TYPE: SOP
TITLE: AttribComposite SOP

AttribComposite is used to composite vertex, point, primitive, and/or detail
attributes between two or more selections.

The attributes may be explicitly specified in the corresponding attribute text
field. Exclusion is specified by preceding an attribute name with the carat
character (^). All available attributes can be specified by leaving the field
blank or entering an asterisk (*) in the field. If the first attribute is
preceded by a carat then all attributes are assumed to be transferred except
where explicitly excluded. In all other cases, no attributes are assumed
except where explicitly included.

The specified attributes of the ordered inputs are composited in sequence.
The attributes are first scaled by the corresponding blending weights and then
composited using the specified compositing operator. The available operators
include Mean, Max, Min, Over, and Under. The Mean operator determines the
weighted average of the input attributes. The Max and Min operators determine
the maximum and the minimum of the weighted input attributes respectively.
For the Mean, Max, and Min operators, the specified Alpha Attribute affords
a per-point, per-primitive, or per-vertex weight distribution. The Over and
Under operators perform two of the standard alpha blending operations where the
alpha values are taken from the specified Alpha Attribute. The Over operator
scales the incoming weighted input attribute by its alpha value and adds it to
the current intermediate output attribute scaled by one minus that alpha value:

source * alpha + destination * (1 - alpha).

The Under operator is performed in
a similar manner but with the alpha weights swapped:

source * (1 - alpha) + destination * alpha.

If the Alpha Attribute does not exist for a particular input, then the alpha
mask for that input is assumed to be 1.

Parameters:
    Selection Index		- Specifies which input to use when generating
				  the cooked selection.		/selectionidx
    Detail			- Detail attributes to composite.
    Primitives			- Primitive attributes to composite.
    Points			- Point attributes to composite.
    Vertices			- Vertex attributes to composite.
    Blend #			- Controls contribution of geometry inputs.
				    /blend0 /blend1 /blend2 /...
    Alpha Attribute		- Attribute containing the alpha mask.
    Compositing Operation	- Operator to composite with.

See also: Attribute, AttribCreate, Point, Primitive, Vertex, BlendShapes
