diff --git a/sjplayer/src/sjplayer/CircleElement.d b/sjplayer/src/sjplayer/CircleElement.d
index b801555..783eb99 100644
--- a/sjplayer/src/sjplayer/CircleElement.d
+++ b/sjplayer/src/sjplayer/CircleElement.d
@@ -7,7 +7,8 @@ import std.algorithm,
 import gl4d;
 
 import sjplayer.ElementDrawer,
-       sjplayer.ElementInterface;
+       sjplayer.ElementInterface,
+       sjplayer.util.linalg;
 
 ///
 class CircleElement : ElementInterface {
@@ -36,34 +37,14 @@ class CircleElement : ElementInterface {
     if (!alive) return DamageCalculationResult(0, 0);
 
     const m = matrix.inverse;
-
     const a = (m * vec3(p1, 1)).xy;
     const b = (m * vec3(p2, 1)).xy;
-    const s = b - a;
+    const d = CalculateDistanceOriginAndLineSegment(a, b);
 
-    const s_length = s.length;
-    if (s_length == 0) {
-      // TODO: nearness calculation
-      return DamageCalculationResult(a.length < 1? damage: 0, 0);
+    if (d <= 1) {
+      return DamageCalculationResult(damage, 0);
     }
-
-    const d = cross(vec3(s, 0), vec3(a, 0)).length / s_length;
-    if (d > 1) {
-      const nearness = (1 - (d-1).min(1f)).pow(2);
-      return DamageCalculationResult(0, nearness * nearness_coe);
-    }
-
-    const a_length = a.length;
-    const b_length = b.length;
-
-    const hit =
-      a.dot(s) * b.dot(s) <= 0 ||
-      a_length < 1 ||
-      b_length < 1;
-    if (hit) return DamageCalculationResult(damage, 0);
-
-    // TODO: nearness calculation
-    return DamageCalculationResult(0, 0);
+    return DamageCalculationResult(0, 1 - (d-1).clamp(0, 1));
   }
 
   ///
diff --git a/sjplayer/src/sjplayer/util/linalg.d b/sjplayer/src/sjplayer/util/linalg.d
new file mode 100644
index 0000000..83196ac
--- /dev/null
+++ b/sjplayer/src/sjplayer/util/linalg.d
@@ -0,0 +1,32 @@
+/// License: MIT
+module sjplayer.util.linalg;
+
+import std.algorithm;
+
+import gl4d;
+
+///
+float CalculateDistanceOriginAndLineSegment(vec2 a, vec2 b) {
+  const s     = b - a;
+  const s_len = s.length;
+
+  if (s_len == 0) return a.length;
+
+  if (dot(a, s) * dot(b, s) < 0) {
+    return cross(vec3(s, 0), vec3(a, 0)).length / s_len;
+  }
+  return min(a.length, b.length);
+}
+///
+unittest {
+  import std;
+  assert(CalculateDistanceOriginAndLineSegment(
+        vec2(0, 0), vec2(0, 0)).approxEqual(0f));
+
+  assert(CalculateDistanceOriginAndLineSegment(
+        vec2(-1, 1), vec2(1, 1)).approxEqual(1f));
+  assert(CalculateDistanceOriginAndLineSegment(
+        vec2(1, 1), vec2(2, 1)).approxEqual(sqrt(2f)));
+  assert(CalculateDistanceOriginAndLineSegment(
+        vec2(-2, 1), vec2(-1, 1)).approxEqual(sqrt(2f)));
+}