Geometry Nodes: Draw curve data in the viewport

This patch adds relatively small changes to the curve draw
cache implementation in order to draw the curve data in the
viewport. The dependency graph iterator is also modified
so that it iterates over the curve geometry component, which
is presented to users as `Curve` data with a pointer to the
`CurveEval`

The idea with the spline data type in geometry nodes is that
curve data itself is only the control points, and any evaluated
data with faces is a mesh. That is mostly expected elsewhere in
Blender anyway. This means it's only necessary to implement
wire edge drawing of `CurveEval` data.

Adding a `CurveEval` pointer to `Curve` is in line with changes
I'd like to make in the future like using `CurveEval` in more places
such as edit mode.

An alternate solution involves converting the curve wire data
to a mesh, however, that requires copying all of the data, and
since avoiding it is rather simple and is in-line with future plans
anyway, I think doing it this way is better.

Differential Revision: https://developer.blender.org/D11351

1 files changed, 33 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/geometry_component_curve.cc b/source/blender/blenkernel/intern/geometry_component_curve.cc
index be3fdf26cb3..de8dc355557 100644
--- a/source/blender/blenkernel/intern/geometry_component_curve.cc
+++ b/source/blender/blenkernel/intern/geometry_component_curve.cc
@@ -14,9 +14,14 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
+#include "DNA_ID_enums.h"
+#include "DNA_curve_types.h"
+
 #include "BKE_attribute_access.hh"
 #include "BKE_attribute_math.hh"
+#include "BKE_curve.h"
 #include "BKE_geometry_set.hh"
+#include "BKE_lib_id.h"
 #include "BKE_spline.hh"
 
 #include "attribute_access_intern.hh"
@@ -58,6 +63,11 @@ void CurveComponent::clear()
     if (ownership_ == GeometryOwnershipType::Owned) {
       delete curve_;
     }
+    if (curve_for_render_ != nullptr) {
+      BKE_id_free(nullptr, curve_for_render_);
+      curve_for_render_ = nullptr;
+    }
+
     curve_ = nullptr;
   }
 }
@@ -118,6 +128,29 @@ void CurveComponent::ensure_owns_direct_data()
   }
 }
 
+/**
+ * Create empty curve data used for rendering the spline's wire edges.
+ * \note See comment on #curve_for_render_ for further explanation.
+ */
+const Curve *CurveComponent::get_curve_for_render() const
+{
+  if (curve_ == nullptr) {
+    return nullptr;
+  }
+  if (curve_for_render_ != nullptr) {
+    return curve_for_render_;
+  }
+  std::lock_guard lock{curve_for_render_mutex_};
+  if (curve_for_render_ != nullptr) {
+    return curve_for_render_;
+  }
+
+  curve_for_render_ = (Curve *)BKE_id_new_nomain(ID_CU, nullptr);
+  curve_for_render_->curve_eval = curve_;
+
+  return curve_for_render_;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */