Fix #31193: Normals don't have any Z component

Issue was caused by heavily non-uniform scale applied on object.
Run scale correction on face and vertex normals draw if there's non-uniform scale.

1 files changed, 29 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/math_matrix.c b/source/blender/blenlib/intern/math_matrix.c
index bb0b8897b15..b3b58dca1a6 100644
--- a/source/blender/blenlib/intern/math_matrix.c
+++ b/source/blender/blenlib/intern/math_matrix.c
@@ -866,6 +866,35 @@ int is_orthonormal_m4(float m[][4])
 	return 0;
 }
 
+int is_uniform_scaled_m3(float m[][3])
+{
+	const float eps = 1e-7;
+	float t[3][3];
+	float l1, l2, l3, l4, l5, l6;
+
+	copy_m3_m3(t, m);
+	transpose_m3(t);
+
+	l1 = len_squared_v3(m[0]);
+	l2 = len_squared_v3(m[1]);
+	l3 = len_squared_v3(m[2]);
+
+	l4 = len_squared_v3(t[0]);
+	l5 = len_squared_v3(t[1]);
+	l6 = len_squared_v3(t[2]);
+
+	if (fabsf(l2 - l1) <= eps &&
+	    fabsf(l3 - l1) <= eps &&
+	    fabsf(l4 - l1) <= eps &&
+	    fabsf(l5 - l1) <= eps &&
+	    fabsf(l6 - l1) <= eps)
+	{
+		return 1;
+	}
+
+	return 0;
+}
+
 void normalize_m3(float mat[][3])
 {
 	normalize_v3(mat[0]);