gpu,gpu/backend: implement generic backend.NewDevice

NewDevice creates a Device given an API, which is the necessary GPU
resources for a backend.

Convert gpu.New to take an API instead of a backend.Device directly.

In turn, this frees us to later unexport the backend package along with
the backend implementations (for now just gioui.org/gpu/gl for OpenGL).
It also allows programs that embed Gio (such as gioui.org/example/glfw)
to freely choose a backend, not just OpenGL.

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

app/headless/backend_test.go

@@ -170,7 +170,7 @@ func newBackend(t *testing.T) backend.Device {
 	if err := ctx.MakeCurrent(); err != nil {
 		t.Fatal(err)
 	}
-	b, err := ctx.Backend()
+	b, err := backend.NewDevice(ctx.API())
 	if err != nil {
 		t.Fatal(err)
 	}

app/headless/headless.go

@@ -25,7 +25,7 @@ type Window struct {
 }
 
 type context interface {
-	Backend() (backend.Device, error)
+	API() gpu.API
 	MakeCurrent() error
 	ReleaseCurrent()
 	Release()
@@ -42,7 +42,8 @@ func NewWindow(width, height int) (*Window, error) {
 		ctx:  ctx,
 	}
 	err = contextDo(ctx, func() error {
-		dev, err := ctx.Backend()
+		api := ctx.API()
+		dev, err := backend.NewDevice(api)
 		if err != nil {
 			return err
 		}
@@ -62,7 +63,7 @@ func NewWindow(width, height int) (*Window, error) {
 			fboTex.Release()
 			return err
 		}
-		gp, err := gpu.New(dev)
+		gp, err := gpu.New(api)
 		if err != nil {
 			fbo.Release()
 			fboTex.Release()

app/headless/headless_darwin.go

@@ -3,9 +3,7 @@
 package headless
 
 import (
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
-
+	"gioui.org/gpu"
 	_ "gioui.org/app/internal/cocoainit"
 )
 
@@ -32,6 +30,10 @@ func newGLContext() (context, error) {
 	return &nsContext{ctx: ctx}, nil
 }
 
+func (c *nsContext) API() gpu.API {
+	return gpu.OpenGL{}
+}
+
 func (c *nsContext) MakeCurrent() error {
 	C.gio_headless_makeCurrentContext(c.ctx)
 	if !c.prepared {
@@ -45,10 +47,6 @@ func (c *nsContext) ReleaseCurrent() {
 	C.gio_headless_clearCurrentContext(c.ctx)
 }
 
-func (c *nsContext) Backend() (backend.Device, error) {
-	return gl.NewBackend(nil)
-}
-
 func (d *nsContext) Release() {
 	if d.ctx != 0 {
 		C.gio_headless_releaseContext(d.ctx)

app/headless/headless_js.go

@@ -6,8 +6,7 @@ import (
 	"errors"
 	"syscall/js"
 
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
+	"gioui.org/gpu"
 	"gioui.org/internal/glimpl"
 )
 
@@ -31,8 +30,8 @@ func newGLContext() (context, error) {
 	return c, nil
 }
 
-func (c *jsContext) Backend() (backend.Device, error) {
-	return gl.NewBackend(glimpl.Context(c.ctx))
+func (c *jsContext) API() gpu.API {
+	return gpu.OpenGL{Context: glimpl.Context(c.ctx)}
 }
 
 func (c *jsContext) Release() {

app/headless/headless_windows.go

@@ -3,8 +3,10 @@
 package headless
 
 import (
+	"unsafe"
+
+	"gioui.org/gpu"
 	"gioui.org/app/internal/d3d11"
-	"gioui.org/gpu/backend"
 )
 
 type d3d11Context struct {
@@ -19,12 +21,8 @@ func newContext() (context, error) {
 	return &d3d11Context{dev: dev}, nil
 }
 
-func (c *d3d11Context) Backend() (backend.Device, error) {
-	backend, err := d3d11.NewBackend(c.dev.Handle)
-	if err != nil {
-		return nil, err
-	}
-	return backend, nil
+func (c *d3d11Context) API() gpu.API {
+	return gpu.Direct3D11{Device: unsafe.Pointer(c.dev.Handle)}
 }
 
 func (c *d3d11Context) MakeCurrent() error {

app/internal/d3d11/backend_windows.go

@@ -109,6 +109,10 @@ type SwapChain struct {
 	fbo     *Framebuffer
 }
 
+func init() {
+	backend.NewDirect3D11Device = newDirect3D11Device
+}
+
 func NewDevice() (*Device, error) {
 	var flags uint32
 	if debug {
@@ -237,7 +241,8 @@ func (s *SwapChain) Present() error {
 	return s.swchain.Present(1, 0)
 }
 
-func NewBackend(dev *_ID3D11Device) (*Backend, error) {
+func newDirect3D11Device(api backend.Direct3D11) (backend.Device, error) {
+	dev := (*_ID3D11Device)(api.Device)
 	b := &Backend{
 		dev: dev,
 		ctx: dev.GetImmediateContext(),

app/internal/egl/egl.go

@@ -11,8 +11,7 @@ import (
 	"strings"
 
 	"gioui.org/app/internal/srgb"
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
+	"gioui.org/gpu"
 	"gioui.org/internal/glimpl"
 )
 
@@ -118,8 +117,8 @@ func NewContext(disp NativeDisplayType) (*Context, error) {
 	return c, nil
 }
 
-func (c *Context) Backend() (backend.Device, error) {
-	return gl.NewBackend(nil)
+func (c *Context) API() gpu.API {
+	return gpu.OpenGL{}
 }
 
 func (c *Context) ReleaseSurface() {

app/internal/window/d3d11_windows.go

@@ -3,8 +3,10 @@
 package window
 
 import (
+	"unsafe"
+
+	"gioui.org/gpu"
 	"gioui.org/app/internal/d3d11"
-	"gioui.org/gpu/backend"
 )
 
 type d3d11Context struct {
@@ -34,8 +36,8 @@ func init() {
 	})
 }
 
-func (c *d3d11Context) Backend() (backend.Device, error) {
-	return d3d11.NewBackend(c.dev.Handle)
+func (c *d3d11Context) API() gpu.API {
+	return gpu.Direct3D11{Device: unsafe.Pointer(c.dev.Handle)}
 }
 
 func (c *d3d11Context) Present() error {

app/internal/window/gl_ios.go

@@ -21,8 +21,7 @@ import (
 	"errors"
 	"fmt"
 
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
+	"gioui.org/gpu"
 	"gioui.org/internal/glimpl"
 )
 
@@ -56,8 +55,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Backend() (backend.Device, error) {
-	return gl.NewBackend(nil)
+func (c *context) API() gpu.API {
+	return gpu.OpenGL{}
 }
 
 func (c *context) Release() {

app/internal/window/gl_js.go

@@ -7,8 +7,7 @@ import (
 	"syscall/js"
 
 	"gioui.org/app/internal/srgb"
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
+	"gioui.org/gpu"
 	"gioui.org/internal/glimpl"
 )
 
@@ -39,8 +38,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Backend() (backend.Device, error) {
-	return gl.NewBackend(glimpl.Context(c.ctx))
+func (c *context) API() gpu.API {
+	return gpu.OpenGL{Context: glimpl.Context(c.ctx)}
 }
 
 func (c *context) Release() {

app/internal/window/gl_macos.go

@@ -5,8 +5,7 @@
 package window
 
 import (
-	"gioui.org/gpu/backend"
-	"gioui.org/gpu/gl"
+	"gioui.org/gpu"
 	"gioui.org/internal/glimpl"
 )
 
@@ -48,8 +47,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Backend() (backend.Device, error) {
-	return gl.NewBackend(nil)
+func (c *context) API() gpu.API {
+	return gpu.OpenGL{}
 }
 
 func (c *context) Release() {

app/internal/window/window.go

@@ -7,7 +7,7 @@ package window
 import (
 	"errors"
 
-	"gioui.org/gpu/backend"
+	"gioui.org/gpu"
 	"gioui.org/io/event"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
@@ -33,7 +33,7 @@ type Callbacks interface {
 }
 
 type Context interface {
-	Backend() (backend.Device, error)
+	API() gpu.API
 	Present() error
 	MakeCurrent() error
 	Release()

app/loop.go

@@ -67,12 +67,7 @@ func (l *renderLoop) renderLoop(ctx window.Context) error {
 			initErr <- err
 			return
 		}
-		b, err := ctx.Backend()
-		if err != nil {
-			initErr <- err
-			return
-		}
-		g, err := gpu.New(b)
+		g, err := gpu.New(ctx.API())
 		if err != nil {
 			initErr <- err
 			return

cmd/gogio/androidbuild.go

@@ -7,8 +7,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"golang.org/x/sync/errgroup"
-	"golang.org/x/tools/go/packages"
 	"io"
 	"io/ioutil"
 	"os"
@@ -18,6 +16,9 @@ import (
 	"strconv"
 	"strings"
 	"text/template"
+
+	"golang.org/x/sync/errgroup"
+	"golang.org/x/tools/go/packages"
 )
 
 type androidTools struct {

cmd/gogio/windowsbuild.go

@@ -4,9 +4,6 @@ import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
-	"github.com/akavel/rsrc/binutil"
-	"github.com/akavel/rsrc/coff"
-	"golang.org/x/text/encoding/unicode"
 	"image/png"
 	"io"
 	"math"
@@ -17,6 +14,10 @@ import (
 	"strconv"
 	"strings"
 	"text/template"
+
+	"github.com/akavel/rsrc/binutil"
+	"github.com/akavel/rsrc/coff"
+	"golang.org/x/text/encoding/unicode"
 )
 
 func buildWindows(tmpDir string, bi *buildInfo) error {

gpu/api.go

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import "gioui.org/gpu/backend"
+
+// An API carries the necessary GPU API specific resources to create a Device.
+// There is an API type for each supported GPU API such as OpenGL and Direct3D.
+type API = backend.API
+
+// OpenGL denotes the OpenGL or OpenGL ES API.
+type OpenGL = backend.OpenGL
+
+// Direct3D11 denotes the Direct3D API.
+type Direct3D11 = backend.Direct3D11

gpu/backend/api.go

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package backend
+
+import (
+	"fmt"
+	"unsafe"
+
+	"gioui.org/internal/glimpl"
+)
+
+// See gpu/api.go for documentation for the API types
+
+type API interface {
+	implementsAPI()
+}
+
+type OpenGL struct {
+	// Context contains the WebGL context for WebAssembly platforms. It is
+	// empty for all other platforms; an OpenGL context is assumed current when
+	// calling NewDevice.
+	Context glimpl.Context
+}
+
+type Direct3D11 struct {
+	// Device contains a *ID3D11Device.
+	Device unsafe.Pointer
+}
+
+// API specific device constructors.
+var (
+	NewOpenGLDevice     func(api OpenGL) (Device, error)
+	NewDirect3D11Device func(api Direct3D11) (Device, error)
+)
+
+// NewDevice creates a new Device given the api.
+//
+// Note that the device does not assume ownership of the resources contained in
+// api; the caller must ensure the resources are valid until the device is
+// released.
+func NewDevice(api API) (Device, error) {
+	switch api := api.(type) {
+	case OpenGL:
+		if NewOpenGLDevice != nil {
+			return NewOpenGLDevice(api)
+		}
+	case Direct3D11:
+		if NewDirect3D11Device != nil {
+			return NewDirect3D11Device(api)
+		}
+	}
+	return nil, fmt.Errorf("backend: no backend available for the API %T", api)
+}
+
+func (OpenGL) implementsAPI()     {}
+func (Direct3D11) implementsAPI() {}

gpu/gl/backend.go

@@ -123,12 +123,12 @@ const (
 	storageBindings = 32
 )
 
-// NewBackend returns a new Backend.
-//
-// Pass a WebGL context if GOOS is "js", otherwise pass nil for the current
-// context.
-func NewBackend(ctx Context) (*Backend, error) {
-	f, err := glimpl.NewFunctions(ctx)
+func init() {
+	backend.NewOpenGLDevice = newOpenGLDevice
+}
+
+func newOpenGLDevice(api backend.OpenGL) (backend.Device, error) {
+	f, err := glimpl.NewFunctions(api.Context)
 	if err != nil {
 		return nil, err
 	}

gpu/gpu.go

@@ -28,6 +28,9 @@ import (
 	"gioui.org/layout"
 	"gioui.org/op"
 	"gioui.org/op/clip"
+
+	// Register backend.
+	_ "gioui.org/gpu/gl"
 )
 
 type GPU interface {
@@ -380,14 +383,18 @@ const (
 	materialTexture
 )
 
-func New(ctx backend.Device) (GPU, error) {
+func New(api API) (GPU, error) {
+	d, err := backend.NewDevice(api)
+	if err != nil {
+		return nil, err
+	}
 	forceCompute := os.Getenv("GIORENDERER") == "forcecompute"
-	feats := ctx.Caps().Features
+	feats := d.Caps().Features
 	switch {
 	case !forceCompute && feats.Has(backend.FeatureFloatRenderTargets):
-		return newGPU(ctx)
+		return newGPU(d)
 	case feats.Has(backend.FeatureCompute):
-		return newCompute(ctx)
+		return newCompute(d)
 	default:
 		return nil, errors.New("gpu: no support for float render targets nor compute")
 	}