= 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|/shading/textures_uvs] , spline weight (W), and normal, for example, are stored as point attributes. You can use the values of attributes in [expressions|/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|Node:sop/attribute]. This lets you store custom per-point information relevant to your model you can use later in [expressions|/expressions] . To see the attributes on the geometry in a node, press ((RMB)) on the node's tile in the network editor and choose __Spreadsheet__ to open the [geometry spreadsheet|/ref/panes/geosheet] for the node. [Particles|/particles] also have attributes, and attributes are very important when geometry and particle systems interact. For example, particles [emitted|/particles/emit] 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|Node:pop/attribtransfer]. == 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. table>> tr>> th>> Name th>> Type th>> Size th>> On th>> Description tr>> td>>`mat` td>> index td>> 1 td>> Detail, Primitive td>> Material name specification tr>> td>>`rishade` td>> index td>> 1 td>> Detail, Primitive td>> RenderMan shader name tr>> td>>`Ca` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Ambient color (override) tr>> td>>`Cd` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Diffuse color (override) tr>> td>>`Cs` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Specular color (override) tr>> td>>`Cr` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Reflect color (override) tr>> td>>`Ct` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Transmit color (override) tr>> td>>`Ce` td>> float td>> 3 td>> Detail, Primitive, Point, Vertex td>> Emission color (override) tr>> td>>`Alpha` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Alpha para/perp (override) tr>> td>>`rough` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Roughness (override) tr>> td>>`fresnel` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Fresnel coefficient (override) tr>> td>>`apara` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Alpha parallel (override) tr>> td>>`aperp` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Alpha perp (override) tr>> td>>`aroll` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Alpha roll off (override) tr>> td>>`shadow` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Shadow intensity (override) tr>> td>>`sbias` td>> float td>> 1 td>> Detail, Primitive, Point, Vertex td>> Shadow bias (override) tr>> td>>`N` td>> vector td>> 3 td>> Primitive, Point td>> Surface Normal tr>> td>>`v` td>> vector td>> 3 td>> Point td>> Velocity tr>> td>>`uv` td>> float td>> 3 td>> Point, Vertex td>> Texture coordinates (UVW) tr>> td>>`lod` td>> float td>> 1 td>> Detail, Primitive td>> Level of detail tr>> td>>`dir` td>> vector td>> 3 td>> Primitive td>> Vector for attractor force tr>> td>>`fedge` td>> float td>> 1 td>> Primitive td>> Edge force for attractor tr>> td>>`fvortex` td>> float td>> 1 td>> Primitive td>> Vortex force for attractor tr>> td>>`fspiral` td>> float td>> 1 td>> Primitive td>> Spiral force for attractor tr>> td>>`mass` td>> float td>> 1 td>> Point td>> Mass tr>> td>>`drag` td>> float td>> 1 td>> Point td>> Coefficient of drag tr>> td>>`life` td>> float td>> 2 td>> Point td>> Life time (index 0=time alive index 1=death time) tr>> td>>`id` td>> float td>> 1 td>> Point td>> Identifying tag tr>> td>>`rest` td>> float td>> 3 td>> Point td>> Rest position