Attributes
Describes what attributes are and lists some common attributes.
Overview
Attributes are named values stored on vertices, points, primitives, and surfaces. Point color, position, UV coordinates , spline weight (W), and normal, for example, are stored as point attributes.
You can use the values of attributes in expressions to reshape, color, etc. points. For example, you could set the per-point color based on the vertical (Y) position of the point.
Some attributes (such as position) are automatically set by Houdini as you model the points, but you can also manually set attributes and add your own custom attributes.
The surface operators in the Attributes group of the tab menu exist to set different types of attributes. You can also set or create arbitrary attributes to particles using the Attribute SOP. This lets you store custom per-point information relevant to your model you can use later in expressions .
To see the attributes on the geometry in a node, press 
on the node’s tile in the network editor and choose Spreadsheet to open the geometry spreadsheet for the node.
Particles also have attributes, and attributes are very important when geometry and particle systems interact. For example, particles emitted from geometry inherit (by default) the attributes of the point from which they are emitted, and you can create interesting effects by transferring attributes between surfaces and particles using the Attribute Transfer POP.
Well-known attributes
The order of precedence for attributes from highest to lowest is:
Vertex Attributes
Point Attributes
Primitive Attributes
Detail Attributes
Attributes with a higher order of precedence override similar attributes with a lower order of precedence.
| Name | Type | Size | On | Description |
|---|---|---|---|---|
| index | 1 | Detail, Primitive | Material name specification |
| index | 1 | Detail, Primitive | RenderMan shader name |
| float | 3 | Detail, Primitive, Point, Vertex | Ambient color (override) |
| float | 3 | Detail, Primitive, Point, Vertex | Diffuse color (override) |
| float | 3 | Detail, Primitive, Point, Vertex | Specular color (override) |
| float | 3 | Detail, Primitive, Point, Vertex | Reflect color (override) |
| float | 3 | Detail, Primitive, Point, Vertex | Transmit color (override) |
| float | 3 | Detail, Primitive, Point, Vertex | Emission color (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Alpha para/perp (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Roughness (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Fresnel coefficient (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Alpha parallel (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Alpha perp (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Alpha roll off (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Shadow intensity (override) |
| float | 1 | Detail, Primitive, Point, Vertex | Shadow bias (override) |
| vector | 3 | Primitive, Point | Surface Normal |
| vector | 3 | Point | Velocity |
| float | 3 | Point, Vertex | Texture coordinates (UVW) |
| float | 1 | Detail, Primitive | Level of detail |
| vector | 3 | Primitive | Vector for attractor force |
| float | 1 | Primitive | Edge force for attractor |
| float | 1 | Primitive | Vortex force for attractor |
| float | 1 | Primitive | Spiral force for attractor |
| float | 1 | Point | Mass |
| float | 1 | Point | Coefficient of drag |
| float | 2 | Point | Life time (index 0=time alive index 1=death time) |
| float | 1 | Point | Identifying tag |
| float | 3 | Point | Rest position |