diff --git a/graphics.go b/graphics.go
index 954486107..19fe241b7 100644
--- a/graphics.go
+++ b/graphics.go
@@ -26,12 +26,12 @@ const (
 	FilterLinear                // linear filter
 )
 
-func glFilter(c *opengl.Context, filter Filter) opengl.Filter {
+func glFilter(filter Filter) opengl.Filter {
 	switch filter {
 	case FilterNearest:
-		return c.Nearest
+		return opengl.Nearest
 	case FilterLinear:
-		return c.Linear
+		return opengl.Linear
 	}
 	panic("not reach")
 }
diff --git a/image.go b/image.go
index 3a2693cb4..57e671c19 100644
--- a/image.go
+++ b/image.go
@@ -23,7 +23,6 @@ import (
 
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/graphics/opengl"
-	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
 type images struct {
@@ -79,7 +78,7 @@ func (i *images) restorePixels(context *opengl.Context) error {
 		}
 	}
 	for img := range i.images {
-		if err := img.restorePixels(context); err != nil {
+		if err := img.restorePixels(); err != nil {
 			return err
 		}
 	}
@@ -210,7 +209,7 @@ func NewImage(width, height int, filter Filter) (*Image, error) {
 	}
 	imageM.Lock()
 	defer imageM.Unlock()
-	image.image, err = graphics.NewImage(width, height, glFilter(ui.GLContext(), filter))
+	image.image, err = graphics.NewImage(width, height, glFilter(filter))
 	if err != nil {
 		return nil, err
 	}
@@ -251,7 +250,7 @@ func NewImageFromImage(source image.Image, filter Filter) (*Image, error) {
 	imageM.Lock()
 	defer imageM.Unlock()
 	var err error
-	img.image, err = graphics.NewImageFromImage(rgbaImg, glFilter(ui.GLContext(), filter))
+	img.image, err = graphics.NewImageFromImage(rgbaImg, glFilter(filter))
 	if err != nil {
 		// TODO: texture should be removed here?
 		return nil, err
diff --git a/imageimpl.go b/imageimpl.go
index 65ee61169..3217af27d 100644
--- a/imageimpl.go
+++ b/imageimpl.go
@@ -133,7 +133,7 @@ func (i *imageImpl) savePixels(context *opengl.Context) error {
 	return nil
 }
 
-func (i *imageImpl) restorePixels(context *opengl.Context) error {
+func (i *imageImpl) restorePixels() error {
 	if i.screen {
 		return nil
 	}
@@ -146,14 +146,14 @@ func (i *imageImpl) restorePixels(context *opengl.Context) error {
 			copy(img.Pix[j*img.Stride:], i.pixels[j*i.width*4:(j+1)*i.width*4])
 		}
 		var err error
-		i.image, err = graphics.NewImageFromImage(img, glFilter(context, i.filter))
+		i.image, err = graphics.NewImageFromImage(img, glFilter(i.filter))
 		if err != nil {
 			return err
 		}
 		return nil
 	}
 	var err error
-	i.image, err = graphics.NewImage(i.width, i.height, glFilter(context, i.filter))
+	i.image, err = graphics.NewImage(i.width, i.height, glFilter(i.filter))
 	if err != nil {
 		return err
 	}
diff --git a/internal/graphics/command.go b/internal/graphics/command.go
index 41dad7200..985b13ffa 100644
--- a/internal/graphics/command.go
+++ b/internal/graphics/command.go
@@ -52,7 +52,7 @@ func (q *commandQueue) Flush(context *opengl.Context) error {
 		}
 	}
 	if 0 < len(vertices) {
-		context.BufferSubData(context.ArrayBuffer, vertices)
+		context.BufferSubData(opengl.ArrayBuffer, vertices)
 	}
 	// NOTE: WebGL doesn't seem to have Check gl.MAX_ELEMENTS_VERTICES or gl.MAX_ELEMENTS_INDICES so far.
 	// Let's use them to compare to len(quads) in the future.
@@ -122,7 +122,7 @@ func (c *drawImageCommand) Exec(context *opengl.Context) error {
 	defer p.end()
 	// TODO: We should call glBindBuffer here?
 	// The buffer is already bound at begin() but it is counterintuitive.
-	context.DrawElements(context.Triangles, 6*n, theCommandQueue.indexOffsetInBytes)
+	context.DrawElements(opengl.Triangles, 6*n, theCommandQueue.indexOffsetInBytes)
 	theCommandQueue.indexOffsetInBytes += 6 * n * 2
 	return nil
 }
diff --git a/internal/graphics/opengl/context.go b/internal/graphics/opengl/context.go
index eb9ca9b37..4a2768994 100644
--- a/internal/graphics/opengl/context.go
+++ b/internal/graphics/opengl/context.go
@@ -14,7 +14,7 @@
 
 package opengl
 
-type Context struct {
+var (
 	Nearest            Filter
 	Linear             Filter
 	VertexShader       ShaderType
@@ -25,12 +25,16 @@ type Context struct {
 	StaticDraw         BufferUsage
 	Triangles          Mode
 	Lines              Mode
-	zero               operation
-	one                operation
-	srcAlpha           operation
-	dstAlpha           operation
-	oneMinusSrcAlpha   operation
-	oneMinusDstAlpha   operation
+
+	zero             operation
+	one              operation
+	srcAlpha         operation
+	dstAlpha         operation
+	oneMinusSrcAlpha operation
+	oneMinusDstAlpha operation
+)
+
+type Context struct {
 	locationCache      *locationCache
 	screenFramebuffer  Framebuffer // This might not be the default frame buffer '0' (e.g. iOS).
 	lastFramebuffer    Framebuffer
diff --git a/internal/graphics/opengl/context_desktop.go b/internal/graphics/opengl/context_desktop.go
index 2ea6bc113..eef44f394 100644
--- a/internal/graphics/opengl/context_desktop.go
+++ b/internal/graphics/opengl/context_desktop.go
@@ -43,30 +43,34 @@ func (p Program) id() programID {
 	return programID(p)
 }
 
+func init() {
+	Nearest = gl.NEAREST
+	Linear = gl.LINEAR
+	VertexShader = gl.VERTEX_SHADER
+	FragmentShader = gl.FRAGMENT_SHADER
+	ArrayBuffer = gl.ARRAY_BUFFER
+	ElementArrayBuffer = gl.ELEMENT_ARRAY_BUFFER
+	DynamicDraw = gl.DYNAMIC_DRAW
+	StaticDraw = gl.STATIC_DRAW
+	Triangles = gl.TRIANGLES
+	Lines = gl.LINES
+
+	zero = gl.ZERO
+	one = gl.ONE
+	srcAlpha = gl.SRC_ALPHA
+	dstAlpha = gl.DST_ALPHA
+	oneMinusSrcAlpha = gl.ONE_MINUS_SRC_ALPHA
+	oneMinusDstAlpha = gl.ONE_MINUS_DST_ALPHA
+}
+
 type context struct {
 	funcs chan func()
 }
 
 func NewContext() (*Context, error) {
 	c := &Context{
-		Nearest:            gl.NEAREST,
-		Linear:             gl.LINEAR,
-		VertexShader:       gl.VERTEX_SHADER,
-		FragmentShader:     gl.FRAGMENT_SHADER,
-		ArrayBuffer:        gl.ARRAY_BUFFER,
-		ElementArrayBuffer: gl.ELEMENT_ARRAY_BUFFER,
-		DynamicDraw:        gl.DYNAMIC_DRAW,
-		StaticDraw:         gl.STATIC_DRAW,
-		Triangles:          gl.TRIANGLES,
-		Lines:              gl.LINES,
-		zero:               gl.ZERO,
-		one:                gl.ONE,
-		srcAlpha:           gl.SRC_ALPHA,
-		dstAlpha:           gl.DST_ALPHA,
-		oneMinusSrcAlpha:   gl.ONE_MINUS_SRC_ALPHA,
-		oneMinusDstAlpha:   gl.ONE_MINUS_DST_ALPHA,
-		locationCache:      newLocationCache(),
-		lastCompositeMode:  CompositeModeUnknown,
+		locationCache:     newLocationCache(),
+		lastCompositeMode: CompositeModeUnknown,
 	}
 	c.funcs = make(chan func())
 	return c, nil
@@ -145,7 +149,7 @@ func (c *Context) BlendFunc(mode CompositeMode) {
 			return nil
 		}
 		c.lastCompositeMode = mode
-		s, d := c.operations(mode)
+		s, d := operations(mode)
 		gl.BlendFunc(uint32(s), uint32(d))
 		return nil
 	})
diff --git a/internal/graphics/opengl/context_js.go b/internal/graphics/opengl/context_js.go
index aa7f8a68c..8cfaa3694 100644
--- a/internal/graphics/opengl/context_js.go
+++ b/internal/graphics/opengl/context_js.go
@@ -58,6 +58,27 @@ func (p Program) id() programID {
 	return programID(p.Get("__ebiten_programId").Int())
 }
 
+func init() {
+	c := js.Global.Get("WebGLRenderingContext")
+	Nearest = Filter(c.Get("NEAREST").Int())
+	Linear = Filter(c.Get("LINEAR").Int())
+	VertexShader = ShaderType(c.Get("VERTEX_SHADER").Int())
+	FragmentShader = ShaderType(c.Get("FRAGMENT_SHADER").Int())
+	ArrayBuffer = BufferType(c.Get("ARRAY_BUFFER").Int())
+	ElementArrayBuffer = BufferType(c.Get("ELEMENT_ARRAY_BUFFER").Int())
+	DynamicDraw = BufferUsage(c.Get("DYNAMIC_DRAW").Int())
+	StaticDraw = BufferUsage(c.Get("STATIC_DRAW").Int())
+	Triangles = Mode(c.Get("TRIANGLES").Int())
+	Lines = Mode(c.Get("LINES").Int())
+
+	zero = operation(c.Get("ZERO").Int())
+	one = operation(c.Get("ONE").Int())
+	srcAlpha = operation(c.Get("SRC_ALPHA").Int())
+	dstAlpha = operation(c.Get("DST_ALPHA").Int())
+	oneMinusSrcAlpha = operation(c.Get("ONE_MINUS_SRC_ALPHA").Int())
+	oneMinusDstAlpha = operation(c.Get("ONE_MINUS_DST_ALPHA").Int())
+}
+
 type context struct {
 	gl            *webgl.Context
 	lastProgramID programID
@@ -89,24 +110,8 @@ func NewContext() (*Context, error) {
 	}
 
 	c := &Context{
-		Nearest:            Filter(gl.NEAREST),
-		Linear:             Filter(gl.LINEAR),
-		VertexShader:       ShaderType(gl.VERTEX_SHADER),
-		FragmentShader:     ShaderType(gl.FRAGMENT_SHADER),
-		ArrayBuffer:        BufferType(gl.ARRAY_BUFFER),
-		ElementArrayBuffer: BufferType(gl.ELEMENT_ARRAY_BUFFER),
-		DynamicDraw:        BufferUsage(gl.DYNAMIC_DRAW),
-		StaticDraw:         BufferUsage(gl.STATIC_DRAW),
-		Triangles:          Mode(gl.TRIANGLES),
-		Lines:              Mode(gl.LINES),
-		zero:               operation(gl.ZERO),
-		one:                operation(gl.ONE),
-		srcAlpha:           operation(gl.SRC_ALPHA),
-		dstAlpha:           operation(gl.DST_ALPHA),
-		oneMinusSrcAlpha:   operation(gl.ONE_MINUS_SRC_ALPHA),
-		oneMinusDstAlpha:   operation(gl.ONE_MINUS_DST_ALPHA),
-		locationCache:      newLocationCache(),
-		lastCompositeMode:  CompositeModeUnknown,
+		locationCache:     newLocationCache(),
+		lastCompositeMode: CompositeModeUnknown,
 	}
 	c.gl = gl
 	c.init()
@@ -141,7 +146,7 @@ func (c *Context) BlendFunc(mode CompositeMode) {
 		return
 	}
 	c.lastCompositeMode = mode
-	s, d := c.operations(mode)
+	s, d := operations(mode)
 	gl := c.gl
 	gl.BlendFunc(int(s), int(d))
 }
diff --git a/internal/graphics/opengl/context_mobile.go b/internal/graphics/opengl/context_mobile.go
index 7b6261185..e566761b9 100644
--- a/internal/graphics/opengl/context_mobile.go
+++ b/internal/graphics/opengl/context_mobile.go
@@ -40,6 +40,26 @@ func (p Program) id() programID {
 	return programID(p.Value)
 }
 
+func init() {
+	Nearest = mgl.NEAREST
+	Linear = mgl.LINEAR
+	VertexShader = mgl.VERTEX_SHADER
+	FragmentShader = mgl.FRAGMENT_SHADER
+	ArrayBuffer = mgl.ARRAY_BUFFER
+	ElementArrayBuffer = mgl.ELEMENT_ARRAY_BUFFER
+	DynamicDraw = mgl.DYNAMIC_DRAW
+	StaticDraw = mgl.STATIC_DRAW
+	Triangles = mgl.TRIANGLES
+	Lines = mgl.LINES
+
+	zero = mgl.ZERO
+	one = mgl.ONE
+	srcAlpha = mgl.SRC_ALPHA
+	dstAlpha = mgl.DST_ALPHA
+	oneMinusSrcAlpha = mgl.ONE_MINUS_SRC_ALPHA
+	oneMinusDstAlpha = mgl.ONE_MINUS_DST_ALPHA
+}
+
 type context struct {
 	gl          mgl.Context
 	worker      mgl.Worker
@@ -48,24 +68,8 @@ type context struct {
 
 func NewContext() (*Context, error) {
 	c := &Context{
-		Nearest:            mgl.NEAREST,
-		Linear:             mgl.LINEAR,
-		VertexShader:       mgl.VERTEX_SHADER,
-		FragmentShader:     mgl.FRAGMENT_SHADER,
-		ArrayBuffer:        mgl.ARRAY_BUFFER,
-		ElementArrayBuffer: mgl.ELEMENT_ARRAY_BUFFER,
-		DynamicDraw:        mgl.DYNAMIC_DRAW,
-		StaticDraw:         mgl.STATIC_DRAW,
-		Triangles:          mgl.TRIANGLES,
-		Lines:              mgl.LINES,
-		zero:               mgl.ZERO,
-		one:                mgl.ONE,
-		srcAlpha:           mgl.SRC_ALPHA,
-		dstAlpha:           mgl.DST_ALPHA,
-		oneMinusSrcAlpha:   mgl.ONE_MINUS_SRC_ALPHA,
-		oneMinusDstAlpha:   mgl.ONE_MINUS_DST_ALPHA,
-		locationCache:      newLocationCache(),
-		lastCompositeMode:  CompositeModeUnknown,
+		locationCache:     newLocationCache(),
+		lastCompositeMode: CompositeModeUnknown,
 	}
 	c.gl, c.worker = mgl.NewContext()
 	c.initialized = make(chan struct{})
@@ -112,7 +116,7 @@ func (c *Context) BlendFunc(mode CompositeMode) {
 		return
 	}
 	c.lastCompositeMode = mode
-	s, d := c.operations(mode)
+	s, d := operations(mode)
 	gl.BlendFunc(mgl.Enum(s), mgl.Enum(d))
 }
 
diff --git a/internal/graphics/opengl/types.go b/internal/graphics/opengl/types.go
index e60c6d4d0..ea4cc95f6 100644
--- a/internal/graphics/opengl/types.go
+++ b/internal/graphics/opengl/types.go
@@ -40,34 +40,34 @@ const (
 	CompositeModeUnknown
 )
 
-func (c *Context) operations(mode CompositeMode) (src operation, dst operation) {
+func operations(mode CompositeMode) (src operation, dst operation) {
 	switch mode {
 	case CompositeModeSourceOver:
-		return c.one, c.oneMinusSrcAlpha
+		return one, oneMinusSrcAlpha
 	case CompositeModeClear:
-		return c.zero, c.zero
+		return zero, zero
 	case CompositeModeCopy:
-		return c.one, c.zero
+		return one, zero
 	case CompositeModeDestination:
-		return c.zero, c.one
+		return zero, one
 	case CompositeModeDestinationOver:
-		return c.oneMinusDstAlpha, c.one
+		return oneMinusDstAlpha, one
 	case CompositeModeSourceIn:
-		return c.dstAlpha, c.zero
+		return dstAlpha, zero
 	case CompositeModeDestinationIn:
-		return c.zero, c.srcAlpha
+		return zero, srcAlpha
 	case CompositeModeSourceOut:
-		return c.oneMinusDstAlpha, c.zero
+		return oneMinusDstAlpha, zero
 	case CompositeModeDestinationOut:
-		return c.zero, c.oneMinusSrcAlpha
+		return zero, oneMinusSrcAlpha
 	case CompositeModeSourceAtop:
-		return c.dstAlpha, c.oneMinusSrcAlpha
+		return dstAlpha, oneMinusSrcAlpha
 	case CompositeModeDestinationAtop:
-		return c.oneMinusDstAlpha, c.srcAlpha
+		return oneMinusDstAlpha, srcAlpha
 	case CompositeModeXor:
-		return c.oneMinusDstAlpha, c.oneMinusSrcAlpha
+		return oneMinusDstAlpha, oneMinusSrcAlpha
 	case CompositeModeLighter:
-		return c.one, c.one
+		return one, one
 	default:
 		panic("not reach")
 	}
diff --git a/internal/graphics/program.go b/internal/graphics/program.go
index 9fc08c1e2..e39ee1044 100644
--- a/internal/graphics/program.go
+++ b/internal/graphics/program.go
@@ -61,13 +61,13 @@ func (s *openGLState) initialize(c *opengl.Context) error {
 	s.lastColorMatrixTranslation = nil
 	s.lastTexture = zeroTexture
 
-	shaderVertexModelviewNative, err := c.NewShader(c.VertexShader, shader(c, shaderVertexModelview))
+	shaderVertexModelviewNative, err := c.NewShader(opengl.VertexShader, shader(c, shaderVertexModelview))
 	if err != nil {
 		panic(fmt.Sprintf("graphics: shader compiling error:\n%s", err))
 	}
 	defer c.DeleteShader(shaderVertexModelviewNative)
 
-	shaderFragmentTextureNative, err := c.NewShader(c.FragmentShader, shader(c, shaderFragmentTexture))
+	shaderFragmentTextureNative, err := c.NewShader(opengl.FragmentShader, shader(c, shaderFragmentTexture))
 	if err != nil {
 		panic(fmt.Sprintf("graphics: shader compiling error:\n%s", err))
 	}
@@ -82,7 +82,7 @@ func (s *openGLState) initialize(c *opengl.Context) error {
 	}
 
 	const stride = 8 // (2 [vertices] + 2 [texels]) * 2 [sizeof(int16)/bytes]
-	c.NewBuffer(c.ArrayBuffer, 4*stride*MaxQuads, c.DynamicDraw)
+	c.NewBuffer(opengl.ArrayBuffer, 4*stride*MaxQuads, opengl.DynamicDraw)
 
 	indices := make([]uint16, 6*MaxQuads)
 	for i := uint16(0); i < MaxQuads; i++ {
@@ -93,7 +93,7 @@ func (s *openGLState) initialize(c *opengl.Context) error {
 		indices[6*i+4] = 4*i + 2
 		indices[6*i+5] = 4*i + 3
 	}
-	s.indexBufferQuads = c.NewBuffer(c.ElementArrayBuffer, indices, c.StaticDraw)
+	s.indexBufferQuads = c.NewBuffer(opengl.ElementArrayBuffer, indices, opengl.StaticDraw)
 
 	return nil
 }