Fields
Fields¶
A Field represents a function that outputs a value based on an
arbitrary number of inputs. The inputs for a specific field evaluation
are provided by a FieldContext.
A typical example is a field that computes a displacement vector for
every vertex on a mesh based on its position. In this case the
FieldContext is the mesh with the position attribute.
Fields can be build, composed and evaluated at run-time. They are stored
in a directed tree graph data structure, whereby each node is a
FieldNode and edges are dependencies. A FieldNode has an
arbitrary number of inputs and at least one output. A Field is a
specific output of a FieldNode. The inputs of a FieldNode are
other fields. All fields are immutable once they are built.
There are two different types of field nodes:
FieldInput: Has no input and exactly one output. It represents an input to the entire field when it is evaluated. During evaluation, the value of this input is based on aFieldContext.FieldOperation: Has an arbitrary number of field inputs and at least one output. Its main use is to compose multiple existing fields into new fields.
Given one or more fields and a FieldContext, the fields can be
evaluated using the FieldEvaluator class.
Generic and Typed Fields¶
Most of the time, when working with fields, they have a specific type
that is known at compile time. In this case, the Field<T> class
should be used. This class is a wrapper around a more generic GField
class (where G stands for "generic"). A GField is a field whose type
is only known at run-time. When converting from a GField to a
Field<T> there is a run-time assert that makes sure that the
conversion is valid.