Geometry Nodes: fields and anonymous attributes

This implements the initial core framework for fields and anonymous
attributes (also see T91274).

The new functionality is hidden behind the "Geometry Nodes Fields"
feature flag. When enabled in the user preferences, the following
new nodes become available: `Position`, `Index`, `Normal`,
`Set Position` and `Attribute Capture`.

Socket inspection has not been updated to work with fields yet.

Besides these changes at the user level, this patch contains the
ground work for:
* building and evaluating fields at run-time (`FN_fields.hh`) and
* creating and accessing anonymous attributes on geometry
  (`BKE_anonymous_attribute.h`).

For evaluating fields we use a new so called multi-function procedure
(`FN_multi_function_procedure.hh`). It allows composing multi-functions
in arbitrary ways and supports efficient evaluation as is required by
fields. See `FN_multi_function_procedure.hh` for more details on how
this evaluation mechanism can be used.

A new `AttributeIDRef` has been added which allows handling named
and anonymous attributes in the same way in many places.

Hans and I worked on this patch together.

Differential Revision: https://developer.blender.org/D12414

1 files changed, 569 insertions, 0 deletions

diff --git a/source/blender/functions/intern/field.cc b/source/blender/functions/intern/field.cc
new file mode 100644
index 00000000000..fa7dea97b7f
--- /dev/null
+++ b/source/blender/functions/intern/field.cc
@@ -0,0 +1,569 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include "BLI_map.hh"
+#include "BLI_multi_value_map.hh"
+#include "BLI_set.hh"
+#include "BLI_stack.hh"
+#include "BLI_vector_set.hh"
+
+#include "FN_field.hh"
+
+namespace blender::fn {
+
+/* --------------------------------------------------------------------
+ * Field Evaluation.
+ */
+
+struct FieldTreeInfo {
+  /**
+   * When fields are built, they only have references to the fields that they depend on. This map
+   * allows traversal of fields in the opposite direction. So for every field it stores the other
+   * fields that depend on it directly.
+   */
+  MultiValueMap<GFieldRef, GFieldRef> field_users;
+  /**
+   * The same field input may exist in the field tree as as separate nodes due to the way
+   * the tree is constructed. This set contains every different input only once.
+   */
+  VectorSet<std::reference_wrapper<const FieldInput>> deduplicated_field_inputs;
+};
+
+/**
+ * Collects some information from the field tree that is required by later steps.
+ */
+static FieldTreeInfo preprocess_field_tree(Span<GFieldRef> entry_fields)
+{
+  FieldTreeInfo field_tree_info;
+
+  Stack<GFieldRef> fields_to_check;
+  Set<GFieldRef> handled_fields;
+
+  for (GFieldRef field : entry_fields) {
+    if (handled_fields.add(field)) {
+      fields_to_check.push(field);
+    }
+  }
+
+  while (!fields_to_check.is_empty()) {
+    GFieldRef field = fields_to_check.pop();
+    if (field.node().is_input()) {
+      const FieldInput &field_input = static_cast<const FieldInput &>(field.node());
+      field_tree_info.deduplicated_field_inputs.add(field_input);
+      continue;
+    }
+    BLI_assert(field.node().is_operation());
+    const FieldOperation &operation = static_cast<const FieldOperation &>(field.node());
+    for (const GFieldRef operation_input : operation.inputs()) {
+      field_tree_info.field_users.add(operation_input, field);
+      if (handled_fields.add(operation_input)) {
+        fields_to_check.push(operation_input);
+      }
+    }
+  }
+  return field_tree_info;
+}
+
+/**
+ * Retrieves the data from the context that is passed as input into the field.
+ */
+static Vector<const GVArray *> get_field_context_inputs(
+    ResourceScope &scope,
+    const IndexMask mask,
+    const FieldContext &context,
+    const Span<std::reference_wrapper<const FieldInput>> field_inputs)
+{
+  Vector<const GVArray *> field_context_inputs;
+  for (const FieldInput &field_input : field_inputs) {
+    const GVArray *varray = context.get_varray_for_input(field_input, mask, scope);
+    if (varray == nullptr) {
+      const CPPType &type = field_input.cpp_type();
+      varray = &scope.construct<GVArray_For_SingleValueRef>(
+          __func__, type, mask.min_array_size(), type.default_value());
+    }
+    field_context_inputs.append(varray);
+  }
+  return field_context_inputs;
+}
+
+/**
+ * \return A set that contains all fields from the field tree that depend on an input that varies
+ * for different indices.
+ */
+static Set<GFieldRef> find_varying_fields(const FieldTreeInfo &field_tree_info,
+                                          Span<const GVArray *> field_context_inputs)
+{
+  Set<GFieldRef> found_fields;
+  Stack<GFieldRef> fields_to_check;
+
+  /* The varying fields are the ones that depend on inputs that are not constant. Therefore we
+   * start the tree search at the non-constant input fields and traverse through all fields that
+   * depend on them. */
+  for (const int i : field_context_inputs.index_range()) {
+    const GVArray *varray = field_context_inputs[i];
+    if (varray->is_single()) {
+      continue;
+    }
+    const FieldInput &field_input = field_tree_info.deduplicated_field_inputs[i];
+    const GFieldRef field_input_field{field_input, 0};
+    const Span<GFieldRef> users = field_tree_info.field_users.lookup(field_input_field);
+    for (const GFieldRef &field : users) {
+      if (found_fields.add(field)) {
+        fields_to_check.push(field);
+      }
+    }
+  }
+  while (!fields_to_check.is_empty()) {
+    GFieldRef field = fields_to_check.pop();
+    const Span<GFieldRef> users = field_tree_info.field_users.lookup(field);
+    for (GFieldRef field : users) {
+      if (found_fields.add(field)) {
+        fields_to_check.push(field);
+      }
+    }
+  }
+  return found_fields;
+}
+
+/**
+ * Builds the #procedure so that it computes the the fields.
+ */
+static void build_multi_function_procedure_for_fields(MFProcedure &procedure,
+                                                      ResourceScope &scope,
+                                                      const FieldTreeInfo &field_tree_info,
+                                                      Span<GFieldRef> output_fields)
+{
+  MFProcedureBuilder builder{procedure};
+  /* Every input, intermediate and output field corresponds to a variable in the procedure. */
+  Map<GFieldRef, MFVariable *> variable_by_field;
+
+  /* Start by adding the field inputs as parameters to the procedure. */
+  for (const FieldInput &field_input : field_tree_info.deduplicated_field_inputs) {
+    MFVariable &variable = builder.add_input_parameter(
+        MFDataType::ForSingle(field_input.cpp_type()), field_input.debug_name());
+    variable_by_field.add_new({field_input, 0}, &variable);
+  }
+
+  /* Utility struct that is used to do proper depth first search traversal of the tree below. */
+  struct FieldWithIndex {
+    GFieldRef field;
+    int current_input_index = 0;
+  };
+
+  for (GFieldRef field : output_fields) {
+    /* We start a new stack for each output field to make sure that a field pushed later to the
+     * stack does never depend on a field that was pushed before. */
+    Stack<FieldWithIndex> fields_to_check;
+    fields_to_check.push({field, 0});
+    while (!fields_to_check.is_empty()) {
+      FieldWithIndex &field_with_index = fields_to_check.peek();
+      const GFieldRef &field = field_with_index.field;
+      if (variable_by_field.contains(field)) {
+        /* The field has been handled already. */
+        fields_to_check.pop();
+        continue;
+      }
+      /* Field inputs should already be handled above. */
+      BLI_assert(field.node().is_operation());
+
+      const FieldOperation &operation = static_cast<const FieldOperation &>(field.node());
+      const Span<GField> operation_inputs = operation.inputs();
+
+      if (field_with_index.current_input_index < operation_inputs.size()) {
+        /* Not all inputs are handled yet. Push the next input field to the stack and increment the
+         * input index. */
+        fields_to_check.push({operation_inputs[field_with_index.current_input_index]});
+        field_with_index.current_input_index++;
+      }
+      else {
+        /* All inputs variables are ready, now add the function call. */
+        Vector<MFVariable *> input_variables;
+        for (const GField &field : operation_inputs) {
+          input_variables.append(variable_by_field.lookup(field));
+        }
+        const MultiFunction &multi_function = operation.multi_function();
+        Vector<MFVariable *> output_variables = builder.add_call(multi_function, input_variables);
+        /* Add newly created variables to the map. */
+        for (const int i : output_variables.index_range()) {
+          variable_by_field.add_new({operation, i}, output_variables[i]);
+        }
+      }
+    }
+  }
+
+  /* Add output parameters to the procedure. */
+  Set<MFVariable *> already_output_variables;
+  for (const GFieldRef &field : output_fields) {
+    MFVariable *variable = variable_by_field.lookup(field);
+    if (!already_output_variables.add(variable)) {
+      /* One variable can be output at most once. To output the same value twice, we have to make
+       * a copy first. */
+      const MultiFunction &copy_fn = scope.construct<CustomMF_GenericCopy>(
+          __func__, "copy", variable->data_type());
+      variable = builder.add_call<1>(copy_fn, {variable})[0];
+    }
+    builder.add_output_parameter(*variable);
+  }
+
+  /* Remove the variables that should not be destructed from the map. */
+  for (const GFieldRef &field : output_fields) {
+    variable_by_field.remove(field);
+  }
+  /* Add destructor calls for the remaining variables. */
+  for (MFVariable *variable : variable_by_field.values()) {
+    builder.add_destruct(*variable);
+  }
+
+  builder.add_return();
+
+  // std::cout << procedure.to_dot() << "\n";
+  BLI_assert(procedure.validate());
+}
+
+/**
+ * Utility class that destructs elements from a partially initialized array.
+ */
+struct PartiallyInitializedArray : NonCopyable, NonMovable {
+  void *buffer;
+  IndexMask mask;
+  const CPPType *type;
+
+  ~PartiallyInitializedArray()
+  {
+    this->type->destruct_indices(this->buffer, this->mask);
+  }
+};
+
+/**
+ * Evaluate fields in the given context. If possible, multiple fields should be evaluated together,
+ * because that can be more efficient when they share common sub-fields.
+ *
+ * \param scope: The resource scope that owns data that makes up the output virtual arrays. Make
+ *   sure the scope is not destructed when the output virtual arrays are still used.
+ * \param fields_to_evaluate: The fields that should be evaluated together.
+ * \param mask: Determines which indices are computed. The mask may be referenced by the returned
+ *   virtual arrays. So the underlying indices (if applicable) should live longer then #scope.
+ * \param context: The context that the field is evaluated in. Used to retrieve data from each
+ *   #FieldInput in the field network.
+ * \param dst_varrays: If provided, the computed data will be written into those virtual arrays
+ *   instead of into newly created ones. That allows making the computed data live longer than
+ *   #scope and is more efficient when the data will be written into those virtual arrays
+ *   later anyway.
+ * \return The computed virtual arrays for each provided field. If #dst_varrays is passed, the
+ *   provided virtual arrays are returned.
+ */
+Vector<const GVArray *> evaluate_fields(ResourceScope &scope,
+                                        Span<GFieldRef> fields_to_evaluate,
+                                        IndexMask mask,
+                                        const FieldContext &context,
+                                        Span<GVMutableArray *> dst_varrays)
+{
+  Vector<const GVArray *> r_varrays(fields_to_evaluate.size(), nullptr);
+  const int array_size = mask.min_array_size();
+
+  /* Destination arrays are optional. Create a small utility method to access them. */
+  auto get_dst_varray_if_available = [&](int index) -> GVMutableArray * {
+    if (dst_varrays.is_empty()) {
+      return nullptr;
+    }
+    BLI_assert(dst_varrays[index] == nullptr || dst_varrays[index]->size() >= array_size);
+    return dst_varrays[index];
+  };
+
+  /* Traverse the field tree and prepare some data that is used in later steps. */
+  FieldTreeInfo field_tree_info = preprocess_field_tree(fields_to_evaluate);
+
+  /* Get inputs that will be passed into the field when evaluated. */
+  Vector<const GVArray *> field_context_inputs = get_field_context_inputs(
+      scope, mask, context, field_tree_info.deduplicated_field_inputs);
+
+  /* Finish fields that output an input varray directly. For those we don't have to do any further
+   * processing. */
+  for (const int out_index : fields_to_evaluate.index_range()) {
+    const GFieldRef &field = fields_to_evaluate[out_index];
+    if (!field.node().is_input()) {
+      continue;
+    }
+    const FieldInput &field_input = static_cast<const FieldInput &>(field.node());
+    const int field_input_index = field_tree_info.deduplicated_field_inputs.index_of(field_input);
+    const GVArray *varray = field_context_inputs[field_input_index];
+    r_varrays[out_index] = varray;
+  }
+
+  Set<GFieldRef> varying_fields = find_varying_fields(field_tree_info, field_context_inputs);
+
+  /* Separate fields into two categories. Those that are constant and need to be evaluated only
+   * once, and those that need to be evaluated for every index. */
+  Vector<GFieldRef> varying_fields_to_evaluate;
+  Vector<int> varying_field_indices;
+  Vector<GFieldRef> constant_fields_to_evaluate;
+  Vector<int> constant_field_indices;
+  for (const int i : fields_to_evaluate.index_range()) {
+    if (r_varrays[i] != nullptr) {
+      /* Already done. */
+      continue;
+    }
+    GFieldRef field = fields_to_evaluate[i];
+    if (varying_fields.contains(field)) {
+      varying_fields_to_evaluate.append(field);
+      varying_field_indices.append(i);
+    }
+    else {
+      constant_fields_to_evaluate.append(field);
+      constant_field_indices.append(i);
+    }
+  }
+
+  /* Evaluate varying fields if necessary. */
+  if (!varying_fields_to_evaluate.is_empty()) {
+    /* Build the procedure for those fields. */
+    MFProcedure procedure;
+    build_multi_function_procedure_for_fields(
+        procedure, scope, field_tree_info, varying_fields_to_evaluate);
+    MFProcedureExecutor procedure_executor{"Procedure", procedure};
+    MFParamsBuilder mf_params{procedure_executor, array_size};
+    MFContextBuilder mf_context;
+
+    /* Provide inputs to the procedure executor. */
+    for (const GVArray *varray : field_context_inputs) {
+      mf_params.add_readonly_single_input(*varray);
+    }
+
+    for (const int i : varying_fields_to_evaluate.index_range()) {
+      const GFieldRef &field = varying_fields_to_evaluate[i];
+      const CPPType &type = field.cpp_type();
+      const int out_index = varying_field_indices[i];
+
+      /* Try to get an existing virtual array that the result should be written into. */
+      GVMutableArray *output_varray = get_dst_varray_if_available(out_index);
+      void *buffer;
+      if (output_varray == nullptr || !output_varray->is_span()) {
+        /* Allocate a new buffer for the computed result. */
+        buffer = scope.linear_allocator().allocate(type.size() * array_size, type.alignment());
+
+        /* Make sure that elements in the buffer will be destructed. */
+        PartiallyInitializedArray &destruct_helper = scope.construct<PartiallyInitializedArray>(
+            __func__);
+        destruct_helper.buffer = buffer;
+        destruct_helper.mask = mask;
+        destruct_helper.type = &type;
+
+        r_varrays[out_index] = &scope.construct<GVArray_For_GSpan>(
+            __func__, GSpan{type, buffer, array_size});
+      }
+      else {
+        /* Write the result into the existing span. */
+        buffer = output_varray->get_internal_span().data();
+
+        r_varrays[out_index] = output_varray;
+      }
+
+      /* Pass output buffer to the procedure executor. */
+      const GMutableSpan span{type, buffer, array_size};
+      mf_params.add_uninitialized_single_output(span);
+    }
+
+    procedure_executor.call(mask, mf_params, mf_context);
+  }
+
+  /* Evaluate constant fields if necessary. */
+  if (!constant_fields_to_evaluate.is_empty()) {
+    /* Build the procedure for those fields. */
+    MFProcedure procedure;
+    build_multi_function_procedure_for_fields(
+        procedure, scope, field_tree_info, constant_fields_to_evaluate);
+    MFProcedureExecutor procedure_executor{"Procedure", procedure};
+    MFParamsBuilder mf_params{procedure_executor, 1};
+    MFContextBuilder mf_context;
+
+    /* Provide inputs to the procedure executor. */
+    for (const GVArray *varray : field_context_inputs) {
+      mf_params.add_readonly_single_input(*varray);
+    }
+
+    for (const int i : constant_fields_to_evaluate.index_range()) {
+      const GFieldRef &field = constant_fields_to_evaluate[i];
+      const CPPType &type = field.cpp_type();
+      /* Allocate memory where the computed value will be stored in. */
+      void *buffer = scope.linear_allocator().allocate(type.size(), type.alignment());
+
+      /* Use this to make sure that the value is destructed in the end. */
+      PartiallyInitializedArray &destruct_helper = scope.construct<PartiallyInitializedArray>(
+          __func__);
+      destruct_helper.buffer = buffer;
+      destruct_helper.mask = IndexRange(1);
+      destruct_helper.type = &type;
+
+      /* Pass output buffer to the procedure executor. */
+      mf_params.add_uninitialized_single_output({type, buffer, 1});
+
+      /* Create virtual array that can be used after the procedure has been executed below. */
+      const int out_index = constant_field_indices[i];
+      r_varrays[out_index] = &scope.construct<GVArray_For_SingleValueRef>(
+          __func__, type, array_size, buffer);
+    }
+
+    procedure_executor.call(IndexRange(1), mf_params, mf_context);
+  }
+
+  /* Copy data to supplied destination arrays if necessary. In some cases the evaluation above has
+   * written the computed data in the right place already. */
+  if (!dst_varrays.is_empty()) {
+    for (const int out_index : fields_to_evaluate.index_range()) {
+      GVMutableArray *output_varray = get_dst_varray_if_available(out_index);
+      if (output_varray == nullptr) {
+        /* Caller did not provide a destination for this output. */
+        continue;
+      }
+      const GVArray *computed_varray = r_varrays[out_index];
+      BLI_assert(computed_varray->type() == output_varray->type());
+      if (output_varray == computed_varray) {
+        /* The result has been written into the destination provided by the caller already. */
+        continue;
+      }
+      /* Still have to copy over the data in the destination provided by the caller. */
+      if (output_varray->is_span()) {
+        /* Materialize into a span. */
+        computed_varray->materialize_to_uninitialized(output_varray->get_internal_span().data());
+      }
+      else {
+        /* Slower materialize into a different structure. */
+        const CPPType &type = computed_varray->type();
+        BUFFER_FOR_CPP_TYPE_VALUE(type, buffer);
+        for (const int i : mask) {
+          computed_varray->get_to_uninitialized(i, buffer);
+          output_varray->set_by_relocate(i, buffer);
+        }
+      }
+      r_varrays[out_index] = output_varray;
+    }
+  }
+  return r_varrays;
+}
+
+void evaluate_constant_field(const GField &field, void *r_value)
+{
+  ResourceScope scope;
+  FieldContext context;
+  Vector<const GVArray *> varrays = evaluate_fields(scope, {field}, IndexRange(1), context);
+  varrays[0]->get_to_uninitialized(0, r_value);
+}
+
+const GVArray *FieldContext::get_varray_for_input(const FieldInput &field_input,
+                                                  IndexMask mask,
+                                                  ResourceScope &scope) const
+{
+  /* By default ask the field input to create the varray. Another field context might overwrite
+   * the context here. */
+  return field_input.get_varray_for_context(*this, mask, scope);
+}
+
+/* --------------------------------------------------------------------
+ * FieldEvaluator.
+ */
+
+static Vector<int64_t> indices_from_selection(const VArray<bool> &selection)
+{
+  /* If the selection is just a single value, it's best to avoid calling this
+   * function when constructing an IndexMask and use an IndexRange instead. */
+  BLI_assert(!selection.is_single());
+
+  Vector<int64_t> indices;
+  if (selection.is_span()) {
+    Span<bool> span = selection.get_internal_span();
+    for (const int64_t i : span.index_range()) {
+      if (span[i]) {
+        indices.append(i);
+      }
+    }
+  }
+  else {
+    for (const int i : selection.index_range()) {
+      if (selection[i]) {
+        indices.append(i);
+      }
+    }
+  }
+  return indices;
+}
+
+int FieldEvaluator::add_with_destination(GField field, GVMutableArray &dst)
+{
+  const int field_index = fields_to_evaluate_.append_and_get_index(std::move(field));
+  dst_varrays_.append(&dst);
+  output_pointer_infos_.append({});
+  return field_index;
+}
+
+int FieldEvaluator::add_with_destination(GField field, GMutableSpan dst)
+{
+  GVMutableArray &varray = scope_.construct<GVMutableArray_For_GMutableSpan>(__func__, dst);
+  return this->add_with_destination(std::move(field), varray);
+}
+
+int FieldEvaluator::add(GField field, const GVArray **varray_ptr)
+{
+  const int field_index = fields_to_evaluate_.append_and_get_index(std::move(field));
+  dst_varrays_.append(nullptr);
+  output_pointer_infos_.append(OutputPointerInfo{
+      varray_ptr, [](void *dst, const GVArray &varray, ResourceScope &UNUSED(scope)) {
+        *(const GVArray **)dst = &varray;
+      }});
+  return field_index;
+}
+
+int FieldEvaluator::add(GField field)
+{
+  const int field_index = fields_to_evaluate_.append_and_get_index(std::move(field));
+  dst_varrays_.append(nullptr);
+  output_pointer_infos_.append({});
+  return field_index;
+}
+
+void FieldEvaluator::evaluate()
+{
+  BLI_assert_msg(!is_evaluated_, "Cannot evaluate fields twice.");
+  Array<GFieldRef> fields(fields_to_evaluate_.size());
+  for (const int i : fields_to_evaluate_.index_range()) {
+    fields[i] = fields_to_evaluate_[i];
+  }
+  evaluated_varrays_ = evaluate_fields(scope_, fields, mask_, context_, dst_varrays_);
+  BLI_assert(fields_to_evaluate_.size() == evaluated_varrays_.size());
+  for (const int i : fields_to_evaluate_.index_range()) {
+    OutputPointerInfo &info = output_pointer_infos_[i];
+    if (info.dst != nullptr) {
+      info.set(info.dst, *evaluated_varrays_[i], scope_);
+    }
+  }
+  is_evaluated_ = true;
+}
+
+IndexMask FieldEvaluator::get_evaluated_as_mask(const int field_index)
+{
+  const GVArray &varray = this->get_evaluated(field_index);
+  GVArray_Typed<bool> typed_varray{varray};
+
+  if (typed_varray->is_single()) {
+    if (typed_varray->get_internal_single()) {
+      return IndexRange(typed_varray.size());
+    }
+    return IndexRange(0);
+  }
+
+  return scope_.add_value(indices_from_selection(*typed_varray), __func__).as_span();
+}
+
+}  // namespace blender::fn