app,app/headless: expose Backends from window and headless contexts

This is a refactoring change to prepare for another gpu.Backend
implementations.

Notably, app/loop.go no longer imports gpu/gl.

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

app/headless/headless.go

@@ -26,6 +26,7 @@ type Window struct {
 
 type context interface {
 	Functions() *glimpl.Functions
+	Backend() (gpu.Backend, error)
 	MakeCurrent() error
 	ReleaseCurrent()
 	Release()
@@ -53,7 +54,7 @@ func NewWindow(width, height int) (*Window, error) {
 			ctx.Release()
 			return err
 		}
-		backend, err := gl.NewBackend(f)
+		backend, err := ctx.Backend()
 		if err != nil {
 			fbo.Release()
 			ctx.Release()

app/headless/headless_darwin.go

@@ -4,6 +4,8 @@ package headless
 
 import (
 	"gioui.org/app/internal/glimpl"
+	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 )
 
 /*
@@ -38,6 +40,10 @@ func (c *nsContext) ReleaseCurrent() {
 	C.gio_headless_clearCurrentContext(c.ctx)
 }
 
+func (c *nsContext) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.c)
+}
+
 func (c *nsContext) Functions() *glimpl.Functions {
 	return c.c
 }

app/headless/headless_js.go

@@ -7,6 +7,8 @@ import (
 	"syscall/js"
 
 	"gioui.org/app/internal/glimpl"
+	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 )
 
 type jsContext struct {
@@ -37,6 +39,10 @@ func newContext() (*jsContext, error) {
 	return c, nil
 }
 
+func (c *jsContext) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.f)
+}
+
 func (c *jsContext) Functions() *glimpl.Functions {
 	return c.f
 }

app/internal/egl/egl.go

@@ -12,6 +12,8 @@ import (
 
 	"gioui.org/app/internal/glimpl"
 	"gioui.org/app/internal/srgb"
+	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 )
 
 type Context struct {
@@ -119,6 +121,10 @@ func (c *Context) Functions() *glimpl.Functions {
 	return c.c
 }
 
+func (c *Context) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.c)
+}
+
 func (c *Context) ReleaseSurface() {
 	if c.eglSurf == nilEGLSurface {
 		return

app/internal/window/gl_ios.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 
 	"gioui.org/app/internal/glimpl"
+	"gioui.org/gpu"
 	"gioui.org/gpu/gl"
 )
 
@@ -50,8 +51,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Functions() *glimpl.Functions {
-	return c.c
+func (c *context) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.c)
 }
 
 func (c *context) Release() {

app/internal/window/gl_js.go

@@ -8,6 +8,8 @@ import (
 
 	"gioui.org/app/internal/glimpl"
 	"gioui.org/app/internal/srgb"
+	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 )
 
 type context struct {
@@ -45,8 +47,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Functions() *glimpl.Functions {
-	return c.f
+func (c *context) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.f)
 }
 
 func (c *context) Release() {

app/internal/window/gl_macos.go

@@ -6,6 +6,8 @@ package window
 
 import (
 	"gioui.org/app/internal/glimpl"
+	"gioui.org/gpu"
+	"gioui.org/gpu/gl"
 )
 
 /*
@@ -40,8 +42,8 @@ func newContext(w *window) (*context, error) {
 	return c, nil
 }
 
-func (c *context) Functions() *glimpl.Functions {
-	return c.c
+func (c *context) Backend() (gpu.Backend, error) {
+	return gl.NewBackend(c.c)
 }
 
 func (c *context) Release() {

app/internal/window/window.go

@@ -9,7 +9,7 @@ import (
 	"math"
 	"time"
 
-	"gioui.org/app/internal/glimpl"
+	"gioui.org/gpu"
 	"gioui.org/io/event"
 	"gioui.org/io/system"
 	"gioui.org/unit"
@@ -32,7 +32,7 @@ type Callbacks interface {
 }
 
 type Context interface {
-	Functions() *glimpl.Functions
+	Backend() (gpu.Backend, error)
 	Present() error
 	MakeCurrent() error
 	Release()

app/loop.go

@@ -8,7 +8,6 @@ import (
 
 	"gioui.org/app/internal/window"
 	"gioui.org/gpu"
-	"gioui.org/gpu/gl"
 	"gioui.org/op"
 )
 
@@ -54,7 +53,7 @@ func newLoop(ctx window.Context) (*renderLoop, error) {
 	return l, nil
 }
 
-func (l *renderLoop) renderLoop(glctx window.Context) error {
+func (l *renderLoop) renderLoop(ctx window.Context) error {
 	// GL Operations must happen on a single OS thread, so
 	// pass initialization result through a channel.
 	initErr := make(chan error)
@@ -63,38 +62,38 @@ func (l *renderLoop) renderLoop(glctx window.Context) error {
 		runtime.LockOSThread()
 		// Don't UnlockOSThread to avoid reuse by the Go runtime.
 
-		if err := glctx.MakeCurrent(); err != nil {
+		if err := ctx.MakeCurrent(); err != nil {
 			initErr <- err
 			return
 		}
-		ctx, err := gl.NewBackend(glctx.Functions())
+		b, err := ctx.Backend()
 		if err != nil {
 			initErr <- err
 			return
 		}
-		g, err := gpu.New(ctx)
+		g, err := gpu.New(b)
 		if err != nil {
 			initErr <- err
 			return
 		}
-		defer glctx.Release()
+		defer ctx.Release()
 		initErr <- nil
 	loop:
 		for {
 			select {
 			case <-l.refresh:
-				l.refreshErr <- glctx.MakeCurrent()
+				l.refreshErr <- ctx.MakeCurrent()
 			case frame := <-l.frames:
-				glctx.Lock()
+				ctx.Lock()
 				g.Collect(frame.viewport, frame.ops)
 				// Signal that we're done with the frame ops.
 				l.ack <- struct{}{}
 				g.BeginFrame()
 				var res frameResult
-				res.err = glctx.Present()
+				res.err = ctx.Present()
 				g.EndFrame()
 				res.profile = g.Profile()
-				glctx.Unlock()
+				ctx.Unlock()
 				l.results <- res
 			case <-l.stop:
 				break loop