the top level tools.

Draw Tool

Enter while drawing a curve

Finish drawing the curve.

⇧ Shift + Enter while drawing curve

Finish drawing curve and close it.

⌃ Ctrl + ⇧ Shift

Hold to create a straight line segment while drawing Bézier curves.

⌃ Ctrl + Drag

Start curved segment after straight segment.

⌃ Ctrl while dragging tangents

Freeze incoming tangent handle in place.

A

Hold to create an arc segment while drawing Bézier curves.

click on existing end point

Continue drawing existing curve from end point, or join the curve to the end point if already actively drawing a curve.

click on existing mid point

Begin drawing new curve from branch point, or create a branch point with this point and continue if already actively drawing a curve.

⌃ Ctrl + click on existing curve

Insert point into existing curve.

Edit Tool

click on curve segment

Select surrounding anchor points.

⌃ Ctrl + drag on anchor point

Re-pull tangent handles and make point type balanced.

⇧ Shift + click curve

Select entire curve.

⇧ Shift + drag curve

Move entire curve.

Drag on curve

Reshape Bézier curve, or move polyline/NURBS segment.

1

Make selected point(s) corner.

2

Make selected point(s) smooth.

3

Make selected point(s) balanced.

4

Make selected point(s) auto.

Drag tangent handle line

Rotate tangent handles without affecting distances.

⌃ Ctrl while moving points/handles

Constrain to vertical, horizontal, or diagonal.

⌃ Ctrl + click on existing curve

Insert a vertex into the curve at the position under the cursor.

Ctrl+C

Copy all curves with any selected points.

Ctrl+V

Paste all copied curves to the world position under the cursor on the current Edit Plane.

Orient Tool

A with selected

Create new target orientation point(s).

⌦ Del with selected points

Remove target orientation point(s).

click point

Show orient handle on target orientation point.

drag circle orientation gadget

Rotate target orientations around curve tangent.

Scale Tool

A with selected

Create new target scale point(s).

⌦ Del with selected points

Remove target scale point(s).

click point

Show orient handle on target scale point.

drag scale gadget

Change target scale on the given point.

Tips and notes

  • In a Perspective viewport, interactive drawing automatically snaps to the plane the view is facing (or, if the construction plane is active, to the construction plane).

    You may want to switch to an orthographic viewport so you can draw on a flat plane without worrying about skew from the camera angle.

  • You can select an edit point or control point and enable Show Handle to show a transform handle to move the point in 3D space.

  • There may be issues with drawing curves in a shaded display mode. The viewer does not do always do a perfect job filling Bezier curves. Even when just drawing polylines, having closed curves be filled/shaded can be distracting. You can press W in the viewer to switch to wireframe mode to view closed curves without shading.

  • You can turn on drag tracers that show the change in position when moving points or tangents in the preferences by turning on Interactive Tools > Show Additional Drag Guides for Interactive States.

  • You can enable Synchronize Keys per Curve to automatically create channels and keyframes on all vertices on a curve whenever any point on that curve is keyed. This is very useful when tracing shapes to ensure all points on the curve are fully keyed so that their positions do not accidentally change when editing a separate keyframe.

Outputs

The output is a set of curve primitives, each created with the Primitive Type and Order that they were created with. Additionally, if there is any animation created, there is an an Animation packed primitive in the output geometry. This Animation primitive stores the collection of geometry channels that store the animation for each point. The points are mapped to their geometry channels with the channel_name attribute on the points and the name attribute inside the Animation primitive which stores a prefix (which point it corresponds to) and a suffix (which animation component it corresponds to).

Parameters

Stashed Geometry

A geometry data parameter storing the current curve geometry and animation.

Reset All Changes

Press to reset all changes and animation.

Apply Keys

Whether to apply geometry channels to the output geometry.

State Settings

General Settings

Live Update Mode

Whether to update the output continuously during interactive drags or only on mouse-up.

Synchronize Keys per Curve

When on, keep keys synchronized across all points on each curve. This will create new keyframes on any channel belonging to points on that curve if another channel on that curve has an existing keyframe at that time.

Edit Plane

The plane that points are placed on and drags are computed with respect to.

Axis Aligned

Use the XY, YZ, or XZ plane that is most orthogonal to the view direction.

View Plane

Use the plane normal to the view direction.

Show Preview Curve

When to show the additional preview drawable. By default it is set to During Interactive Operations which will only show the preview curve while dragging in edit mode or drawing in draw mode. Alternatively, by setting it to Always, you can make this extra drawable always be shown which may be helpful when tracing images or drawing on other geometry.

Edit Settings

Show Handle

Whether to show the handle to control the selected points.

Approximate Bezier Shape after Delete

When deleting points on bezier curves, whether to move the tangents of the resulting segment to best approximate the overall shape from before the deletion.

Match Polygon Shape when Converting

When converting from Polygon to Bezier or NURBs, whether to keep the over all polygon shape by inserting new control vertices, or to instead reinterpret the polygon as the Bezier or NURBs curve hull.

Resample Divs

The number of divisions per span when resampling from Bezier or NURBs to polygon.

Enable Soft Transform

Whether to use soft transform when transforming points in edit mode.

Soft Transform Radius

The soft transform radius applied when transforming points in edit mode.

Draw Settings

Primitive Type

The type of primitive to create when creating new curves in draw mode.

New Anchor Type

The type of bezier anchor points to create when drawing new points in draw mode.

Order

The order of the curves to create when creating new curves in draw mode.

Orient and Scale Settings

Show Orient Guide

When to show the orientation and scale guide.

Orient Guide Components

Which components of the orientation and scale guide to show.

Orient Guide Scale

The scale applied to the orientation and scale guide geometry.

Change all Selected Orientations and Scales

Whether to rotate or scale all selected orient or scale points when dragging the handles in their respective modes.

Output

Output Channel Primitives

Whether to include the Animation data in the output geometry, including the Channel Name Attribute and the Animation packed primitive containing the channel primitives.

Animation Primitive Name

The name given to the animation packed primitive that stores all of the geometry channels that define the curve animation.

Channel Name Attribute

The name of the point attribute on the curves that specifies which geometry channel primitive drives each point’s animation.

Output Corners Group

Whether to output the corner points as a group.

Corner Points

The name of the group to store the corner points in.

Output Smooth Group

Whether to output the smooth points as a group.

Smooth Points

The name of the group to store the smooth points in.

Output Auto Group

Whether to output the auto points as a group.

Auto Points

The name of the group to store the auto points in.

Output Scale Group

Whether to output the scale points as a group.

Scale Points

The name of the group to store the scale points in.

Output Orient Group

Whether to output the orient points as a group.

Orient Points

The name of the group to store the orient points in.

Tangent Type

How to compute the tantent on the curves.

Output X Axis

Whether to output the X axis.

X Axis

The name of the attribute to store the X axis in.

Output Y Axis

Whether to output the Y axis.

Y Axis

The name of the attribute to store the Y axis in.

Output Z Axis

Whether to output the Z axis. This is the vector attribute that stores the tangent as computed by Tangent Type.

Z Axis

The name of the attribute to store the Z axis in.

Output Quaternion

Whether to output the quaternion orient attribute.

Quaternion

The name to give the quaternion orient attribute.

Enable Output Radius

Whether to output the pscale attribute.

Radius Attribute

The name of the output pscale attribute.

See also

Copernicus nodes