Geometry Nodes: Initial basic curve data support

This patch adds initial curve support to geometry nodes. Currently
there is only one node available, the "Curve to Mesh" node, T87428.

However, the aim of the changes here is larger than just supporting
curve data in nodes-- it also uses the opportunity to add better spline
data structures, intended to replace the existing curve evaluation code.
The curve code in Blender is quite old, and it's generally regarded as
some of the messiest, hardest-to-understand code as well. The classes
in `BKE_spline.hh` aim to be faster, more extensible, and much more
easily understandable. Further explanation can be found in comments in
that file.

Initial builtin spline attributes are supported-- reading and writing
from the `cyclic` and `resolution` attributes works with any of the
attribute nodes. Also, only Z-up normal calculation is implemented
at the moment, and tilts do not apply yet.

**Limitations**
 - For now, you must bring curves into the node tree with an "Object
   Info" node. Changes to the curve modifier stack will come later.
 - Converting to a mesh is necessary to visualize the curve data.

Further progress can be tracked in: T87245
Higher level design document: https://wiki.blender.org/wiki/Modules/Physics_Nodes/Projects/EverythingNodes/CurveNodes

Differential Revision: https://developer.blender.org/D11091

1 files changed, 299 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/geometry_component_curve.cc b/source/blender/blenkernel/intern/geometry_component_curve.cc
new file mode 100644
index 00000000000..0490d577b88
--- /dev/null
+++ b/source/blender/blenkernel/intern/geometry_component_curve.cc
@@ -0,0 +1,299 @@
+/*
+ * 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 "BKE_spline.hh"
+
+#include "BKE_attribute_access.hh"
+#include "BKE_attribute_math.hh"
+#include "BKE_geometry_set.hh"
+
+#include "attribute_access_intern.hh"
+
+/* -------------------------------------------------------------------- */
+/** \name Geometry Component Implementation
+ * \{ */
+
+CurveComponent::CurveComponent() : GeometryComponent(GEO_COMPONENT_TYPE_CURVE)
+{
+}
+
+CurveComponent::~CurveComponent()
+{
+  this->clear();
+}
+
+GeometryComponent *CurveComponent::copy() const
+{
+  CurveComponent *new_component = new CurveComponent();
+  if (curve_ != nullptr) {
+    new_component->curve_ = curve_->copy();
+    new_component->ownership_ = GeometryOwnershipType::Owned;
+  }
+  return new_component;
+}
+
+void CurveComponent::clear()
+{
+  BLI_assert(this->is_mutable());
+  if (curve_ != nullptr) {
+    if (ownership_ == GeometryOwnershipType::Owned) {
+      delete curve_;
+    }
+    curve_ = nullptr;
+  }
+}
+
+bool CurveComponent::has_curve() const
+{
+  return curve_ != nullptr;
+}
+
+/* Clear the component and replace it with the new curve. */
+void CurveComponent::replace(CurveEval *curve, GeometryOwnershipType ownership)
+{
+  BLI_assert(this->is_mutable());
+  this->clear();
+  curve_ = curve;
+  ownership_ = ownership;
+}
+
+CurveEval *CurveComponent::release()
+{
+  BLI_assert(this->is_mutable());
+  CurveEval *curve = curve_;
+  curve_ = nullptr;
+  return curve;
+}
+
+const CurveEval *CurveComponent::get_for_read() const
+{
+  return curve_;
+}
+
+CurveEval *CurveComponent::get_for_write()
+{
+  BLI_assert(this->is_mutable());
+  if (ownership_ == GeometryOwnershipType::ReadOnly) {
+    curve_ = curve_->copy();
+    ownership_ = GeometryOwnershipType::Owned;
+  }
+  return curve_;
+}
+
+bool CurveComponent::is_empty() const
+{
+  return curve_ == nullptr;
+}
+
+bool CurveComponent::owns_direct_data() const
+{
+  return ownership_ == GeometryOwnershipType::Owned;
+}
+
+void CurveComponent::ensure_owns_direct_data()
+{
+  BLI_assert(this->is_mutable());
+  if (ownership_ != GeometryOwnershipType::Owned) {
+    curve_ = curve_->copy();
+    ownership_ = GeometryOwnershipType::Owned;
+  }
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Attribute Access
+ * \{ */
+
+int CurveComponent::attribute_domain_size(const AttributeDomain domain) const
+{
+  if (curve_ == nullptr) {
+    return 0;
+  }
+  if (domain == ATTR_DOMAIN_POINT) {
+    int total = 0;
+    for (const SplinePtr &spline : curve_->splines) {
+      total += spline->size();
+    }
+    return total;
+  }
+  if (domain == ATTR_DOMAIN_CURVE) {
+    return curve_->splines.size();
+  }
+  return 0;
+}
+
+namespace blender::bke {
+
+class BuiltinSplineAttributeProvider final : public BuiltinAttributeProvider {
+  using AsReadAttribute = GVArrayPtr (*)(const CurveEval &data);
+  using AsWriteAttribute = GVMutableArrayPtr (*)(CurveEval &data);
+  using UpdateOnWrite = void (*)(Spline &spline);
+  const AsReadAttribute as_read_attribute_;
+  const AsWriteAttribute as_write_attribute_;
+
+ public:
+  BuiltinSplineAttributeProvider(std::string attribute_name,
+                                 const CustomDataType attribute_type,
+                                 const WritableEnum writable,
+                                 const AsReadAttribute as_read_attribute,
+                                 const AsWriteAttribute as_write_attribute)
+      : BuiltinAttributeProvider(std::move(attribute_name),
+                                 ATTR_DOMAIN_CURVE,
+                                 attribute_type,
+                                 BuiltinAttributeProvider::NonCreatable,
+                                 writable,
+                                 BuiltinAttributeProvider::NonDeletable),
+        as_read_attribute_(as_read_attribute),
+        as_write_attribute_(as_write_attribute)
+  {
+  }
+
+  GVArrayPtr try_get_for_read(const GeometryComponent &component) const final
+  {
+    const CurveComponent &curve_component = static_cast<const CurveComponent &>(component);
+    const CurveEval *curve = curve_component.get_for_read();
+    if (curve == nullptr) {
+      return {};
+    }
+
+    return as_read_attribute_(*curve);
+  }
+
+  GVMutableArrayPtr try_get_for_write(GeometryComponent &component) const final
+  {
+    if (writable_ != Writable) {
+      return {};
+    }
+    CurveComponent &curve_component = static_cast<CurveComponent &>(component);
+    CurveEval *curve = curve_component.get_for_write();
+    if (curve == nullptr) {
+      return {};
+    }
+
+    return as_write_attribute_(*curve);
+  }
+
+  bool try_delete(GeometryComponent &UNUSED(component)) const final
+  {
+    return false;
+  }
+
+  bool try_create(GeometryComponent &UNUSED(component),
+                  const AttributeInit &UNUSED(initializer)) const final
+  {
+    return false;
+  }
+
+  bool exists(const GeometryComponent &component) const final
+  {
+    return component.attribute_domain_size(ATTR_DOMAIN_CURVE) != 0;
+  }
+};
+
+static int get_spline_resolution(const SplinePtr &spline)
+{
+  if (const BezierSpline *bezier_spline = dynamic_cast<const BezierSpline *>(spline.get())) {
+    return bezier_spline->resolution();
+  }
+  if (const NURBSpline *nurb_spline = dynamic_cast<const NURBSpline *>(spline.get())) {
+    return nurb_spline->resolution();
+  }
+  return 1;
+}
+
+static void set_spline_resolution(SplinePtr &spline, const int resolution)
+{
+  if (BezierSpline *bezier_spline = dynamic_cast<BezierSpline *>(spline.get())) {
+    bezier_spline->set_resolution(std::max(resolution, 1));
+  }
+  if (NURBSpline *nurb_spline = dynamic_cast<NURBSpline *>(spline.get())) {
+    nurb_spline->set_resolution(std::max(resolution, 1));
+  }
+}
+
+static GVArrayPtr make_resolution_read_attribute(const CurveEval &curve)
+{
+  return std::make_unique<fn::GVArray_For_DerivedSpan<SplinePtr, int, get_spline_resolution>>(
+      curve.splines.as_span());
+}
+
+static GVMutableArrayPtr make_resolution_write_attribute(CurveEval &curve)
+{
+  return std::make_unique<fn::GVMutableArray_For_DerivedSpan<SplinePtr,
+                                                             int,
+                                                             get_spline_resolution,
+                                                             set_spline_resolution>>(
+      curve.splines.as_mutable_span());
+}
+
+static bool get_cyclic_value(const SplinePtr &spline)
+{
+  return spline->is_cyclic();
+}
+
+static void set_cyclic_value(SplinePtr &spline, const bool value)
+{
+  if (spline->is_cyclic() != value) {
+    spline->set_cyclic(value);
+    spline->mark_cache_invalid();
+  }
+}
+
+static GVArrayPtr make_cyclic_read_attribute(const CurveEval &curve)
+{
+  return std::make_unique<fn::GVArray_For_DerivedSpan<SplinePtr, bool, get_cyclic_value>>(
+      curve.splines.as_span());
+}
+
+static GVMutableArrayPtr make_cyclic_write_attribute(CurveEval &curve)
+{
+  return std::make_unique<
+      fn::GVMutableArray_For_DerivedSpan<SplinePtr, bool, get_cyclic_value, set_cyclic_value>>(
+      curve.splines.as_mutable_span());
+}
+
+/**
+ * In this function all the attribute providers for a curve component are created. Most data
+ * in this function is statically allocated, because it does not change over time.
+ */
+static ComponentAttributeProviders create_attribute_providers_for_curve()
+{
+  static BuiltinSplineAttributeProvider resolution("resolution",
+                                                   CD_PROP_INT32,
+                                                   BuiltinAttributeProvider::Writable,
+                                                   make_resolution_read_attribute,
+                                                   make_resolution_write_attribute);
+
+  static BuiltinSplineAttributeProvider cyclic("cyclic",
+                                               CD_PROP_BOOL,
+                                               BuiltinAttributeProvider::Writable,
+                                               make_cyclic_read_attribute,
+                                               make_cyclic_write_attribute);
+
+  return ComponentAttributeProviders({&resolution, &cyclic}, {});
+}
+
+}  // namespace blender::bke
+
+const blender::bke::ComponentAttributeProviders *CurveComponent::get_attribute_providers() const
+{
+  static blender::bke::ComponentAttributeProviders providers =
+      blender::bke::create_attribute_providers_for_curve();
+  return &providers;
+}
+
+/** \} */