diff --git a/camera.go b/camera.go
index 1b3594b..18d2c80 100644
--- a/camera.go
+++ b/camera.go
@@ -4,6 +4,7 @@ package gg
 // for the main window.
 type Camera struct {
 	Transform
+	buf *Matrix
 }
 
 // Returns the matrix satysfying camera
@@ -12,22 +13,24 @@ type Camera struct {
 // transform to display on the screen.
 // (Should implement buffering it so we do not
 //  need to calculate it each time for each object. )
-func (c *Camera)RealMatrix(
-	e *Engine,
-) Matrix {
+func (c *Camera)RealMatrix() Matrix {
 	g := &Matrix{}
 	g.Translate(-c.P.X, -c.P.Y)
 	g.Rotate(c.R)
 	g.Scale(c.S.X, c.S.Y)
 	g.Translate(c.RA.X, c.RA.Y)
 
+	c.buf = g
+
 	return *g
 }
 
-func (c *Camera) AbsMatrix(
-	e *Engine,
-) Matrix {
-	m := c.RealMatrix(e)
+// The matrix to convert things into the 
+// inside engine representation, 
+// get the position of cursor inside the world
+// basing on its window position.
+func (c *Camera) AbsMatrix() Matrix {
+	m := c.RealMatrix()
 	m.Invert()
 	return m
 }
diff --git a/cmd/test/main.go b/cmd/test/main.go
index c1323a0..d155262 100644
--- a/cmd/test/main.go
+++ b/cmd/test/main.go
@@ -11,6 +11,8 @@ import (
 	"math/rand"
 )
 
+type Context = gg.Context
+
 const (
 	HighestL gg.Layer = -iota
 	DebugL
@@ -28,6 +30,7 @@ type Player struct {
 }
 
 type Debug struct {
+	gg.Visibility
 	gg.Layer
 }
 
@@ -98,11 +101,15 @@ func NewRect() *Rect {
 	return ret
 }
 
-func (r *Rect) Update(e *gg.Engine) error {
+func (r *Rect) Update(c *Context) error {
 	//r.R += 0.3 * e.DT()
+	r.P = c.AbsCursorPosition()
 	return nil
 }
 
+func (r *Rect) Event(c *Context) {
+}
+
 var (
 	playerImg *gg.Image
 	player    *Player
@@ -134,8 +141,8 @@ func NewPlayer() *Player {
 	return ret
 }
 
-func (p *Player) Draw(e *gg.Engine, i *gg.Image) {
-	p.Sprite.Draw(e, i)
+func (p *Player) Draw(c *Context) {
+	p.Sprite.Draw(c)
 	t := p.Transform
 	t.S.X *= 4.
 	t.S.Y *= 4.
@@ -146,31 +153,31 @@ func (p *Player) Draw(e *gg.Engine, i *gg.Image) {
 		Rectangle: rectMove,
 		Color:     gg.Color{0, 0, gg.MaxColorV, gg.MaxColorV},
 	}
-	r.Draw(e, i)
+	r.Draw(c)
 }
 
-func (p *Player) Start(e *gg.Engine, v ...any) {
+func (p *Player) Start(c *Context) {
 	fmt.Println("starting")
-	c := e.Camera()
-	c.RA = gg.V(360, 240)
+	cam := c.Camera()
+	cam.RA = gg.V(360, 240)
 }
 
-func (p *Player) Update(e *gg.Engine) error {
-	dt := e.DT()
-	c := e.Camera()
-	keys := e.Keys()
+func (p *Player) Update(c *Context) error {
+	dt := c.DT()
+	cam := c.Camera()
+	keys := c.Keys()
 
 	p.Uniforms["Random"] = any(rand.Float32())
 	for _, v := range keys {
 		switch v {
 		case ebiten.KeyArrowUp:
-			c.P.Y += p.MoveSpeed * dt
+			cam.P.Y += p.MoveSpeed * dt
 		case ebiten.KeyArrowLeft:
-			c.P.X -= p.MoveSpeed * dt
+			cam.P.X -= p.MoveSpeed * dt
 		case ebiten.KeyArrowDown:
-			c.P.Y -= p.MoveSpeed * dt
+			cam.P.Y -= p.MoveSpeed * dt
 		case ebiten.KeyArrowRight:
-			c.P.X += p.MoveSpeed * dt
+			cam.P.X += p.MoveSpeed * dt
 		case ebiten.KeyW:
 			p.P.Y += p.MoveSpeed * dt
 		case ebiten.KeyA:
@@ -180,61 +187,61 @@ func (p *Player) Update(e *gg.Engine) error {
 		case ebiten.KeyD:
 			p.P.X += p.MoveSpeed * dt
 		case ebiten.KeyR:
-			c.R += gg.Pi * p.ScaleSpeed * dt
+			cam.R += gg.Pi * p.ScaleSpeed * dt
 		case ebiten.KeyT:
-			c.R -= gg.Pi * p.ScaleSpeed * dt
+			cam.R -= gg.Pi * p.ScaleSpeed * dt
 		case ebiten.KeyRightBracket:
-			if e.IsPressed(ebiten.KeyShift) {
+			if c.IsPressed(gg.KeyShift) {
 				p.R -= gg.Pi * 0.3 * dt
 			} else {
 				p.R += gg.Pi * 0.3 * dt
 			}
-		case ebiten.KeyF:
-			if e.IsPressed(ebiten.KeyShift) {
-				c.S.X -= gg.Pi * p.ScaleSpeed * dt
+		case gg.KeyF:
+			if c.IsPressed(ebiten.KeyShift) {
+				cam.S.X -= gg.Pi * p.ScaleSpeed * dt
 			} else {
-				c.S.X += gg.Pi * p.ScaleSpeed * dt
+				cam.S.X += gg.Pi * p.ScaleSpeed * dt
 			}
-		case ebiten.KeyG:
-			if e.IsPressed(ebiten.KeyShift) {
-				c.S.Y -= gg.Pi * p.ScaleSpeed * dt
+		case gg.KeyG:
+			if c.IsPressed(ebiten.KeyShift) {
+				cam.S.Y -= gg.Pi * p.ScaleSpeed * dt
 			} else {
-				c.S.Y += gg.Pi * p.ScaleSpeed * dt
+				cam.S.Y += gg.Pi * p.ScaleSpeed * dt
 			}
-		case ebiten.KeyZ:
-			if e.IsPressed(ebiten.KeyShift) {
-				c.RA.X -= gg.Pi * p.MoveSpeed * dt
+		case gg.KeyZ:
+			if c.IsPressed(ebiten.KeyShift) {
+				cam.RA.X -= gg.Pi * p.MoveSpeed * dt
 			} else {
-				c.RA.X += gg.Pi * p.MoveSpeed * dt
+				cam.RA.X += gg.Pi * p.MoveSpeed * dt
 			}
-		case ebiten.KeyX:
-			if e.IsPressed(ebiten.KeyShift) {
-				c.RA.Y -= gg.Pi * p.MoveSpeed * dt
+		case gg.KeyX:
+			if c.IsPressed(ebiten.KeyShift) {
+				cam.RA.Y -= gg.Pi * p.MoveSpeed * dt
 			} else {
-				c.RA.Y += gg.Pi * p.MoveSpeed * dt
+				cam.RA.Y += gg.Pi * p.MoveSpeed * dt
 			}
-		case ebiten.KeyV:
-			if e.IsPressed(ebiten.KeyShift) {
+		case gg.KeyV:
+			if c.IsPressed(ebiten.KeyShift) {
 				tri.R -= gg.Pi * 0.3 * dt
 			} else {
 				tri.R += gg.Pi * 0.3 * dt
 			}
-		case ebiten.KeyLeftBracket:
-			if e.IsPressed(ebiten.KeyShift) {
+		case gg.KeyLeftBracket:
+			if c.IsPressed(ebiten.KeyShift) {
 				rect.R -= gg.Pi * 0.3 * dt
 			} else {
 				rect.R += gg.Pi * 0.3 * dt
 			}
-		case ebiten.Key0:
-			e.Del(p)
-		case ebiten.KeyB:
+		case gg.Key0:
+			c.Del(p)
+		case gg.KeyB:
 		}
 	}
 
 	return nil
 }
 
-func (p *Player) Event(e *gg.Engine, ev any) {
+func (p *Player) Signal(e *gg.Engine, ev any) {
 	fmt.Println("event:", ev)
 	switch ec := ev.(type) {
 	case *gg.KeyDown:
@@ -249,10 +256,8 @@ func (p *Player) Event(e *gg.Engine, ev any) {
 	}
 }
 
-func (d *Debug) Draw(
-	e *gg.Engine,
-	i *gg.Image,
-) {
+func (d *Debug) Draw(c *Context) {
+	e := c.Engine
 	keyStrs := []string{}
 	for _, k := range e.Keys() {
 		keyStrs = append(keyStrs, k.String())
@@ -270,7 +275,7 @@ func (d *Debug) Draw(
 	keyStrs = append(keyStrs, fmt.Sprintf("%v", e.CursorPosition()))
 	keyStrs = append(keyStrs, fmt.Sprintf("%v", e.AbsCursorPosition()))
 
-	e.DebugPrint(i,
+	e.DebugPrint(c.Image,
 		strings.Join(keyStrs, ", "))
 
 }
diff --git a/context.go b/context.go
new file mode 100644
index 0000000..749a18f
--- /dev/null
+++ b/context.go
@@ -0,0 +1,7 @@
+package gg
+
+type Context struct {
+	*Engine
+	*Image
+	Event any
+}
diff --git a/engine.go b/engine.go
index dbbba1e..3bfdf78 100644
--- a/engine.go
+++ b/engine.go
@@ -96,7 +96,9 @@ func (e *Engine) Add(b any) error {
 
 	starter, ok := b.(Starter)
 	if ok {
-		starter.Start(e)
+		starter.Start(&Context{
+			Engine: e,
+		})
 	}
 
 	e.objects.Set(object, struct{}{})
@@ -113,7 +115,9 @@ func (e *Engine) Del(b any) error {
 
 	deleter, ok := b.(Deleter)
 	if ok {
-		deleter.Delete(e)
+		deleter.Delete(&Context{
+			Engine: e,
+		})
 	}
 
 	e.objects.Del(b)
@@ -152,14 +156,19 @@ func (e *engine) Update() error {
 		eventer, ok := object.(Eventer)
 		if ok {
 			for _, event := range events {
-				eventer.Event(eng, event)
+				eventer.Event(&Context{
+					Engine: eng,
+					Event: event,
+				})
 			}
 		}
 		updater, ok := object.(Updater)
 		if !ok {
 			continue
 		}
-		err = updater.Update(eng)
+		err = updater.Update(&Context{
+			Engine: eng,
+		})
 		if err != nil {
 			return err
 		}
@@ -193,7 +202,10 @@ func (e *engine) Draw(i *ebiten.Image) {
 	layers := maps.NewSparse[Layer, []Drawer](nil, m)
 	for layer := range layers.Chan() {
 		for _, drawer := range layer {
-			drawer.Draw(eng, i)
+			drawer.Draw(&Context{
+				Engine: eng,
+				Image: i,
+			})
 		}
 	}
 }
diff --git a/event.go b/event.go
index f645849..cd11f41 100644
--- a/event.go
+++ b/event.go
@@ -4,10 +4,6 @@ import (
 	//"github.com/hajimehoshi/ebiten/v2"
 )
 
-type Eventer interface {
-	Event(e *Engine, ev any)
-}
-
 func keyDiff(s1, s2 []Key) []Key {
     combinedSlice := append(s1, s2...)
     dm := make(map[Key]int)
@@ -37,7 +33,6 @@ type KeyUp struct {
 	Key
 }
 
-
 type MouseButtonDown struct {
 	MouseButton
 	P Vector
diff --git a/line.go b/line.go
index 35b793a..5068fc2 100644
--- a/line.go
+++ b/line.go
@@ -2,7 +2,7 @@ package gg
 
 import (
 	"math"
-	"fmt"
+	//"fmt"
 )
 
 // The type represents mathematical equation of line and line itself.
diff --git a/mouse.go b/mouse.go
index bedb13a..3574c31 100644
--- a/mouse.go
+++ b/mouse.go
@@ -13,7 +13,7 @@ func (e *Engine) CursorPosition() Vector {
 
 func (e *Engine) AbsCursorPosition() Vector {
 	m := &Matrix{}
-	m.Concat(e.Camera().AbsMatrix(e))
+	m.Concat(e.Camera().AbsMatrix())
 	return e.CursorPosition().Apply(m)
 }
 
diff --git a/object.go b/object.go
index b7a1527..ee1b747 100644
--- a/object.go
+++ b/object.go
@@ -1,28 +1,35 @@
 package gg
 
+// Implementing the interface lets the object
+// to handle emited events.
+type Eventer interface {
+	Event(*Context)
+}
+
 // Implementing the interface type
 // will call the function OnStart
 // when first appear on scene BEFORE
 // the OnUpdate.
 // The v value will be get from Add function.
 type Starter interface {
-	Start(*Engine)
+	Start(*Context)
 }
 
 // Implementing the interface type
 // will call the function on each
 // engine iteration.
 type Updater interface {
-	Update(*Engine) error
+	Update(*Context) error
 }
 
 // Implementing the interface type
 // will call the function on deleting
 // the object.
 type Deleter interface {
-	Delete(*Engine, ...any)
+	Delete(*Context)
 }
 
+// Feat to embed for turning visibility on and off.
 type Visibility struct {
 	Visible bool
 }
@@ -30,15 +37,16 @@ func (v Visibility) IsVisible() bool {
 	return v.Visible
 }
 
+// Feat to embed to make colorful objects.
 type Colority struct {
 	Color Color
 }
 
 // The interface describes anything that can be
 // drawn. It will be drew corresponding to
-// the layers order.
+// the layers order so the layer must be returned.
 type Drawer interface {
-	Draw(*Engine, *Image)
+	Draw(*Context)
 	GetLayer() Layer
 	IsVisible() bool
 }
diff --git a/polygon.go b/polygon.go
index ce4cc9b..d5b5a6f 100644
--- a/polygon.go
+++ b/polygon.go
@@ -38,15 +38,12 @@ func (p *Polygon) MakeTriangles() Triangles {
 	return ret
 }
 
-func (p *DrawablePolygon) Draw(
-	e *Engine,
-	i *Image,
-) {
+func (p *DrawablePolygon) Draw(c *Context) {
 	(&DrawableTriangles{
 		Visibility: p.Visibility,
 		Colority: p.Colority,
 		ShaderOptions: p.ShaderOptions,
 		Triangles: p.MakeTriangles(),
-	}).Draw(e, i)
+	}).Draw(c)
 }
 
diff --git a/rect.go b/rect.go
index cfcff88..a27434c 100644
--- a/rect.go
+++ b/rect.go
@@ -73,12 +73,9 @@ func (r *DrawableRectangle) IsVisible() bool {
 	return r.Visible
 }
 
-func (r *DrawableRectangle) Draw(
-	e *Engine,
-	i *Image,
-) {
+func (r *DrawableRectangle) Draw(c *Context) {
 	m := r.Matrix()
-	rm := e.Camera().RealMatrix(e)
+	rm := c.Camera().RealMatrix()
 	m.Concat(rm)
 	// Draw solid color if no shader.
 	if r.Shader == nil {
@@ -89,7 +86,7 @@ func (r *DrawableRectangle) Draw(
 		opts := &ebiten.DrawImageOptions{
 			GeoM: m,
 		}
-		i.DrawImage(img, opts)
+		c.DrawImage(img, opts)
 		return
 	}
 	
@@ -117,6 +114,6 @@ func (r *DrawableRectangle) Draw(
 		Images: r.Images,
 		Uniforms: r.Uniforms,
 	}
-	i.DrawRectShader(w, h, r.Shader, opts)
+	c.DrawRectShader(w, h, r.Shader, opts)
 }
 
diff --git a/sprite.go b/sprite.go
index c383368..d98dffa 100644
--- a/sprite.go
+++ b/sprite.go
@@ -10,10 +10,7 @@ type Sprite struct {
 	Floating, Visible bool
 }
 
-func (s *Sprite) Draw(
-	e *Engine,
-	i *Image,
-) {
+func (s *Sprite) Draw(c *Context) {
 	// Nothing to draw.
 	if s.Images[0] == nil {
 		return
@@ -23,16 +20,14 @@ func (s *Sprite) Draw(
 	m := &Matrix{}
 	m.Concat(t.Matrix())
 	if !s.Floating {
-		m.Concat(e.Camera().RealMatrix(
-			e,
-		))
+		m.Concat(c.Camera().RealMatrix())
 	}
 
 	// Drawing without shader.
 	if s.Shader == nil {
 		opts := &ebiten.DrawImageOptions{}
 		opts.GeoM = *m
-		i.DrawImage(s.Images[0], opts)
+		c.DrawImage(s.Images[0], opts)
 		return
 	}
 	
@@ -43,7 +38,7 @@ func (s *Sprite) Draw(
 		Uniforms: s.Uniforms,
 		GeoM: *m,
 	}
-	i.DrawRectShader(w, h, s.Shader, opts)
+	c.DrawRectShader(w, h, s.Shader, opts)
 }
 
 // Check is sprite is visible.
diff --git a/triangle.go b/triangle.go
index 282db5b..42c24f3 100644
--- a/triangle.go
+++ b/triangle.go
@@ -88,11 +88,8 @@ func (ts Triangles) ContainsPoint(p Point) bool {
 	return false
 }
 
-func (r *DrawableTriangles) Draw(
-	e *Engine,
-	i *Image,
-) {
-	m := e.Camera().RealMatrix(e)
+func (r *DrawableTriangles) Draw(c *Context) {
+	m := c.Camera().RealMatrix()
 	cm := &m
 	
 	// Draw solid color if no shader.
@@ -115,7 +112,7 @@ func (r *DrawableTriangles) Draw(
 		img := NewImage(1, 1)
 		img.Set(0, 0, r.Color)
 		
-		i.DrawTriangles(vs, is, img, &r.DrawTrianglesOptions)
+		c.DrawTriangles(vs, is, img, &r.DrawTrianglesOptions)
 		return
 	}
 	
diff --git a/vector.go b/vector.go
index e369896..0d0a678 100644
--- a/vector.go
+++ b/vector.go
@@ -14,10 +14,6 @@ type Point = Vector
 type Vectors []Vector
 type Points []Point
 
-type PointContainer interface {
-	ContainsPoint(Point) bool
-}
-
 func V(x, y Float) Vector {
 	return Vector{x, y}
 }