Cleanup GLFW init to avoid needing a sync.Once

This replaces my previous PR which had to be reverted due to an issue with the application not having started. This cleans up some of the init code to avoid calling init multiple times (when starting and when creating a new windows).
It also includes an extra change to set up the device field more coherently.

Replaces fyne-io#4177

app/app.go

@@ -153,6 +153,11 @@ func newAppWithDriver(d fyne.Driver, id string) fyne.App {
 	repository.Register("http", httpHandler)
 	repository.Register("https", httpHandler)
 
+	// Run .Init() after app has been set up.
+	if driver, ok := d.(interface{ Init() }); ok {
+		driver.Init()
+	}
+
 	return newApp
 }
 

internal/driver/glfw/driver.go

@@ -89,10 +89,6 @@ func (d *gLDriver) AbsolutePositionForObject(co fyne.CanvasObject) fyne.Position
 }
 
 func (d *gLDriver) Device() fyne.Device {
-	if d.device == nil {
-		d.device = &glDevice{}
-	}
-
 	return d.device
 }
 
@@ -177,5 +173,6 @@ func NewGLDriver() *gLDriver {
 		drawDone:     make(chan struct{}),
 		waitForStart: make(chan struct{}),
 		animation:    &animation.Runner{},
+		device:       &glDevice{},
 	}
 }

internal/driver/glfw/loop.go

@@ -2,7 +2,6 @@ package glfw
 
 import (
 	"runtime"
-	"sync"
 	"sync/atomic"
 	"time"
 
@@ -29,7 +28,6 @@ type drawData struct {
 var funcQueue = make(chan funcData)
 var drawFuncQueue = make(chan drawData)
 var running uint32 // atomic bool, 0 or 1
-var initOnce = &sync.Once{}
 
 // Arrange that main.main runs on main thread.
 func init() {
@@ -110,7 +108,6 @@ func (d *gLDriver) runGL() {
 	}
 	close(d.waitForStart) // Signal that execution can continue.
 
-	d.initGLFW()
 	if d.trayStart != nil {
 		d.trayStart()
 	}

internal/driver/glfw/loop_desktop.go

@@ -11,17 +11,16 @@ import (
 	"github.com/go-gl/glfw/v3.3/glfw"
 )
 
-func (d *gLDriver) initGLFW() {
-	initOnce.Do(func() {
-		err := glfw.Init()
-		if err != nil {
-			fyne.LogError("failed to initialise GLFW", err)
-			return
-		}
-
-		initCursors()
-		d.startDrawThread()
-	})
+// Init makes the driver ready to run. Needs to be called after app is created.
+func (d *gLDriver) Init() {
+	err := glfw.Init()
+	if err != nil {
+		fyne.LogError("failed to initialise GLFW", err)
+		return
+	}
+
+	initCursors()
+	d.startDrawThread()
 }
 
 func (d *gLDriver) tryPollEvents() {

internal/driver/glfw/loop_goxjs.go

@@ -12,16 +12,15 @@ import (
 	glfw "github.com/fyne-io/glfw-js"
 )
 
-func (d *gLDriver) initGLFW() {
-	initOnce.Do(func() {
-		err := glfw.Init(gl.ContextWatcher)
-		if err != nil {
-			fyne.LogError("failed to initialise GLFW", err)
-			return
-		}
-
-		d.startDrawThread()
-	})
+// Init makes the driver ready to run. Needs to be called after app is created.
+func (d *gLDriver) Init() {
+	err := glfw.Init(gl.ContextWatcher)
+	if err != nil {
+		fyne.LogError("failed to initialise GLFW", err)
+		return
+	}
+
+	d.startDrawThread()
 }
 
 func (d *gLDriver) tryPollEvents() {

internal/driver/glfw/window.go

@@ -948,13 +948,11 @@ func (d *gLDriver) CreateWindow(title string) fyne.Window {
 }
 
 func (d *gLDriver) createWindow(title string, decorate bool) fyne.Window {
-	var ret *window
 	if title == "" {
 		title = defaultTitle
 	}
+	var ret *window
 	runOnMain(func() {
-		d.initGLFW()
-
 		ret = &window{title: title, decorate: decorate, driver: d}
 		// This queue is destroyed when the window is closed.
 		ret.InitEventQueue()

internal/driver/glfw/window_test.go

@@ -36,7 +36,6 @@ func init() {
 // TestMain makes sure that our driver is running on the main thread.
 // This must be done for some of our tests to function correctly.
 func TestMain(m *testing.M) {
-	d.initGLFW()
 	go func() {
 		// Wait for GLFW loop to be running.
 		// If we try to create windows before the context is created, this will fail with an exception.