From 38c7378949b3323471c6e0c30842331db3b85af7 Mon Sep 17 00:00:00 2001
From: Johnny Matthews <johnny.matthews@gmail.com>
Date: Sun, 23 Jan 2022 12:29:37 -0600
Subject: Geometry Nodes: Relative Handle Position Mode Add a boolean option to
 have the Curve Handle Position input node return the position of the handle
 relative to each point position.

Differential Revision: https://developer.blender.org/D12947
---
 .../geometry/nodes/node_geo_input_curve_handles.cc | 80 +++++++++++++++++++++-
 1 file changed, 78 insertions(+), 2 deletions(-)

diff --git a/source/blender/nodes/geometry/nodes/node_geo_input_curve_handles.cc b/source/blender/nodes/geometry/nodes/node_geo_input_curve_handles.cc
index c3c26736e88..fbf6b521fd8 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_input_curve_handles.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_input_curve_handles.cc
@@ -14,20 +14,96 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
+#include "BKE_spline.hh"
+
 #include "node_geometry_util.hh"
 
 namespace blender::nodes::node_geo_input_curve_handles_cc {
 
 static void node_declare(NodeDeclarationBuilder &b)
 {
+  b.add_input<decl::Bool>(N_("Relative")).default_value(false).supports_field();
   b.add_output<decl::Vector>(N_("Left")).field_source();
   b.add_output<decl::Vector>(N_("Right")).field_source();
 }
 
+class HandlePositionFieldInput final : public GeometryFieldInput {
+  Field<bool> relative_;
+  bool left_;
+
+ public:
+  HandlePositionFieldInput(Field<bool> relative, bool left)
+      : GeometryFieldInput(CPPType::get<float3>(), "Handle"), relative_(relative), left_(left)
+  {
+  }
+
+  GVArray get_varray_for_context(const GeometryComponent &component,
+                                 const AttributeDomain domain,
+                                 IndexMask mask) const final
+  {
+    if (component.type() != GEO_COMPONENT_TYPE_CURVE) {
+      return {};
+    }
+
+    GeometryComponentFieldContext field_context{component, ATTR_DOMAIN_POINT};
+    fn::FieldEvaluator evaluator(field_context, &mask);
+    evaluator.add(relative_);
+    evaluator.evaluate();
+    const VArray<bool> &relative = evaluator.get_evaluated<bool>(0);
+
+    VArray<float3> positions = component.attribute_get_for_read<float3>(
+        "position", ATTR_DOMAIN_POINT, {0, 0, 0});
+
+    StringRef side = left_ ? "handle_left" : "handle_right";
+    VArray<float3> handles = component.attribute_get_for_read<float3>(
+        side, ATTR_DOMAIN_POINT, {0, 0, 0});
+
+    if (relative.is_single()) {
+      if (relative.get_internal_single()) {
+        Array<float3> output(positions.size());
+        for (const int i : positions.index_range()) {
+          output[i] = handles[i] - positions[i];
+        }
+        return component.attribute_try_adapt_domain<float3>(
+            VArray<float3>::ForContainer(std::move(output)), ATTR_DOMAIN_POINT, domain);
+      }
+      return component.attribute_try_adapt_domain<float3>(handles, ATTR_DOMAIN_POINT, domain);
+    }
+
+    Array<float3> output(positions.size());
+    for (const int i : positions.index_range()) {
+      if (relative[i]) {
+        output[i] = handles[i] - positions[i];
+      }
+      else {
+        output[i] = handles[i];
+      }
+    }
+    return component.attribute_try_adapt_domain<float3>(
+        VArray<float3>::ForContainer(std::move(output)), ATTR_DOMAIN_POINT, domain);
+  }
+
+  uint64_t hash() const override
+  {
+    return get_default_hash_2(relative_, left_);
+  }
+
+  bool is_equal_to(const fn::FieldNode &other) const override
+  {
+    if (const HandlePositionFieldInput *other_handle =
+            dynamic_cast<const HandlePositionFieldInput *>(&other)) {
+      return relative_ == other_handle->relative_ && left_ == other_handle->left_;
+    }
+    return false;
+  }
+};
+
 static void node_geo_exec(GeoNodeExecParams params)
 {
-  Field<float3> left_field = AttributeFieldInput::Create<float3>("handle_left");
-  Field<float3> right_field = AttributeFieldInput::Create<float3>("handle_right");
+  Field<bool> relative = params.extract_input<Field<bool>>("Relative");
+  Field<float3> left_field{std::make_shared<HandlePositionFieldInput>(relative, true)};
+  Field<float3> right_field{std::make_shared<HandlePositionFieldInput>(relative, false)};
+
   params.set_output("Left", std::move(left_field));
   params.set_output("Right", std::move(right_field));
 }
-- 
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