gpu,gpu/gl: introduce Backend

A recent change made the OpenGL functions an interface of the functions
required for the implementation of GPU, a renderer for Gio operations.
That allowed for running Gio on external systems where OpenGL is
available.

However, to allow for non-OpenGL flavored backends such as Vulkan,
Metal and Direct3D, this change introduces Backend for the high-level
operations required by GPU. This change also adds a concrete backend
to package gl.

Type Backend is a first cut heavily based on OpenGL. Future changes will add
more backends, where the Backend interface quite possibly will need refinement.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/headless/headless.go

@@ -51,7 +51,13 @@ func NewWindow(width, height int) (*Window, error) {
 			ctx.Release()
 			return err
 		}
-		gpu, err := gpu.New(f)
+		backend, err := gl.NewBackend(f)
+		if err != nil {
+			fbo.Release()
+			ctx.Release()
+			return err
+		}
+		gpu, err := gpu.New(backend)
 		if err != nil {
 			fbo.Release()
 			ctx.Release()

app/internal/egl/egl_windows.go

@@ -11,7 +11,7 @@ import (
 	syscall "golang.org/x/sys/windows"
 
 	"gioui.org/app/internal/glimpl"
-	"gioui.org/gpu/gl"
+	gunsafe "gioui.org/internal/unsafe"
 )
 
 type (
@@ -157,7 +157,7 @@ func eglTerminate(disp _EGLDisplay) bool {
 
 func eglQueryString(disp _EGLDisplay, name _EGLint) string {
 	r, _, _ := _eglQueryString.Call(uintptr(disp), uintptr(name))
-	return gl.GoString(gl.SliceOf(r))
+	return gunsafe.GoString(gunsafe.SliceOf(r))
 }
 
 // issue34474KeepAlive calls runtime.KeepAlive as a

app/internal/glimpl/gl_windows.go

@@ -11,6 +11,7 @@ import (
 	"golang.org/x/sys/windows"
 
 	"gioui.org/gpu/gl"
+	gunsafe "gioui.org/internal/unsafe"
 )
 
 var (
@@ -290,7 +291,7 @@ func (c *Functions) GetShaderInfoLog(s gl.Shader) string {
 }
 func (c *Functions) GetString(pname gl.Enum) string {
 	s, _, _ := syscall.Syscall(_glGetString.Addr(), 1, uintptr(pname), 0, 0)
-	return gl.GoString(gl.SliceOf(s))
+	return gunsafe.GoString(gunsafe.SliceOf(s))
 }
 func (c *Functions) GetUniformLocation(p gl.Program, name string) gl.Uniform {
 	cname := cString(name)

app/loop.go

@@ -8,6 +8,7 @@ import (
 
 	"gioui.org/app/internal/window"
 	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 	"gioui.org/op"
 )
 
@@ -66,7 +67,12 @@ func (l *renderLoop) renderLoop(glctx window.Context) error {
 			initErr <- err
 			return
 		}
-		g, err := gpu.New(glctx.Functions())
+		ctx, err := gl.NewBackend(glctx.Functions())
+		if err != nil {
+			initErr <- err
+			return
+		}
+		g, err := gpu.New(ctx)
 		if err != nil {
 			initErr <- err
 			return

gpu/backend.go

@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import (
+	"image"
+	"time"
+)
+
+// Backend represents the abstraction of underlying GPU
+// APIs such as OpenGL, Direct3D useful for rendering Gio
+// operations.
+type Backend interface {
+	BeginFrame()
+	EndFrame()
+	Caps() Caps
+	NewTimer() Timer
+	// IsContinuousTime reports whether all timer measurements
+	// are valid at the point of call.
+	IsTimeContinuous() bool
+	NewTexture(minFilter, magFilter TextureFilter) Texture
+	DefaultFramebuffer() Framebuffer
+	NilTexture() Texture
+	NewFramebuffer() Framebuffer
+	NewBuffer(typ BufferType) Buffer
+	NewProgram(vertexShader, fragmentShader string, attribMap []string) (Program, error)
+	SetupVertexArray(slot int, size int, dataType DataType, stride, offset int)
+
+	DepthFunc(f DepthFunc)
+	ClearColor(r, g, b, a float32)
+	ClearDepth(d float32)
+	Clear(buffers BufferAttachments)
+	Viewport(x, y, width, height int)
+	DrawArrays(mode DrawMode, off, count int)
+	DrawElements(mode DrawMode, off, count int)
+	SetBlend(enable bool)
+	SetDepthTest(enable bool)
+	DepthMask(mask bool)
+	BlendFunc(sfactor, dfactor BlendFactor)
+}
+
+type BlendFactor uint8
+
+type DrawMode uint8
+
+type BufferAttachments uint
+
+type TextureFilter uint8
+type TextureFormat uint8
+
+type BufferType uint8
+type BufferUsage uint8
+
+type DataType uint8
+
+type DepthFunc uint8
+
+type Features uint
+
+type Caps struct {
+	Features       Features
+	MaxTextureSize int
+}
+
+type Program interface {
+	Bind()
+	Release()
+	UniformFor(uniform string) Uniform
+	Uniform1i(u Uniform, v int)
+	Uniform1f(u Uniform, v float32)
+	Uniform2f(u Uniform, v0, v1 float32)
+	Uniform4f(u Uniform, v0, v1, v2, v3 float32)
+}
+
+type Uniform interface{}
+
+type Buffer interface {
+	Bind()
+	Upload(usage BufferUsage, data []byte)
+	Release()
+}
+
+type Framebuffer interface {
+	Bind()
+	BindTexture(t Texture)
+	Invalidate()
+	Release()
+	IsComplete() error
+}
+
+type Timer interface {
+	Begin()
+	End()
+	Duration() (time.Duration, bool)
+	Release()
+}
+
+type Texture interface {
+	Upload(img *image.RGBA)
+	Release()
+	Bind(unit int)
+	Resize(format TextureFormat, width, height int)
+}
+
+const (
+	BufferAttachmentColor BufferAttachments = 1 << iota
+	BufferAttachmentDepth
+)
+
+const (
+	DepthFuncGreater DepthFunc = iota
+)
+
+const (
+	DataTypeFloat DataType = iota
+	DataTypeShort
+)
+
+const (
+	BufferUsageStaticDraw BufferUsage = iota
+)
+
+const (
+	BufferTypeIndices BufferType = iota
+	BufferTypeData
+)
+
+const (
+	TextureFormatSRGB TextureFormat = iota
+	TextureFormatFloat
+)
+
+const (
+	FilterNearest TextureFilter = iota
+	FilterLinear
+)
+
+const (
+	FeatureTimers Features = iota
+)
+
+const (
+	DrawModeTriangleStrip DrawMode = iota
+	DrawModeTriangles
+)
+
+const (
+	BlendFactorOne BlendFactor = iota
+	BlendFactorOneMinusSrcAlpha
+	BlendFactorZero
+	BlendFactorDstColor
+)
+
+func (f Features) Has(feats Features) bool {
+	return f&feats == feats
+}

gpu/caches.go

@@ -43,11 +43,11 @@ func (r *resourceCache) put(key interface{}, val resource) {
 	r.newRes[key] = val
 }
 
-func (r *resourceCache) frame(ctx *context) {
+func (r *resourceCache) frame() {
 	for k, v := range r.res {
 		if _, exists := r.newRes[k]; !exists {
 			delete(r.res, k)
-			v.release(ctx)
+			v.release()
 		}
 	}
 	for k, v := range r.newRes {
@@ -56,9 +56,9 @@ func (r *resourceCache) frame(ctx *context) {
 	}
 }
 
-func (r *resourceCache) release(ctx *context) {
+func (r *resourceCache) release() {
 	for _, v := range r.newRes {
-		v.release(ctx)
+		v.release()
 	}
 	r.newRes = nil
 	r.res = nil
@@ -87,11 +87,11 @@ func (r *opCache) put(key ops.Key, val resource) {
 	r.newRes[key] = val
 }
 
-func (r *opCache) frame(ctx *context) {
+func (r *opCache) frame() {
 	for k, v := range r.res {
 		if _, exists := r.newRes[k]; !exists {
 			delete(r.res, k)
-			v.release(ctx)
+			v.release()
 		}
 	}
 	for k, v := range r.newRes {
@@ -100,9 +100,9 @@ func (r *opCache) frame(ctx *context) {
 	}
 }
 
-func (r *opCache) release(ctx *context) {
+func (r *opCache) release() {
 	for _, v := range r.newRes {
-		v.release(ctx)
+		v.release()
 	}
 	r.newRes = nil
 	r.res = nil

gpu/context.go

@@ -1,128 +0,0 @@
-// SPDX-License-Identifier: Unlicense OR MIT
-
-package gpu
-
-import (
-	"errors"
-	"strings"
-
-	"gioui.org/gpu/gl"
-)
-
-type context struct {
-	caps caps
-	gl.Functions
-}
-
-type caps struct {
-	EXT_disjoint_timer_query bool
-	// floatTriple holds the settings for floating point
-	// textures.
-	floatTriple textureTriple
-	// Single channel alpha textures.
-	alphaTriple textureTriple
-	srgbaTriple textureTriple
-}
-
-// textureTriple holds the type settings for
-// a TexImage2D call.
-type textureTriple struct {
-	internalFormat int
-	format         gl.Enum
-	typ            gl.Enum
-}
-
-func newContext(glctx gl.Functions) (*context, error) {
-	ctx := &context{
-		Functions: glctx,
-	}
-	exts := strings.Split(ctx.GetString(gl.EXTENSIONS), " ")
-	glVer := ctx.GetString(gl.VERSION)
-	ver, err := gl.ParseGLVersion(glVer)
-	if err != nil {
-		return nil, err
-	}
-	floatTriple, err := floatTripleFor(ctx, ver, exts)
-	if err != nil {
-		return nil, err
-	}
-	srgbaTriple, err := srgbaTripleFor(ver, exts)
-	if err != nil {
-		return nil, err
-	}
-	hasTimers := hasExtension(exts, "GL_EXT_disjoint_timer_query_webgl2") || hasExtension(exts, "GL_EXT_disjoint_timer_query")
-	ctx.caps = caps{
-		EXT_disjoint_timer_query: hasTimers,
-		floatTriple:              floatTriple,
-		alphaTriple:              alphaTripleFor(ver),
-		srgbaTriple:              srgbaTriple,
-	}
-	return ctx, nil
-}
-
-// floatTripleFor determines the best texture triple for floating point FBOs.
-func floatTripleFor(ctx *context, ver [2]int, exts []string) (textureTriple, error) {
-	var triples []textureTriple
-	if ver[0] >= 3 {
-		triples = append(triples, textureTriple{gl.R16F, gl.Enum(gl.RED), gl.Enum(gl.HALF_FLOAT)})
-	}
-	if hasExtension(exts, "GL_OES_texture_half_float") && hasExtension(exts, "GL_EXT_color_buffer_half_float") {
-		// Try single channel.
-		triples = append(triples, textureTriple{gl.LUMINANCE, gl.Enum(gl.LUMINANCE), gl.Enum(gl.HALF_FLOAT_OES)})
-		// Fallback to 4 channels.
-		triples = append(triples, textureTriple{gl.RGBA, gl.Enum(gl.RGBA), gl.Enum(gl.HALF_FLOAT_OES)})
-	}
-	if hasExtension(exts, "GL_OES_texture_float") || hasExtension(exts, "GL_EXT_color_buffer_float") {
-		triples = append(triples, textureTriple{gl.RGBA, gl.Enum(gl.RGBA), gl.Enum(gl.FLOAT)})
-	}
-	tex := ctx.CreateTexture()
-	defer ctx.DeleteTexture(tex)
-	ctx.BindTexture(gl.TEXTURE_2D, tex)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
-	fbo := ctx.CreateFramebuffer()
-	defer ctx.DeleteFramebuffer(fbo)
-	defFBO := gl.Framebuffer(ctx.GetBinding(gl.FRAMEBUFFER_BINDING))
-	ctx.BindFramebuffer(gl.FRAMEBUFFER, fbo)
-	defer ctx.BindFramebuffer(gl.FRAMEBUFFER, defFBO)
-	for _, tt := range triples {
-		const size = 256
-		ctx.TexImage2D(gl.TEXTURE_2D, 0, tt.internalFormat, size, size, tt.format, tt.typ, nil)
-		ctx.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, 0)
-		if st := ctx.CheckFramebufferStatus(gl.FRAMEBUFFER); st == gl.FRAMEBUFFER_COMPLETE {
-			return tt, nil
-		}
-	}
-	return textureTriple{}, errors.New("floating point fbos not supported")
-}
-
-func srgbaTripleFor(ver [2]int, exts []string) (textureTriple, error) {
-	switch {
-	case ver[0] >= 3:
-		return textureTriple{gl.SRGB8_ALPHA8, gl.Enum(gl.RGBA), gl.Enum(gl.UNSIGNED_BYTE)}, nil
-	case hasExtension(exts, "GL_EXT_sRGB"):
-		return textureTriple{gl.SRGB_ALPHA_EXT, gl.Enum(gl.SRGB_ALPHA_EXT), gl.Enum(gl.UNSIGNED_BYTE)}, nil
-	default:
-		return textureTriple{}, errors.New("no sRGB texture formats found")
-	}
-}
-
-func alphaTripleFor(ver [2]int) textureTriple {
-	intf, f := gl.R8, gl.Enum(gl.RED)
-	if ver[0] < 3 {
-		// R8, RED not supported on OpenGL ES 2.0.
-		intf, f = gl.LUMINANCE, gl.Enum(gl.LUMINANCE)
-	}
-	return textureTriple{intf, f, gl.UNSIGNED_BYTE}
-}
-
-func hasExtension(exts []string, ext string) bool {
-	for _, e := range exts {
-		if ext == e {
-			return true
-		}
-	}
-	return false
-}

gpu/gl/backend.go

@@ -0,0 +1,514 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gl
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"strings"
+	"time"
+
+	"gioui.org/gpu"
+)
+
+// Backend implements gpu.Backend.
+type Backend struct {
+	funcs  Functions
+	defFBO *gpuFramebuffer
+
+	state glstate
+
+	feats gpu.Caps
+	// floatTriple holds the settings for floating point
+	// textures.
+	floatTriple textureTriple
+	// Single channel alpha textures.
+	alphaTriple textureTriple
+	srgbaTriple textureTriple
+}
+
+// State tracking.
+type glstate struct {
+	// nattr is the current number of enabled vertex arrays.
+	nattr    int
+	prog     *gpuProgram
+	texUnits [2]*gpuTexture
+}
+
+type gpuTimer struct {
+	funcs Functions
+	obj   Query
+}
+
+type gpuTexture struct {
+	backend *Backend
+	obj     Texture
+}
+
+type gpuFramebuffer struct {
+	funcs Functions
+	obj   Framebuffer
+}
+
+type gpuBuffer struct {
+	funcs Functions
+	obj   Buffer
+	typ   Enum
+}
+
+type gpuProgram struct {
+	backend *Backend
+	obj     Program
+	nattr   int
+}
+
+// textureTriple holds the type settings for
+// a TexImage2D call.
+type textureTriple struct {
+	internalFormat int
+	format         Enum
+	typ            Enum
+}
+
+func NewBackend(f Functions) (*Backend, error) {
+	exts := strings.Split(f.GetString(EXTENSIONS), " ")
+	glVer := f.GetString(VERSION)
+	ver, err := parseGLVersion(glVer)
+	if err != nil {
+		return nil, err
+	}
+	floatTriple, err := floatTripleFor(f, ver, exts)
+	if err != nil {
+		return nil, err
+	}
+	srgbaTriple, err := srgbaTripleFor(ver, exts)
+	if err != nil {
+		return nil, err
+	}
+	defFBO := Framebuffer(f.GetBinding(FRAMEBUFFER_BINDING))
+	b := &Backend{
+		defFBO:      &gpuFramebuffer{funcs: f, obj: defFBO},
+		funcs:       f,
+		floatTriple: floatTriple,
+		alphaTriple: alphaTripleFor(ver),
+		srgbaTriple: srgbaTriple,
+	}
+	if hasExtension(exts, "GL_EXT_disjoint_timer_query_webgl2") || hasExtension(exts, "GL_EXT_disjoint_timer_query") {
+		b.feats.Features |= gpu.FeatureTimers
+	}
+	b.feats.MaxTextureSize = f.GetInteger(MAX_TEXTURE_SIZE)
+	return b, nil
+}
+
+func (b *Backend) BeginFrame() {
+	// Assume GL state is reset.
+	b.state = glstate{}
+}
+
+func (b *Backend) EndFrame() {
+	b.funcs.ActiveTexture(TEXTURE0)
+}
+
+func (b *Backend) Caps() gpu.Caps {
+	return b.feats
+}
+
+func (b *Backend) NewTimer() gpu.Timer {
+	return &gpuTimer{
+		funcs: b.funcs,
+		obj:   b.funcs.CreateQuery(),
+	}
+}
+
+func (b *Backend) IsTimeContinuous() bool {
+	return b.funcs.GetInteger(GPU_DISJOINT_EXT) == FALSE
+}
+
+func (b *Backend) NewFramebuffer() gpu.Framebuffer {
+	fb := b.funcs.CreateFramebuffer()
+	return &gpuFramebuffer{funcs: b.funcs, obj: fb}
+}
+
+func (b *Backend) NilTexture() gpu.Texture {
+	return &gpuTexture{backend: b}
+}
+
+func (b *Backend) DefaultFramebuffer() gpu.Framebuffer {
+	return b.defFBO
+}
+
+func (b *Backend) NewTexture(minFilter, magFilter gpu.TextureFilter) gpu.Texture {
+	tex := &gpuTexture{backend: b, obj: b.funcs.CreateTexture()}
+	tex.Bind(0)
+	b.funcs.TexParameteri(TEXTURE_2D, TEXTURE_MAG_FILTER, toTexFilter(magFilter))
+	b.funcs.TexParameteri(TEXTURE_2D, TEXTURE_MIN_FILTER, toTexFilter(minFilter))
+	b.funcs.TexParameteri(TEXTURE_2D, TEXTURE_WRAP_S, CLAMP_TO_EDGE)
+	b.funcs.TexParameteri(TEXTURE_2D, TEXTURE_WRAP_T, CLAMP_TO_EDGE)
+	return tex
+}
+
+func (b *Backend) NewBuffer(typ gpu.BufferType) gpu.Buffer {
+	obj := b.funcs.CreateBuffer()
+	var gltyp Enum
+	switch typ {
+	case gpu.BufferTypeData:
+		gltyp = ARRAY_BUFFER
+	case gpu.BufferTypeIndices:
+		gltyp = ELEMENT_ARRAY_BUFFER
+	default:
+		panic("unsupported buffer type")
+	}
+	return &gpuBuffer{funcs: b.funcs, obj: obj, typ: gltyp}
+}
+
+func (b *Backend) bindTexture(unit int, t *gpuTexture) {
+	if b.state.texUnits[unit] != t {
+		b.funcs.ActiveTexture(TEXTURE0 + Enum(unit))
+		b.funcs.BindTexture(TEXTURE_2D, t.obj)
+		b.state.texUnits[unit] = t
+	}
+}
+
+func (b *Backend) useProgram(p *gpuProgram) {
+	if b.state.prog != p {
+		p.backend.funcs.UseProgram(p.obj)
+		b.state.prog = p
+	}
+}
+
+func (b *Backend) enableVertexArrays(n int) {
+	// Enable needed arrays.
+	for i := b.state.nattr; i < n; i++ {
+		b.funcs.EnableVertexAttribArray(Attrib(i))
+	}
+	// Disable extra arrays.
+	for i := n; i < b.state.nattr; i++ {
+		b.funcs.DisableVertexAttribArray(Attrib(i))
+	}
+	b.state.nattr = n
+}
+
+func (b *Backend) SetDepthTest(enable bool) {
+	if enable {
+		b.funcs.Enable(DEPTH_TEST)
+	} else {
+		b.funcs.Disable(DEPTH_TEST)
+	}
+}
+
+func (b *Backend) BlendFunc(sfactor, dfactor gpu.BlendFactor) {
+	b.funcs.BlendFunc(toGLBlendFactor(sfactor), toGLBlendFactor(dfactor))
+}
+
+func toGLBlendFactor(f gpu.BlendFactor) Enum {
+	switch f {
+	case gpu.BlendFactorOne:
+		return ONE
+	case gpu.BlendFactorOneMinusSrcAlpha:
+		return ONE_MINUS_SRC_ALPHA
+	case gpu.BlendFactorZero:
+		return ZERO
+	case gpu.BlendFactorDstColor:
+		return DST_COLOR
+	default:
+		panic("unsupported blend factor")
+	}
+}
+
+func (b *Backend) DepthMask(mask bool) {
+	b.funcs.DepthMask(mask)
+}
+
+func (b *Backend) SetBlend(enable bool) {
+	if enable {
+		b.funcs.Enable(BLEND)
+	} else {
+		b.funcs.Disable(BLEND)
+	}
+}
+
+func (b *Backend) DrawElements(mode gpu.DrawMode, off, count int) {
+	b.funcs.DrawElements(toGLDrawMode(mode), count, UNSIGNED_SHORT, off)
+}
+
+func (b *Backend) DrawArrays(mode gpu.DrawMode, off, count int) {
+	b.funcs.DrawArrays(toGLDrawMode(mode), off, count)
+}
+
+func toGLDrawMode(mode gpu.DrawMode) Enum {
+	switch mode {
+	case gpu.DrawModeTriangleStrip:
+		return TRIANGLE_STRIP
+	case gpu.DrawModeTriangles:
+		return TRIANGLES
+	default:
+		panic("unsupported draw mode")
+	}
+}
+
+func (b *Backend) Viewport(x, y, width, height int) {
+	b.funcs.Viewport(x, y, width, height)
+}
+
+func (b *Backend) Clear(attachments gpu.BufferAttachments) {
+	var mask Enum
+	if attachments&gpu.BufferAttachmentColor != 0 {
+		mask |= COLOR_BUFFER_BIT
+	}
+	if attachments&gpu.BufferAttachmentDepth != 0 {
+		mask |= DEPTH_BUFFER_BIT
+	}
+	b.funcs.Clear(mask)
+}
+
+func (b *Backend) ClearDepth(d float32) {
+	b.funcs.ClearDepthf(d)
+}
+
+func (b *Backend) ClearColor(colR, colG, colB, colA float32) {
+	b.funcs.ClearColor(colR, colG, colB, colA)
+}
+
+func (b *Backend) DepthFunc(f gpu.DepthFunc) {
+	var glfunc Enum
+	switch f {
+	case gpu.DepthFuncGreater:
+		glfunc = GREATER
+	default:
+		panic("unsupported depth func")
+	}
+	b.funcs.DepthFunc(glfunc)
+}
+
+func (b *Backend) NewProgram(vssrc, fssrc string, attr []string) (gpu.Program, error) {
+	p, err := createProgram(b.funcs, vssrc, fssrc, attr)
+	if err != nil {
+		return nil, err
+	}
+	return &gpuProgram{backend: b, obj: p, nattr: len(attr)}, nil
+}
+
+func (p *gpuProgram) Uniform1i(u gpu.Uniform, v int) {
+	p.Bind()
+	p.backend.funcs.Uniform1i(u.(Uniform), v)
+}
+
+func (p *gpuProgram) Uniform1f(u gpu.Uniform, v0 float32) {
+	p.Bind()
+	p.backend.funcs.Uniform1f(u.(Uniform), v0)
+}
+
+func (p *gpuProgram) Uniform2f(u gpu.Uniform, v0, v1 float32) {
+	p.Bind()
+	p.backend.funcs.Uniform2f(u.(Uniform), v0, v1)
+}
+
+func (p *gpuProgram) Uniform4f(u gpu.Uniform, v0, v1, v2, v3 float32) {
+	p.Bind()
+	p.backend.funcs.Uniform4f(u.(Uniform), v0, v1, v2, v3)
+}
+
+func (p *gpuProgram) Bind() {
+	p.backend.useProgram(p)
+	p.backend.enableVertexArrays(p.nattr)
+}
+
+func (p *gpuProgram) UniformFor(uniform string) gpu.Uniform {
+	f := p.backend.funcs
+	return getUniformLocation(f, p.obj, uniform)
+}
+
+func (b *Backend) SetupVertexArray(slot int, size int, dataType gpu.DataType, stride, offset int) {
+	var gltyp Enum
+	switch dataType {
+	case gpu.DataTypeFloat:
+		gltyp = FLOAT
+	case gpu.DataTypeShort:
+		gltyp = SHORT
+	default:
+		panic("unsupported data type")
+	}
+	b.funcs.VertexAttribPointer(Attrib(slot), size, gltyp, false, stride, offset)
+}
+
+func (p *gpuProgram) Release() {
+	p.backend.funcs.DeleteProgram(p.obj)
+}
+
+func (b *gpuBuffer) Release() {
+	b.funcs.DeleteBuffer(b.obj)
+}
+
+func (b *gpuBuffer) Bind() {
+	b.funcs.BindBuffer(b.typ, b.obj)
+}
+
+func (b *gpuBuffer) Upload(usage gpu.BufferUsage, data []byte) {
+	b.Bind()
+	var glusage Enum
+	switch usage {
+	case gpu.BufferUsageStaticDraw:
+		glusage = STATIC_DRAW
+	default:
+		panic("unsupported buffer usage")
+	}
+	b.funcs.BufferData(b.typ, data, glusage)
+}
+
+func (f *gpuFramebuffer) IsComplete() error {
+	if st := f.funcs.CheckFramebufferStatus(FRAMEBUFFER); st != FRAMEBUFFER_COMPLETE {
+		return fmt.Errorf("incomplete framebuffer, status = 0x%x, err = %d", st, f.funcs.GetError())
+	}
+	return nil
+}
+
+func (f *gpuFramebuffer) Bind() {
+	f.funcs.BindFramebuffer(FRAMEBUFFER, f.obj)
+}
+
+func (f *gpuFramebuffer) Invalidate() {
+	f.Bind()
+	f.funcs.InvalidateFramebuffer(FRAMEBUFFER, COLOR_ATTACHMENT0)
+}
+
+func (f *gpuFramebuffer) Release() {
+	f.funcs.DeleteFramebuffer(f.obj)
+}
+
+func (f *gpuFramebuffer) BindTexture(t gpu.Texture) {
+	gltex := t.(*gpuTexture)
+	f.Bind()
+	f.funcs.FramebufferTexture2D(FRAMEBUFFER, COLOR_ATTACHMENT0, TEXTURE_2D, gltex.obj, 0)
+}
+
+func toTexFilter(f gpu.TextureFilter) int {
+	switch f {
+	case gpu.FilterNearest:
+		return NEAREST
+	case gpu.FilterLinear:
+		return LINEAR
+	default:
+		panic("unsupported texture filter")
+	}
+}
+
+func (t *gpuTexture) Bind(unit int) {
+	t.backend.bindTexture(unit, t)
+}
+
+func (t *gpuTexture) Release() {
+	t.backend.funcs.DeleteTexture(t.obj)
+}
+
+func (t *gpuTexture) Resize(format gpu.TextureFormat, width, height int) {
+	t.Bind(0)
+	tt := t.backend.floatTriple
+	t.backend.funcs.TexImage2D(TEXTURE_2D, 0, tt.internalFormat, width, height, tt.format, tt.typ, nil)
+}
+
+func (t *gpuTexture) Upload(img *image.RGBA) {
+	t.Bind(0)
+	var pixels []byte
+	b := img.Bounds()
+	w, h := b.Dx(), b.Dy()
+	if img.Stride != w*4 {
+		panic("unsupported stride")
+	}
+	start := (b.Min.X + b.Min.Y*w) * 4
+	end := (b.Max.X + (b.Max.Y-1)*w) * 4
+	pixels = img.Pix[start:end]
+	tt := t.backend.srgbaTriple
+	t.backend.funcs.TexImage2D(TEXTURE_2D, 0, tt.internalFormat, w, h, tt.format, tt.typ, pixels)
+}
+
+func (t *gpuTimer) Begin() {
+	t.funcs.BeginQuery(TIME_ELAPSED_EXT, t.obj)
+}
+
+func (t *gpuTimer) End() {
+	t.funcs.EndQuery(TIME_ELAPSED_EXT)
+}
+
+func (t *gpuTimer) ready() bool {
+	return t.funcs.GetQueryObjectuiv(t.obj, QUERY_RESULT_AVAILABLE) == TRUE
+}
+
+func (t *gpuTimer) Release() {
+	t.funcs.DeleteQuery(t.obj)
+}
+
+func (t *gpuTimer) Duration() (time.Duration, bool) {
+	if !t.ready() {
+		return 0, false
+	}
+	nanos := t.funcs.GetQueryObjectuiv(t.obj, QUERY_RESULT)
+	return time.Duration(nanos), true
+}
+
+// floatTripleFor determines the best texture triple for floating point FBOs.
+func floatTripleFor(f Functions, ver [2]int, exts []string) (textureTriple, error) {
+	var triples []textureTriple
+	if ver[0] >= 3 {
+		triples = append(triples, textureTriple{R16F, Enum(RED), Enum(HALF_FLOAT)})
+	}
+	if hasExtension(exts, "GL_OES_texture_half_float") && hasExtension(exts, "GL_EXT_color_buffer_half_float") {
+		// Try single channel.
+		triples = append(triples, textureTriple{LUMINANCE, Enum(LUMINANCE), Enum(HALF_FLOAT_OES)})
+		// Fallback to 4 channels.
+		triples = append(triples, textureTriple{RGBA, Enum(RGBA), Enum(HALF_FLOAT_OES)})
+	}
+	if hasExtension(exts, "GL_OES_texture_float") || hasExtension(exts, "GL_EXT_color_buffer_float") {
+		triples = append(triples, textureTriple{RGBA, Enum(RGBA), Enum(FLOAT)})
+	}
+	tex := f.CreateTexture()
+	defer f.DeleteTexture(tex)
+	f.BindTexture(TEXTURE_2D, tex)
+	f.TexParameteri(TEXTURE_2D, TEXTURE_WRAP_S, CLAMP_TO_EDGE)
+	f.TexParameteri(TEXTURE_2D, TEXTURE_WRAP_T, CLAMP_TO_EDGE)
+	f.TexParameteri(TEXTURE_2D, TEXTURE_MAG_FILTER, NEAREST)
+	f.TexParameteri(TEXTURE_2D, TEXTURE_MIN_FILTER, NEAREST)
+	fbo := f.CreateFramebuffer()
+	defer f.DeleteFramebuffer(fbo)
+	defFBO := Framebuffer(f.GetBinding(FRAMEBUFFER_BINDING))
+	f.BindFramebuffer(FRAMEBUFFER, fbo)
+	defer f.BindFramebuffer(FRAMEBUFFER, defFBO)
+	for _, tt := range triples {
+		const size = 256
+		f.TexImage2D(TEXTURE_2D, 0, tt.internalFormat, size, size, tt.format, tt.typ, nil)
+		f.FramebufferTexture2D(FRAMEBUFFER, COLOR_ATTACHMENT0, TEXTURE_2D, tex, 0)
+		if st := f.CheckFramebufferStatus(FRAMEBUFFER); st == FRAMEBUFFER_COMPLETE {
+			return tt, nil
+		}
+	}
+	return textureTriple{}, errors.New("floating point fbos not supported")
+}
+
+func srgbaTripleFor(ver [2]int, exts []string) (textureTriple, error) {
+	switch {
+	case ver[0] >= 3:
+		return textureTriple{SRGB8_ALPHA8, Enum(RGBA), Enum(UNSIGNED_BYTE)}, nil
+	case hasExtension(exts, "GL_EXT_sRGB"):
+		return textureTriple{SRGB_ALPHA_EXT, Enum(SRGB_ALPHA_EXT), Enum(UNSIGNED_BYTE)}, nil
+	default:
+		return textureTriple{}, errors.New("no sRGB texture formats found")
+	}
+}
+
+func alphaTripleFor(ver [2]int) textureTriple {
+	intf, f := R8, Enum(RED)
+	if ver[0] < 3 {
+		// R8, RED not supported on OpenGL ES 2.0.
+		intf, f = LUMINANCE, Enum(LUMINANCE)
+	}
+	return textureTriple{intf, f, UNSIGNED_BYTE}
+}
+
+func hasExtension(exts []string, ext string) bool {
+	for _, e := range exts {
+		if ext == e {
+			return true
+		}
+	}
+	return false
+}

gpu/gl/gl.go

@@ -21,6 +21,7 @@ const (
 	DST_COLOR                             = 0x306
 	ELEMENT_ARRAY_BUFFER                  = 0x8893
 	EXTENSIONS                            = 0x1f03
+	FALSE                                 = 0
 	FLOAT                                 = 0x1406
 	FRAGMENT_SHADER                       = 0x8b30
 	FRAMEBUFFER                           = 0x8d40
@@ -69,6 +70,7 @@ const (
 	TEXTURE1                              = 0x84c1
 	TRIANGLE_STRIP                        = 0x5
 	TRIANGLES                             = 0x4
+	TRUE                                  = 1
 	UNPACK_ALIGNMENT                      = 0xcf5
 	UNSIGNED_BYTE                         = 0x1401
 	UNSIGNED_SHORT                        = 0x1403

gpu/gl/srgb.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"runtime"
 	"strings"
+
+	"gioui.org/internal/unsafe"
 )
 
 // SRGBFBO implements an intermediate sRGB FBO
@@ -26,7 +28,7 @@ type SRGBFBO struct {
 func NewSRGBFBO(f Functions) (*SRGBFBO, error) {
 	var es3 bool
 	glVer := f.GetString(VERSION)
-	ver, err := ParseGLVersion(glVer)
+	ver, err := parseGLVersion(glVer)
 	if err != nil {
 		return nil, err
 	}
@@ -55,17 +57,17 @@ func NewSRGBFBO(f Functions) (*SRGBFBO, error) {
 
 func (s *SRGBFBO) Blit() {
 	if !s.blitted {
-		prog, err := CreateProgram(s.c, blitVSrc, blitFSrc, []string{"pos", "uv"})
+		prog, err := createProgram(s.c, blitVSrc, blitFSrc, []string{"pos", "uv"})
 		if err != nil {
 			panic(err)
 		}
 		s.prog = prog
 		s.c.UseProgram(prog)
-		s.c.Uniform1i(GetUniformLocation(s.c, prog, "tex"), 0)
+		s.c.Uniform1i(getUniformLocation(s.c, prog, "tex"), 0)
 		s.quad = s.c.CreateBuffer()
 		s.c.BindBuffer(ARRAY_BUFFER, s.quad)
 		s.c.BufferData(ARRAY_BUFFER,
-			BytesView([]float32{
+			unsafe.BytesView([]float32{
 				-1, +1, 0, 1,
 				+1, +1, 1, 1,
 				-1, -1, 0, 0,

gpu/gl/util.go

@@ -5,12 +5,10 @@ package gl
 import (
 	"errors"
 	"fmt"
-	"reflect"
 	"strings"
-	"unsafe"
 )
 
-func CreateProgram(ctx Functions, vsSrc, fsSrc string, attribs []string) (Program, error) {
+func createProgram(ctx Functions, vsSrc, fsSrc string, attribs []string) (Program, error) {
 	vs, err := createShader(ctx, VERTEX_SHADER, vsSrc)
 	if err != nil {
 		return Program{}, err
@@ -39,7 +37,7 @@ func CreateProgram(ctx Functions, vsSrc, fsSrc string, attribs []string) (Progra
 	return prog, nil
 }
 
-func GetUniformLocation(ctx Functions, prog Program, name string) Uniform {
+func getUniformLocation(ctx Functions, prog Program, name string) Uniform {
 	loc := ctx.GetUniformLocation(prog, name)
 	if !loc.Valid() {
 		panic(fmt.Errorf("uniform %s not found", name))
@@ -62,19 +60,7 @@ func createShader(ctx Functions, typ Enum, src string) (Shader, error) {
 	return sh, nil
 }
 
-// BytesView returns a byte slice view of a slice.
-func BytesView(s interface{}) []byte {
-	v := reflect.ValueOf(s)
-	first := v.Index(0)
-	sz := int(first.Type().Size())
-	return *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
-		Data: uintptr(unsafe.Pointer((*reflect.SliceHeader)(unsafe.Pointer(first.UnsafeAddr())))),
-		Len:  v.Len() * sz,
-		Cap:  v.Cap() * sz,
-	}))
-}
-
-func ParseGLVersion(glVer string) ([2]int, error) {
+func parseGLVersion(glVer string) ([2]int, error) {
 	var ver [2]int
 	if _, err := fmt.Sscanf(glVer, "OpenGL ES %d.%d", &ver[0], &ver[1]); err == nil {
 		return ver, nil
@@ -87,28 +73,3 @@ func ParseGLVersion(glVer string) ([2]int, error) {
 	}
 	return ver, fmt.Errorf("failed to parse OpenGL ES version (%s)", glVer)
 }
-
-func SliceOf(s uintptr) []byte {
-	if s == 0 {
-		return nil
-	}
-	sh := reflect.SliceHeader{
-		Data: s,
-		Len:  1 << 30,
-		Cap:  1 << 30,
-	}
-	return *(*[]byte)(unsafe.Pointer(&sh))
-}
-
-// GoString convert a NUL-terminated C string
-// to a Go string.
-func GoString(s []byte) string {
-	i := 0
-	for {
-		if s[i] == 0 {
-			break
-		}
-		i++
-	}
-	return string(s[:i])
-}

gpu/gpu.go

@@ -18,10 +18,10 @@ import (
 	"unsafe"
 
 	"gioui.org/f32"
-	"gioui.org/gpu/gl"
 	"gioui.org/internal/opconst"
 	"gioui.org/internal/ops"
 	"gioui.org/internal/path"
+	gunsafe "gioui.org/internal/unsafe"
 	"gioui.org/op"
 	"gioui.org/op/paint"
 )
@@ -35,12 +35,12 @@ type GPU struct {
 	frameStart                                        time.Time
 	zopsTimer, stencilTimer, coverTimer, cleanupTimer *timer
 	drawOps                                           drawOps
-	ctx                                               *context
+	ctx                                               Backend
 	renderer                                          *renderer
 }
 
 type renderer struct {
-	ctx           *context
+	ctx           Backend
 	blitter       *blitter
 	pather        *pather
 	packer        packer
@@ -189,25 +189,25 @@ func decodePaintOp(data []byte) paint.PaintOp {
 type clipType uint8
 
 type resource interface {
-	release(ctx *context)
+	release()
 }
 
 type texture struct {
 	src *image.RGBA
-	id  gl.Texture
+	tex Texture
 }
 
 type blitter struct {
-	ctx      *context
+	ctx      Backend
 	viewport image.Point
-	prog     [2]gl.Program
+	prog     [2]Program
 	vars     [2]struct {
-		z                   gl.Uniform
-		uScale, uOffset     gl.Uniform
-		uUVScale, uUVOffset gl.Uniform
-		uColor              gl.Uniform
+		z                   Uniform
+		uScale, uOffset     Uniform
+		uUVScale, uUVOffset Uniform
+		uColor              Uniform
 	}
-	quadVerts gl.Buffer
+	quadVerts Buffer
 }
 
 type materialType uint8
@@ -224,12 +224,15 @@ const (
 )
 
 var (
-	blitAttribs           = []string{"pos", "uv"}
-	attribPos   gl.Attrib = 0
-	attribUV    gl.Attrib = 1
+	blitAttribs = []string{"pos", "uv"}
 )
 
-func New(ctx gl.Functions) (*GPU, error) {
+const (
+	attribPos = 0
+	attribUV  = 1
+)
+
+func New(ctx Backend) (*GPU, error) {
 	g := &GPU{
 		pathCache: newOpCache(),
 		cache:     newResourceCache(),
@@ -240,11 +243,7 @@ func New(ctx gl.Functions) (*GPU, error) {
 	return g, nil
 }
 
-func (g *GPU) init(glctx gl.Functions) error {
-	ctx, err := newContext(glctx)
-	if err != nil {
-		return err
-	}
+func (g *GPU) init(ctx Backend) error {
 	g.ctx = ctx
 	g.renderer = newRenderer(ctx)
 	return nil
@@ -252,8 +251,8 @@ func (g *GPU) init(glctx gl.Functions) error {
 
 func (g *GPU) Release() {
 	g.renderer.release()
-	g.pathCache.release(g.ctx)
-	g.cache.release(g.ctx)
+	g.pathCache.release()
+	g.cache.release()
 	if g.timers != nil {
 		g.timers.release()
 	}
@@ -265,7 +264,7 @@ func (g *GPU) Collect(viewport image.Point, frameOps *op.Ops) {
 	g.drawOps.reset(g.cache, viewport)
 	g.drawOps.collect(g.cache, frameOps, viewport)
 	g.frameStart = time.Now()
-	if g.drawOps.profile && g.timers == nil && g.ctx.caps.EXT_disjoint_timer_query {
+	if g.drawOps.profile && g.timers == nil && g.ctx.Caps().Features.Has(FeatureTimers) {
 		g.timers = newTimers(g.ctx)
 		g.zopsTimer = g.timers.newTimer()
 		g.stencilTimer = g.timers.newTimer()
@@ -282,6 +281,8 @@ func (g *GPU) Collect(viewport image.Point, frameOps *op.Ops) {
 }
 
 func (g *GPU) BeginFrame() {
+	g.ctx.BeginFrame()
+	defer g.ctx.EndFrame()
 	viewport := g.renderer.blitter.viewport
 	for _, img := range g.drawOps.imageOps {
 		expandPathOp(img.path, img.clip)
@@ -289,15 +290,15 @@ func (g *GPU) BeginFrame() {
 	if g.drawOps.profile {
 		g.zopsTimer.begin()
 	}
-	g.ctx.DepthFunc(gl.GREATER)
+	g.ctx.DepthFunc(DepthFuncGreater)
 	g.ctx.ClearColor(g.drawOps.clearColor[0], g.drawOps.clearColor[1], g.drawOps.clearColor[2], 1.0)
-	g.ctx.ClearDepthf(0.0)
-	g.ctx.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
+	g.ctx.ClearDepth(0.0)
+	g.ctx.Clear(BufferAttachmentColor | BufferAttachmentDepth)
 	g.ctx.Viewport(0, 0, viewport.X, viewport.Y)
 	g.renderer.drawZOps(g.drawOps.zimageOps)
 	g.zopsTimer.end()
 	g.stencilTimer.begin()
-	g.ctx.Enable(gl.BLEND)
+	g.ctx.SetBlend(true)
 	g.renderer.packStencils(&g.drawOps.pathOps)
 	g.renderer.stencilClips(g.pathCache, g.drawOps.pathOps)
 	g.renderer.packIntersections(g.drawOps.imageOps)
@@ -306,15 +307,15 @@ func (g *GPU) BeginFrame() {
 	g.coverTimer.begin()
 	g.ctx.Viewport(0, 0, viewport.X, viewport.Y)
 	g.renderer.drawOps(g.drawOps.imageOps)
-	g.ctx.Disable(gl.BLEND)
+	g.ctx.SetBlend(false)
 	g.renderer.pather.stenciler.invalidateFBO()
 	g.coverTimer.end()
 }
 
 func (g *GPU) EndFrame() {
 	g.cleanupTimer.begin()
-	g.cache.frame(g.ctx)
-	g.pathCache.frame(g.ctx)
+	g.cache.frame()
+	g.pathCache.frame()
 	g.cleanupTimer.end()
 	if g.drawOps.profile && g.timers.ready() {
 		zt, st, covt, cleant := g.zopsTimer.Elapsed, g.stencilTimer.Elapsed, g.coverTimer.Elapsed, g.cleanupTimer.Elapsed
@@ -331,29 +332,28 @@ func (g *GPU) Profile() string {
 	return g.profile
 }
 
-func (r *renderer) texHandle(t *texture) gl.Texture {
-	if t.id.Valid() {
-		return t.id
+func (r *renderer) texHandle(t *texture) Texture {
+	if t.tex != nil {
+		return t.tex
 	}
-	t.id = createTexture(r.ctx)
-	r.ctx.BindTexture(gl.TEXTURE_2D, t.id)
-	r.uploadTexture(t.src)
-	return t.id
+	t.tex = r.ctx.NewTexture(FilterLinear, FilterLinear)
+	t.tex.Upload(t.src)
+	return t.tex
 }
 
-func (t *texture) release(ctx *context) {
-	if t.id.Valid() {
-		ctx.DeleteTexture(t.id)
+func (t *texture) release() {
+	if t.tex != nil {
+		t.tex.Release()
 	}
 }
 
-func newRenderer(ctx *context) *renderer {
+func newRenderer(ctx Backend) *renderer {
 	r := &renderer{
 		ctx:     ctx,
 		blitter: newBlitter(ctx),
 		pather:  newPather(ctx),
 	}
-	r.packer.maxDim = ctx.GetInteger(gl.MAX_TEXTURE_SIZE)
+	r.packer.maxDim = ctx.Caps().MaxTextureSize
 	r.intersections.maxDim = r.packer.maxDim
 	return r
 }
@@ -363,53 +363,50 @@ func (r *renderer) release() {
 	r.blitter.release()
 }
 
-func newBlitter(ctx *context) *blitter {
+func newBlitter(ctx Backend) *blitter {
 	prog, err := createColorPrograms(ctx, blitVSrc, blitFSrc)
 	if err != nil {
 		panic(err)
 	}
-	quadVerts := ctx.CreateBuffer()
-	ctx.BindBuffer(gl.ARRAY_BUFFER, quadVerts)
-	ctx.BufferData(gl.ARRAY_BUFFER,
-		gl.BytesView([]float32{
+	quadVerts := ctx.NewBuffer(BufferTypeData)
+	quadVerts.Upload(BufferUsageStaticDraw,
+		gunsafe.BytesView([]float32{
 			-1, +1, 0, 0,
 			+1, +1, 1, 0,
 			-1, -1, 0, 1,
 			+1, -1, 1, 1,
-		}),
-		gl.STATIC_DRAW)
+		}))
 	b := &blitter{
 		ctx:       ctx,
 		prog:      prog,
 		quadVerts: quadVerts,
 	}
 	for i, prog := range prog {
-		ctx.UseProgram(prog)
 		switch materialType(i) {
 		case materialTexture:
-			uTex := gl.GetUniformLocation(ctx.Functions, prog, "tex")
-			ctx.Uniform1i(uTex, 0)
-			b.vars[i].uUVScale = gl.GetUniformLocation(ctx.Functions, prog, "uvScale")
-			b.vars[i].uUVOffset = gl.GetUniformLocation(ctx.Functions, prog, "uvOffset")
+			uTex := prog.UniformFor("tex")
+			prog.Uniform1i(uTex, 0)
+			b.vars[i].uUVScale = prog.UniformFor("uvScale")
+			b.vars[i].uUVOffset = prog.UniformFor("uvOffset")
 		case materialColor:
-			b.vars[i].uColor = gl.GetUniformLocation(ctx.Functions, prog, "color")
+			b.vars[i].uColor = prog.UniformFor("color")
 		}
-		b.vars[i].z = gl.GetUniformLocation(ctx.Functions, prog, "z")
-		b.vars[i].uScale = gl.GetUniformLocation(ctx.Functions, prog, "scale")
-		b.vars[i].uOffset = gl.GetUniformLocation(ctx.Functions, prog, "offset")
+		b.vars[i].z = prog.UniformFor("z")
+		b.vars[i].uScale = prog.UniformFor("scale")
+		b.vars[i].uOffset = prog.UniformFor("offset")
 	}
 	return b
 }
 
 func (b *blitter) release() {
-	b.ctx.DeleteBuffer(b.quadVerts)
+	b.quadVerts.Release()
 	for _, p := range b.prog {
-		b.ctx.DeleteProgram(p)
+		p.Release()
 	}
 }
 
-func createColorPrograms(ctx *context, vsSrc, fsSrc string) ([2]gl.Program, error) {
-	var prog [2]gl.Program
+func createColorPrograms(ctx Backend, vsSrc, fsSrc string) ([2]Program, error) {
+	var prog [2]Program
 	frep := strings.NewReplacer(
 		"HEADER", `
 uniform sampler2D tex;
@@ -418,7 +415,7 @@ uniform sampler2D tex;
 	)
 	fsSrcTex := frep.Replace(fsSrc)
 	var err error
-	prog[materialTexture], err = gl.CreateProgram(ctx.Functions, vsSrc, fsSrcTex, blitAttribs)
+	prog[materialTexture], err = ctx.NewProgram(vsSrc, fsSrcTex, blitAttribs)
 	if err != nil {
 		return prog, err
 	}
@@ -429,9 +426,9 @@ uniform vec4 color;
 		"GET_COLOR", `color`,
 	)
 	fsSrcCol := frep.Replace(fsSrc)
-	prog[materialColor], err = gl.CreateProgram(ctx.Functions, vsSrc, fsSrcCol, blitAttribs)
+	prog[materialColor], err = ctx.NewProgram(vsSrc, fsSrcCol, blitAttribs)
 	if err != nil {
-		ctx.DeleteProgram(prog[materialTexture])
+		prog[materialTexture].Release()
 		return prog, err
 	}
 	return prog, nil
@@ -447,8 +444,8 @@ func (r *renderer) stencilClips(pathCache *opCache, ops []*pathOp) {
 		if fbo != p.place.Idx {
 			fbo = p.place.Idx
 			f := r.pather.stenciler.cover(fbo)
-			bindFramebuffer(r.ctx, f.fbo)
-			r.ctx.Clear(gl.COLOR_BUFFER_BIT)
+			bindFramebuffer(f.fbo)
+			r.ctx.Clear(BufferAttachmentColor)
 		}
 		data, _ := pathCache.get(p.pathKey)
 		r.pather.stencilPath(p.clip, p.off, p.place.Pos, data.(*pathData))
@@ -462,11 +459,9 @@ func (r *renderer) intersect(ops []imageOp) {
 	}
 	fbo := -1
 	r.pather.stenciler.beginIntersect(r.intersections.sizes)
-	r.ctx.BindBuffer(gl.ARRAY_BUFFER, r.blitter.quadVerts)
-	r.ctx.VertexAttribPointer(attribPos, 2, gl.FLOAT, false, 4*4, 0)
-	r.ctx.VertexAttribPointer(attribUV, 2, gl.FLOAT, false, 4*4, 4*2)
-	r.ctx.EnableVertexAttribArray(attribPos)
-	r.ctx.EnableVertexAttribArray(attribUV)
+	r.blitter.quadVerts.Bind()
+	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
+	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
 	for _, img := range ops {
 		if img.clipType != clipTypeIntersection {
 			continue
@@ -474,14 +469,12 @@ func (r *renderer) intersect(ops []imageOp) {
 		if fbo != img.place.Idx {
 			fbo = img.place.Idx
 			f := r.pather.stenciler.intersections.fbos[fbo]
-			bindFramebuffer(r.ctx, f.fbo)
-			r.ctx.Clear(gl.COLOR_BUFFER_BIT)
+			bindFramebuffer(f.fbo)
+			r.ctx.Clear(BufferAttachmentColor)
 		}
 		r.ctx.Viewport(img.place.Pos.X, img.place.Pos.Y, img.clip.Dx(), img.clip.Dy())
 		r.intersectPath(img.path, img.clip)
 	}
-	r.ctx.DisableVertexAttribArray(attribPos)
-	r.ctx.DisableVertexAttribArray(attribUV)
 	r.pather.stenciler.endIntersect()
 }
 
@@ -498,11 +491,11 @@ func (r *renderer) intersectPath(p *pathOp, clip image.Rectangle) {
 		Max: o.Add(clip.Size()),
 	}
 	fbo := r.pather.stenciler.cover(p.place.Idx)
-	r.ctx.BindTexture(gl.TEXTURE_2D, fbo.tex)
+	fbo.tex.Bind(0)
 	coverScale, coverOff := texSpaceTransform(toRectF(uv), fbo.size)
-	r.ctx.Uniform2f(r.pather.stenciler.uIntersectUVScale, coverScale.X, coverScale.Y)
-	r.ctx.Uniform2f(r.pather.stenciler.uIntersectUVOffset, coverOff.X, coverOff.Y)
-	r.ctx.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
+	r.pather.stenciler.iprog.Uniform2f(r.pather.stenciler.uIntersectUVScale, coverScale.X, coverScale.Y)
+	r.pather.stenciler.iprog.Uniform2f(r.pather.stenciler.uIntersectUVOffset, coverOff.X, coverOff.Y)
+	r.ctx.DrawArrays(DrawModeTriangleStrip, 0, 4)
 }
 
 func (r *renderer) packIntersections(ops []imageOp) {
@@ -778,44 +771,38 @@ func (d *drawState) materialFor(cache *resourceCache, rect f32.Rectangle, off f3
 }
 
 func (r *renderer) drawZOps(ops []imageOp) {
-	r.ctx.Enable(gl.DEPTH_TEST)
-	r.ctx.BindBuffer(gl.ARRAY_BUFFER, r.blitter.quadVerts)
-	r.ctx.VertexAttribPointer(attribPos, 2, gl.FLOAT, false, 4*4, 0)
-	r.ctx.VertexAttribPointer(attribUV, 2, gl.FLOAT, false, 4*4, 4*2)
-	r.ctx.EnableVertexAttribArray(attribPos)
-	r.ctx.EnableVertexAttribArray(attribUV)
+	r.ctx.SetDepthTest(true)
+	r.blitter.quadVerts.Bind()
+	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
+	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
 	// Render front to back.
 	for i := len(ops) - 1; i >= 0; i-- {
 		img := ops[i]
 		m := img.material
 		switch m.material {
 		case materialTexture:
-			r.ctx.BindTexture(gl.TEXTURE_2D, r.texHandle(m.texture))
+			r.texHandle(m.texture).Bind(0)
 		}
 		drc := img.clip
 		scale, off := clipSpaceTransform(drc, r.blitter.viewport)
 		r.blitter.blit(img.z, m.material, m.color, scale, off, m.uvScale, m.uvOffset)
 	}
-	r.ctx.DisableVertexAttribArray(attribPos)
-	r.ctx.DisableVertexAttribArray(attribUV)
-	r.ctx.Disable(gl.DEPTH_TEST)
+	r.ctx.SetDepthTest(false)
 }
 
 func (r *renderer) drawOps(ops []imageOp) {
-	r.ctx.Enable(gl.DEPTH_TEST)
+	r.ctx.SetDepthTest(true)
 	r.ctx.DepthMask(false)
-	r.ctx.BlendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA)
-	r.ctx.BindBuffer(gl.ARRAY_BUFFER, r.blitter.quadVerts)
-	r.ctx.VertexAttribPointer(attribPos, 2, gl.FLOAT, false, 4*4, 0)
-	r.ctx.VertexAttribPointer(attribUV, 2, gl.FLOAT, false, 4*4, 4*2)
-	r.ctx.EnableVertexAttribArray(attribPos)
-	r.ctx.EnableVertexAttribArray(attribUV)
-	var coverTex gl.Texture
+	r.ctx.BlendFunc(BlendFactorOne, BlendFactorOneMinusSrcAlpha)
+	r.blitter.quadVerts.Bind()
+	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
+	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
+	var coverTex Texture
 	for _, img := range ops {
 		m := img.material
 		switch m.material {
 		case materialTexture:
-			r.ctx.BindTexture(gl.TEXTURE_2D, r.texHandle(m.texture))
+			r.texHandle(m.texture).Bind(0)
 		}
 		drc := img.clip
 		scale, off := clipSpaceTransform(drc, r.blitter.viewport)
@@ -829,11 +816,9 @@ func (r *renderer) drawOps(ops []imageOp) {
 		case clipTypeIntersection:
 			fbo = r.pather.stenciler.intersections.fbos[img.place.Idx]
 		}
-		if !coverTex.Equal(fbo.tex) {
+		if coverTex != fbo.tex {
 			coverTex = fbo.tex
-			r.ctx.ActiveTexture(gl.TEXTURE1)
-			r.ctx.BindTexture(gl.TEXTURE_2D, coverTex)
-			r.ctx.ActiveTexture(gl.TEXTURE0)
+			coverTex.Bind(1)
 		}
 		uv := image.Rectangle{
 			Min: img.place.Pos,
@@ -842,24 +827,8 @@ func (r *renderer) drawOps(ops []imageOp) {
 		coverScale, coverOff := texSpaceTransform(toRectF(uv), fbo.size)
 		r.pather.cover(img.z, m.material, m.color, scale, off, m.uvScale, m.uvOffset, coverScale, coverOff)
 	}
-	r.ctx.DisableVertexAttribArray(attribPos)
-	r.ctx.DisableVertexAttribArray(attribUV)
 	r.ctx.DepthMask(true)
-	r.ctx.Disable(gl.DEPTH_TEST)
-}
-
-func (r *renderer) uploadTexture(img *image.RGBA) {
-	var pixels []byte
-	b := img.Bounds()
-	w, h := b.Dx(), b.Dy()
-	if img.Stride != w*4 {
-		panic("unsupported stride")
-	}
-	start := (b.Min.X + b.Min.Y*w) * 4
-	end := (b.Max.X + (b.Max.Y-1)*w) * 4
-	pixels = img.Pix[start:end]
-	tt := r.ctx.caps.srgbaTriple
-	r.ctx.TexImage2D(gl.TEXTURE_2D, 0, tt.internalFormat, w, h, tt.format, tt.typ, pixels)
+	r.ctx.SetDepthTest(false)
 }
 
 func gamma(r, g, b, a uint32) [4]float32 {
@@ -879,18 +848,19 @@ func gamma(r, g, b, a uint32) [4]float32 {
 }
 
 func (b *blitter) blit(z float32, mat materialType, col [4]float32, scale, off, uvScale, uvOff f32.Point) {
-	b.ctx.UseProgram(b.prog[mat])
+	p := b.prog[mat]
+	p.Bind()
 	switch mat {
 	case materialColor:
-		b.ctx.Uniform4f(b.vars[mat].uColor, col[0], col[1], col[2], col[3])
+		p.Uniform4f(b.vars[mat].uColor, col[0], col[1], col[2], col[3])
 	case materialTexture:
-		b.ctx.Uniform2f(b.vars[mat].uUVScale, uvScale.X, uvScale.Y)
-		b.ctx.Uniform2f(b.vars[mat].uUVOffset, uvOff.X, uvOff.Y)
+		p.Uniform2f(b.vars[mat].uUVScale, uvScale.X, uvScale.Y)
+		p.Uniform2f(b.vars[mat].uUVOffset, uvOff.X, uvOff.Y)
 	}
-	b.ctx.Uniform1f(b.vars[mat].z, z)
-	b.ctx.Uniform2f(b.vars[mat].uScale, scale.X, scale.Y)
-	b.ctx.Uniform2f(b.vars[mat].uOffset, off.X, off.Y)
-	b.ctx.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
+	p.Uniform1f(b.vars[mat].z, z)
+	p.Uniform2f(b.vars[mat].uScale, scale.X, scale.Y)
+	p.Uniform2f(b.vars[mat].uOffset, off.X, off.Y)
+	b.ctx.DrawArrays(DrawModeTriangleStrip, 0, 4)
 }
 
 // texSpaceTransform return the scale and offset that transforms the given subimage
@@ -925,23 +895,13 @@ func clipSpaceTransform(r image.Rectangle, viewport image.Point) (f32.Point, f32
 	return scale, offset
 }
 
-func bindFramebuffer(ctx *context, fbo gl.Framebuffer) {
-	ctx.BindFramebuffer(gl.FRAMEBUFFER, fbo)
-	if st := ctx.CheckFramebufferStatus(gl.FRAMEBUFFER); st != gl.FRAMEBUFFER_COMPLETE {
-		panic(fmt.Errorf("AA FBO not complete; status = 0x%x, err = %d", st, ctx.GetError()))
+func bindFramebuffer(fbo Framebuffer) {
+	fbo.Bind()
+	if err := fbo.IsComplete(); err != nil {
+		panic(fmt.Errorf("AA FBO not complete: %v", err))
 	}
 }
 
-func createTexture(ctx *context) gl.Texture {
-	tex := ctx.CreateTexture()
-	ctx.BindTexture(gl.TEXTURE_2D, tex)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
-	ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
-	return tex
-}
-
 // Fill in maximal Y coordinates of the NW and NE corners.
 func fillMaxY(verts []byte) {
 	contour := 0

gpu/path.go

@@ -10,12 +10,12 @@ import (
 	"unsafe"
 
 	"gioui.org/f32"
-	"gioui.org/gpu/gl"
 	"gioui.org/internal/path"
+	gunsafe "gioui.org/internal/unsafe"
 )
 
 type pather struct {
-	ctx *context
+	ctx Backend
 
 	viewport image.Point
 
@@ -24,30 +24,30 @@ type pather struct {
 }
 
 type coverer struct {
-	ctx  *context
-	prog [2]gl.Program
+	ctx  Backend
+	prog [2]Program
 	vars [2]struct {
-		z                             gl.Uniform
-		uScale, uOffset               gl.Uniform
-		uUVScale, uUVOffset           gl.Uniform
-		uCoverUVScale, uCoverUVOffset gl.Uniform
-		uColor                        gl.Uniform
+		z                             Uniform
+		uScale, uOffset               Uniform
+		uUVScale, uUVOffset           Uniform
+		uCoverUVScale, uCoverUVOffset Uniform
+		uColor                        Uniform
 	}
 }
 
 type stenciler struct {
-	ctx                *context
-	defFBO             gl.Framebuffer
+	ctx                Backend
+	defFBO             Framebuffer
 	indexBufQuads      int
-	prog               gl.Program
-	iprog              gl.Program
+	prog               Program
+	iprog              Program
 	fbos               fboSet
 	intersections      fboSet
-	uScale, uOffset    gl.Uniform
-	uPathOffset        gl.Uniform
-	uIntersectUVOffset gl.Uniform
-	uIntersectUVScale  gl.Uniform
-	indexBuf           gl.Buffer
+	uScale, uOffset    Uniform
+	uPathOffset        Uniform
+	uIntersectUVOffset Uniform
+	uIntersectUVScale  Uniform
+	indexBuf           Buffer
 }
 
 type fboSet struct {
@@ -56,27 +56,29 @@ type fboSet struct {
 
 type stencilFBO struct {
 	size image.Point
-	fbo  gl.Framebuffer
-	tex  gl.Texture
+	fbo  Framebuffer
+	tex  Texture
 }
 
 type pathData struct {
 	ncurves int
-	data    gl.Buffer
+	data    Buffer
 }
 
 var (
-	pathAttribs                = []string{"corner", "maxy", "from", "ctrl", "to"}
-	attribPathCorner gl.Attrib = 0
-	attribPathMaxY   gl.Attrib = 1
-	attribPathFrom   gl.Attrib = 2
-	attribPathCtrl   gl.Attrib = 3
-	attribPathTo     gl.Attrib = 4
-
+	pathAttribs      = []string{"corner", "maxy", "from", "ctrl", "to"}
 	intersectAttribs = []string{"pos", "uv"}
 )
 
-func newPather(ctx *context) *pather {
+const (
+	attribPathCorner = 0
+	attribPathMaxY   = 1
+	attribPathFrom   = 2
+	attribPathCtrl   = 3
+	attribPathTo     = 4
+)
+
+func newPather(ctx Backend) *pather {
 	return &pather{
 		ctx:       ctx,
 		stenciler: newStenciler(ctx),
@@ -84,7 +86,7 @@ func newPather(ctx *context) *pather {
 	}
 }
 
-func newCoverer(ctx *context) *coverer {
+func newCoverer(ctx Backend) *coverer {
 	prog, err := createColorPrograms(ctx, coverVSrc, coverFSrc)
 	if err != nil {
 		panic(err)
@@ -94,68 +96,58 @@ func newCoverer(ctx *context) *coverer {
 		prog: prog,
 	}
 	for i, prog := range prog {
-		ctx.UseProgram(prog)
 		switch materialType(i) {
 		case materialTexture:
-			uTex := gl.GetUniformLocation(ctx.Functions, prog, "tex")
-			ctx.Uniform1i(uTex, 0)
-			c.vars[i].uUVScale = gl.GetUniformLocation(ctx.Functions, prog, "uvScale")
-			c.vars[i].uUVOffset = gl.GetUniformLocation(ctx.Functions, prog, "uvOffset")
+			uTex := prog.UniformFor("tex")
+			prog.Uniform1i(uTex, 0)
+			c.vars[i].uUVScale = prog.UniformFor("uvScale")
+			c.vars[i].uUVOffset = prog.UniformFor("uvOffset")
 		case materialColor:
-			c.vars[i].uColor = gl.GetUniformLocation(ctx.Functions, prog, "color")
+			c.vars[i].uColor = prog.UniformFor("color")
 		}
-		uCover := gl.GetUniformLocation(ctx.Functions, prog, "cover")
-		ctx.Uniform1i(uCover, 1)
-		c.vars[i].z = gl.GetUniformLocation(ctx.Functions, prog, "z")
-		c.vars[i].uScale = gl.GetUniformLocation(ctx.Functions, prog, "scale")
-		c.vars[i].uOffset = gl.GetUniformLocation(ctx.Functions, prog, "offset")
-		c.vars[i].uCoverUVScale = gl.GetUniformLocation(ctx.Functions, prog, "uvCoverScale")
-		c.vars[i].uCoverUVOffset = gl.GetUniformLocation(ctx.Functions, prog, "uvCoverOffset")
+		uCover := prog.UniformFor("cover")
+		prog.Uniform1i(uCover, 1)
+		c.vars[i].z = prog.UniformFor("z")
+		c.vars[i].uScale = prog.UniformFor("scale")
+		c.vars[i].uOffset = prog.UniformFor("offset")
+		c.vars[i].uCoverUVScale = prog.UniformFor("uvCoverScale")
+		c.vars[i].uCoverUVOffset = prog.UniformFor("uvCoverOffset")
 	}
 	return c
 }
 
-func newStenciler(ctx *context) *stenciler {
-	defFBO := gl.Framebuffer(ctx.GetBinding(gl.FRAMEBUFFER_BINDING))
-	prog, err := gl.CreateProgram(ctx.Functions, stencilVSrc, stencilFSrc, pathAttribs)
+func newStenciler(ctx Backend) *stenciler {
+	defFBO := ctx.DefaultFramebuffer()
+	prog, err := ctx.NewProgram(stencilVSrc, stencilFSrc, pathAttribs)
 	if err != nil {
 		panic(err)
 	}
-	ctx.UseProgram(prog)
-	iprog, err := gl.CreateProgram(ctx.Functions, intersectVSrc, intersectFSrc, intersectAttribs)
+	iprog, err := ctx.NewProgram(intersectVSrc, intersectFSrc, intersectAttribs)
 	if err != nil {
 		panic(err)
 	}
-	coverLoc := gl.GetUniformLocation(ctx.Functions, iprog, "cover")
-	ctx.UseProgram(iprog)
-	ctx.Uniform1i(coverLoc, 0)
+	coverLoc := iprog.UniformFor("cover")
+	iprog.Uniform1i(coverLoc, 0)
 	return &stenciler{
 		ctx:                ctx,
 		defFBO:             defFBO,
 		prog:               prog,
 		iprog:              iprog,
-		uScale:             gl.GetUniformLocation(ctx.Functions, prog, "scale"),
-		uOffset:            gl.GetUniformLocation(ctx.Functions, prog, "offset"),
-		uPathOffset:        gl.GetUniformLocation(ctx.Functions, prog, "pathOffset"),
-		uIntersectUVScale:  gl.GetUniformLocation(ctx.Functions, iprog, "uvScale"),
-		uIntersectUVOffset: gl.GetUniformLocation(ctx.Functions, iprog, "uvOffset"),
-		indexBuf:           ctx.CreateBuffer(),
+		uScale:             prog.UniformFor("scale"),
+		uOffset:            prog.UniformFor("offset"),
+		uPathOffset:        prog.UniformFor("pathOffset"),
+		uIntersectUVScale:  iprog.UniformFor("uvScale"),
+		uIntersectUVOffset: iprog.UniformFor("uvOffset"),
+		indexBuf:           ctx.NewBuffer(BufferTypeIndices),
 	}
 }
 
-func (s *fboSet) resize(ctx *context, sizes []image.Point) {
+func (s *fboSet) resize(ctx Backend, sizes []image.Point) {
 	// Add fbos.
 	for i := len(s.fbos); i < len(sizes); i++ {
-		tex := ctx.CreateTexture()
-		ctx.BindTexture(gl.TEXTURE_2D, tex)
-		ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
-		ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
-		ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
-		ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
-		fbo := ctx.CreateFramebuffer()
 		s.fbos = append(s.fbos, stencilFBO{
-			fbo: fbo,
-			tex: tex,
+			fbo: ctx.NewFramebuffer(),
+			tex: ctx.NewTexture(FilterNearest, FilterNearest),
 		})
 	}
 	// Resize fbos.
@@ -168,37 +160,33 @@ func (s *fboSet) resize(ctx *context, sizes []image.Point) {
 		resize = resize || waste > 1.2
 		if resize {
 			f.size = sz
-			ctx.BindTexture(gl.TEXTURE_2D, f.tex)
-			tt := ctx.caps.floatTriple
-			ctx.TexImage2D(gl.TEXTURE_2D, 0, tt.internalFormat, sz.X, sz.Y, tt.format, tt.typ, nil)
-			ctx.BindFramebuffer(gl.FRAMEBUFFER, f.fbo)
-			ctx.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, f.tex, 0)
+			f.tex.Resize(TextureFormatFloat, sz.X, sz.Y)
+			f.fbo.BindTexture(f.tex)
 		}
 	}
 	// Delete extra fbos.
 	s.delete(ctx, len(sizes))
 }
 
-func (s *fboSet) invalidate(ctx *context) {
+func (s *fboSet) invalidate(ctx Backend) {
 	for _, f := range s.fbos {
-		ctx.BindFramebuffer(gl.FRAMEBUFFER, f.fbo)
-		ctx.InvalidateFramebuffer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0)
+		f.fbo.Invalidate()
 	}
 }
 
-func (s *fboSet) delete(ctx *context, idx int) {
+func (s *fboSet) delete(ctx Backend, idx int) {
 	for i := idx; i < len(s.fbos); i++ {
 		f := s.fbos[i]
-		ctx.DeleteFramebuffer(f.fbo)
-		ctx.DeleteTexture(f.tex)
+		f.fbo.Release()
+		f.tex.Release()
 	}
 	s.fbos = s.fbos[:idx]
 }
 
 func (s *stenciler) release() {
 	s.fbos.delete(s.ctx, 0)
-	s.ctx.DeleteProgram(s.prog)
-	s.ctx.DeleteBuffer(s.indexBuf)
+	s.prog.Release()
+	s.indexBuf.Release()
 }
 
 func (p *pather) release() {
@@ -208,22 +196,21 @@ func (p *pather) release() {
 
 func (c *coverer) release() {
 	for _, p := range c.prog {
-		c.ctx.DeleteProgram(p)
+		p.Release()
 	}
 }
 
-func buildPath(ctx *context, p []byte) *pathData {
-	buf := ctx.CreateBuffer()
-	ctx.BindBuffer(gl.ARRAY_BUFFER, buf)
-	ctx.BufferData(gl.ARRAY_BUFFER, p, gl.STATIC_DRAW)
+func buildPath(ctx Backend, p []byte) *pathData {
+	buf := ctx.NewBuffer(BufferTypeData)
+	buf.Upload(BufferUsageStaticDraw, p)
 	return &pathData{
 		ncurves: len(p) / path.VertStride,
 		data:    buf,
 	}
 }
 
-func (p *pathData) release(ctx *context) {
-	ctx.DeleteBuffer(p.data)
+func (p *pathData) release() {
+	p.data.Release()
 }
 
 func (p *pather) begin(sizes []image.Point) {
@@ -239,26 +226,24 @@ func (p *pather) stencilPath(bounds image.Rectangle, offset f32.Point, uv image.
 }
 
 func (s *stenciler) beginIntersect(sizes []image.Point) {
-	s.ctx.ActiveTexture(gl.TEXTURE1)
-	s.ctx.BindTexture(gl.TEXTURE_2D, gl.Texture{})
-	s.ctx.ActiveTexture(gl.TEXTURE0)
-	s.ctx.BlendFunc(gl.DST_COLOR, gl.ZERO)
+	s.ctx.NilTexture().Bind(1)
+	s.ctx.BlendFunc(BlendFactorDstColor, BlendFactorZero)
 	// 8 bit coverage is enough, but OpenGL ES only supports single channel
 	// floating point formats. Replace with GL_RGB+GL_UNSIGNED_BYTE if
 	// no floating point support is available.
 	s.intersections.resize(s.ctx, sizes)
 	s.ctx.ClearColor(1.0, 0.0, 0.0, 0.0)
-	s.ctx.UseProgram(s.iprog)
+	s.iprog.Bind()
 }
 
 func (s *stenciler) endIntersect() {
-	s.ctx.BindFramebuffer(gl.FRAMEBUFFER, s.defFBO)
+	s.defFBO.Bind()
 }
 
 func (s *stenciler) invalidateFBO() {
 	s.intersections.invalidate(s.ctx)
 	s.fbos.invalidate(s.ctx)
-	s.ctx.BindFramebuffer(gl.FRAMEBUFFER, s.defFBO)
+	s.defFBO.Bind()
 }
 
 func (s *stenciler) cover(idx int) stencilFBO {
@@ -266,31 +251,24 @@ func (s *stenciler) cover(idx int) stencilFBO {
 }
 
 func (s *stenciler) begin(sizes []image.Point) {
-	s.ctx.ActiveTexture(gl.TEXTURE1)
-	s.ctx.BindTexture(gl.TEXTURE_2D, gl.Texture{})
-	s.ctx.ActiveTexture(gl.TEXTURE0)
-	s.ctx.BlendFunc(gl.ONE, gl.ONE)
+	s.ctx.NilTexture().Bind(1)
+	s.ctx.BlendFunc(BlendFactorOne, BlendFactorOne)
 	s.fbos.resize(s.ctx, sizes)
 	s.ctx.ClearColor(0.0, 0.0, 0.0, 0.0)
-	s.ctx.UseProgram(s.prog)
-	s.ctx.EnableVertexAttribArray(attribPathCorner)
-	s.ctx.EnableVertexAttribArray(attribPathMaxY)
-	s.ctx.EnableVertexAttribArray(attribPathFrom)
-	s.ctx.EnableVertexAttribArray(attribPathCtrl)
-	s.ctx.EnableVertexAttribArray(attribPathTo)
-	s.ctx.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, s.indexBuf)
+	s.prog.Bind()
+	s.indexBuf.Bind()
 }
 
 func (s *stenciler) stencilPath(bounds image.Rectangle, offset f32.Point, uv image.Point, data *pathData) {
-	s.ctx.BindBuffer(gl.ARRAY_BUFFER, data.data)
+	data.data.Bind()
 	s.ctx.Viewport(uv.X, uv.Y, bounds.Dx(), bounds.Dy())
 	// Transform UI coordinates to OpenGL coordinates.
 	texSize := f32.Point{X: float32(bounds.Dx()), Y: float32(bounds.Dy())}
 	scale := f32.Point{X: 2 / texSize.X, Y: 2 / texSize.Y}
 	orig := f32.Point{X: -1 - float32(bounds.Min.X)*2/texSize.X, Y: -1 - float32(bounds.Min.Y)*2/texSize.Y}
-	s.ctx.Uniform2f(s.uScale, scale.X, scale.Y)
-	s.ctx.Uniform2f(s.uOffset, orig.X, orig.Y)
-	s.ctx.Uniform2f(s.uPathOffset, offset.X, offset.Y)
+	s.prog.Uniform2f(s.uScale, scale.X, scale.Y)
+	s.prog.Uniform2f(s.uOffset, orig.X, orig.Y)
+	s.prog.Uniform2f(s.uPathOffset, offset.X, offset.Y)
 	// Draw in batches that fit in uint16 indices.
 	start := 0
 	nquads := data.ncurves / 4
@@ -311,27 +289,22 @@ func (s *stenciler) stencilPath(bounds image.Rectangle, offset f32.Point, uv ima
 				indices[i*6+4] = i*4 + 1
 				indices[i*6+5] = i*4 + 3
 			}
-			s.ctx.BufferData(gl.ELEMENT_ARRAY_BUFFER, gl.BytesView(indices), gl.STATIC_DRAW)
+			s.indexBuf.Upload(BufferUsageStaticDraw, gunsafe.BytesView(indices))
 			s.indexBufQuads = batch
 		}
 		off := path.VertStride * start * 4
-		s.ctx.VertexAttribPointer(attribPathCorner, 2, gl.SHORT, false, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CornerX)))
-		s.ctx.VertexAttribPointer(attribPathMaxY, 1, gl.FLOAT, false, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).MaxY)))
-		s.ctx.VertexAttribPointer(attribPathFrom, 2, gl.FLOAT, false, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).FromX)))
-		s.ctx.VertexAttribPointer(attribPathCtrl, 2, gl.FLOAT, false, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CtrlX)))
-		s.ctx.VertexAttribPointer(attribPathTo, 2, gl.FLOAT, false, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).ToX)))
-		s.ctx.DrawElements(gl.TRIANGLES, batch*6, gl.UNSIGNED_SHORT, 0)
+		s.ctx.SetupVertexArray(attribPathCorner, 2, DataTypeShort, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CornerX)))
+		s.ctx.SetupVertexArray(attribPathMaxY, 1, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).MaxY)))
+		s.ctx.SetupVertexArray(attribPathFrom, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).FromX)))
+		s.ctx.SetupVertexArray(attribPathCtrl, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CtrlX)))
+		s.ctx.SetupVertexArray(attribPathTo, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).ToX)))
+		s.ctx.DrawElements(DrawModeTriangles, 0, batch*6)
 		start += batch
 	}
 }
 
 func (s *stenciler) end() {
-	s.ctx.DisableVertexAttribArray(attribPathCorner)
-	s.ctx.DisableVertexAttribArray(attribPathMaxY)
-	s.ctx.DisableVertexAttribArray(attribPathFrom)
-	s.ctx.DisableVertexAttribArray(attribPathCtrl)
-	s.ctx.DisableVertexAttribArray(attribPathTo)
-	s.ctx.BindFramebuffer(gl.FRAMEBUFFER, s.defFBO)
+	s.defFBO.Bind()
 }
 
 func (p *pather) cover(z float32, mat materialType, col [4]float32, scale, off, uvScale, uvOff, coverScale, coverOff f32.Point) {
@@ -339,20 +312,21 @@ func (p *pather) cover(z float32, mat materialType, col [4]float32, scale, off,
 }
 
 func (c *coverer) cover(z float32, mat materialType, col [4]float32, scale, off, uvScale, uvOff, coverScale, coverOff f32.Point) {
-	c.ctx.UseProgram(c.prog[mat])
+	p := c.prog[mat]
+	p.Bind()
 	switch mat {
 	case materialColor:
-		c.ctx.Uniform4f(c.vars[mat].uColor, col[0], col[1], col[2], col[3])
+		p.Uniform4f(c.vars[mat].uColor, col[0], col[1], col[2], col[3])
 	case materialTexture:
-		c.ctx.Uniform2f(c.vars[mat].uUVScale, uvScale.X, uvScale.Y)
-		c.ctx.Uniform2f(c.vars[mat].uUVOffset, uvOff.X, uvOff.Y)
+		p.Uniform2f(c.vars[mat].uUVScale, uvScale.X, uvScale.Y)
+		p.Uniform2f(c.vars[mat].uUVOffset, uvOff.X, uvOff.Y)
 	}
-	c.ctx.Uniform1f(c.vars[mat].z, z)
-	c.ctx.Uniform2f(c.vars[mat].uScale, scale.X, scale.Y)
-	c.ctx.Uniform2f(c.vars[mat].uOffset, off.X, off.Y)
-	c.ctx.Uniform2f(c.vars[mat].uCoverUVScale, coverScale.X, coverScale.Y)
-	c.ctx.Uniform2f(c.vars[mat].uCoverUVOffset, coverOff.X, coverOff.Y)
-	c.ctx.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
+	p.Uniform1f(c.vars[mat].z, z)
+	p.Uniform2f(c.vars[mat].uScale, scale.X, scale.Y)
+	p.Uniform2f(c.vars[mat].uOffset, off.X, off.Y)
+	p.Uniform2f(c.vars[mat].uCoverUVScale, coverScale.X, coverScale.Y)
+	p.Uniform2f(c.vars[mat].uCoverUVOffset, coverOff.X, coverOff.Y)
+	c.ctx.DrawArrays(DrawModeTriangleStrip, 0, 4)
 }
 
 const stencilVSrc = `

gpu/timer.go

@@ -4,19 +4,17 @@ package gpu
 
 import (
 	"time"
-
-	"gioui.org/gpu/gl"
 )
 
 type timers struct {
-	ctx    *context
-	timers []*timer
+	backend Backend
+	timers  []*timer
 }
 
 type timer struct {
 	Elapsed time.Duration
-	ctx     *context
-	obj     gl.Query
+	backend Backend
+	timer   Timer
 	state   timerState
 }
 
@@ -28,9 +26,9 @@ const (
 	timerWaiting
 )
 
-func newTimers(ctx *context) *timers {
+func newTimers(b Backend) *timers {
 	return &timers{
-		ctx: ctx,
+		backend: b,
 	}
 }
 
@@ -39,8 +37,8 @@ func (t *timers) newTimer() *timer {
 		return nil
 	}
 	tt := &timer{
-		ctx: t.ctx,
-		obj: t.ctx.CreateQuery(),
+		backend: t.backend,
+		timer:   t.backend.NewTimer(),
 	}
 	t.timers = append(t.timers, tt)
 	return tt
@@ -50,7 +48,7 @@ func (t *timer) begin() {
 	if t == nil || t.state != timerIdle {
 		return
 	}
-	t.ctx.BeginQuery(gl.TIME_ELAPSED_EXT, t.obj)
+	t.timer.Begin()
 	t.state = timerRunning
 }
 
@@ -58,7 +56,7 @@ func (t *timer) end() {
 	if t == nil || t.state != timerRunning {
 		return
 	}
-	t.ctx.EndQuery(gl.TIME_ELAPSED_EXT)
+	t.timer.End()
 	t.state = timerWaiting
 }
 
@@ -67,19 +65,20 @@ func (t *timers) ready() bool {
 		return false
 	}
 	for _, tt := range t.timers {
-		if tt.state != timerWaiting {
+		switch tt.state {
+		case timerIdle:
+			continue
+		case timerRunning:
 			return false
 		}
-		if t.ctx.GetQueryObjectuiv(tt.obj, gl.QUERY_RESULT_AVAILABLE) == 0 {
+		d, ok := tt.timer.Duration()
+		if !ok {
 			return false
 		}
-	}
-	for _, tt := range t.timers {
 		tt.state = timerIdle
-		nanos := t.ctx.GetQueryObjectuiv(tt.obj, gl.QUERY_RESULT)
-		tt.Elapsed = time.Duration(nanos)
+		tt.Elapsed = d
 	}
-	return t.ctx.GetInteger(gl.GPU_DISJOINT_EXT) == 0
+	return t.backend.IsTimeContinuous()
 }
 
 func (t *timers) release() {
@@ -87,7 +86,7 @@ func (t *timers) release() {
 		return
 	}
 	for _, tt := range t.timers {
-		t.ctx.DeleteQuery(tt.obj)
+		tt.timer.Release()
 	}
 	t.timers = nil
 }

internal/unsafe/unsafe.go

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package unsafe
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// BytesView returns a byte slice view of a slice.
+func BytesView(s interface{}) []byte {
+	v := reflect.ValueOf(s)
+	first := v.Index(0)
+	sz := int(first.Type().Size())
+	return *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
+		Data: uintptr(unsafe.Pointer((*reflect.SliceHeader)(unsafe.Pointer(first.UnsafeAddr())))),
+		Len:  v.Len() * sz,
+		Cap:  v.Cap() * sz,
+	}))
+}
+
+// SliceOf returns a slice from a (native) pointer.
+func SliceOf(s uintptr) []byte {
+	if s == 0 {
+		return nil
+	}
+	sh := reflect.SliceHeader{
+		Data: s,
+		Len:  1 << 30,
+		Cap:  1 << 30,
+	}
+	return *(*[]byte)(unsafe.Pointer(&sh))
+}
+
+// GoString convert a NUL-terminated C string
+// to a Go string.
+func GoString(s []byte) string {
+	i := 0
+	for {
+		if s[i] == 0 {
+			break
+		}
+		i++
+	}
+	return string(s[:i])
+}

internal/unsafe/unsafe_test.go

@@ -1,4 +1,6 @@
-package gl
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package unsafe
 
 import (
 	"testing"