path: root/source/blender/functions/intern/field.cc

/*
 * 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 {

struct FieldTreeInfo {
  /**
   * When fields are build, 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 what other
   * fields directly depend on it.
   */
  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 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.has_input_node()) {
      const FieldInput &field_input = static_cast<const FieldInput &>(field.node());
      field_tree_info.deduplicated_field_inputs.add(field_input);
      continue;
    }
    BLI_assert(field.has_operation_node());
    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.try_get_varray_for_context(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 those. */
  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.has_operation_node());

      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_hints: 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_hints were 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_hints)
{
  Vector<const GVArray *> r_varrays(fields_to_evaluate.size(), nullptr);

  /* Destination hints are optional. Create a small utility method to access them. */
  auto get_dst_hint_if_available = [&](int index) -> GVMutableArray * {
    if (dst_hints.is_empty()) {
      return nullptr;
    }
    return dst_hints[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 a context 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.has_input_node()) {
      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);
    }
  }

  const int array_size = mask.min_array_size();

  /* 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, mask.min_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_hint_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 destination hints if still necessary. In some cases the evaluation above has
   * written the computed data in the right place already. */
  if (!dst_hints.is_empty()) {
    for (const int out_index : fields_to_evaluate.index_range()) {
      GVMutableArray *output_varray = get_dst_hint_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);
}

void evaluate_fields_to_spans(Span<GFieldRef> fields_to_evaluate,
                              IndexMask mask,
                              const FieldContext &context,
                              Span<GMutableSpan> out_spans)
{
  ResourceScope scope;
  Vector<GVMutableArray *> varrays;
  for (GMutableSpan span : out_spans) {
    varrays.append(&scope.construct<GVMutableArray_For_GMutableSpan>(__func__, span));
  }
  evaluate_fields(scope, fields_to_evaluate, mask, context, varrays);
}

const GVArray *FieldContext::try_get_varray_for_context(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.try_get_varray_for_context(*this, mask, scope);
}

}  // namespace blender::fn