Geometry Nodes: use virtual arrays in internal attribute api

A virtual array is a data structure that is similar to a normal array
in that its elements can be accessed by an index. However, a virtual
array does not have to be a contiguous array internally. Instead, its
elements can be layed out arbitrarily while element access happens
through a virtual function call. However, the virtual array data
structures are designed so that the virtual function call can be avoided
in cases where it could become a bottleneck.

Most commonly, a virtual array is backed by an actual array/span or
is a single value internally, that is the same for every index.
Besides those, there are many more specialized virtual arrays like the
ones that provides vertex positions based on the `MVert` struct or
vertex group weights.

Not all attributes used by geometry nodes are stored in simple contiguous
arrays. To provide uniform access to all kinds of attributes, the attribute
API has to provide virtual array functionality that hides the implementation
details of attributes.

Before this refactor, the attribute API provided its own virtual array
implementation as part of the `ReadAttribute` and `WriteAttribute` types.
That resulted in unnecessary code duplication with the virtual array system.
Even worse, it bound many algorithms used by geometry nodes to the specifics
of the attribute API, even though they could also use different data sources
(such as data from sockets, default values, later results of expressions, ...).

This refactor removes the `ReadAttribute` and `WriteAttribute` types and
replaces them with `GVArray` and `GVMutableArray` respectively. The `GV`
stands for "generic virtual". The "generic" means that the data type contained
in those virtual arrays is only known at run-time. There are the corresponding
statically typed types `VArray<T>` and `VMutableArray<T>` as well.

No regressions are expected from this refactor. It does come with one
improvement for users. The attribute API can convert the data type
on write now. This is especially useful when writing to builtin attributes
like `material_index` with e.g. the Attribute Math node (which usually
just writes to float attributes, while `material_index` is an integer attribute).

Differential Revision: https://developer.blender.org/D10994

1 files changed, 19 insertions, 24 deletions

diff --git a/source/blender/editors/space_spreadsheet/spreadsheet_data_source_geometry.cc b/source/blender/editors/space_spreadsheet/spreadsheet_data_source_geometry.cc
index 520d29ce306..405f0cd9455 100644
--- a/source/blender/editors/space_spreadsheet/spreadsheet_data_source_geometry.cc
+++ b/source/blender/editors/space_spreadsheet/spreadsheet_data_source_geometry.cc
@@ -78,24 +78,25 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
 {
   std::lock_guard lock{mutex_};
 
-  bke::ReadAttributePtr attribute_ptr = component_->attribute_try_get_for_read(column_id.name);
-  if (!attribute_ptr) {
+  bke::ReadAttributeLookup attribute = component_->attribute_try_get_for_read(column_id.name);
+  if (!attribute) {
     return {};
   }
-  const bke::ReadAttribute *attribute = scope_.add(std::move(attribute_ptr), __func__);
-  if (attribute->domain() != domain_) {
+  const fn::GVArray *varray = scope_.add(std::move(attribute.varray), __func__);
+  if (attribute.domain != domain_) {
     return {};
   }
-  int domain_size = attribute->size();
-  switch (attribute->custom_data_type()) {
+  int domain_size = varray->size();
+  const CustomDataType type = bke::cpp_type_to_custom_data_type(varray->type());
+  switch (type) {
     case CD_PROP_FLOAT:
       if (column_id.index != -1) {
         return {};
       }
       return column_values_from_function(
-          column_id.name, domain_size, [attribute](int index, CellValue &r_cell_value) {
+          column_id.name, domain_size, [varray](int index, CellValue &r_cell_value) {
             float value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_float = value;
           });
     case CD_PROP_INT32:
@@ -103,9 +104,9 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
         return {};
       }
       return column_values_from_function(
-          column_id.name, domain_size, [attribute](int index, CellValue &r_cell_value) {
+          column_id.name, domain_size, [varray](int index, CellValue &r_cell_value) {
             int value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_int = value;
           });
     case CD_PROP_BOOL:
@@ -113,9 +114,9 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
         return {};
       }
       return column_values_from_function(
-          column_id.name, domain_size, [attribute](int index, CellValue &r_cell_value) {
+          column_id.name, domain_size, [varray](int index, CellValue &r_cell_value) {
             bool value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_bool = value;
           });
     case CD_PROP_FLOAT2: {
@@ -125,11 +126,9 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
       const std::array<const char *, 2> suffixes = {" X", " Y"};
       const std::string name = StringRef(column_id.name) + suffixes[column_id.index];
       return column_values_from_function(
-          name,
-          domain_size,
-          [attribute, axis = column_id.index](int index, CellValue &r_cell_value) {
+          name, domain_size, [varray, axis = column_id.index](int index, CellValue &r_cell_value) {
             float2 value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_float = value[axis];
           });
     }
@@ -140,11 +139,9 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
       const std::array<const char *, 3> suffixes = {" X", " Y", " Z"};
       const std::string name = StringRef(column_id.name) + suffixes[column_id.index];
       return column_values_from_function(
-          name,
-          domain_size,
-          [attribute, axis = column_id.index](int index, CellValue &r_cell_value) {
+          name, domain_size, [varray, axis = column_id.index](int index, CellValue &r_cell_value) {
             float3 value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_float = value[axis];
           });
     }
@@ -155,11 +152,9 @@ std::unique_ptr<ColumnValues> GeometryDataSource::get_column_values(
       const std::array<const char *, 4> suffixes = {" R", " G", " B", " A"};
       const std::string name = StringRef(column_id.name) + suffixes[column_id.index];
       return column_values_from_function(
-          name,
-          domain_size,
-          [attribute, axis = column_id.index](int index, CellValue &r_cell_value) {
+          name, domain_size, [varray, axis = column_id.index](int index, CellValue &r_cell_value) {
             Color4f value;
-            attribute->get(index, &value);
+            varray->get(index, &value);
             r_cell_value.value_float = value[axis];
           });
     }