widget: [API] move Decorations state update to Actions

Similar to a previous change for Clickable and Bool this change separates
state changes from Decorations.Layout to Actions so that access may
happen before Layout.

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

app/window.go

@@ -1024,7 +1024,7 @@ func (w *Window) decorate(d driver, e system.FrameEvent, o *op.Ops) (size, offse
 	}
 	style.Layout(gtx)
 	// Update the window based on the actions on the decorations.
-	w.Perform(deco.Actions())
+	w.Perform(deco.Update(gtx))
 	// Offset to place the frame content below the decorations.
 	decoHeight := gtx.Dp(w.decorations.Config.decoHeight)
 	if w.decorations.currentHeight != decoHeight {

widget/decorations.go

@@ -12,12 +12,11 @@ import (
 
 // Decorations handles the states of window decorations.
 type Decorations struct {
-	clicks []Clickable
+	clicks map[int]*Clickable
 	resize [8]struct {
 		gesture.Hover
 		gesture.Drag
 	}
-	actions   system.Action
 	maximized bool
 }
 
@@ -30,27 +29,18 @@ func (d *Decorations) LayoutMove(gtx layout.Context, w layout.Widget) layout.Dim
 }
 
 // Clickable returns the clickable for the given single action.
-func (d *Decorations) Clickable(gtx layout.Context, action system.Action) *Clickable {
+func (d *Decorations) Clickable(action system.Action) *Clickable {
 	if bits.OnesCount(uint(action)) != 1 {
 		panic(fmt.Errorf("not a single action"))
 	}
 	idx := bits.TrailingZeros(uint(action))
-	if n := idx - len(d.clicks); n >= 0 {
-		d.clicks = append(d.clicks, make([]Clickable, n+1)...)
-	}
-	click := &d.clicks[idx]
-	if click.Clicked(gtx) {
-		if action == system.ActionMaximize {
-			if d.maximized {
-				d.maximized = false
-				d.actions |= system.ActionUnmaximize
-			} else {
-				d.maximized = true
-				d.actions |= system.ActionMaximize
-			}
-		} else {
-			d.actions |= action
+	click, found := d.clicks[idx]
+	if !found {
+		click = new(Clickable)
+		if d.clicks == nil {
+			d.clicks = make(map[int]*Clickable)
 		}
+		d.clicks[idx] = click
 	}
 	return click
 }
@@ -66,11 +56,27 @@ func (d *Decorations) Perform(actions system.Action) {
 	}
 }
 
-// Actions returns the set of actions activated by the user.
-func (d *Decorations) Actions() system.Action {
-	a := d.actions
-	d.actions = 0
-	return a
+// 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
+	for idx, clk := range d.clicks {
+		if !clk.Clicked(gtx) {
+			continue
+		}
+		action := system.Action(1 << idx)
+		switch {
+		case action == system.ActionMaximize && d.maximized:
+			action = system.ActionUnmaximize
+		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.

widget/material/decorations.go

@@ -85,7 +85,7 @@ func (d DecorationsStyle) layoutDecorations(gtx layout.Context) layout.Dimension
 				default:
 					continue
 				}
-				cl := d.Decorations.Clickable(gtx, a)
+				cl := d.Decorations.Clickable(a)
 				dims := cl.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
 					semantic.Button.Add(gtx.Ops)
 					return layout.Stack{Alignment: layout.Center}.Layout(gtx,