diff --git a/sjplayer/src/sjplayer/CircleElement.d b/sjplayer/src/sjplayer/CircleElement.d
index dbaaf37..a2000ce 100644
--- a/sjplayer/src/sjplayer/CircleElement.d
+++ b/sjplayer/src/sjplayer/CircleElement.d
@@ -2,13 +2,11 @@
 module sjplayer.CircleElement;
 
 import std.algorithm,
-       std.conv,
-       std.math,
-       std.exception;
+       std.math;
 
 import gl4d;
 
-import sjplayer.ElementDrawerInterface,
+import sjplayer.ElementDrawer,
        sjplayer.ElementInterface;
 
 ///
@@ -80,69 +78,10 @@ class CircleElement : ElementInterface {
 }
 
 ///
-class CircleElementDrawer : ElementDrawerInterface {
- public:
-  ///
-  this(CircleElementProgram program, in CircleElement[] elements)
-      in (program)
-      in (elements.length > 0) {
-    program_  = program;
-    elements_ = elements;
-
-    vao_       = VertexArray.Create();
-    verts_     = ArrayBuffer.Create();
-    instances_ = ArrayBuffer.Create();
-
-    vao_.Bind();
-    program_.SetupVertexArray(vao_, verts_, instances_);
-
-    verts_.Bind();
-    ArrayBufferAllocator verts_allocator;
-    with (verts_allocator) {
-      const v = [vec2(-1, 1), vec2(1, 1), vec2(1, -1), vec2(-1, -1),];
-      data  = v.ptr;
-      size  = typeof(v[0]).sizeof * v.length;
-      usage = GL_STATIC_DRAW;
-      Allocate(verts_);
-    }
-
-    instances_.Bind();
-    ArrayBufferAllocator instance_allocator;
-    with (instance_allocator) {
-      size  = CircleElement.Instance.sizeof * elements.length;
-      usage = GL_DYNAMIC_DRAW;
-      Allocate(instances_);
-    }
-  }
-
-  override void Draw() {
-    size_t alive_count;
-
-    instances_.Bind();
-    ArrayBufferOverwriter instance_writer;
-    foreach (const element; elements_.filter!"a.alive") with (instance_writer) {
-      data   = &element.instance;
-      offset = alive_count++ * CircleElement.Instance.sizeof;
-      size   = CircleElement.Instance.sizeof;
-      Overwrite(instances_);
-    }
-
-    program_.Use();
-    vao_.Bind();
-
-    if (alive_count == 0) return;
-    gl.DrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, alive_count.to!int);
-  }
-
- private:
-  CircleElementProgram program_;
-
-  const CircleElement[] elements_;
-
-  ArrayBufferRef verts_;
-  ArrayBufferRef instances_;
-  VertexArrayRef vao_;
-}
+alias CircleElementDrawer = ElementDrawer!(
+    CircleElementProgram,
+    CircleElement,
+    [vec2(-1, 1), vec2(1, 1), vec2(1, -1), vec2(-1, -1)]);
 
 ///
 class CircleElementProgram {
diff --git a/sjplayer/src/sjplayer/ElementDrawer.d b/sjplayer/src/sjplayer/ElementDrawer.d
new file mode 100644
index 0000000..a34eaea
--- /dev/null
+++ b/sjplayer/src/sjplayer/ElementDrawer.d
@@ -0,0 +1,79 @@
+/// License: MIT
+module sjplayer.ElementDrawer;
+
+import std.algorithm,
+       std.conv;
+
+import gl4d;
+
+import sjplayer.ElementDrawerInterface;
+
+///
+class ElementDrawer(Program, Element, vec2[] vertices) :
+  ElementDrawerInterface {
+ public:
+  ///
+  alias Instance = typeof(Element.instance);
+
+  ///
+  this(Program program, in Element[] elements)
+      in (program)
+      in (elements.length > 0) {
+    program_  = program;
+    elements_ = elements;
+
+    vao_       = VertexArray.Create();
+    verts_     = ArrayBuffer.Create();
+    instances_ = ArrayBuffer.Create();
+
+    vao_.Bind();
+    program_.SetupVertexArray(vao_, verts_, instances_);
+
+    verts_.Bind();
+    ArrayBufferAllocator verts_allocator;
+    with (verts_allocator) {
+      const v = vertices;  // place to memory
+
+      data  = v.ptr;
+      size  = typeof(v[0]).sizeof * v.length;
+      usage = GL_STATIC_DRAW;
+      Allocate(verts_);
+    }
+
+    instances_.Bind();
+    ArrayBufferAllocator instance_allocator;
+    with (instance_allocator) {
+      size  = Instance.sizeof * elements.length;
+      usage = GL_DYNAMIC_DRAW;
+      Allocate(instances_);
+    }
+  }
+
+  override void Draw() {
+    size_t alive_count;
+
+    instances_.Bind();
+    {
+      auto ptr = instances_.MapToWrite!Instance();
+      foreach (const element; elements_.filter!"a.alive") {
+        ptr[alive_count++] = element.instance;
+      }
+    }
+
+    program_.Use();
+    vao_.Bind();
+
+    if (alive_count == 0) return;
+    gl.DrawArraysInstanced(
+        GL_TRIANGLE_FAN, 0, vertices.length.to!int, alive_count.to!int);
+  }
+
+ private:
+  Program program_;
+
+  const Element[] elements_;
+
+  ArrayBufferRef verts_;
+  ArrayBufferRef instances_;
+  VertexArrayRef vao_;
+}