Curves: new Add brush

This adds a new Add brush for the new curves object type in sculpt mode.
The brush is used to insert new curves (typically hair) on the surface object.

Supported features:
* Add single curve exactly at the cursor position when `Add Amount` is 1.
* Front faces only.
* Independent interpolate shape and interpolate length settings.
* Smooth and flat shading affects curve shape interpolation.
* Spherical and projection brush.

This also adds the `surface_triangle_index` and `surface_triangle_coordinate`
attributes. Those store information about what position on the surface each
added curve is attached to:
* `surface_triangle_index` (`int`): Index of the internal triangle that a curve
  is attached to. `-1` when the curve is not attached to the surface.
* `surface_triangle_coordinate` (`float2`): First two numbers of a barycentric
  coordinate that reference a specific position within the triangle.

Ref T96444.

Differential Revision: https://developer.blender.org/D14340

1 files changed, 22 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/curves_geometry.cc b/source/blender/blenkernel/intern/curves_geometry.cc
index 45f3bf36381..db69fbc4063 100644
--- a/source/blender/blenkernel/intern/curves_geometry.cc
+++ b/source/blender/blenkernel/intern/curves_geometry.cc
@@ -31,6 +31,8 @@ static const std::string ATTR_HANDLE_POSITION_RIGHT = "handle_right";
 static const std::string ATTR_NURBS_ORDER = "nurbs_order";
 static const std::string ATTR_NURBS_WEIGHT = "nurbs_weight";
 static const std::string ATTR_NURBS_KNOTS_MODE = "knots_mode";
+static const std::string ATTR_SURFACE_TRIANGLE_INDEX = "surface_triangle_index";
+static const std::string ATTR_SURFACE_TRIANGLE_COORDINATE = "surface_triangle_coordinate";
 
 /* -------------------------------------------------------------------- */
 /** \name Constructors/Destructor
@@ -378,6 +380,26 @@ MutableSpan<int8_t> CurvesGeometry::nurbs_knots_modes()
   return get_mutable_attribute<int8_t>(*this, ATTR_DOMAIN_CURVE, ATTR_NURBS_KNOTS_MODE);
 }
 
+VArray<int> CurvesGeometry::surface_triangle_indices() const
+{
+  return get_varray_attribute<int>(*this, ATTR_DOMAIN_CURVE, ATTR_SURFACE_TRIANGLE_INDEX, -1);
+}
+
+MutableSpan<int> CurvesGeometry::surface_triangle_indices()
+{
+  return get_mutable_attribute<int>(*this, ATTR_DOMAIN_CURVE, ATTR_SURFACE_TRIANGLE_INDEX);
+}
+
+Span<float2> CurvesGeometry::surface_triangle_coords() const
+{
+  return get_span_attribute<float2>(*this, ATTR_DOMAIN_CURVE, ATTR_SURFACE_TRIANGLE_COORDINATE);
+}
+
+MutableSpan<float2> CurvesGeometry::surface_triangle_coords()
+{
+  return get_mutable_attribute<float2>(*this, ATTR_DOMAIN_CURVE, ATTR_SURFACE_TRIANGLE_COORDINATE);
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */