Geometry Nodes: Curve tangent node

This node outputs the direction vector, or tangent of a curve at every
control point. For poly splines this is simply the evaluated tangents,
so it all works very simply. For Bezier splines it uses the tangent at
the evaluated point corresponding to each control point, and NURBS
are interpereted as poly splines built from their control points.

Internally the node is called "Input Tangent" to simplify using it for
mesh tangents as well in the future like the "Normal" node.

Differential Revision: https://developer.blender.org/D12581

1 files changed, 174 insertions, 0 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_input_tangent.cc b/source/blender/nodes/geometry/nodes/node_geo_input_tangent.cc
new file mode 100644
index 00000000000..68788709f1e
--- /dev/null
+++ b/source/blender/nodes/geometry/nodes/node_geo_input_tangent.cc
@@ -0,0 +1,174 @@
+/*
+ * 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_task.hh"
+
+#include "BKE_spline.hh"
+
+#include "node_geometry_util.hh"
+
+namespace blender::nodes {
+
+static void geo_node_input_tangent_declare(NodeDeclarationBuilder &b)
+{
+  b.add_output<decl::Vector>("Tangent");
+}
+
+static void calculate_bezier_tangents(const BezierSpline &spline, MutableSpan<float3> tangents)
+{
+  Span<int> offsets = spline.control_point_offsets();
+  Span<float3> evaluated_tangents = spline.evaluated_tangents();
+  for (const int i : IndexRange(spline.size())) {
+    tangents[i] = evaluated_tangents[offsets[i]];
+  }
+}
+
+static void calculate_poly_tangents(const PolySpline &spline, MutableSpan<float3> tangents)
+{
+  tangents.copy_from(spline.evaluated_tangents());
+}
+
+/**
+ * Because NURBS control points are not necessarily on the path, the tangent at the control points
+ * is not well defined, so create a temporary poly spline to find the tangents. This requires extra
+ * copying currently, but may be more efficient in the future if attributes have some form of CoW.
+ */
+static void calculate_nurbs_tangents(const NURBSpline &spline, MutableSpan<float3> tangents)
+{
+  PolySpline poly_spline;
+  poly_spline.resize(spline.size());
+  poly_spline.positions().copy_from(spline.positions());
+  tangents.copy_from(poly_spline.evaluated_tangents());
+}
+
+static Array<float3> curve_tangent_point_domain(const CurveEval &curve)
+{
+  Span<SplinePtr> splines = curve.splines();
+  Array<int> offsets = curve.control_point_offsets();
+  const int total_size = offsets.last();
+  Array<float3> tangents(total_size);
+
+  threading::parallel_for(splines.index_range(), 128, [&](IndexRange range) {
+    for (const int i : range) {
+      const Spline &spline = *splines[i];
+      MutableSpan spline_tangents{tangents.as_mutable_span().slice(offsets[i], spline.size())};
+      switch (splines[i]->type()) {
+        case Spline::Type::Bezier: {
+          calculate_bezier_tangents(static_cast<const BezierSpline &>(spline), spline_tangents);
+          break;
+        }
+        case Spline::Type::Poly: {
+          calculate_poly_tangents(static_cast<const PolySpline &>(spline), spline_tangents);
+          break;
+        }
+        case Spline::Type::NURBS: {
+          calculate_nurbs_tangents(static_cast<const NURBSpline &>(spline), spline_tangents);
+          break;
+        }
+      }
+    }
+  });
+  return tangents;
+}
+
+static const GVArray *construct_curve_tangent_gvarray(const CurveComponent &component,
+                                                      const AttributeDomain domain,
+                                                      ResourceScope &scope)
+{
+  const CurveEval *curve = component.get_for_read();
+  if (curve == nullptr) {
+    return nullptr;
+  }
+
+  if (domain == ATTR_DOMAIN_POINT) {
+    const Span<SplinePtr> splines = curve->splines();
+
+    /* Use a reference to evaluated tangents if possible to avoid an allocation and a copy.
+     * This is only possible when there is only one poly spline. */
+    if (splines.size() == 1 && splines.first()->type() == Spline::Type::Poly) {
+      const PolySpline &spline = static_cast<PolySpline &>(*splines.first());
+      return &scope.construct<fn::GVArray_For_Span<float3>>(spline.evaluated_tangents());
+    }
+
+    Array<float3> tangents = curve_tangent_point_domain(*curve);
+    return &scope.construct<fn::GVArray_For_ArrayContainer<Array<float3>>>(std::move(tangents));
+  }
+
+  if (domain == ATTR_DOMAIN_CURVE) {
+    Array<float3> point_tangents = curve_tangent_point_domain(*curve);
+    GVArrayPtr gvarray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<float3>>>(
+        std::move(point_tangents));
+    GVArrayPtr spline_tangents = component.attribute_try_adapt_domain(
+        std::move(gvarray), ATTR_DOMAIN_POINT, ATTR_DOMAIN_CURVE);
+    return scope.add_value(std::move(spline_tangents)).get();
+  }
+
+  return nullptr;
+}
+
+class TangentFieldInput final : public fn::FieldInput {
+ public:
+  TangentFieldInput() : fn::FieldInput(CPPType::get<float3>(), "Tangent")
+  {
+  }
+
+  const GVArray *get_varray_for_context(const fn::FieldContext &context,
+                                        IndexMask UNUSED(mask),
+                                        ResourceScope &scope) const final
+  {
+    if (const GeometryComponentFieldContext *geometry_context =
+            dynamic_cast<const GeometryComponentFieldContext *>(&context)) {
+
+      const GeometryComponent &component = geometry_context->geometry_component();
+      const AttributeDomain domain = geometry_context->domain();
+
+      if (component.type() == GEO_COMPONENT_TYPE_CURVE) {
+        const CurveComponent &curve_component = static_cast<const CurveComponent &>(component);
+        return construct_curve_tangent_gvarray(curve_component, domain, scope);
+      }
+    }
+    return nullptr;
+  }
+
+  uint64_t hash() const override
+  {
+    /* Some random constant hash. */
+    return 91827364589;
+  }
+
+  bool is_equal_to(const fn::FieldNode &other) const override
+  {
+    return dynamic_cast<const TangentFieldInput *>(&other) != nullptr;
+  }
+};
+
+static void geo_node_input_tangent_exec(GeoNodeExecParams params)
+{
+  Field<float3> tangent_field{std::make_shared<TangentFieldInput>()};
+  params.set_output("Tangent", std::move(tangent_field));
+}
+
+}  // namespace blender::nodes
+
+void register_node_type_geo_input_tangent()
+{
+  static bNodeType ntype;
+
+  geo_node_type_base(&ntype, GEO_NODE_INPUT_TANGENT, "Curve Tangent", NODE_CLASS_INPUT, 0);
+  ntype.geometry_node_execute = blender::nodes::geo_node_input_tangent_exec;
+  ntype.declare = blender::nodes::geo_node_input_tangent_declare;
+  nodeRegisterType(&ntype);
+}