graphicsdriver/opengl: Use native GLES functions for mobiles

After this change, GL functions for mobiles, especially Android, are
native ones instead of golang.org/x/mobile/gl functions in order to
reduce goroutine context switches.

On gomobile-build, golang.org/x/mobile/gl functions are still used.

Fixes #1387

internal/graphicsdriver/opengl/context_mobile.go

@@ -20,20 +20,17 @@ import (
 	"errors"
 	"fmt"
 
-	// TODO: Remove this dependency (#1387)
-	mgl "golang.org/x/mobile/gl"
-
 	"github.com/hajimehoshi/ebiten/v2/internal/driver"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl/gles"
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
 )
 
 type (
-	textureNative     mgl.Texture
+	textureNative     uint32
-	framebufferNative mgl.Framebuffer
+	framebufferNative uint32
-	shader            mgl.Shader
+	shader            uint32
-	program           mgl.Program
+	program           uint32
-	buffer            mgl.Buffer
+	buffer            uint32
 )
 
 func (t textureNative) equal(rhs textureNative) bool {
@@ -59,8 +56,8 @@ func (p program) equal(rhs program) bool {
 var InvalidTexture textureNative
 
 type (
-	uniformLocation mgl.Uniform
+	uniformLocation int32
-	attribLocation  mgl.Attrib
+	attribLocation  int32
 )
 
 func (u uniformLocation) equal(rhs uniformLocation) bool {
@@ -69,14 +66,14 @@ func (u uniformLocation) equal(rhs uniformLocation) bool {
 
 type programID uint32
 
-var (
+const (
-	invalidTexture     = textureNative(mgl.Texture{})
+	invalidTexture     = 0
-	invalidFramebuffer = framebufferNative(mgl.Framebuffer{Value: (1 << 32) - 1})
+	invalidFramebuffer = (1 << 32) - 1
-	invalidUniform     = uniformLocation(mgl.Uniform{Value: -1})
+	invalidUniform     = -1
 )
 
 func getProgramID(p program) programID {
-	return programID(p.Value)
+	return programID(p)
 }
 
 const (
@@ -98,7 +95,7 @@ const (
 )
 
 type contextImpl struct {
-	gl mgl.Context
+	ctx gles.Context
 }
 
 func (c *context) reset() error {
@@ -108,115 +105,105 @@ func (c *context) reset() error {
 	c.lastViewportWidth = 0
 	c.lastViewportHeight = 0
 	c.lastCompositeMode = driver.CompositeModeUnknown
-	c.gl.Enable(gles.BLEND)
+	c.ctx.Enable(gles.BLEND)
 	c.blendFunc(driver.CompositeModeSourceOver)
-	f := c.gl.GetInteger(gles.FRAMEBUFFER_BINDING)
+	f := make([]int32, 1)
-	c.screenFramebuffer = framebufferNative(mgl.Framebuffer{uint32(f)})
+	c.ctx.GetIntegerv(f, gles.FRAMEBUFFER_BINDING)
+	c.screenFramebuffer = framebufferNative(f[0])
 	// TODO: Need to update screenFramebufferWidth/Height?
 	return nil
 }
 
 func (c *context) blendFunc(mode driver.CompositeMode) {
-	gl := c.gl
 	if c.lastCompositeMode == mode {
 		return
 	}
 	c.lastCompositeMode = mode
 	s, d := mode.Operations()
 	s2, d2 := convertOperation(s), convertOperation(d)
-	gl.BlendFunc(mgl.Enum(s2), mgl.Enum(d2))
+	c.ctx.BlendFunc(uint32(s2), uint32(d2))
 }
 
 func (c *context) newTexture(width, height int) (textureNative, error) {
-	gl := c.gl
+	t := c.ctx.GenTextures(1)[0]
-	t := gl.CreateTexture()
+	if t <= 0 {
-	if t.Value <= 0 {
+		return 0, errors.New("opengl: creating texture failed")
-		return textureNative{}, errors.New("opengl: creating texture failed")
 	}
-	gl.PixelStorei(gles.UNPACK_ALIGNMENT, 4)
+	c.ctx.PixelStorei(gles.UNPACK_ALIGNMENT, 4)
 	c.bindTexture(textureNative(t))
 
-	gl.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_MAG_FILTER, gles.NEAREST)
+	c.ctx.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_MAG_FILTER, gles.NEAREST)
-	gl.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_MIN_FILTER, gles.NEAREST)
+	c.ctx.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_MIN_FILTER, gles.NEAREST)
-	gl.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_WRAP_S, gles.CLAMP_TO_EDGE)
+	c.ctx.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_WRAP_S, gles.CLAMP_TO_EDGE)
-	gl.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_WRAP_T, gles.CLAMP_TO_EDGE)
+	c.ctx.TexParameteri(gles.TEXTURE_2D, gles.TEXTURE_WRAP_T, gles.CLAMP_TO_EDGE)
-	gl.TexImage2D(gles.TEXTURE_2D, 0, gles.RGBA, width, height, gles.RGBA, gles.UNSIGNED_BYTE, nil)
+	c.ctx.TexImage2D(gles.TEXTURE_2D, 0, gles.RGBA, int32(width), int32(height), gles.RGBA, gles.UNSIGNED_BYTE, nil)
 
 	return textureNative(t), nil
 }
 
 func (c *context) bindFramebufferImpl(f framebufferNative) {
-	gl := c.gl
+	c.ctx.BindFramebuffer(gles.FRAMEBUFFER, uint32(f))
-	gl.BindFramebuffer(gles.FRAMEBUFFER, mgl.Framebuffer(f))
 }
 
 func (c *context) framebufferPixels(f *framebuffer, width, height int) []byte {
-	gl := c.gl
+	c.ctx.Flush()
-	gl.Flush()
 
 	c.bindFramebuffer(f.native)
 
 	pixels := make([]byte, 4*width*height)
-	gl.ReadPixels(pixels, 0, 0, width, height, gles.RGBA, gles.UNSIGNED_BYTE)
+	c.ctx.ReadPixels(pixels, 0, 0, int32(width), int32(height), gles.RGBA, gles.UNSIGNED_BYTE)
 	return pixels
 }
 
 func (c *context) activeTexture(idx int) {
-	gl := c.gl
+	c.ctx.ActiveTexture(uint32(gles.TEXTURE0 + idx))
-	gl.ActiveTexture(mgl.Enum(gles.TEXTURE0 + idx))
 }
 
 func (c *context) bindTextureImpl(t textureNative) {
-	gl := c.gl
+	c.ctx.BindTexture(gles.TEXTURE_2D, uint32(t))
-	gl.BindTexture(gles.TEXTURE_2D, mgl.Texture(t))
 }
 
 func (c *context) deleteTexture(t textureNative) {
-	gl := c.gl
+	if !c.ctx.IsTexture(uint32(t)) {
-	if !gl.IsTexture(mgl.Texture(t)) {
 		return
 	}
 	if c.lastTexture == t {
 		c.lastTexture = invalidTexture
 	}
-	gl.DeleteTexture(mgl.Texture(t))
+	c.ctx.DeleteTextures([]uint32{uint32(t)})
 }
 
 func (c *context) isTexture(t textureNative) bool {
-	gl := c.gl
+	return c.ctx.IsTexture(uint32(t))
-	return gl.IsTexture(mgl.Texture(t))
 }
 
 func (c *context) newFramebuffer(texture textureNative) (framebufferNative, error) {
-	gl := c.gl
+	f := c.ctx.GenFramebuffers(1)[0]
-	f := gl.CreateFramebuffer()
+	if f <= 0 {
-	if f.Value <= 0 {
+		return 0, fmt.Errorf("opengl: creating framebuffer failed: the returned value is not positive but %d", f)
-		return framebufferNative{}, fmt.Errorf("opengl: creating framebuffer failed: the returned value is not positive but %d", f.Value)
 	}
 	c.bindFramebuffer(framebufferNative(f))
 
-	gl.FramebufferTexture2D(gles.FRAMEBUFFER, gles.COLOR_ATTACHMENT0, gles.TEXTURE_2D, mgl.Texture(texture), 0)
+	c.ctx.FramebufferTexture2D(gles.FRAMEBUFFER, gles.COLOR_ATTACHMENT0, gles.TEXTURE_2D, uint32(texture), 0)
-	s := gl.CheckFramebufferStatus(gles.FRAMEBUFFER)
+	s := c.ctx.CheckFramebufferStatus(gles.FRAMEBUFFER)
 	if s != gles.FRAMEBUFFER_COMPLETE {
 		if s != 0 {
-			return framebufferNative{}, fmt.Errorf("opengl: creating framebuffer failed: %v", s)
+			return 0, fmt.Errorf("opengl: creating framebuffer failed: %v", s)
 		}
-		if e := gl.GetError(); e != gles.NO_ERROR {
+		if e := c.ctx.GetError(); e != gles.NO_ERROR {
-			return framebufferNative{}, fmt.Errorf("opengl: creating framebuffer failed: (glGetError) %d", e)
+			return 0, fmt.Errorf("opengl: creating framebuffer failed: (glGetError) %d", e)
 		}
-		return framebufferNative{}, fmt.Errorf("opengl: creating framebuffer failed: unknown error")
+		return 0, fmt.Errorf("opengl: creating framebuffer failed: unknown error")
 	}
 	return framebufferNative(f), nil
 }
 
 func (c *context) setViewportImpl(width, height int) {
-	gl := c.gl
+	c.ctx.Viewport(0, 0, int32(width), int32(height))
-	gl.Viewport(0, 0, width, height)
 }
 
 func (c *context) deleteFramebuffer(f framebufferNative) {
-	gl := c.gl
+	if !c.ctx.IsFramebuffer(uint32(f)) {
-	if !gl.IsFramebuffer(mgl.Framebuffer(f)) {
 		return
 	}
 	// If a framebuffer to be deleted is bound, a newly bound framebuffer
@@ -227,96 +214,89 @@ func (c *context) deleteFramebuffer(f framebufferNative) {
 		c.lastViewportWidth = 0
 		c.lastViewportHeight = 0
 	}
-	gl.DeleteFramebuffer(mgl.Framebuffer(f))
+	c.ctx.DeleteFramebuffers([]uint32{uint32(f)})
 }
 
 func (c *context) newShader(shaderType shaderType, source string) (shader, error) {
-	gl := c.gl
+	s := c.ctx.CreateShader(uint32(shaderType))
-	s := gl.CreateShader(mgl.Enum(shaderType))
+	if s == 0 {
-	if s.Value == 0 {
+		return 0, fmt.Errorf("opengl: glCreateShader failed: shader type: %d", shaderType)
-		return shader{}, fmt.Errorf("opengl: glCreateShader failed: shader type: %d", shaderType)
 	}
-	gl.ShaderSource(s, source)
+	c.ctx.ShaderSource(s, source)
-	gl.CompileShader(s)
+	c.ctx.CompileShader(s)
 
-	v := gl.GetShaderi(s, gles.COMPILE_STATUS)
+	v := make([]int32, 1)
-	if v == gles.FALSE {
+	c.ctx.GetShaderiv(v, s, gles.COMPILE_STATUS)
-		log := gl.GetShaderInfoLog(s)
+	if v[0] == gles.FALSE {
-		return shader{}, fmt.Errorf("opengl: shader compile failed: %s", log)
+		log := c.ctx.GetShaderInfoLog(s)
+		return 0, fmt.Errorf("opengl: shader compile failed: %s", log)
 	}
 	return shader(s), nil
 }
 
 func (c *context) deleteShader(s shader) {
-	gl := c.gl
+	c.ctx.DeleteShader(uint32(s))
-	gl.DeleteShader(mgl.Shader(s))
 }
 
 func (c *context) newProgram(shaders []shader, attributes []string) (program, error) {
-	gl := c.gl
+	p := c.ctx.CreateProgram()
-	p := gl.CreateProgram()
+	if p == 0 {
-	if p.Value == 0 {
+		return 0, errors.New("opengl: glCreateProgram failed")
-		return program{}, errors.New("opengl: glCreateProgram failed")
 	}
 
 	for _, shader := range shaders {
-		gl.AttachShader(p, mgl.Shader(shader))
+		c.ctx.AttachShader(p, uint32(shader))
 	}
 
 	for i, name := range attributes {
-		gl.BindAttribLocation(p, mgl.Attrib{Value: uint(i)}, name)
+		c.ctx.BindAttribLocation(p, uint32(i), name)
 	}
 
-	gl.LinkProgram(p)
+	c.ctx.LinkProgram(p)
-	v := gl.GetProgrami(p, gles.LINK_STATUS)
+	v := make([]int32, 1)
-	if v == gles.FALSE {
+	c.ctx.GetProgramiv(v, p, gles.LINK_STATUS)
-		info := gl.GetProgramInfoLog(p)
+	if v[0] == gles.FALSE {
-		return program{}, fmt.Errorf("opengl: program error: %s", info)
+		info := c.ctx.GetProgramInfoLog(p)
+		return 0, fmt.Errorf("opengl: program error: %s", info)
 	}
 	return program(p), nil
 }
 
 func (c *context) useProgram(p program) {
-	gl := c.gl
+	c.ctx.UseProgram(uint32(p))
-	gl.UseProgram(mgl.Program(p))
 }
 
 func (c *context) deleteProgram(p program) {
-	gl := c.gl
+	if !c.ctx.IsProgram(uint32(p)) {
-	if !gl.IsProgram(mgl.Program(p)) {
 		return
 	}
-	gl.DeleteProgram(mgl.Program(p))
+	c.ctx.DeleteProgram(uint32(p))
 }
 
 func (c *context) getUniformLocationImpl(p program, location string) uniformLocation {
-	gl := c.gl
+	u := uniformLocation(c.ctx.GetUniformLocation(uint32(p), location))
-	u := uniformLocation(gl.GetUniformLocation(mgl.Program(p), location))
 	return u
 }
 
 func (c *context) uniformInt(p program, location string, v int) bool {
-	gl := c.gl
 	l := c.locationCache.GetUniformLocation(c, p, location)
 	if l == invalidUniform {
 		return false
 	}
-	gl.Uniform1i(mgl.Uniform(l), v)
+	c.ctx.Uniform1i(int32(l), int32(v))
 	return true
 }
 
 func (c *context) uniformFloat(p program, location string, v float32) bool {
-	gl := c.gl
 	l := c.locationCache.GetUniformLocation(c, p, location)
 	if l == invalidUniform {
 		return false
 	}
-	gl.Uniform1f(mgl.Uniform(l), v)
+	c.ctx.Uniform1f(int32(l), v)
 	return true
 }
 
 func (c *context) uniformFloats(p program, location string, v []float32, typ shaderir.Type) bool {
-	gl := c.gl
 	l := c.locationCache.GetUniformLocation(c, p, location)
 	if l == invalidUniform {
 		return false
@@ -329,19 +309,19 @@ func (c *context) uniformFloats(p program, location string, v []float32, typ sha
 
 	switch base {
 	case shaderir.Float:
-		gl.Uniform1fv(mgl.Uniform(l), v)
+		c.ctx.Uniform1fv(int32(l), v)
 	case shaderir.Vec2:
-		gl.Uniform2fv(mgl.Uniform(l), v)
+		c.ctx.Uniform2fv(int32(l), v)
 	case shaderir.Vec3:
-		gl.Uniform3fv(mgl.Uniform(l), v)
+		c.ctx.Uniform3fv(int32(l), v)
 	case shaderir.Vec4:
-		gl.Uniform4fv(mgl.Uniform(l), v)
+		c.ctx.Uniform4fv(int32(l), v)
 	case shaderir.Mat2:
-		gl.UniformMatrix2fv(mgl.Uniform(l), v)
+		c.ctx.UniformMatrix2fv(int32(l), false, v)
 	case shaderir.Mat3:
-		gl.UniformMatrix3fv(mgl.Uniform(l), v)
+		c.ctx.UniformMatrix3fv(int32(l), false, v)
 	case shaderir.Mat4:
-		gl.UniformMatrix4fv(mgl.Uniform(l), v)
+		c.ctx.UniformMatrix4fv(int32(l), false, v)
 	default:
 		panic(fmt.Sprintf("opengl: unexpected type: %s", typ.String()))
 	}
@@ -349,75 +329,64 @@ func (c *context) uniformFloats(p program, location string, v []float32, typ sha
 }
 
 func (c *context) vertexAttribPointer(p program, index int, size int, dataType dataType, stride int, offset int) {
-	gl := c.gl
+	c.ctx.VertexAttribPointer(uint32(index), int32(size), uint32(dataType), false, int32(stride), offset)
-	gl.VertexAttribPointer(mgl.Attrib{Value: uint(index)}, size, mgl.Enum(dataType), false, stride, offset)
 }
 
 func (c *context) enableVertexAttribArray(p program, index int) {
-	gl := c.gl
+	c.ctx.EnableVertexAttribArray(uint32(index))
-	gl.EnableVertexAttribArray(mgl.Attrib{Value: uint(index)})
 }
 
 func (c *context) disableVertexAttribArray(p program, index int) {
-	gl := c.gl
+	c.ctx.DisableVertexAttribArray(uint32(index))
-	gl.DisableVertexAttribArray(mgl.Attrib{Value: uint(index)})
 }
 
 func (c *context) newArrayBuffer(size int) buffer {
-	gl := c.gl
+	b := c.ctx.GenBuffers(1)[0]
-	b := gl.CreateBuffer()
+	c.ctx.BindBuffer(uint32(arrayBuffer), b)
-	gl.BindBuffer(mgl.Enum(arrayBuffer), b)
+	c.ctx.BufferData(uint32(arrayBuffer), size, nil, uint32(dynamicDraw))
-	gl.BufferInit(mgl.Enum(arrayBuffer), size, mgl.Enum(dynamicDraw))
 	return buffer(b)
 }
 
 func (c *context) newElementArrayBuffer(size int) buffer {
-	gl := c.gl
+	b := c.ctx.GenBuffers(1)[0]
-	b := gl.CreateBuffer()
+	c.ctx.BindBuffer(uint32(elementArrayBuffer), b)
-	gl.BindBuffer(mgl.Enum(elementArrayBuffer), b)
+	c.ctx.BufferData(uint32(elementArrayBuffer), size, nil, uint32(dynamicDraw))
-	gl.BufferInit(mgl.Enum(elementArrayBuffer), size, mgl.Enum(dynamicDraw))
 	return buffer(b)
 }
 
 func (c *context) bindBuffer(bufferType bufferType, b buffer) {
-	gl := c.gl
+	c.ctx.BindBuffer(uint32(bufferType), uint32(b))
-	gl.BindBuffer(mgl.Enum(bufferType), mgl.Buffer(b))
 }
 
 func (c *context) arrayBufferSubData(data []float32) {
-	gl := c.gl
+	c.ctx.BufferSubData(uint32(arrayBuffer), 0, float32sToBytes(data))
-	gl.BufferSubData(mgl.Enum(arrayBuffer), 0, float32sToBytes(data))
 }
 
 func (c *context) elementArrayBufferSubData(data []uint16) {
-	gl := c.gl
+	c.ctx.BufferSubData(uint32(elementArrayBuffer), 0, uint16sToBytes(data))
-	gl.BufferSubData(mgl.Enum(elementArrayBuffer), 0, uint16sToBytes(data))
 }
 
 func (c *context) deleteBuffer(b buffer) {
-	gl := c.gl
+	c.ctx.DeleteBuffers([]uint32{uint32(b)})
-	gl.DeleteBuffer(mgl.Buffer(b))
 }
 
 func (c *context) drawElements(len int, offsetInBytes int) {
-	gl := c.gl
+	c.ctx.DrawElements(gles.TRIANGLES, int32(len), gles.UNSIGNED_SHORT, offsetInBytes)
-	gl.DrawElements(gles.TRIANGLES, len, gles.UNSIGNED_SHORT, offsetInBytes)
 }
 
 func (c *context) maxTextureSizeImpl() int {
-	gl := c.gl
+	v := make([]int32, 1)
-	return gl.GetInteger(gles.MAX_TEXTURE_SIZE)
+	c.ctx.GetIntegerv(v, gles.MAX_TEXTURE_SIZE)
+	return int(v[0])
 }
 
 func (c *context) getShaderPrecisionFormatPrecision() int {
-	gl := c.gl
+	_, _, p := c.ctx.GetShaderPrecisionFormat(gles.FRAGMENT_SHADER, gles.HIGH_FLOAT)
-	_, _, p := gl.GetShaderPrecisionFormat(gles.FRAGMENT_SHADER, gles.HIGH_FLOAT)
 	return p
 }
 
 func (c *context) flush() {
-	gl := c.gl
+	c.ctx.Flush()
-	gl.Flush()
 }
 
 func (c *context) needsRestoring() bool {
@@ -432,18 +401,16 @@ func (c *context) canUsePBO() bool {
 
 func (c *context) texSubImage2D(t textureNative, width, height int, args []*driver.ReplacePixelsArgs) {
 	c.bindTexture(t)
-	gl := c.gl
 	for _, a := range args {
-		gl.TexSubImage2D(gles.TEXTURE_2D, 0, a.X, a.Y, a.Width, a.Height, gles.RGBA, gles.UNSIGNED_BYTE, a.Pixels)
+		c.ctx.TexSubImage2D(gles.TEXTURE_2D, 0, int32(a.X), int32(a.Y), int32(a.Width), int32(a.Height), gles.RGBA, gles.UNSIGNED_BYTE, a.Pixels)
 	}
 }
 
 func (c *context) newPixelBufferObject(width, height int) buffer {
-	gl := c.gl
+	b := c.ctx.GenBuffers(1)[0]
-	b := gl.CreateBuffer()
+	c.ctx.BindBuffer(gles.PIXEL_UNPACK_BUFFER, b)
-	gl.BindBuffer(gles.PIXEL_UNPACK_BUFFER, b)
+	c.ctx.BufferData(gles.PIXEL_UNPACK_BUFFER, 4*width*height, nil, gles.STREAM_DRAW)
-	gl.BufferInit(gles.PIXEL_UNPACK_BUFFER, 4*width*height, gles.STREAM_DRAW)
+	c.ctx.BindBuffer(gles.PIXEL_UNPACK_BUFFER, 0)
-	gl.BindBuffer(gles.PIXEL_UNPACK_BUFFER, mgl.Buffer{0})
 	return buffer(b)
 }
 
@@ -451,17 +418,16 @@ func (c *context) replacePixelsWithPBO(buffer buffer, t textureNative, width, he
 	// This implementation is not used yet so far. See the comment at canUsePBO.
 
 	c.bindTexture(t)
-	gl := c.gl
+	c.ctx.BindBuffer(gles.PIXEL_UNPACK_BUFFER, uint32(buffer))
-	gl.BindBuffer(gles.PIXEL_UNPACK_BUFFER, mgl.Buffer(buffer))
 
 	stride := 4 * width
 	for _, a := range args {
 		offset := 4 * (a.Y*width + a.X)
 		for j := 0; j < a.Height; j++ {
-			gl.BufferSubData(gles.PIXEL_UNPACK_BUFFER, offset+stride*j, a.Pixels[4*a.Width*j:4*a.Width*(j+1)])
+			c.ctx.BufferSubData(gles.PIXEL_UNPACK_BUFFER, offset+stride*j, a.Pixels[4*a.Width*j:4*a.Width*(j+1)])
 		}
 	}
 
-	gl.TexSubImage2D(gles.TEXTURE_2D, 0, 0, 0, width, height, gles.RGBA, gles.UNSIGNED_BYTE, nil)
+	c.ctx.TexSubImage2D(gles.TEXTURE_2D, 0, 0, 0, int32(width), int32(height), gles.RGBA, gles.UNSIGNED_BYTE, nil)
-	gl.BindBuffer(gles.PIXEL_UNPACK_BUFFER, mgl.Buffer{0})
+	c.ctx.BindBuffer(gles.PIXEL_UNPACK_BUFFER, 0)
 }

internal/graphicsdriver/opengl/gles/default.go

@@ -0,0 +1,313 @@
+// Copyright 2020 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build android ios
+
+package gles
+
+// #cgo android CFLAGS:  -Dos_android
+// #cgo android LDFLAGS: -lGLESv2
+// #cgo ios     CFLAGS:  -Dos_ios
+// #cgo ios     LDFLAGS: -framework OpenGLES
+//
+// #if defined(os_android)
+//   #include <GLES2/gl2.h>
+// #endif
+//
+// #if defined(os_ios)
+//   #include <OpenGLES/ES2/glext.h>
+// #endif
+import "C"
+
+import (
+	"unsafe"
+)
+
+func glBool(x bool) C.GLboolean {
+	if x {
+		return TRUE
+	}
+	return FALSE
+}
+
+type DefaultContext struct{}
+
+func (DefaultContext) ActiveTexture(texture uint32) {
+	C.glActiveTexture(C.GLenum(texture))
+}
+
+func (DefaultContext) AttachShader(program uint32, shader uint32) {
+	C.glAttachShader(C.GLuint(program), C.GLuint(shader))
+}
+
+func (DefaultContext) BindAttribLocation(program uint32, index uint32, name string) {
+	s, free := cString(name)
+	defer free()
+	C.glBindAttribLocation(C.GLuint(program), C.GLuint(index), (*C.GLchar)(unsafe.Pointer(s)))
+}
+
+func (DefaultContext) BindBuffer(target uint32, buffer uint32) {
+	C.glBindBuffer(C.GLenum(target), C.GLuint(buffer))
+}
+
+func (DefaultContext) BindFramebuffer(target uint32, framebuffer uint32) {
+	C.glBindFramebuffer(C.GLenum(target), C.GLuint(framebuffer))
+}
+
+func (DefaultContext) BindTexture(target uint32, texture uint32) {
+	C.glBindTexture(C.GLenum(target), C.GLuint(texture))
+}
+
+func (DefaultContext) BlendFunc(sfactor uint32, dfactor uint32) {
+	C.glBlendFunc(C.GLenum(sfactor), C.GLenum(dfactor))
+}
+
+func (DefaultContext) BufferData(target uint32, size int, data []byte, usage uint32) {
+	var p *byte
+	if data != nil {
+		p = &data[0]
+	}
+	C.glBufferData(C.GLenum(target), C.GLsizeiptr(size), unsafe.Pointer(p), C.GLenum(usage))
+}
+
+func (DefaultContext) BufferSubData(target uint32, offset int, data []byte) {
+	C.glBufferSubData(C.GLenum(target), C.GLintptr(offset), C.GLsizeiptr(len(data)), unsafe.Pointer(&data[0]))
+}
+
+func (DefaultContext) CheckFramebufferStatus(target uint32) uint32 {
+	return uint32(C.glCheckFramebufferStatus(C.GLenum(target)))
+}
+
+func (DefaultContext) CompileShader(shader uint32) {
+	C.glCompileShader(C.GLuint(shader))
+}
+
+func (DefaultContext) CreateProgram() uint32 {
+	return uint32(C.glCreateProgram())
+}
+
+func (DefaultContext) CreateShader(xtype uint32) uint32 {
+	return uint32(C.glCreateShader(C.GLenum(xtype)))
+}
+
+func (DefaultContext) DeleteBuffers(buffers []uint32) {
+	C.glDeleteBuffers(C.GLsizei(len(buffers)), (*C.GLuint)(unsafe.Pointer(&buffers[0])))
+}
+
+func (DefaultContext) DeleteFramebuffers(framebuffers []uint32) {
+	C.glDeleteFramebuffers(C.GLsizei(len(framebuffers)), (*C.GLuint)(unsafe.Pointer(&framebuffers[0])))
+}
+
+func (DefaultContext) DeleteProgram(program uint32) {
+	C.glDeleteProgram(C.GLuint(program))
+}
+
+func (DefaultContext) DeleteShader(shader uint32) {
+	C.glDeleteShader(C.GLuint(shader))
+}
+
+func (DefaultContext) DeleteTextures(textures []uint32) {
+	C.glDeleteTextures(C.GLsizei(len(textures)), (*C.GLuint)(unsafe.Pointer(&textures[0])))
+}
+
+func (DefaultContext) DisableVertexAttribArray(index uint32) {
+	C.glDisableVertexAttribArray(C.GLuint(index))
+}
+
+func (DefaultContext) DrawElements(mode uint32, count int32, xtype uint32, offset int) {
+	C.glDrawElements(C.GLenum(mode), C.GLsizei(count), C.GLenum(xtype), unsafe.Pointer(uintptr(offset)))
+}
+
+func (DefaultContext) Enable(cap uint32) {
+	C.glEnable(C.GLenum(cap))
+}
+
+func (DefaultContext) EnableVertexAttribArray(index uint32) {
+	C.glEnableVertexAttribArray(C.GLuint(index))
+}
+
+func (DefaultContext) Flush() {
+	C.glFlush()
+}
+
+func (DefaultContext) FramebufferTexture2D(target uint32, attachment uint32, textarget uint32, texture uint32, level int32) {
+	C.glFramebufferTexture2D(C.GLenum(target), C.GLenum(attachment), C.GLenum(textarget), C.GLuint(texture), C.GLint(level))
+}
+
+func (DefaultContext) GenBuffers(n int32) []uint32 {
+	buffers := make([]uint32, n)
+	C.glGenBuffers(C.GLsizei(n), (*C.GLuint)(unsafe.Pointer(&buffers[0])))
+	return buffers
+}
+
+func (DefaultContext) GenFramebuffers(n int32) []uint32 {
+	framebuffers := make([]uint32, n)
+	C.glGenFramebuffers(C.GLsizei(n), (*C.GLuint)(unsafe.Pointer(&framebuffers[0])))
+	return framebuffers
+}
+
+func (DefaultContext) GenTextures(n int32) []uint32 {
+	textures := make([]uint32, n)
+	C.glGenTextures(C.GLsizei(n), (*C.GLuint)(unsafe.Pointer(&textures[0])))
+	return textures
+}
+
+func (DefaultContext) GetError() uint32 {
+	return uint32(C.glGetError())
+}
+
+func (DefaultContext) GetIntegerv(dst []int32, pname uint32) {
+	C.glGetIntegerv(C.GLenum(pname), (*C.GLint)(unsafe.Pointer(&dst[0])))
+}
+
+func (DefaultContext) GetProgramiv(dst []int32, program uint32, pname uint32) {
+	C.glGetProgramiv(C.GLuint(program), C.GLenum(pname), (*C.GLint)(unsafe.Pointer(&dst[0])))
+}
+
+func (d DefaultContext) GetProgramInfoLog(program uint32) string {
+	buflens := make([]int32, 1)
+	d.GetProgramiv(buflens, program, INFO_LOG_LENGTH)
+	buflen := buflens[0]
+	if buflen == 0 {
+		return ""
+	}
+	buf := make([]byte, buflen)
+	var length int32
+	C.glGetProgramInfoLog(C.GLuint(program), C.GLsizei(buflen), (*C.GLsizei)(unsafe.Pointer(&length)), (*C.GLchar)(unsafe.Pointer(&buf[0])))
+	return string(buf[:length])
+}
+
+func (DefaultContext) GetShaderiv(dst []int32, shader uint32, pname uint32) {
+	C.glGetShaderiv(C.GLuint(shader), C.GLenum(pname), (*C.GLint)(unsafe.Pointer(&dst[0])))
+}
+
+func (d DefaultContext) GetShaderInfoLog(shader uint32) string {
+	buflens := make([]int32, 1)
+	d.GetShaderiv(buflens, shader, INFO_LOG_LENGTH)
+	buflen := buflens[0]
+	if buflen == 0 {
+		return ""
+	}
+	buf := make([]byte, buflen)
+	var length int32
+	C.glGetShaderInfoLog(C.GLuint(shader), C.GLsizei(buflen), (*C.GLsizei)(unsafe.Pointer(&length)), (*C.GLchar)(unsafe.Pointer(&buf[0])))
+	return string(buf[:length])
+}
+
+func (DefaultContext) GetShaderPrecisionFormat(shadertype uint32, precisiontype uint32) (rangeLow, rangeHigh, precision int) {
+	var r [2]int32
+	var p int32
+	C.glGetShaderPrecisionFormat(C.GLenum(shadertype), C.GLenum(precisiontype), (*C.GLint)(unsafe.Pointer(&r[0])), (*C.GLint)(unsafe.Pointer(&p)))
+	return int(r[0]), int(r[1]), int(p)
+}
+
+func (DefaultContext) GetUniformLocation(program uint32, name string) int32 {
+	s, free := cString(name)
+	defer free()
+	return int32(C.glGetUniformLocation(C.GLuint(program), (*C.GLchar)(unsafe.Pointer(s))))
+}
+
+func (DefaultContext) IsFramebuffer(framebuffer uint32) bool {
+	return C.glIsFramebuffer(C.GLuint(framebuffer)) != FALSE
+}
+
+func (DefaultContext) IsProgram(program uint32) bool {
+	return C.glIsProgram(C.GLuint(program)) != FALSE
+}
+
+func (DefaultContext) IsTexture(texture uint32) bool {
+	return C.glIsTexture(C.GLuint(texture)) != FALSE
+}
+
+func (DefaultContext) LinkProgram(program uint32) {
+	C.glLinkProgram(C.GLuint(program))
+}
+
+func (DefaultContext) PixelStorei(pname uint32, param int32) {
+	C.glPixelStorei(C.GLenum(pname), C.GLint(param))
+}
+
+func (DefaultContext) ReadPixels(dst []byte, x int32, y int32, width int32, height int32, format uint32, xtype uint32) {
+	C.glReadPixels(C.GLint(x), C.GLint(y), C.GLsizei(width), C.GLsizei(height), C.GLenum(format), C.GLenum(xtype), unsafe.Pointer(&dst[0]))
+}
+
+func (DefaultContext) ShaderSource(shader uint32, xstring string) {
+	s, free := cStringPtr(xstring)
+	defer free()
+	C.glShaderSource(C.GLuint(shader), 1, (**C.GLchar)(unsafe.Pointer(s)), nil)
+}
+
+func (DefaultContext) TexImage2D(target uint32, level int32, internalformat int32, width int32, height int32, format uint32, xtype uint32, pixels []byte) {
+	var p *byte
+	if pixels != nil {
+		p = &pixels[0]
+	}
+	C.glTexImage2D(C.GLenum(target), C.GLint(level), C.GLint(internalformat), C.GLsizei(width), C.GLsizei(height), 0 /* border */, C.GLenum(format), C.GLenum(xtype), unsafe.Pointer(p))
+}
+
+func (DefaultContext) TexParameteri(target uint32, pname uint32, param int32) {
+	C.glTexParameteri(C.GLenum(target), C.GLenum(pname), C.GLint(param))
+}
+
+func (DefaultContext) TexSubImage2D(target uint32, level int32, xoffset int32, yoffset int32, width int32, height int32, format uint32, xtype uint32, pixels []byte) {
+	C.glTexSubImage2D(C.GLenum(target), C.GLint(level), C.GLint(xoffset), C.GLint(yoffset), C.GLsizei(width), C.GLsizei(height), C.GLenum(format), C.GLenum(xtype), unsafe.Pointer(&pixels[0]))
+}
+
+func (DefaultContext) Uniform1f(location int32, v0 float32) {
+	C.glUniform1f(C.GLint(location), C.GLfloat(v0))
+}
+
+func (DefaultContext) Uniform1fv(location int32, value []float32) {
+	C.glUniform1fv(C.GLint(location), C.GLsizei(len(value)), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) Uniform1i(location int32, v0 int32) {
+	C.glUniform1i(C.GLint(location), C.GLint(v0))
+}
+
+func (DefaultContext) Uniform2fv(location int32, value []float32) {
+	C.glUniform2fv(C.GLint(location), C.GLsizei(len(value)/2), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) Uniform3fv(location int32, value []float32) {
+	C.glUniform3fv(C.GLint(location), C.GLsizei(len(value)/3), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) Uniform4fv(location int32, value []float32) {
+	C.glUniform4fv(C.GLint(location), C.GLsizei(len(value)/4), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) UniformMatrix2fv(location int32, transpose bool, value []float32) {
+	C.glUniformMatrix2fv(C.GLint(location), C.GLsizei(len(value)/4), glBool(transpose), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) UniformMatrix3fv(location int32, transpose bool, value []float32) {
+	C.glUniformMatrix3fv(C.GLint(location), C.GLsizei(len(value)/9), glBool(transpose), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) UniformMatrix4fv(location int32, transpose bool, value []float32) {
+	C.glUniformMatrix4fv(C.GLint(location), C.GLsizei(len(value)/16), glBool(transpose), (*C.GLfloat)(unsafe.Pointer(&value[0])))
+}
+
+func (DefaultContext) UseProgram(program uint32) {
+	C.glUseProgram(C.GLuint(program))
+}
+
+func (DefaultContext) VertexAttribPointer(index uint32, size int32, xtype uint32, normalized bool, stride int32, offset int) {
+	C.glVertexAttribPointer(C.GLuint(index), C.GLint(size), C.GLenum(xtype), glBool(normalized), C.GLsizei(stride), unsafe.Pointer(uintptr(offset)))
+}
+
+func (DefaultContext) Viewport(x int32, y int32, width int32, height int32) {
+	C.glViewport(C.GLint(x), C.GLint(y), C.GLsizei(width), C.GLsizei(height))
+}

internal/graphicsdriver/opengl/gles/gomobile.go

@@ -0,0 +1,298 @@
+// Copyright 2020 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build android ios
+
+package gles
+
+import (
+	"golang.org/x/mobile/gl"
+)
+
+type GomobileContext struct {
+	ctx gl.Context
+}
+
+func gmProgram(program uint32) gl.Program {
+	return gl.Program{
+		Init:  true,
+		Value: program,
+	}
+}
+
+func NewGomobileContext(ctx gl.Context) *GomobileContext {
+	return &GomobileContext{ctx}
+}
+
+func (g *GomobileContext) ActiveTexture(texture uint32) {
+	g.ctx.ActiveTexture(gl.Enum(texture))
+}
+
+func (g *GomobileContext) AttachShader(program uint32, shader uint32) {
+	g.ctx.AttachShader(gmProgram(program), gl.Shader{Value: shader})
+}
+
+func (g *GomobileContext) BindAttribLocation(program uint32, index uint32, name string) {
+	g.ctx.BindAttribLocation(gmProgram(program), gl.Attrib{Value: uint(index)}, name)
+}
+
+func (g *GomobileContext) BindBuffer(target uint32, buffer uint32) {
+	g.ctx.BindBuffer(gl.Enum(target), gl.Buffer{Value: buffer})
+}
+
+func (g *GomobileContext) BindFramebuffer(target uint32, framebuffer uint32) {
+	g.ctx.BindFramebuffer(gl.Enum(target), gl.Framebuffer{Value: framebuffer})
+}
+
+func (g *GomobileContext) BindTexture(target uint32, texture uint32) {
+	g.ctx.BindTexture(gl.Enum(target), gl.Texture{Value: texture})
+}
+
+func (g *GomobileContext) BlendFunc(sfactor uint32, dfactor uint32) {
+	g.ctx.BlendFunc(gl.Enum(sfactor), gl.Enum(dfactor))
+}
+
+func (g *GomobileContext) BufferData(target uint32, size int, data []byte, usage uint32) {
+	if data == nil {
+		g.ctx.BufferInit(gl.Enum(target), size, gl.Enum(usage))
+	} else {
+		if size != len(data) {
+			panic("gles: size and len(data) must be same at BufferData")
+		}
+		g.ctx.BufferData(gl.Enum(target), data, gl.Enum(usage))
+	}
+}
+
+func (g *GomobileContext) BufferSubData(target uint32, offset int, data []byte) {
+	g.ctx.BufferSubData(gl.Enum(target), offset, data)
+}
+
+func (g *GomobileContext) CheckFramebufferStatus(target uint32) uint32 {
+	return uint32(g.ctx.CheckFramebufferStatus(gl.Enum(target)))
+}
+
+func (g *GomobileContext) CompileShader(shader uint32) {
+	g.ctx.CompileShader(gl.Shader{Value: shader})
+}
+
+func (g *GomobileContext) CreateProgram() uint32 {
+	return g.ctx.CreateProgram().Value
+}
+
+func (g *GomobileContext) CreateShader(xtype uint32) uint32 {
+	return g.ctx.CreateShader(gl.Enum(xtype)).Value
+}
+
+func (g *GomobileContext) DeleteBuffers(buffers []uint32) {
+	for _, b := range buffers {
+		g.ctx.DeleteBuffer(gl.Buffer{Value: b})
+	}
+}
+
+func (g *GomobileContext) DeleteFramebuffers(framebuffers []uint32) {
+	for _, b := range framebuffers {
+		g.ctx.DeleteFramebuffer(gl.Framebuffer{Value: b})
+	}
+}
+
+func (g *GomobileContext) DeleteProgram(program uint32) {
+	g.ctx.DeleteProgram(gmProgram(program))
+}
+
+func (g *GomobileContext) DeleteShader(shader uint32) {
+	g.ctx.DeleteShader(gl.Shader{Value: shader})
+}
+
+func (g *GomobileContext) DeleteTextures(textures []uint32) {
+	for _, t := range textures {
+		g.ctx.DeleteTexture(gl.Texture{Value: t})
+	}
+}
+
+func (g *GomobileContext) DisableVertexAttribArray(index uint32) {
+	g.ctx.DisableVertexAttribArray(gl.Attrib{Value: uint(index)})
+}
+
+func (g *GomobileContext) DrawElements(mode uint32, count int32, xtype uint32, offset int) {
+	g.ctx.DrawElements(gl.Enum(mode), int(count), gl.Enum(xtype), offset)
+}
+
+func (g *GomobileContext) Enable(cap uint32) {
+	g.ctx.Enable(gl.Enum(gl.Enum(cap)))
+}
+
+func (g *GomobileContext) EnableVertexAttribArray(index uint32) {
+	g.ctx.EnableVertexAttribArray(gl.Attrib{Value: uint(index)})
+}
+
+func (g *GomobileContext) Flush() {
+	g.ctx.Flush()
+}
+
+func (g *GomobileContext) FramebufferTexture2D(target uint32, attachment uint32, textarget uint32, texture uint32, level int32) {
+	g.ctx.FramebufferTexture2D(gl.Enum(target), gl.Enum(attachment), gl.Enum(textarget), gl.Texture{Value: texture}, int(level))
+}
+
+func (g *GomobileContext) GenBuffers(n int32) []uint32 {
+	buffers := make([]uint32, n)
+	for i := range buffers {
+		buffers[i] = g.ctx.CreateBuffer().Value
+	}
+	return buffers
+}
+
+func (g *GomobileContext) GenFramebuffers(n int32) []uint32 {
+	framebuffers := make([]uint32, n)
+	for i := range framebuffers {
+		framebuffers[i] = g.ctx.CreateFramebuffer().Value
+	}
+	return framebuffers
+}
+
+func (g *GomobileContext) GenTextures(n int32) []uint32 {
+	textures := make([]uint32, n)
+	for i := range textures {
+		textures[i] = g.ctx.CreateTexture().Value
+	}
+	return textures
+}
+
+func (g *GomobileContext) GetError() uint32 {
+	return uint32(g.ctx.GetError())
+}
+
+func (g *GomobileContext) GetIntegerv(dst []int32, pname uint32) {
+	g.ctx.GetIntegerv(dst, gl.Enum(pname))
+}
+
+func (g *GomobileContext) GetProgramiv(dst []int32, program uint32, pname uint32) {
+	dst[0] = int32(g.ctx.GetProgrami(gmProgram(program), gl.Enum(pname)))
+}
+
+func (g *GomobileContext) GetProgramInfoLog(program uint32) string {
+	return g.ctx.GetProgramInfoLog(gmProgram(program))
+}
+
+func (g *GomobileContext) GetShaderiv(dst []int32, shader uint32, pname uint32) {
+	dst[0] = int32(g.ctx.GetShaderi(gl.Shader{Value: shader}, gl.Enum(pname)))
+}
+
+func (g *GomobileContext) GetShaderInfoLog(shader uint32) string {
+	return g.ctx.GetShaderInfoLog(gl.Shader{Value: shader})
+}
+
+func (g *GomobileContext) GetShaderPrecisionFormat(shadertype uint32, precisiontype uint32) (rangeLow, rangeHigh, precision int) {
+	return g.ctx.GetShaderPrecisionFormat(gl.Enum(shadertype), gl.Enum(precisiontype))
+}
+
+func (g *GomobileContext) GetUniformLocation(program uint32, name string) int32 {
+	return g.ctx.GetUniformLocation(gmProgram(program), name).Value
+}
+
+func (g *GomobileContext) IsFramebuffer(framebuffer uint32) bool {
+	return g.ctx.IsFramebuffer(gl.Framebuffer{Value: framebuffer})
+}
+
+func (g *GomobileContext) IsProgram(program uint32) bool {
+	return g.ctx.IsProgram(gmProgram(program))
+}
+
+func (g *GomobileContext) IsTexture(texture uint32) bool {
+	return g.ctx.IsTexture(gl.Texture{Value: texture})
+}
+
+func (g *GomobileContext) LinkProgram(program uint32) {
+	g.ctx.LinkProgram(gmProgram(program))
+}
+
+func (g *GomobileContext) PixelStorei(pname uint32, param int32) {
+	g.ctx.PixelStorei(gl.Enum(pname), param)
+}
+
+func (g *GomobileContext) ReadPixels(dst []byte, x int32, y int32, width int32, height int32, format uint32, xtype uint32) {
+	g.ctx.ReadPixels(dst, int(x), int(y), int(width), int(height), gl.Enum(format), gl.Enum(xtype))
+}
+
+func (g *GomobileContext) ShaderSource(shader uint32, xstring string) {
+	g.ctx.ShaderSource(gl.Shader{Value: shader}, xstring)
+}
+
+func (g *GomobileContext) TexImage2D(target uint32, level int32, internalformat int32, width int32, height int32, format uint32, xtype uint32, pixels []byte) {
+	g.ctx.TexImage2D(gl.Enum(target), int(level), int(internalformat), int(width), int(height), gl.Enum(format), gl.Enum(xtype), pixels)
+}
+
+func (g *GomobileContext) TexParameteri(target uint32, pname uint32, param int32) {
+	g.ctx.TexParameteri(gl.Enum(target), gl.Enum(pname), int(param))
+}
+
+func (g *GomobileContext) TexSubImage2D(target uint32, level int32, xoffset int32, yoffset int32, width int32, height int32, format uint32, xtype uint32, pixels []byte) {
+	g.ctx.TexSubImage2D(gl.Enum(target), int(level), int(xoffset), int(yoffset), int(width), int(height), gl.Enum(format), gl.Enum(xtype), pixels)
+}
+
+func (g *GomobileContext) Uniform1f(location int32, v0 float32) {
+	g.ctx.Uniform1f(gl.Uniform{Value: location}, v0)
+}
+
+func (g *GomobileContext) Uniform1fv(location int32, value []float32) {
+	g.ctx.Uniform1fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) Uniform1i(location int32, v0 int32) {
+	g.ctx.Uniform1i(gl.Uniform{Value: location}, int(v0))
+}
+
+func (g *GomobileContext) Uniform2fv(location int32, value []float32) {
+	g.ctx.Uniform2fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) Uniform3fv(location int32, value []float32) {
+	g.ctx.Uniform3fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) Uniform4fv(location int32, value []float32) {
+	g.ctx.Uniform4fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) UniformMatrix2fv(location int32, transpose bool, value []float32) {
+	if transpose {
+		panic("gles: UniformMatrix2fv with transpose is not implemented")
+	}
+	g.ctx.UniformMatrix2fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) UniformMatrix3fv(location int32, transpose bool, value []float32) {
+	if transpose {
+		panic("gles: UniformMatrix3fv with transpose is not implemented")
+	}
+	g.ctx.UniformMatrix3fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) UniformMatrix4fv(location int32, transpose bool, value []float32) {
+	if transpose {
+		panic("gles: UniformMatrix4fv with transpose is not implemented")
+	}
+	g.ctx.UniformMatrix4fv(gl.Uniform{Value: location}, value)
+}
+
+func (g *GomobileContext) UseProgram(program uint32) {
+	g.ctx.UseProgram(gmProgram(program))
+}
+
+func (g *GomobileContext) VertexAttribPointer(index uint32, size int32, xtype uint32, normalized bool, stride int32, offset int) {
+	g.ctx.VertexAttribPointer(gl.Attrib{Value: uint(index)}, int(size), gl.Enum(xtype), normalized, int(stride), int(offset))
+}
+
+func (g *GomobileContext) Viewport(x int32, y int32, width int32, height int32) {
+	g.ctx.Viewport(int(x), int(y), int(width), int(height))
+}

internal/graphicsdriver/opengl/gles/interface.go

@@ -0,0 +1,77 @@
+// Copyright 2020 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build android ios
+
+package gles
+
+type Context interface {
+	ActiveTexture(texture uint32)
+	AttachShader(program uint32, shader uint32)
+	BindAttribLocation(program uint32, index uint32, name string)
+	BindBuffer(target uint32, buffer uint32)
+	BindFramebuffer(target uint32, framebuffer uint32)
+	BindTexture(target uint32, texture uint32)
+	BlendFunc(sfactor uint32, dfactor uint32)
+	BufferData(target uint32, size int, data []byte, usage uint32)
+	BufferSubData(target uint32, offset int, data []byte)
+	CheckFramebufferStatus(target uint32) uint32
+	CompileShader(shader uint32)
+	CreateProgram() uint32
+	CreateShader(xtype uint32) uint32
+	DeleteBuffers(buffers []uint32)
+	DeleteFramebuffers(framebuffers []uint32)
+	DeleteProgram(program uint32)
+	DeleteShader(shader uint32)
+	DeleteTextures(textures []uint32)
+	DisableVertexAttribArray(index uint32)
+	DrawElements(mode uint32, count int32, xtype uint32, offset int)
+	Enable(cap uint32)
+	EnableVertexAttribArray(index uint32)
+	Flush()
+	FramebufferTexture2D(target uint32, attachment uint32, textarget uint32, texture uint32, level int32)
+	GenBuffers(n int32) []uint32
+	GenFramebuffers(n int32) []uint32
+	GenTextures(n int32) []uint32
+	GetError() uint32
+	GetIntegerv(dst []int32, pname uint32)
+	GetProgramiv(dst []int32, program uint32, pname uint32)
+	GetProgramInfoLog(program uint32) string
+	GetShaderiv(dst []int32, shader uint32, pname uint32)
+	GetShaderInfoLog(shader uint32) string
+	GetShaderPrecisionFormat(shadertype uint32, precisiontype uint32) (rangeLow, rangeHigh, precision int)
+	GetUniformLocation(program uint32, name string) int32
+	IsFramebuffer(framebuffer uint32) bool
+	IsProgram(program uint32) bool
+	IsTexture(texture uint32) bool
+	LinkProgram(program uint32)
+	PixelStorei(pname uint32, param int32)
+	ReadPixels(dst []byte, x int32, y int32, width int32, height int32, format uint32, xtype uint32)
+	ShaderSource(shader uint32, xstring string)
+	TexImage2D(target uint32, level int32, internalformat int32, width int32, height int32, format uint32, xtype uint32, pixels []byte)
+	TexParameteri(target uint32, pname uint32, param int32)
+	TexSubImage2D(target uint32, level int32, xoffset int32, yoffset int32, width int32, height int32, format uint32, xtype uint32, pixels []byte)
+	Uniform1f(location int32, v0 float32)
+	Uniform1fv(location int32, value []float32)
+	Uniform1i(location int32, v0 int32)
+	Uniform2fv(location int32, value []float32)
+	Uniform3fv(location int32, value []float32)
+	Uniform4fv(location int32, value []float32)
+	UniformMatrix2fv(location int32, transpose bool, value []float32)
+	UniformMatrix3fv(location int32, transpose bool, value []float32)
+	UniformMatrix4fv(location int32, transpose bool, value []float32)
+	UseProgram(program uint32)
+	VertexAttribPointer(index uint32, size int32, xtype uint32, normalized bool, stride int32, offset int)
+	Viewport(x int32, y int32, width int32, height int32)
+}

internal/graphicsdriver/opengl/gles/str.go

@@ -0,0 +1,39 @@
+// Copyright 2020 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build android ios
+
+package gles
+
+// #include <stdlib.h>
+import "C"
+
+import (
+	"unsafe"
+)
+
+func cString(str string) (uintptr, func()) {
+	ptr := C.CString(str)
+	return uintptr(unsafe.Pointer(ptr)), func() { C.free(unsafe.Pointer(ptr)) }
+}
+
+func cStringPtr(str string) (uintptr, func()) {
+	s, free := cString(str)
+	ptr := C.malloc(C.size_t(unsafe.Sizeof((*int)(nil))))
+	*(*uintptr)(ptr) = s
+	return uintptr(ptr), func() {
+		free()
+		C.free(ptr)
+	}
+}

internal/graphicsdriver/opengl/graphics_mobile.go

@@ -18,8 +18,14 @@ package opengl
 
 import (
 	"golang.org/x/mobile/gl"
+
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl/gles"
 )
 
-func (g *Graphics) SetMobileGLContext(context gl.Context) {
+func init() {
-	g.context.gl = context
+	theGraphics.context.ctx = gles.DefaultContext{}
+}
+
+func (g *Graphics) SetGomobileGLContext(context gl.Context) {
+	g.context.ctx = gles.NewGomobileContext(context)
 }

internal/uidriver/mobile/ui.go

@@ -21,7 +21,6 @@ import (
 	"runtime/debug"
 	"sync"
 	"sync/atomic"
-	"time"
 	"unicode"
 
 	"golang.org/x/mobile/app"
@@ -84,45 +83,6 @@ func (u *UserInterface) Update() error {
 	}
 
 	renderCh <- struct{}{}
-	if u.Graphics().IsGL() {
-		if u.glWorker == nil {
-			panic("mobile: glWorker must be initialized but not")
-		}
-
-		workAvailable := u.glWorker.WorkAvailable()
-		for {
-			// When the two channels don't receive for a while, call DoWork forcibly to avoid freeze
-			// (#1322, #1332).
-			//
-			// In theory, this timeout should not be necessary. However, it looks like this 'select'
-			// statement sometimes blocks forever on some Android devices like Pixel 4(a). Apparently
-			// workAvailable sometimes not receives even though there are queued OpenGL functions.
-			// Call DoWork for such case as a symptomatic treatment.
-			//
-			// Calling DoWork without waiting for workAvailable is safe. If there are no tasks, DoWork
-			// should return immediately.
-			//
-			// TODO: Fix the root cause. Note that this is pretty hard since e.g., logging affects the
-			// scheduling and freezing might not happen with logging.
-			t := time.NewTimer(100 * time.Millisecond)
-
-			select {
-			case <-workAvailable:
-				if !t.Stop() {
-					<-t.C
-				}
-				u.glWorker.DoWork()
-			case <-renderEndCh:
-				if !t.Stop() {
-					<-t.C
-				}
-				return nil
-			case <-t.C:
-				u.glWorker.DoWork()
-			}
-		}
-	}
-
 	go func() {
 		<-renderEndCh
 		u.t.Call(func() error {
@@ -152,7 +112,6 @@ type UserInterface struct {
 	input Input
 
 	t *thread.Thread
-	glWorker gl.Worker
 
 	m sync.RWMutex
 }
@@ -306,14 +265,11 @@ func (u *UserInterface) run(context driver.UIContext, mainloop bool) (err error)
 
 	u.context = context
 
-	if u.Graphics().IsGL() {
-		var ctx gl.Context
 	if mainloop {
-			ctx = <-glContextCh
+		// When mainloop is true, gomobile-build is used. In this case, GL functions must be called via
-		} else {
+		// gl.Context so that they are called on the appropriate thread.
-			ctx, u.glWorker = gl.NewContext()
+		ctx := <-glContextCh
-		}
+		u.Graphics().(*opengl.Graphics).SetGomobileGLContext(ctx)
-		u.Graphics().(*opengl.Graphics).SetMobileGLContext(ctx)
 	} else {
 		u.t = thread.New()
 		graphicscommand.SetMainThread(u.t)