Fix: Apply tilt in curves data-block normals calculation

The ported normal calculation from ceed37fc5cbb466a0 neglected to
use the tilt attribute to rotate the normals around the tangents.
This commit adds that behavior back, adding a new math header file
to avoid duplicating the rotation function for normalized axes.

Differential Revision: https://developer.blender.org/D14655

1 files changed, 26 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/math_rotation.cc b/source/blender/blenlib/intern/math_rotation.cc
new file mode 100644
index 00000000000..74300d55954
--- /dev/null
+++ b/source/blender/blenlib/intern/math_rotation.cc
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup bli
+ */
+
+#include "BLI_math_base.h"
+#include "BLI_math_rotation.hh"
+#include "BLI_math_vector.h"
+#include "BLI_math_vector.hh"
+
+namespace blender::math {
+
+float3 rotate_direction_around_axis(const float3 &direction, const float3 &axis, const float angle)
+{
+  BLI_ASSERT_UNIT_V3(direction);
+  BLI_ASSERT_UNIT_V3(axis);
+
+  const float3 axis_scaled = axis * math::dot(direction, axis);
+  const float3 diff = direction - axis_scaled;
+  const float3 cross = math::cross(axis, diff);
+
+  return axis_scaled + diff * std::cos(angle) + cross * std::sin(angle);
+}
+
+}  // namespace blender::math