diff --git a/sjplayer/src/sjplayer/Background.d b/sjplayer/src/sjplayer/Background.d
new file mode 100644
index 0000000..99f5560
--- /dev/null
+++ b/sjplayer/src/sjplayer/Background.d
@@ -0,0 +1,112 @@
+/// License: MIT
+module sjplayer.Background;
+
+import gl4d;
+
+///
+class Background {
+ public:
+  ///
+  this(BackgroundProgram program) {
+    program_ = program;
+  }
+
+  ///
+  void Initialize() {
+    inner_color = vec4(0, 0, 0, 0);
+    outer_color = vec4(0, 0, 0, 0);
+  }
+  ///
+  void Draw() {
+    program_.Draw(inner_color, outer_color);
+  }
+
+  ///
+  vec4 inner_color;
+  ///
+  vec4 outer_color;
+
+ private:
+  BackgroundProgram program_;
+}
+
+///
+class BackgroundProgram {
+ public:
+  ///
+  enum ShaderHeader = "#version 330 core
+#extension GL_ARB_explicit_uniform_location : enable";
+
+  ///
+  enum VertexShaderSrc = ShaderHeader ~ q{
+    layout(location = 0) in vec2 vert;
+
+    out vec2 uv_;
+
+    void main() {
+      uv_         = vert;
+      gl_Position = vec4(vert, 0, 1);
+    }
+  };
+  ///
+  enum FragmentShaderSrc = ShaderHeader ~ q{
+    layout(location = 0) uniform vec4 inner_color;
+    layout(location = 1) uniform vec4 outer_color;
+
+    in vec2  uv_;
+
+    out vec4 pixel_;
+
+    void main() {
+      pixel_ = (outer_color - inner_color)*length(uv_)/sqrt(2) + outer_color;
+    }
+  };
+
+  ///
+  this() {
+    ProgramLinker linker;
+    linker.vertex   = VertexShader.Compile(VertexShaderSrc);
+    linker.fragment = FragmentShader.Compile(FragmentShaderSrc);
+    program_ = linker.Link();
+    program_.Validate();
+
+    vao_   = VertexArray.Create();
+    verts_ = ArrayBuffer.Create();
+
+    vao_.Bind();
+    VertexArrayAttacher attacher;
+    with (attacher) {
+      index     = 0;
+      type      = GL_FLOAT;
+      dimension = 2;
+      Attach(vao_, verts_);
+    }
+
+    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_);
+    }
+  }
+
+  ///
+  void Draw(vec4 inner, vec4 outer) {
+    program_.Use();
+    program_.uniform!0 = inner;
+    program_.uniform!1 = outer;
+
+    vao_.Bind();
+    gl.DrawArrays(GL_TRIANGLE_FAN, 0, 4);
+  }
+
+ private:
+  ProgramRef program_;
+
+  ArrayBufferRef verts_;
+
+  VertexArrayRef vao_;
+}
diff --git a/sjplayer/src/sjplayer/BackgroundScheduledController.d b/sjplayer/src/sjplayer/BackgroundScheduledController.d
new file mode 100644
index 0000000..5cdc616
--- /dev/null
+++ b/sjplayer/src/sjplayer/BackgroundScheduledController.d
@@ -0,0 +1,65 @@
+/// License: MIT
+module sjplayer.BackgroundScheduledController;
+
+import std.algorithm,
+       std.array,
+       std.exception,
+       std.range.primitives;
+
+import sjscript;
+
+import sjplayer.Background,
+       sjplayer.ContextBuilderInterface,
+       sjplayer.ElementScheduledController,
+       sjplayer.VarStoreInterface,
+       sjplayer.util.Period;
+
+///
+alias BackgroundScheduledController = ElementScheduledController!(
+    Background,
+    [
+      "inner_r": "inner_color.r",
+      "inner_g": "inner_color.g",
+      "inner_b": "inner_color.b",
+      "inner_a": "inner_color.a",
+      "outer_r": "outer_color.r",
+      "outer_g": "outer_color.g",
+      "outer_b": "outer_color.b",
+      "outer_a": "outer_color.a",
+    ]
+  );
+
+///
+struct BackgroundScheduledControllerFactory {
+ public:
+  @disable this();
+
+  ///
+  this(
+      in VarStoreInterface varstore,
+      Background background) {
+    varstore_   = varstore;
+    background_ = background;
+  }
+
+  ///
+  void Create(R)(R params, ContextBuilderInterface builder)
+      if (isInputRange!R && is(ElementType!R == ParametersBlock)) {
+    auto params_array = params.array;
+    params_array.sort!"a.period.start < b.period.start";
+
+    auto before = Period(-1, 0);
+    foreach (param; params_array) {
+      (!param.period.IsPeriodIntersectedToPeriod(before)).enforce();
+    }
+
+    auto ctrl = new BackgroundScheduledController(
+        background_, varstore_, params_array);
+    builder.AddScheduledController(ctrl);
+  }
+
+ private:
+  const VarStoreInterface varstore_;
+
+  Background background_;
+}
diff --git a/sjplayer/src/sjplayer/Context.d b/sjplayer/src/sjplayer/Context.d
index 86b5f51..f2e1217 100644
--- a/sjplayer/src/sjplayer/Context.d
+++ b/sjplayer/src/sjplayer/Context.d
@@ -7,7 +7,8 @@ import std.algorithm,
 
 import sjscript;
 
-import sjplayer.ContextBuilderInterface,
+import sjplayer.Background,
+       sjplayer.ContextBuilderInterface,
        sjplayer.ElementInterface,
        sjplayer.ProgramSet,
        sjplayer.ScheduledControllerInterface,
@@ -21,8 +22,15 @@ class Context {
     auto builder  = new Builder;
     auto varstore = new BlackHole!VarStoreInterface;
 
-    import sjplayer.CircleElementScheduledController;
+    background_ = new Background(programs.Get!BackgroundProgram);
+
+    import sjplayer.BackgroundScheduledController,
+           sjplayer.CircleElementScheduledController;
     auto factories = tuple(
+        tuple(
+          "background",
+          BackgroundScheduledControllerFactory(varstore, background_),
+        ),
         tuple(
           "circle",
           CircleElementScheduledControllerFactory(programs, varstore),
@@ -42,6 +50,8 @@ class Context {
     controllers_.each!destroy;
     drawers_.each!destroy;
     elements_.each!destroy;
+
+    background_.destroy();
   }
 
   ///
@@ -49,6 +59,10 @@ class Context {
     assert(false);  // TODO:
   }
   ///
+  void DrawBackground() {
+    background_.Draw();
+  }
+  ///
   void DrawElements() {
     drawers_.each!(x => x.Draw());
   }
@@ -74,6 +88,8 @@ class Context {
     Appender!(ScheduledControllerInterface[]) controllers;
   }
 
+  Background background_;
+
   ElementInterface[] elements_;
 
   ElementDrawerInterface[] drawers_;
diff --git a/sjplayer/src/sjplayer/ElementScheduledController.d b/sjplayer/src/sjplayer/ElementScheduledController.d
index 707f4af..aeadbd5 100644
--- a/sjplayer/src/sjplayer/ElementScheduledController.d
+++ b/sjplayer/src/sjplayer/ElementScheduledController.d
@@ -17,8 +17,7 @@ import sjplayer.ElementInterface,
 ///
 class ElementScheduledController(
     Element, string[string] ParameterNameMap) :
-  AbstractScheduledControllerWithOperationImpl
-  if (is(Element : ElementInterface)) {
+  AbstractScheduledControllerWithOperationImpl {
  public:
   ///
   enum AliveManagementAvailable =
diff --git a/sjplayer/src/sjplayer/ProgramSet.d b/sjplayer/src/sjplayer/ProgramSet.d
index e9be3fa..2392fa5 100644
--- a/sjplayer/src/sjplayer/ProgramSet.d
+++ b/sjplayer/src/sjplayer/ProgramSet.d
@@ -4,13 +4,17 @@ module sjplayer.ProgramSet;
 import std.meta,
        std.typecons;
 
-import sjplayer.CircleElement;
+import sjplayer.Background,
+       sjplayer.CircleElement;
 
 ///
 class ProgramSet {
  public:
   ///
-  alias Programs = Tuple!(CircleElementProgram);
+  alias Programs = Tuple!(
+      BackgroundProgram,
+      CircleElementProgram
+    );
 
   ///
   this() {
diff --git a/sjplayer/standalone/main.d b/sjplayer/standalone/main.d
index d95b1b2..afae262 100644
--- a/sjplayer/standalone/main.d
+++ b/sjplayer/standalone/main.d
@@ -39,6 +39,7 @@ int main(string[] args) {
     context.OperateScheduledControllers(beat);
 
     gl.Clear(GL_COLOR_BUFFER_BIT);
+    context.DrawBackground();
     context.DrawElements();
     sfWindow_display(win);
   }