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, 105 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/spline_poly.cc b/source/blender/blenkernel/intern/spline_poly.cc
new file mode 100644
index 00000000000..09c578c0503
--- /dev/null
+++ b/source/blender/blenkernel/intern/spline_poly.cc
@@ -0,0 +1,105 @@
+/*
+ * 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_span.hh"
+#include "BLI_virtual_array.hh"
+
+#include "BKE_spline.hh"
+
+using blender::float3;
+using blender::MutableSpan;
+using blender::Span;
+
+SplinePtr PolySpline::copy() const
+{
+  return std::make_unique<PolySpline>(*this);
+}
+
+int PolySpline::size() const
+{
+  const int size = positions_.size();
+  BLI_assert(size == radii_.size());
+  BLI_assert(size == tilts_.size());
+  return size;
+}
+
+void PolySpline::add_point(const float3 position, const float radius, const float tilt)
+{
+  positions_.append(position);
+  radii_.append(radius);
+  tilts_.append(tilt);
+  this->mark_cache_invalid();
+}
+
+MutableSpan<float3> PolySpline::positions()
+{
+  return positions_;
+}
+Span<float3> PolySpline::positions() const
+{
+  return positions_;
+}
+MutableSpan<float> PolySpline::radii()
+{
+  return radii_;
+}
+Span<float> PolySpline::radii() const
+{
+  return radii_;
+}
+MutableSpan<float> PolySpline::tilts()
+{
+  return tilts_;
+}
+Span<float> PolySpline::tilts() const
+{
+  return tilts_;
+}
+
+void PolySpline::mark_cache_invalid()
+{
+  tangent_cache_dirty_ = true;
+  normal_cache_dirty_ = true;
+  length_cache_dirty_ = true;
+}
+
+int PolySpline::evaluated_points_size() const
+{
+  return this->size();
+}
+
+void PolySpline::correct_end_tangents() const
+{
+}
+
+Span<float3> PolySpline::evaluated_positions() const
+{
+  return this->positions();
+}
+
+/**
+ * Poly spline interpolation from control points to evaluated points is a special case, since
+ * the result data is the same as the input data. This function returns a GVArray that points to
+ * the original data. Therefore the lifetime of the returned virtual array must not be longer than
+ * the source data.
+ */
+blender::fn::GVArrayPtr PolySpline::interpolate_to_evaluated_points(
+    const blender::fn::GVArray &source_data) const
+{
+  BLI_assert(source_data.size() == this->size());
+
+  return source_data.shallow_copy();
+}