Geometry Nodes: Support for dynamic attributes on curve splines

With this patch you will be able to add and remove attributes from curve
data inside of geometry nodes. The following is currently implemented:
* Adding attributes with any data type to splines or spline points.
* Support for working with multiple splines at the same time.
* Interaction with the three builtin point attributes.
* Resampling attributes in the resample node.

The following is not implemented in this patch:
* Joining attributes when joining splines with the join geometry node.
* Domain interpolation between spline and point domains.
* More efficient ways to call attribute operations once per spline.

Differential Revision: https://developer.blender.org/D11251

1 files changed, 49 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/curve_eval.cc b/source/blender/blenkernel/intern/curve_eval.cc
index 1679f21516a..9cafe1124b1 100644
--- a/source/blender/blenkernel/intern/curve_eval.cc
+++ b/source/blender/blenkernel/intern/curve_eval.cc
@@ -16,7 +16,9 @@
 
 #include "BLI_array.hh"
 #include "BLI_listbase.h"
+#include "BLI_map.hh"
 #include "BLI_span.hh"
+#include "BLI_string_ref.hh"
 
 #include "DNA_curve_types.h"
 
@@ -26,7 +28,9 @@
 using blender::Array;
 using blender::float3;
 using blender::float4x4;
+using blender::Map;
 using blender::Span;
+using blender::StringRefNull;
 
 blender::Span<SplinePtr> CurveEval::splines() const
 {
@@ -38,6 +42,9 @@ blender::MutableSpan<SplinePtr> CurveEval::splines()
   return splines_;
 }
 
+/**
+ * \warning Call #reallocate on the spline's attributes after adding all splines.
+ */
 void CurveEval::add_spline(SplinePtr spline)
 {
   splines_.append(std::move(spline));
@@ -178,7 +185,7 @@ std::unique_ptr<CurveEval> curve_eval_from_dna_curve(const Curve &dna_curve)
                             bezt.radius,
                             bezt.tilt);
         }
-
+        spline->attributes.reallocate(spline->size());
         curve->add_spline(std::move(spline));
         break;
       }
@@ -192,7 +199,7 @@ std::unique_ptr<CurveEval> curve_eval_from_dna_curve(const Curve &dna_curve)
         for (const BPoint &bp : Span(nurb->bp, nurb->pntsu)) {
           spline->add_point(bp.vec, bp.radius, bp.tilt, bp.vec[3]);
         }
-
+        spline->attributes.reallocate(spline->size());
         curve->add_spline(std::move(spline));
         break;
       }
@@ -203,7 +210,7 @@ std::unique_ptr<CurveEval> curve_eval_from_dna_curve(const Curve &dna_curve)
         for (const BPoint &bp : Span(nurb->bp, nurb->pntsu)) {
           spline->add_point(bp.vec, bp.radius, bp.tilt);
         }
-
+        spline->attributes.reallocate(spline->size());
         curve->add_spline(std::move(spline));
         break;
       }
@@ -214,6 +221,9 @@ std::unique_ptr<CurveEval> curve_eval_from_dna_curve(const Curve &dna_curve)
     }
   }
 
+  /* Though the curve has no attributes, this is necessary to properly set the custom data size. */
+  curve->attributes.reallocate(curve->splines().size());
+
   /* Note: Normal mode is stored separately in each spline to facilitate combining splines
    * from multiple curve objects, where the value may be different. */
   const Spline::NormalCalculationMode normal_mode = normal_mode_from_dna_curve(
@@ -224,3 +234,39 @@ std::unique_ptr<CurveEval> curve_eval_from_dna_curve(const Curve &dna_curve)
 
   return curve;
 }
+
+/**
+ * Check the invariants that curve control point attributes should always uphold, necessary
+ * because attributes are stored on splines rather than in a flat array on the curve:
+ *  - The same set of attributes exists on every spline.
+ *  - Attributes with the same name have the same type on every spline.
+ */
+void CurveEval::assert_valid_point_attributes() const
+{
+#ifdef DEBUG
+  if (splines_.size() == 0) {
+    return;
+  }
+  const int layer_len = splines_.first()->attributes.data.totlayer;
+  Map<StringRefNull, AttributeMetaData> map;
+  for (const SplinePtr &spline : splines_) {
+    BLI_assert(spline->attributes.data.totlayer == layer_len);
+    spline->attributes.foreach_attribute(
+        [&](StringRefNull name, const AttributeMetaData &meta_data) {
+          map.add_or_modify(
+              name,
+              [&](AttributeMetaData *map_data) {
+                /* All unique attribute names should be added on the first spline. */
+                BLI_assert(spline == splines_.first());
+                *map_data = meta_data;
+              },
+              [&](AttributeMetaData *map_data) {
+                /* Attributes on different splines should all have the same type. */
+                BLI_assert(meta_data == *map_data);
+              });
+          return true;
+        },
+        ATTR_DOMAIN_POINT);
+  }
+#endif
+}
\ No newline at end of file