Jacques Lucke
b876ce2a4a
Currently, there are two attribute API. The first, defined in `BKE_attribute.h` is accessible from RNA and C code. The second is implemented with `GeometryComponent` and is only accessible in C++ code. The second is widely used, but only being accessible through the `GeometrySet` API makes it awkward to use, and even impossible for types that don't correspond directly to a geometry component like `CurvesGeometry`. This patch adds a new attribute API, designed to replace the `GeometryComponent` attribute API now, and to eventually replace or be the basis of the other one. The basic idea is that there is an `AttributeAccessor` class that allows code to interact with a set of attributes owned by some geometry. The accessor itself has no ownership. `AttributeAccessor` is a simple type that can be passed around by value. That makes it easy to return it from functions and to store it in containers. For const-correctness, there is also a `MutableAttributeAccessor` that allows changing individual and can add or remove attributes. Currently, `AttributeAccessor` is composed of two pointers. The first is a pointer to the owner of the attribute data. The second is a pointer to a struct with function pointers, that is similar to a virtual function table. The functions know how to access attributes on the owner. The actual attribute access for geometries is still implemented with the `AttributeProvider` pattern, which makes it easy to support different sources of attributes on a geometry and simplifies dealing with built-in attributes. There are different ways to get an attribute accessor for a geometry: * `GeometryComponent.attributes()` * `CurvesGeometry.attributes()` * `bke::mesh_attributes(const Mesh &)` * `bke::pointcloud_attributes(const PointCloud &)` All of these also have a `_for_write` variant that returns a `MutabelAttributeAccessor`. Differential Revision: https://developer.blender.org/D15280