widget: [API] change Decorations to leave the user in control of window state

As suggested by ~egonelbre, Decorations should not be the source of truth
for the windows state, because external gestures may also change state.

This breaking change removes Decorations.Perform and exposes Maximized
as a bool which is the user's responsibility to set.

Fixes: https://todo.sr.ht/~eliasnaur/gio/600
Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/window.go

@@ -656,6 +656,7 @@ func (w *Window) processEvent(e event.Event) bool {
 		}
 		w.coalesced.view = &e2
 	case ConfigEvent:
+		w.decorations.Decorations.Maximized = e2.Config.Mode == Maximized
 		wasFocused := w.decorations.Config.Focused
 		w.decorations.Config = e2.Config
 		e2.Config = w.effectiveConfig()
@@ -801,7 +802,6 @@ func (w *Window) decorate(e FrameEvent, o *op.Ops) image.Point {
 	default:
 		panic(fmt.Errorf("unknown WindowMode %v", m))
 	}
-	deco.Perform(actions)
 	gtx := layout.Context{
 		Ops:         o,
 		Now:         e.Now,

widget/decorations.go

@@ -11,8 +11,11 @@ import (
 
 // Decorations handles the states of window decorations.
 type Decorations struct {
+	// Maximized controls the look and behaviour of the maximize
+	// button. It is the user's responsibility to set Maximized
+	// according to the window state reported through [app.ConfigEvent].
+	Maximized bool
 	clicks    map[int]*Clickable
-	maximized bool
 }
 
 // LayoutMove lays out the widget that makes a window movable.
@@ -40,17 +43,6 @@ func (d *Decorations) Clickable(action system.Action) *Clickable {
 	return click
 }
 
-// Perform updates the decorations as if the specified actions were
-// performed by the user.
-func (d *Decorations) Perform(actions system.Action) {
-	if actions&system.ActionMaximize != 0 {
-		d.maximized = true
-	}
-	if actions&(system.ActionUnmaximize|system.ActionMinimize|system.ActionFullscreen) != 0 {
-		d.maximized = false
-	}
-}
-
 // Update the state and return the set of actions activated by the user.
 func (d *Decorations) Update(gtx layout.Context) system.Action {
 	var actions system.Action
@@ -60,21 +52,12 @@ func (d *Decorations) Update(gtx layout.Context) system.Action {
 		}
 		action := system.Action(1 << idx)
 		switch {
-		case action == system.ActionMaximize && d.maximized:
+		case action == system.ActionMaximize && d.Maximized:
 			action = system.ActionUnmaximize
-		case action == system.ActionUnmaximize && !d.maximized:
+		case action == system.ActionUnmaximize && !d.Maximized:
 			action = system.ActionMaximize
 		}
-		switch action {
-		case system.ActionMaximize, system.ActionUnmaximize:
-			d.maximized = !d.maximized
-		}
 		actions |= action
 	}
 	return actions
 }
-
-// Maximized returns whether the window is maximized.
-func (d *Decorations) Maximized() bool {
-	return d.maximized
-}

widget/material/decorations.go

@@ -75,7 +75,7 @@ func (d DecorationsStyle) layoutDecorations(gtx layout.Context) layout.Dimension
 				case system.ActionMinimize:
 					w = minimizeWindow
 				case system.ActionMaximize:
-					if d.Decorations.Maximized() {
+					if d.Decorations.Maximized {
 						w = maximizedWindow
 					} else {
 						w = maximizeWindow