app: defer window creation until Window.Event is called

We're moving towards making Window.Event, and in the future, Window.Events
create the window and drive the event loop to completion. In that model,
the other Window methods shouldn't create the window.

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

app/window.go

@@ -9,7 +9,6 @@ import (
 	"image/color"
 	"reflect"
 	"runtime"
-	"sync"
 	"time"
 	"unicode/utf8"
 
@@ -36,14 +35,14 @@ type Option func(unit.Metric, *Config)
 
 // Window represents an operating system window.
 //
-// The zero-value Window is useful, and calling any method on
-// it creates and shows a new GUI window. On iOS or Android,
-// the first Window represents the the window previously
-// created by the platform.
+// The zero-value Window is useful; the GUI window is created and shown the first
+// time the [Event] method is called. On iOS or Android, the first Window represents
+// the window previously created by the platform.
 //
-// More than one Window is not supported on iOS, Android,
-// WebAssembly.
+// More than one Window is not supported on iOS, Android, WebAssembly.
 type Window struct {
+	initialOpts []Option
+
 	ctx context
 	gpu gpu.GPU
 	// timer tracks the delayed invalidate goroutine.
@@ -91,7 +90,6 @@ type Window struct {
 	driver   driver
 	// basic is the driver interface that is needed even after the window is gone.
 	basic basicDriver
-	once  sync.Once
 	// coalesced tracks the most recent events waiting to be delivered
 	// to the client.
 	coalesced eventSummary
@@ -273,8 +271,9 @@ func (w *Window) updateState() {
 //
 // Invalidate is safe for concurrent use.
 func (w *Window) Invalidate() {
-	w.init()
-	w.basic.Invalidate()
+	if w.basic != nil {
+		w.basic.Invalidate()
+	}
 }
 
 // Option applies the options to the window. The options are hints; the platform is
@@ -283,7 +282,10 @@ func (w *Window) Option(opts ...Option) {
 	if len(opts) == 0 {
 		return
 	}
-	w.init(opts...)
+	if w.basic == nil {
+		w.initialOpts = append(w.initialOpts, opts...)
+		return
+	}
 	w.Run(func() {
 		cnf := Config{Decorated: w.decorations.enabled}
 		for _, opt := range opts {
@@ -302,13 +304,14 @@ func (w *Window) Option(opts ...Option) {
 }
 
 // Run f in the same thread as the native window event loop, and wait for f to
-// return or the window to close.
+// return or the window to close. If the window has not yet been created,
+// Run calls f directly.
 //
 // Note that most programs should not call Run; configuring a Window with
 // [CustomRenderer] is a notable exception.
 func (w *Window) Run(f func()) {
-	w.init()
 	if w.driver == nil {
+		f()
 		return
 	}
 	done := make(chan struct{})
@@ -680,48 +683,50 @@ func (w *Window) processEvent(e event.Event) bool {
 }
 
 // Event blocks until an event is received from the window, such as
-// [FrameEvent], or until [Invalidate] is called.
+// [FrameEvent], or until [Invalidate] is called. The window is created
+// and shown the first time Event is called.
 func (w *Window) Event() event.Event {
-	w.init()
+	if w.basic == nil {
+		w.init()
+	}
 	return w.basic.Event()
 }
 
-func (w *Window) init(initial ...Option) {
-	w.once.Do(func() {
-		debug.Parse()
-		// Measure decoration height.
-		deco := new(widget.Decorations)
-		theme := material.NewTheme()
-		theme.Shaper = text.NewShaper(text.NoSystemFonts(), text.WithCollection(gofont.Regular()))
-		decoStyle := material.Decorations(theme, deco, 0, "")
-		gtx := layout.Context{
-			Ops: new(op.Ops),
-			// Measure in Dp.
-			Metric: unit.Metric{},
-		}
-		// Allow plenty of space.
-		gtx.Constraints.Max.Y = 200
-		dims := decoStyle.Layout(gtx)
-		decoHeight := unit.Dp(dims.Size.Y)
-		defaultOptions := []Option{
-			Size(800, 600),
-			Title("Gio"),
-			Decorated(true),
-			decoHeightOpt(decoHeight),
-		}
-		options := append(defaultOptions, initial...)
-		var cnf Config
-		cnf.apply(unit.Metric{}, options)
+func (w *Window) init() {
+	debug.Parse()
+	// Measure decoration height.
+	deco := new(widget.Decorations)
+	theme := material.NewTheme()
+	theme.Shaper = text.NewShaper(text.NoSystemFonts(), text.WithCollection(gofont.Regular()))
+	decoStyle := material.Decorations(theme, deco, 0, "")
+	gtx := layout.Context{
+		Ops: new(op.Ops),
+		// Measure in Dp.
+		Metric: unit.Metric{},
+	}
+	// Allow plenty of space.
+	gtx.Constraints.Max.Y = 200
+	dims := decoStyle.Layout(gtx)
+	decoHeight := unit.Dp(dims.Size.Y)
+	defaultOptions := []Option{
+		Size(800, 600),
+		Title("Gio"),
+		Decorated(true),
+		decoHeightOpt(decoHeight),
+	}
+	options := append(defaultOptions, w.initialOpts...)
+	w.initialOpts = nil
+	var cnf Config
+	cnf.apply(unit.Metric{}, options)
 
-		w.nocontext = cnf.CustomRenderer
-		w.decorations.Theme = theme
-		w.decorations.Decorations = deco
-		w.decorations.enabled = cnf.Decorated
-		w.decorations.height = decoHeight
-		w.imeState.compose = key.Range{Start: -1, End: -1}
-		w.semantic.ids = make(map[input.SemanticID]input.SemanticNode)
-		newWindow(&callbacks{w}, options)
-	})
+	w.nocontext = cnf.CustomRenderer
+	w.decorations.Theme = theme
+	w.decorations.Decorations = deco
+	w.decorations.enabled = cnf.Decorated
+	w.decorations.height = decoHeight
+	w.imeState.compose = key.Range{Start: -1, End: -1}
+	w.semantic.ids = make(map[input.SemanticID]input.SemanticNode)
+	newWindow(&callbacks{w}, options)
 }
 
 func (w *Window) updateCursor() {