Curves: Port fillet node to the new data-block

This commit ports the fillet curves node to the new curves data-block,
and moves the fillet node implementation to the geometry module to help
separate the implementation from the node.

The changes are similar to the subdivide node or resample node. I've
resused common utilities where it makes sense, though some things like
the iteration over attributes can be generalized further. The node
is now multi-threaded per-curve and inside each curve, and some buffers
are reused per curve to avoid many allocations.

The code is more explicit now, and though there is more boilerplate to
pass around many spans, the more complex logic should be more readable.

Differential Revision: https://developer.blender.org/D15346

1 files changed, 10 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_index_range.hh b/source/blender/blenlib/BLI_index_range.hh
index bd0a7e5bb7a..6fcc560d856 100644
--- a/source/blender/blenlib/BLI_index_range.hh
+++ b/source/blender/blenlib/BLI_index_range.hh
@@ -198,6 +198,16 @@ class IndexRange {
   }
 
   /**
+   * Get the element one before the beginning. The returned value is undefined when the range is
+   * empty, and the range must start after zero already.
+   */
+  constexpr int64_t one_before_start() const
+  {
+    BLI_assert(start_ > 0);
+    return start_ - 1;
+  }
+
+  /**
    * Get the element one after the end. The returned value is undefined when the range is empty.
    */
   constexpr int64_t one_after_last() const