Geometry Nodes: new geometry attribute API

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

1 files changed, 6 insertions, 6 deletions

diff --git a/source/blender/nodes/intern/geometry_nodes_eval_log.cc b/source/blender/nodes/intern/geometry_nodes_eval_log.cc
index 85dfdf03b82..cf7cbbdc4bf 100644
--- a/source/blender/nodes/intern/geometry_nodes_eval_log.cc
+++ b/source/blender/nodes/intern/geometry_nodes_eval_log.cc
@@ -228,7 +228,7 @@ GeometryValueLog::GeometryValueLog(const GeometrySet &geometry_set, bool log_ful
       all_component_types,
       true,
       [&](const bke::AttributeIDRef &attribute_id,
-          const AttributeMetaData &meta_data,
+          const bke::AttributeMetaData &meta_data,
           const GeometryComponent &UNUSED(component)) {
         if (attribute_id.is_named() && names.add(attribute_id.name())) {
           this->attributes_.append({attribute_id.name(), meta_data.domain, meta_data.data_type});
@@ -241,21 +241,21 @@ GeometryValueLog::GeometryValueLog(const GeometrySet &geometry_set, bool log_ful
       case GEO_COMPONENT_TYPE_MESH: {
         const MeshComponent &mesh_component = *(const MeshComponent *)component;
         MeshInfo &info = this->mesh_info.emplace();
-        info.verts_num = mesh_component.attribute_domain_num(ATTR_DOMAIN_POINT);
-        info.edges_num = mesh_component.attribute_domain_num(ATTR_DOMAIN_EDGE);
-        info.faces_num = mesh_component.attribute_domain_num(ATTR_DOMAIN_FACE);
+        info.verts_num = mesh_component.attribute_domain_size(ATTR_DOMAIN_POINT);
+        info.edges_num = mesh_component.attribute_domain_size(ATTR_DOMAIN_EDGE);
+        info.faces_num = mesh_component.attribute_domain_size(ATTR_DOMAIN_FACE);
         break;
       }
       case GEO_COMPONENT_TYPE_CURVE: {
         const CurveComponent &curve_component = *(const CurveComponent *)component;
         CurveInfo &info = this->curve_info.emplace();
-        info.splines_num = curve_component.attribute_domain_num(ATTR_DOMAIN_CURVE);
+        info.splines_num = curve_component.attribute_domain_size(ATTR_DOMAIN_CURVE);
         break;
       }
       case GEO_COMPONENT_TYPE_POINT_CLOUD: {
         const PointCloudComponent &pointcloud_component = *(const PointCloudComponent *)component;
         PointCloudInfo &info = this->pointcloud_info.emplace();
-        info.points_num = pointcloud_component.attribute_domain_num(ATTR_DOMAIN_POINT);
+        info.points_num = pointcloud_component.attribute_domain_size(ATTR_DOMAIN_POINT);
         break;
       }
       case GEO_COMPONENT_TYPE_INSTANCES: {