From 848ced8fe67ae9fad12671524c4dd6966284e9f0 Mon Sep 17 00:00:00 2001
From: Hans Goudey <hans@blender.org>
Date: Wed, 3 Sep 2025 04:29:08 +0200
Subject: [PATCH] Curves: Parallelize nurbs custom knots offsets cache
 calculation

Build the size for each curve in parallel, then accumulate the sizes
to offsets afterwards. This way it's easy to parallel. Also only count
custom knots for NURBS.

Pull Request: https://projects.blender.org/blender/blender/pulls/145581
---
 .../blenkernel/intern/curves_geometry.cc      | 28 ++++++++++++-------
 .../tests/grease_pencil_merge_test.cc         |  7 +++++
 .../tests/GEO_realize_instances_test.cc       |  1 +
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/source/blender/blenkernel/intern/curves_geometry.cc b/source/blender/blenkernel/intern/curves_geometry.cc
index aa392951a4d..24b2277126f 100644
--- a/source/blender/blenkernel/intern/curves_geometry.cc
+++ b/source/blender/blenkernel/intern/curves_geometry.cc
@@ -548,23 +548,31 @@ IndexMask CurvesGeometry::nurbs_custom_knot_curves(IndexMaskMemory &memory) cons
 OffsetIndices<int> CurvesGeometry::nurbs_custom_knots_by_curve() const
 {
   const CurvesGeometryRuntime &runtime = *this->runtime;
-  if (this->is_empty()) {
+  if (!this->has_curve_with_type(CURVE_TYPE_NURBS)) {
     return {};
   }
   runtime.custom_knot_offsets_cache.ensure([&](Vector<int> &r_data) {
-    r_data.resize(this->curve_num + 1, 0);
+    r_data.resize(this->curve_num + 1);
 
-    const OffsetIndices points_by_curve = this->points_by_curve();
+    const OffsetIndices<int> points_by_curve = this->points_by_curve();
+    const VArray<int8_t> curve_types = this->curve_types();
     const VArray<int8_t> knot_modes = this->nurbs_knots_modes();
     const VArray<int8_t> orders = this->nurbs_orders();
 
-    int knot_count = 0;
-    for (const int curve : this->curves_range()) {
-      knot_count += knot_modes[curve] == NURBS_KNOT_MODE_CUSTOM ?
-                        points_by_curve[curve].size() + orders[curve] :
-                        0;
-      r_data[curve + 1] = knot_count;
-    }
+    threading::parallel_for(this->curves_range(), 1024, [&](const IndexRange range) {
+      for (const int curve : range) {
+        if (curve_types[curve] != CURVE_TYPE_NURBS) {
+          r_data[curve] = 0;
+          continue;
+        }
+        if (knot_modes[curve] != NURBS_KNOT_MODE_CUSTOM) {
+          r_data[curve] = 0;
+          continue;
+        }
+        r_data[curve] = points_by_curve[curve].size() + orders[curve];
+      }
+    });
+    offset_indices::accumulate_counts_to_offsets(r_data.as_mutable_span());
   });
   return OffsetIndices<int>(runtime.custom_knot_offsets_cache.data());
 }
diff --git a/source/blender/editors/grease_pencil/tests/grease_pencil_merge_test.cc b/source/blender/editors/grease_pencil/tests/grease_pencil_merge_test.cc
index 781b8498771..3fd5c762114 100644
--- a/source/blender/editors/grease_pencil/tests/grease_pencil_merge_test.cc
+++ b/source/blender/editors/grease_pencil/tests/grease_pencil_merge_test.cc
@@ -190,21 +190,28 @@ TEST(grease_pencil_merge, merge_keyframes)
 
   Drawing *drawing = grease_pencil.insert_frame(layer1, 0);
   drawing->strokes_for_write().resize(10, 2);
+  drawing->strokes_for_write().update_curve_types();
 
   drawing = grease_pencil.insert_frame(layer2, 0);
   drawing->strokes_for_write().resize(20, 3);
+  drawing->strokes_for_write().update_curve_types();
   drawing = grease_pencil.insert_frame(layer2, 2);
   drawing->strokes_for_write().resize(30, 4);
+  drawing->strokes_for_write().update_curve_types();
 
   drawing = grease_pencil.insert_frame(layer3, 0);
   drawing->strokes_for_write().resize(40, 5);
+  drawing->strokes_for_write().update_curve_types();
   drawing = grease_pencil.insert_frame(layer3, 3);
   drawing->strokes_for_write().resize(50, 6);
+  drawing->strokes_for_write().update_curve_types();
 
   drawing = grease_pencil.insert_frame(layer4, 1);
   drawing->strokes_for_write().resize(60, 7);
+  drawing->strokes_for_write().update_curve_types();
   drawing = grease_pencil.insert_frame(layer4, 3);
   drawing->strokes_for_write().resize(70, 8);
+  drawing->strokes_for_write().update_curve_types();
 
   GreasePencil *merged_grease_pencil = BKE_grease_pencil_new_nomain();
   BKE_grease_pencil_copy_parameters(grease_pencil, *merged_grease_pencil);
diff --git a/source/blender/geometry/tests/GEO_realize_instances_test.cc b/source/blender/geometry/tests/GEO_realize_instances_test.cc
index 536f393de65..465fb6d3a77 100644
--- a/source/blender/geometry/tests/GEO_realize_instances_test.cc
+++ b/source/blender/geometry/tests/GEO_realize_instances_test.cc
@@ -44,6 +44,7 @@ static void create_test_curves(bke::CurvesGeometry &curves, Span<int> offsets)
 
   curves.resize(points_num, curves_num);
   curves.offsets_for_write().copy_from(offsets);
+  curves.update_curve_types();
 
   /* Attribute storing original indices to test point remapping. */
   SpanAttributeWriter<int> test_indices_writer =