Math Lib: add function to get signed angle about an axis

2 files changed, 27 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_math_vector.h b/source/blender/blenlib/BLI_math_vector.h
index aa103c9727f..942097e1ed6 100644
--- a/source/blender/blenlib/BLI_math_vector.h
+++ b/source/blender/blenlib/BLI_math_vector.h
@@ -251,6 +251,7 @@ float angle_v3v3v3(const float a[3], const float b[3], const float c[3]) ATTR_WA
 float cos_v3v3v3(const float p1[3], const float p2[3], const float p3[3]) ATTR_WARN_UNUSED_RESULT;
 float angle_normalized_v3v3(const float v1[3], const float v2[3]) ATTR_WARN_UNUSED_RESULT;
 float angle_on_axis_v3v3v3_v3(const float v1[3], const float v2[3], const float v3[3], const float axis[3]) ATTR_WARN_UNUSED_RESULT;
+float angle_signed_on_axis_v3v3v3_v3(const float v1[3], const float v2[3], const float v3[3], const float axis[3]) ATTR_WARN_UNUSED_RESULT;
 void angle_tri_v3(float angles[3], const float v1[3], const float v2[3], const float v3[3]);
 void angle_quad_v3(float angles[4], const float v1[3], const float v2[3], const float v3[3], const float v4[3]);
 void angle_poly_v3(float *angles, const float *verts[3], int len);
diff --git a/source/blender/blenlib/intern/math_vector.c b/source/blender/blenlib/intern/math_vector.c
index 7cbbaaf383c..15b88fe0c7f 100644
--- a/source/blender/blenlib/intern/math_vector.c
+++ b/source/blender/blenlib/intern/math_vector.c
@@ -467,6 +467,32 @@ float angle_on_axis_v3v3v3_v3(const float v1[3], const float v2[3], const float
 	return angle_v3v3(v1_proj, v2_proj);
 }
 
+float angle_signed_on_axis_v3v3v3_v3(const float v1[3], const float v2[3], const float v3[3], const float axis[3])
+{
+	float v1_proj[3], v2_proj[3], tproj[3];
+	float angle;
+
+	sub_v3_v3v3(v1_proj, v1, v2);
+	sub_v3_v3v3(v2_proj, v3, v2);
+
+	/* project the vectors onto the axis */
+	project_v3_v3v3(tproj, v1_proj, axis);
+	sub_v3_v3(v1_proj, tproj);
+
+	project_v3_v3v3(tproj, v2_proj, axis);
+	sub_v3_v3(v2_proj, tproj);
+
+	angle = angle_v3v3(v1_proj, v2_proj);
+
+	/* calculate the sign (reuse 'tproj') */
+	cross_v3_v3v3(tproj, v2_proj, v1_proj);
+	if (dot_v3v3(tproj, axis) < 0.0f) {
+		angle = ((float)(M_PI * 2.0)) - angle;
+	}
+
+	return angle;
+}
+
 void angle_tri_v3(float angles[3], const float v1[3], const float v2[3], const float v3[3])
 {
 	float ed1[3], ed2[3], ed3[3];