Blend object

Switches or blends between the transformations of several input objects.

The Blend object allows various effects such as blended inputs, animating the parents of objects, sequencing, partial transformation inheritance, three-point orientation, and other effects. It gives you some extra flexibility in setting up parent-child relationships. It operates like the Switch and Sequence blend sops insofar as it takes more than one input and blends or switches those into one output.

Some potential uses of the Blend op are to animate parenting, such as when one character passes an item to another, or to pass on only part of a parents characteristics.

The Blend Object gives you some extra flexibility in setting up parent-child relationships. It operates like the Switch and Sequence blend sops insofar as it takes more than one input and blends or switches those into one output. As with the other objects, such as lights and cameras, the Blend OP can be placed and wired into networks, but its only purpose is to channel data rather than hold it.

Blend allows for a great deal of control over how much influence each of the inputs has over the child object. This can be set either using a weight value for the input or by masking the input to restrict its effect by channels. Each input has its own set of weight and mask controls. There is a special case when you have exactly three inputs which enables the Normal Offset and Orient Axes parameters. The Offset works by moving the child perpendicular to the plane formed by the three inputs; the Orient function rotates the child such that the first input determines the axes center, the second the +X orientation, and the third the +Y orientation.

The Sequence type simply switches between inputs, so the weight and mask controls become inactive. A Sequence value of 0 parents the child to the first input object, a value of 1 parents it to the next, etc. Any value outside the range of inputs will unparent the child.

Parameters

Parents

Type

Method in which parent transforms are combined to produce a unique transform.

Sequence

When the type is set to Sequence this value controls which input parent contributes to the child’s position. It can be used to animate a child from one parent to another. A sequence outside the range of inputs is interpreted as unparenting the child.

When the type is set to Constrain this is similar in operation except that no 'popping' occurs when transferring from one parent to another.

Shortest Path Rotation Blending

(Blend/Sequence Only) This will use the shortest path possible when blending rotations between two inputs. Note that this will not work if not blending all 3 rotation parameters.

Reset Frame

(Constrain Only) Since this behavior is state-dependent this value allows the child to reset itself (ie. zero any accumulated transform) at the frame.

Weight 1

(Blend only) These weights are used to weight each corresponding input parent.

Mask 1

(Blend only) These masks are used to select which component of each parent is used in the blending process.

Normal Offset

(Blend only) When exactly three parents are input, the child position may be offset in the direction perpendicular to the triangular plane they form.

Orient Axes

(Blend only) When exactly three parents are input this option will orient the child’s local axes to match the orientation of the parents as follows:

First Parent	Axes center
Second Parent	Axes +X
Third Parent	Axes +Y

Transform

Keep Position When Parenting

When the object is re-parented, maintain its current world position by changing the object’s transform parameters.

Pre-transform menu

This menu contains options for manipulating the pre-transform values. The pre-transform is an internal transform that is applied prior to the regular transform parameters. This allows you to change the frame of reference for the translate, rotate, scale parameter values below without changing the overall transform.

Clean Transform	This reverts the translate, rotate, scale parameters to their default values while maintaining the same overall transform.
Clean Translates	This sets the translate parameter to (0, 0, 0) while maintaining the same overall transform.
Clean Rotates	This sets the rotate parameter to (0, 0, 0) while maintaining the same overall transform.
Clean Scales	This sets the scale parameter to (1, 1, 1) while maintaining the same overall transform.
Extract Pre-transform	This removes the pre-transform by setting the translate, rotate, and scale parameters in order to maintain the same overall transform. Note that if there were shears in the pre-transform, it can not be completely removed.
Reset Pre-transform	This completely removes the pre-transform without changing any parameters. This will change the overall transform of the object if there are any non-default values in the translate, rotate, and scale parameters.

Transform Order

The left menu chooses the order in which transforms are applied (for example, scale, then rotate, then translate). This can change the position and orientation of the object, in the same way that going a block and turning east takes you to a different place than turning east and then going a block.

The right menu chooses the order in which to rotate around the X, Y, and Z axes. Certain orders can make character joint transforms easier to use, depending on the character.

Translate

Translation along XYZ axes.

Rotation

Degrees rotation about XYZ axes.

Scale

Non-uniform scaling about XYZ axes.

Pivot

Local origin of the object. See also setting the pivot point .

Uniform Scale

Scale the object uniformly along all three axes.

Look At

Object to point to. Constrains an object so its -Z axis always points at another object’s origin.

Look At Up Vector

When specifying a look at, it is possible to specify an up vector for the look at. This controls the roll of this object when looking at the look at object.

Don’t Use Up Vector	Use this option if the look at object does not pass through the Y axis of this object.
Use Up Vector	This precisely defines the direction of the Y axis of this object while looking. The up vector specified should not be parallel to the look at direction. The value used is specified by the Orient Up Vector parameter below.
Use Quaternions	Quaternions are a mathematical representation of a 3D rotation. This method finds the most efficient means of moving from one point to another on a sphere.

Path Object

A reference to the curve node or object you want this object to follow.

Roll

The orientation of the object around the path.

Position

The position of the object along the path. 0.0 means at the beginning of the path, and 1.0 means the end. The integer portion of the position is used as the primitive number inside the geometry while the fractional part indicates the u value on the primitive.

If the primitive number does not exist, then it is wrapped back to the beginning. So for numbers greater than 1.0 in a path object that only have a single primitive, it wraps around to the beginning again. You can easily animate something moving around a circular track simply by continuously increasing the position value.

Keyframe this value to animate the object moving along the path.

Note

The Follow Path tool on the shelf automatically sets keyframes on this parameter that you may want to edit or replace.

The Parameterization option controls how position values between 0 and 1 correspond to knots on the path curve.

Parameterization

Controls how the Position parameter is translated into a point on the path curve. Use Arc-length (the default) to interpolate the position values evenly along the physical length of the curve.

Use Uniform to distribute the position values between the knots of the curve. This lets you slow down the object at certain points by bunching up knots in the path curve. However, it is much more convenient to simply edit the animation curve to control the speed of the object along the path.

Orient Along Path

Orient the object according to the path’s curvature.

Orient Up Vector

The direction vector of the object’s Y axis to orient with.

Auto-Bank factor

Controls automatic banking of the object as it turns corners. Set this to 0 to turn automatic banking off.

Misc

Set Wireframe Color	Use the specified wireframe color
Wireframe Color	The display color of the object
Viewport Selecting Enabled	Object is capable of being picked in viewport.
Select Script	Script to run when the object is picked in the viewport. See select scripts .
Cache Object Transform	Caches object transforms once Houdini calculates them. This is especially useful for objects whose world space position is expensive to calculate (such as Sticky objects), and objects at the end of long parenting chains (such as Bones). This option is turned on by default for Sticky and Bone objects. See OBJ cache preferences for how to control the size of the object transform cache.

Usages in other examples

Example name	Example for