Skip to content

Attribute

In Hakowan, an attribute specifies a specific "column" of the data (i.e. mesh attribute) that will be used to encode various visual channels and textures. Each attribute consists of a name, optional physical unit, and scale. The name identifies the mesh attribute; the scale defines a column-specific transformation before visual encoding. Units are semantic metadata used by automatic legends and observation manifests.

Creating Attributes

The hkw.attribute() function is a convenient alias for creating Attribute objects:

# To specify an attribute from name alone.
# By default, scale is identity.
attr = hkw.attribute(name="normal")

# To specify an attribute from both name and scale.
attr = hkw.attribute(name="normal", scale=hkw.scale.Uniform(factor=2))

# hkw.attribute() is equivalent to hkw.scale.Attribute()
attr = hkw.scale.Attribute(name="normal", scale=hkw.scale.Uniform(factor=2))

temperature = hkw.attribute("temperature", unit="°C")
pressure = hkw.attribute("pressure", unit="Pa", scale=hkw.scale.Log())

The norm() shorthand

hkw.norm() is a convenient shorthand for creating an attribute that represents the per-element magnitude of a vector field. It builds an Attribute carrying a leading Norm scale, turning a vector field (e.g. velocity or displacement) into a derived scalar field. The result can be used anywhere a scalar attribute is expected, such as the size channel (width proportional to magnitude) or a ScalarField texture (color by magnitude).

# These two are equivalent:
attr = hkw.norm("velocity")
attr = hkw.attribute("velocity", scale=hkw.scale.Norm())

# An optional scale is applied *after* the norm is computed.
attr = hkw.norm("velocity", scale=hkw.scale.Normalize(range_min=0.005, range_max=0.02))

# The norm order can be customized (default is Euclidean / L2).
attr = hkw.norm("velocity", order=1)

# Color a surface by the magnitude of a vector field.
mat = hkw.material.Diffuse(reflectance=hkw.texture.ScalarField(data=hkw.norm("velocity")))

Attribute-Like Objects

Many Hakowan functions accept "attribute-like" objects, which can be either:

  • A string: Automatically converted to an Attribute with the given name
  • An Attribute object: Used directly

This allows for convenient shorthand notation:

# These are equivalent:
ch1 = hkw.channel.Position(data=hkw.attribute(name="position"))
ch2 = hkw.channel.Position(data="position")

# These are also equivalent:
tex1 = hkw.texture.ScalarField(data=hkw.attribute(name="curvature"))
tex2 = hkw.texture.ScalarField(data="curvature")