Attribute Math: Improve performance of mixer in some cases

The `DefaultMixer` for mixing generic data types has some issues:
1. The full buffer is always zeroed, even if only some is used.
2. Finalizing also works on all values, even if only some are used.
3. "mixing" doesn't allow setting the first value, requiring that
everything is cleared beforehand.

This commit adds the following functionality:
1. Constructor with the specified `IndexMask` for preliminary zeroing.
2. `set` method to overwrite the value.
3. `finalize` with the specified mask to process a subset of values.

This is useful in situations where you want to use the
DefaultMixer without having to overwrite all the values many times.

A performance improvement was observed for NURBS curve evaluation and
attribute interpolation from the point to curve domain of about 15% and
35% respectively (100,000 curves).

Differential Revision: https://developer.blender.org/D15434

1 files changed, 9 insertions, 5 deletions

diff --git a/source/blender/blenkernel/intern/curves_geometry.cc b/source/blender/blenkernel/intern/curves_geometry.cc
index 7fb4e37f956..c37634b5d3d 100644
--- a/source/blender/blenkernel/intern/curves_geometry.cc
+++ b/source/blender/blenkernel/intern/curves_geometry.cc
@@ -13,6 +13,7 @@
 #include "BLI_index_mask_ops.hh"
 #include "BLI_length_parameterize.hh"
 #include "BLI_math_rotation.hh"
+#include "BLI_task.hh"
 
 #include "DNA_curves_types.h"
 
@@ -1467,12 +1468,15 @@ static void adapt_curve_domain_point_to_curve_impl(const CurvesGeometry &curves,
                                                    MutableSpan<T> r_values)
 {
   attribute_math::DefaultMixer<T> mixer(r_values);
-  for (const int i_curve : IndexRange(curves.curves_num())) {
-    for (const int i_point : curves.points_for_curve(i_curve)) {
-      mixer.mix_in(i_curve, old_values[i_point]);
+
+  threading::parallel_for(curves.curves_range(), 128, [&](const IndexRange range) {
+    for (const int i_curve : range) {
+      for (const int i_point : curves.points_for_curve(i_curve)) {
+        mixer.mix_in(i_curve, old_values[i_point]);
+      }
     }
-  }
-  mixer.finalize();
+    mixer.finalize(range);
+  });
 }
 
 /**