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

4 files changed, 68 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_math_rotation.hh b/source/blender/blenlib/BLI_math_rotation.hh
new file mode 100644
index 00000000000..e8b746b34df
--- /dev/null
+++ b/source/blender/blenlib/BLI_math_rotation.hh
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#pragma once
+
+/** \file
+ * \ingroup bli
+ */
+
+#include "BLI_math_vec_types.hh"
+
+namespace blender::math {
+
+/**
+ * Rotate the unit-length \a direction around the unit-length \a axis by the \a angle.
+ */
+float3 rotate_direction_around_axis(const float3 &direction, const float3 &axis, float angle);
+
+}  // namespace blender::math
diff --git a/source/blender/blenlib/CMakeLists.txt b/source/blender/blenlib/CMakeLists.txt
index 99e07264276..e8a3851e082 100644
--- a/source/blender/blenlib/CMakeLists.txt
+++ b/source/blender/blenlib/CMakeLists.txt
@@ -94,6 +94,7 @@ set(SRC
   intern/math_interp.c
   intern/math_matrix.c
   intern/math_rotation.c
+  intern/math_rotation.cc
   intern/math_solvers.c
   intern/math_statistics.c
   intern/math_time.c
@@ -251,6 +252,7 @@ set(SRC
   BLI_math_matrix.h
   BLI_math_mpq.hh
   BLI_math_rotation.h
+  BLI_math_rotation.hh
   BLI_math_solvers.h
   BLI_math_statistics.h
   BLI_math_time.h
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
diff --git a/source/blender/blenlib/tests/BLI_math_rotation_test.cc b/source/blender/blenlib/tests/BLI_math_rotation_test.cc
index a10e441cfbe..a283118bea2 100644
--- a/source/blender/blenlib/tests/BLI_math_rotation_test.cc
+++ b/source/blender/blenlib/tests/BLI_math_rotation_test.cc
@@ -4,6 +4,8 @@
 
 #include "BLI_math_base.h"
 #include "BLI_math_rotation.h"
+#include "BLI_math_rotation.hh"
+#include "BLI_math_vector.hh"
 
 #include <cmath>
 
@@ -147,3 +149,23 @@ TEST(math_rotation, quat_split_swing_and_twist_negative)
   EXPECT_V4_NEAR(swing, expected_swing, FLT_EPSILON);
   EXPECT_V4_NEAR(twist, expected_twist, FLT_EPSILON);
 }
+
+namespace blender::math::tests {
+
+TEST(math_rotation, RotateDirectionAroundAxis)
+{
+  const float3 a = rotate_direction_around_axis({1, 0, 0}, {0, 0, 1}, M_PI_2);
+  EXPECT_NEAR(a.x, 0.0f, FLT_EPSILON);
+  EXPECT_NEAR(a.y, 1.0f, FLT_EPSILON);
+  EXPECT_NEAR(a.z, 0.0f, FLT_EPSILON);
+  const float3 b = rotate_direction_around_axis({1, 0, 0}, {0, 0, 1}, M_PI);
+  EXPECT_NEAR(b.x, -1.0f, FLT_EPSILON);
+  EXPECT_NEAR(b.y, 0.0f, FLT_EPSILON);
+  EXPECT_NEAR(b.z, 0.0f, FLT_EPSILON);
+  const float3 c = rotate_direction_around_axis({0, 0, 1}, {0, 0, 1}, 0.0f);
+  EXPECT_NEAR(c.x, 0.0f, FLT_EPSILON);
+  EXPECT_NEAR(c.y, 0.0f, FLT_EPSILON);
+  EXPECT_NEAR(c.z, 1.0f, FLT_EPSILON);
+}
+
+}  // namespace blender::math::tests