Fix T90387: division by zero when trying to invert scale

Fix division by zero when `BKE_bone_parent_transform_invert()` inverts a
scale vector with zero components.

Zero values in the to-be-inverted vector are now simply skipped, i.e.
remain zero after inversion. This at least ensures that
`invert_v3_safe(invert_v3_safe(vector))` results in the same vector.

This commit does NOT fix the conceptual problem that an inversion of a
potentially non-invertible vector is relied upon. It just avoids the
division by zero.

1 files changed, 18 insertions, 0 deletions

diff --git a/source/blender/blenlib/tests/BLI_math_vector_test.cc b/source/blender/blenlib/tests/BLI_math_vector_test.cc
index 7e75a521d4c..955f02b8065 100644
--- a/source/blender/blenlib/tests/BLI_math_vector_test.cc
+++ b/source/blender/blenlib/tests/BLI_math_vector_test.cc
@@ -45,3 +45,21 @@ TEST(math_vector, ClampVecWithVecs)
   EXPECT_FLOAT_EQ(1.0f, c[0]);
   EXPECT_FLOAT_EQ(3.0f, c[1]);
 }
+
+TEST(math_vector, test_invert_v3_safe)
+{
+  float v3_with_zeroes[3] = {0.0f, 2.0f, 3.0f};
+  invert_v3_safe(v3_with_zeroes);
+  EXPECT_FLOAT_EQ(0.0f, v3_with_zeroes[0]);
+  EXPECT_FLOAT_EQ(0.5f, v3_with_zeroes[1]);
+  EXPECT_FLOAT_EQ(0.33333333333f, v3_with_zeroes[2]);
+
+  float v3_without_zeroes[3] = {1.0f, 2.0f, 3.0f};
+  float inverted_unsafe[3] = {1.0f, 2.0f, 3.0f};
+  invert_v3_safe(v3_without_zeroes);
+  invert_v3(inverted_unsafe);
+
+  EXPECT_FLOAT_EQ(inverted_unsafe[0], v3_without_zeroes[0]);
+  EXPECT_FLOAT_EQ(inverted_unsafe[1], v3_without_zeroes[1]);
+  EXPECT_FLOAT_EQ(inverted_unsafe[2], v3_without_zeroes[2]);
+}