1 files changed, 62 insertions, 0 deletions
diff --git a/source/blender/blenlib/intern/math_geom_inline.c b/source/blender/blenlib/intern/math_geom_inline.c
index 0e243c5e198..5a64ed63ecf 100644
--- a/source/blender/blenlib/intern/math_geom_inline.c
+++ b/source/blender/blenlib/intern/math_geom_inline.c
@@ -34,6 +34,9 @@
 
 #include <string.h>
 
+/* A few small defines. Keep'em local! */
+#define SMALL_NUMBER  1.e-8f
+
 /********************************** Polygons *********************************/
 
 MINLINE float cross_tri_v2(const float v1[2], const float v2[2], const float v3[2])
@@ -227,4 +230,63 @@ MINLINE float plane_point_side_v3(const float plane[4], const float co[3])
 	return dot_v3v3(co, plane) + plane[3];
 }
 
+/* useful to calculate an even width shell, by taking the angle between 2 planes.
+ * The return value is a scale on the offset.
+ * no angle between planes is 1.0, as the angle between the 2 planes approaches 180d
+ * the distance gets very high, 180d would be inf, but this case isn't valid */
+MINLINE float shell_angle_to_dist(const float angle)
+{
+	return (UNLIKELY(angle < SMALL_NUMBER)) ? 1.0f : fabsf(1.0f / cosf(angle));
+}
+/**
+ * equivalent to ``shell_angle_to_dist(angle_normalized_v3v3(a, b))``
+ */
+MINLINE float shell_v3v3_normalized_to_dist(const float a[3], const float b[3])
+{
+	const float angle_cos = fabsf(dot_v3v3(a, b));
+	BLI_ASSERT_UNIT_V3(a);
+	BLI_ASSERT_UNIT_V3(b);
+	return (UNLIKELY(angle_cos < SMALL_NUMBER)) ? 1.0f : (1.0f / angle_cos);
+}
+/**
+ * equivalent to ``shell_angle_to_dist(angle_normalized_v2v2(a, b))``
+ */
+MINLINE float shell_v2v2_normalized_to_dist(const float a[2], const float b[2])
+{
+	const float angle_cos = fabsf(dot_v2v2(a, b));
+	BLI_ASSERT_UNIT_V2(a);
+	BLI_ASSERT_UNIT_V2(b);
+	return (UNLIKELY(angle_cos < SMALL_NUMBER)) ? 1.0f : (1.0f / angle_cos);
+}
+
+/**
+ * equivalent to ``shell_angle_to_dist(angle_normalized_v3v3(a, b) / 2)``
+ */
+MINLINE float shell_v3v3_mid_normalized_to_dist(const float a[3], const float b[3])
+{
+	float angle_cos;
+	float ab[3];
+	BLI_ASSERT_UNIT_V3(a);
+	BLI_ASSERT_UNIT_V3(b);
+	add_v3_v3v3(ab, a, b);
+	angle_cos = (normalize_v3(ab) != 0.0f) ? fabsf(dot_v3v3(a, ab)) : 0.0f;
+	return (UNLIKELY(angle_cos < SMALL_NUMBER)) ? 1.0f : (1.0f / angle_cos);
+}
+
+/**
+ * equivalent to ``shell_angle_to_dist(angle_normalized_v2v2(a, b) / 2)``
+ */
+MINLINE float shell_v2v2_mid_normalized_to_dist(const float a[2], const float b[2])
+{
+	float angle_cos;
+	float ab[2];
+	BLI_ASSERT_UNIT_V2(a);
+	BLI_ASSERT_UNIT_V2(b);
+	add_v2_v2v2(ab, a, b);
+	angle_cos = (normalize_v2(ab) != 0.0f) ? fabsf(dot_v2v2(a, ab)) : 0.0f;
+	return (UNLIKELY(angle_cos < SMALL_NUMBER)) ? 1.0f : (1.0f / angle_cos);
+}
+
+#undef SMALL_NUMBER
+
 #endif /* __MATH_GEOM_INLINE_C__ */