Geometry Nodes: refactor virtual array system

Goals of this refactor:
* Simplify creating virtual arrays.
* Simplify passing virtual arrays around.
* Simplify converting between typed and generic virtual arrays.
* Reduce memory allocations.

As a quick reminder, a virtual arrays is a data structure that behaves like an
array (i.e. it can be accessed using an index). However, it may not actually
be stored as array internally. The two most important implementations
of virtual arrays are those that correspond to an actual plain array and those
that have the same value for every index. However, many more
implementations exist for various reasons (interfacing with legacy attributes,
unified iterator over all points in multiple splines, ...).

With this refactor the core types (`VArray`, `GVArray`, `VMutableArray` and
`GVMutableArray`) can be used like "normal values". They typically live
on the stack. Before, they were usually inside a `std::unique_ptr`. This makes
passing them around much easier. Creation of new virtual arrays is also
much simpler now due to some constructors. Memory allocations are
reduced by making use of small object optimization inside the core types.

Previously, `VArray` was a class with virtual methods that had to be overridden
to change the behavior of a the virtual array. Now,`VArray` has a fixed size
and has no virtual methods. Instead it contains a `VArrayImpl` that is
similar to the old `VArray`. `VArrayImpl` should rarely ever be used directly,
unless a new virtual array implementation is added.

To support the small object optimization for many `VArrayImpl` classes,
a new `blender::Any` type is added. It is similar to `std::any` with two
additional features. It has an adjustable inline buffer size and alignment.
The inline buffer size of `std::any` can't be relied on and is usually too
small for our use case here. Furthermore, `blender::Any` can store
additional user-defined type information without increasing the
stack size.

Differential Revision: https://developer.blender.org/D12986

1 files changed, 6 insertions, 9 deletions

diff --git a/source/blender/blenkernel/intern/attribute_access_intern.hh b/source/blender/blenkernel/intern/attribute_access_intern.hh
index 140498bdb01..b77d7010efa 100644
--- a/source/blender/blenkernel/intern/attribute_access_intern.hh
+++ b/source/blender/blenkernel/intern/attribute_access_intern.hh
@@ -24,9 +24,6 @@
 
 namespace blender::bke {
 
-using fn::GVArrayPtr;
-using fn::GVMutableArrayPtr;
-
 /**
  * Utility to group together multiple functions that are used to access custom data on geometry
  * components in a generic way.
@@ -86,7 +83,7 @@ class BuiltinAttributeProvider {
   {
   }
 
-  virtual GVArrayPtr try_get_for_read(const GeometryComponent &component) const = 0;
+  virtual GVArray try_get_for_read(const GeometryComponent &component) const = 0;
   virtual WriteAttributeLookup try_get_for_write(GeometryComponent &component) const = 0;
   virtual bool try_delete(GeometryComponent &component) const = 0;
   virtual bool try_create(GeometryComponent &UNUSED(component),
@@ -188,8 +185,8 @@ class CustomDataAttributeProvider final : public DynamicAttributesProvider {
  */
 class NamedLegacyCustomDataProvider final : public DynamicAttributesProvider {
  private:
-  using AsReadAttribute = GVArrayPtr (*)(const void *data, const int domain_size);
-  using AsWriteAttribute = GVMutableArrayPtr (*)(void *data, const int domain_size);
+  using AsReadAttribute = GVArray (*)(const void *data, const int domain_size);
+  using AsWriteAttribute = GVMutableArray (*)(void *data, const int domain_size);
   const AttributeDomain domain_;
   const CustomDataType attribute_type_;
   const CustomDataType stored_type_;
@@ -232,8 +229,8 @@ class NamedLegacyCustomDataProvider final : public DynamicAttributesProvider {
  * if the stored type is the same as the attribute type.
  */
 class BuiltinCustomDataLayerProvider final : public BuiltinAttributeProvider {
-  using AsReadAttribute = GVArrayPtr (*)(const void *data, const int domain_size);
-  using AsWriteAttribute = GVMutableArrayPtr (*)(void *data, const int domain_size);
+  using AsReadAttribute = GVArray (*)(const void *data, const int domain_size);
+  using AsWriteAttribute = GVMutableArray (*)(void *data, const int domain_size);
   using UpdateOnRead = void (*)(const GeometryComponent &component);
   using UpdateOnWrite = void (*)(GeometryComponent &component);
   const CustomDataType stored_type_;
@@ -266,7 +263,7 @@ class BuiltinCustomDataLayerProvider final : public BuiltinAttributeProvider {
   {
   }
 
-  GVArrayPtr try_get_for_read(const GeometryComponent &component) const final;
+  GVArray try_get_for_read(const GeometryComponent &component) const final;
   WriteAttributeLookup try_get_for_write(GeometryComponent &component) const final;
   bool try_delete(GeometryComponent &component) const final;
   bool try_create(GeometryComponent &component, const AttributeInit &initializer) const final;