Geometry Nodes: initial scattering and geometry nodes

This is the initial merge from the geometry-nodes branch.
Nodes:
* Attribute Math
* Boolean
* Edge Split
* Float Compare
* Object Info
* Point Distribute
* Point Instance
* Random Attribute
* Random Float
* Subdivision Surface
* Transform
* Triangulate

It includes the initial evaluation of geometry node groups in the Geometry Nodes modifier.

Notes on the Generic attribute access API

The API adds an indirection for attribute access. That has the following benefits:
* Most code does not have to care about how an attribute is stored internally.
  This is mainly necessary, because we have to deal with "legacy" attributes
  such as vertex weights and attributes that are embedded into other structs
  such as vertex positions.
* When reading from an attribute, we generally don't care what domain the
  attribute is stored on. So we want to abstract away the interpolation that
  that adapts attributes from one domain to another domain (this is not
  actually implemented yet).

Other possible improvements for later iterations include:
* Actually implement interpolation between domains.
* Don't use inheritance for the different attribute types. A single class for read
  access and one for write access might be enough, because we know all the ways
  in which attributes are stored internally. We don't want more different internal
  structures in the future. On the contrary, ideally we can consolidate the different
  storage formats in the future to reduce the need for this indirection.
* Remove the need for heap allocations when creating attribute accessors.

It includes commits from:
* Dalai Felinto
* Hans Goudey
* Jacques Lucke
* Léo Depoix

1 files changed, 255 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_attribute_access.hh b/source/blender/blenkernel/BKE_attribute_access.hh
new file mode 100644
index 00000000000..e58fba36342
--- /dev/null
+++ b/source/blender/blenkernel/BKE_attribute_access.hh
@@ -0,0 +1,255 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <mutex>
+
+#include "FN_cpp_type.hh"
+#include "FN_spans.hh"
+
+#include "BKE_attribute.h"
+
+#include "BLI_float3.hh"
+
+struct Mesh;
+
+namespace blender::bke {
+
+using fn::CPPType;
+
+/**
+ * This class offers an indirection for reading an attribute.
+ * This is useful for the following reasons:
+ * - Blender does not store all attributes the same way.
+ *   The simplest case are custom data layers with primitive types.
+ *   A bit more complex are mesh attributes like the position of vertices,
+ *   which are embedded into the MVert struct.
+ *   Even more complex to access are vertex weights.
+ * - Sometimes attributes are stored on one domain, but we want to access
+ *   the attribute on a different domain. Therefore, we have to interpolate
+ *   between the domains.
+ */
+class ReadAttribute {
+ protected:
+  const AttributeDomain domain_;
+  const CPPType &cpp_type_;
+  const int64_t size_;
+
+  /* Protects the span below, so that no two threads initialize it at the same time. */
+  mutable std::mutex span_mutex_;
+  /* When it is not null, it points to the attribute array or a temporary array that contains all
+   * the attribute values. */
+  mutable void *array_buffer_ = nullptr;
+  /* Is true when the buffer above is owned by the attribute accessor. */
+  mutable bool array_is_temporary_ = false;
+
+ public:
+  ReadAttribute(AttributeDomain domain, const CPPType &cpp_type, const int64_t size)
+      : domain_(domain), cpp_type_(cpp_type), size_(size)
+  {
+  }
+
+  virtual ~ReadAttribute();
+
+  AttributeDomain domain() const
+  {
+    return domain_;
+  }
+
+  const CPPType &cpp_type() const
+  {
+    return cpp_type_;
+  }
+
+  int64_t size() const
+  {
+    return size_;
+  }
+
+  void get(const int64_t index, void *r_value) const
+  {
+    BLI_assert(index < size_);
+    this->get_internal(index, r_value);
+  }
+
+  /* Get a span that contains all attribute values. */
+  fn::GSpan get_span() const;
+
+ protected:
+  /* r_value is expected to be uninitialized. */
+  virtual void get_internal(const int64_t index, void *r_value) const = 0;
+
+  virtual void initialize_span() const;
+};
+
+/**
+ * This exists for similar reasons as the ReadAttribute class, except that
+ * it does not deal with interpolation between domains.
+ */
+class WriteAttribute {
+ protected:
+  const AttributeDomain domain_;
+  const CPPType &cpp_type_;
+  const int64_t size_;
+
+  /* When not null, this points either to the attribute array or to a temporary array. */
+  void *array_buffer_ = nullptr;
+  /* True, when the buffer points to a temporary array. */
+  bool array_is_temporary_ = false;
+  /* This helps to protect agains forgetting to apply changes done to the array. */
+  bool array_should_be_applied_ = false;
+
+ public:
+  WriteAttribute(AttributeDomain domain, const CPPType &cpp_type, const int64_t size)
+      : domain_(domain), cpp_type_(cpp_type), size_(size)
+  {
+  }
+
+  virtual ~WriteAttribute();
+
+  AttributeDomain domain() const
+  {
+    return domain_;
+  }
+
+  const CPPType &cpp_type() const
+  {
+    return cpp_type_;
+  }
+
+  int64_t size() const
+  {
+    return size_;
+  }
+
+  void get(const int64_t index, void *r_value) const
+  {
+    BLI_assert(index < size_);
+    this->get_internal(index, r_value);
+  }
+
+  void set(const int64_t index, const void *value)
+  {
+    BLI_assert(index < size_);
+    this->set_internal(index, value);
+  }
+
+  /* Get a span that new attribute values can be written into. When all values have been changed,
+   * #apply_span has to be called. The span might not contain the original attribute values. */
+  fn::GMutableSpan get_span();
+  /* Write the changes to the span into the actual attribute, if they aren't already. */
+  void apply_span();
+
+ protected:
+  virtual void get_internal(const int64_t index, void *r_value) const = 0;
+  virtual void set_internal(const int64_t index, const void *value) = 0;
+
+  virtual void initialize_span();
+  virtual void apply_span_if_necessary();
+};
+
+using ReadAttributePtr = std::unique_ptr<ReadAttribute>;
+using WriteAttributePtr = std::unique_ptr<WriteAttribute>;
+
+/* This provides type safe access to an attribute. */
+template<typename T> class TypedReadAttribute {
+ private:
+  ReadAttributePtr attribute_;
+
+ public:
+  TypedReadAttribute(ReadAttributePtr attribute) : attribute_(std::move(attribute))
+  {
+    BLI_assert(attribute_);
+    BLI_assert(attribute_->cpp_type().is<T>());
+  }
+
+  int64_t size() const
+  {
+    return attribute_->size();
+  }
+
+  T operator[](const int64_t index) const
+  {
+    BLI_assert(index < attribute_->size());
+    T value;
+    value.~T();
+    attribute_->get(index, &value);
+    return value;
+  }
+
+  /* Get a span to that contains all attribute values for faster and more convenient access. */
+  Span<T> get_span() const
+  {
+    return attribute_->get_span().template typed<T>();
+  }
+};
+
+/* This provides type safe access to an attribute. */
+template<typename T> class TypedWriteAttribute {
+ private:
+  WriteAttributePtr attribute_;
+
+ public:
+  TypedWriteAttribute(WriteAttributePtr attribute) : attribute_(std::move(attribute))
+  {
+    BLI_assert(attribute_);
+    BLI_assert(attribute_->cpp_type().is<T>());
+  }
+
+  int64_t size() const
+  {
+    return attribute_->size();
+  }
+
+  T operator[](const int64_t index) const
+  {
+    BLI_assert(index < attribute_->size());
+    T value;
+    value.~T();
+    attribute_->get(index, &value);
+    return value;
+  }
+
+  void set(const int64_t index, const T &value)
+  {
+    attribute_->set(index, &value);
+  }
+
+  /* Get a span that new values can be written into. Once all values have been updated #apply_span
+   * has to be called. The span might *not* contain the initial attribute values, so one should
+   * generally only write to the span. */
+  MutableSpan<T> get_span()
+  {
+    return attribute_->get_span().typed<T>();
+  }
+
+  /* Write back all changes to the actual attribute, if necessary. */
+  void apply_span()
+  {
+    attribute_->apply_span();
+  }
+};
+
+using FloatReadAttribute = TypedReadAttribute<float>;
+using Float3ReadAttribute = TypedReadAttribute<float3>;
+using FloatWriteAttribute = TypedWriteAttribute<float>;
+using Float3WriteAttribute = TypedWriteAttribute<float3>;
+
+const CPPType *custom_data_type_to_cpp_type(const CustomDataType type);
+CustomDataType cpp_type_to_custom_data_type(const CPPType &type);
+
+}  // namespace blender::bke