app: use material.Decorations on undecorated platforms

This patch implements a mechanism for customizing window
decorations.
If a window is configured with app.Decorated(true), then
the widget/material.Decorations are applied. On Wayland,
the option is automatically set when the server does not
provide window decorations.

Server side decorations are no longer requested.
The Decorated flag is set according to the
server's requests.

Wayland is now the default driver for UNIX platforms.

References: https://todo.sr.ht/~eliasnaur/gio/318
Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

app/window.go

@@ -11,14 +11,18 @@ import (
 	"time"
 
 	"gioui.org/f32"
+	"gioui.org/font/gofont"
 	"gioui.org/gpu"
+	"gioui.org/internal/ops"
 	"gioui.org/io/event"
 	"gioui.org/io/pointer"
 	"gioui.org/io/profile"
 	"gioui.org/io/router"
 	"gioui.org/io/system"
+	"gioui.org/layout"
 	"gioui.org/op"
 	"gioui.org/unit"
+	"gioui.org/widget/material"
 
 	_ "gioui.org/app/internal/log"
 )
@@ -59,8 +63,13 @@ type Window struct {
 	nextFrame    time.Time
 	delayedDraw  *time.Timer
 
-	queue  queue
-	cursor pointer.CursorName
+	queue       queue
+	cursor      pointer.CursorName
+	decorations struct {
+		op.Ops
+		Config
+		*material.Decorations
+	}
 
 	callbacks callbacks
 
@@ -578,9 +587,16 @@ func (w *Window) processEvent(d driver, e event.Event) {
 		w.hasNextFrame = false
 		e2.Frame = w.update
 		e2.Queue = &w.queue
+
+		// Prepare the decorations and update the frame insets.
+		wrapper := &w.decorations.Ops
+		wrapper.Reset()
+		size := e2.Size // save the initial window size as the decorations will change it.
+		e2.FrameEvent.Size = w.decorate(d, e2.FrameEvent, wrapper)
 		w.out <- e2.FrameEvent
 		frame, gotFrame := w.waitFrame()
-		err := w.validateAndProcess(d, e2.Size, e2.Sync, frame)
+		ops.AddCall(&wrapper.Internal, &frame.Internal, ops.PC{}, ops.PCFor(&frame.Internal))
+		err := w.validateAndProcess(d, size, e2.Sync, wrapper)
 		if gotFrame {
 			// We're done with frame, let the client continue.
 			w.frameAck <- struct{}{}
@@ -606,6 +622,9 @@ func (w *Window) processEvent(d driver, e event.Event) {
 		w.out <- e2
 		w.waitAck()
 	case wakeupEvent:
+	case ConfigEvent:
+		w.decorations.Config = e2.Config
+		w.out <- e
 	case event.Event:
 		if w.queue.q.Queue(e2) {
 			w.setNextFrame(time.Time{})
@@ -664,6 +683,59 @@ func (w *Window) updateCursor(d driver) {
 	}
 }
 
+// decorate the window if enabled and returns the corresponding Insets.
+func (w *Window) decorate(d driver, e system.FrameEvent, o *op.Ops) image.Point {
+	if w.decorations.Config.Decorated || w.decorations.Config.Mode == Fullscreen {
+		return e.Size
+	}
+	deco := w.decorations.Decorations
+	if deco == nil {
+		theme := material.NewTheme(gofont.Collection())
+		allActions := system.ActionMinimize | system.ActionMaximize | system.ActionUnmaximize |
+			system.ActionClose | system.ActionMove |
+			system.ActionResizeNorth | system.ActionResizeSouth |
+			system.ActionResizeWest | system.ActionResizeEast |
+			system.ActionResizeNorthWest | system.ActionResizeSouthWest |
+			system.ActionResizeNorthEast | system.ActionResizeSouthEast
+		deco = &material.Decorations{
+			DecorationsStyle: material.Decorate(theme, allActions),
+		}
+		w.decorations.Decorations = deco
+	}
+	// Update the decorations based on the current window mode.
+	var actions system.Action
+	switch m := w.decorations.Config.Mode; m {
+	case Windowed:
+		actions |= system.ActionUnmaximize
+	case Minimized:
+		actions |= system.ActionMinimize
+	case Maximized:
+		actions |= system.ActionMaximize
+	case Fullscreen:
+		actions |= system.ActionFullscreen
+	default:
+		panic(fmt.Errorf("unknown WindowMode %v", m))
+	}
+	deco.Perform(actions)
+	// Update the window based on the actions on the decorations.
+	d.Perform(deco.Actions())
+
+	gtx := layout.Context{
+		Ops:         o,
+		Now:         e.Now,
+		Queue:       e.Queue,
+		Metric:      e.Metric,
+		Constraints: layout.Exact(e.Size),
+	}
+	rec := op.Record(o)
+	dims := deco.Decorate(gtx, w.decorations.Config.Title)
+	op.Defer(o, rec.Stop())
+	// Offset to place the frame content below the decorations.
+	size := image.Point{Y: dims.Size.Y}
+	op.Offset(f32.Point{Y: float32(size.Y)}).Add(o)
+	return e.Size.Sub(size)
+}
+
 // Raise requests that the platform bring this window to the top of all open windows.
 // Some platforms do not allow this except under certain circumstances, such as when
 // a window from the same application already has focus. If the platform does not
@@ -764,3 +836,11 @@ func CustomRenderer(custom bool) Option {
 		cnf.CustomRenderer = custom
 	}
 }
+
+// Decorated controls whether automatic window decorations
+// are enabled.
+func Decorated(enabled bool) Option {
+	return func(_ unit.Metric, cnf *Config) {
+		cnf.Decorated = enabled
+	}
+}