[app,io] Feature/make decoration size available to consumer

app/os.go

@@ -23,6 +23,8 @@ var errOutOfDate = errors.New("app: GPU surface out of date")
 type Config struct {
 	// Size is the window dimensions (Width, Height).
 	Size image.Point
+	// Decoration size is the dimensions of the window's decoration.
+	DecorationSize image.Point
 	// MaxSize is the window maximum allowed dimensions.
 	MaxSize image.Point
 	// MinSize is the window minimum allowed dimensions.

app/window.go

@@ -753,7 +753,7 @@ func (w *Window) processEvent(d driver, e event.Event) {
 		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)
+		e2.FrameEvent.Size, e2.FrameEvent.DecorationSize = w.decorate(d, e2.FrameEvent, wrapper)
 		w.out <- e2.FrameEvent
 		frame, gotFrame := w.waitFrame(d)
 		ops.AddCall(&wrapper.Internal, &frame.Internal, ops.PC{}, ops.PCFor(&frame.Internal))
@@ -791,6 +791,7 @@ func (w *Window) processEvent(d driver, e event.Event) {
 			w.decorations.size = image.Point{}
 		}
 		e2.Config.Size = e2.Config.Size.Sub(w.decorations.size)
+		e2.Config.DecorationSize = w.decorations.size
 		w.out <- e2
 	case event.Event:
 		if w.queue.q.Queue(e2) {
@@ -856,9 +857,9 @@ func (w *Window) fallbackDecorate() bool {
 }
 
 // decorate the window if enabled and returns the corresponding Insets.
-func (w *Window) decorate(d driver, e system.FrameEvent, o *op.Ops) image.Point {
+func (w *Window) decorate(d driver, e system.FrameEvent, o *op.Ops) (image.Point, image.Point) {
 	if !w.fallbackDecorate() {
-		return e.Size
+		return e.Size, image.Point{}
 	}
 	theme := w.decorations.Theme
 	if theme == nil {
@@ -906,13 +907,15 @@ func (w *Window) decorate(d driver, e system.FrameEvent, o *op.Ops) image.Point
 	size := image.Point{Y: dims.Size.Y}
 	op.Offset(f32.Point{Y: float32(size.Y)}).Add(o)
 	appSize := e.Size.Sub(size)
+	decSize := w.decorations.size
 	if w.decorations.size != size {
 		w.decorations.size = size
 		cnf := w.decorations.Config
 		cnf.Size = appSize
+		cnf.DecorationSize = decSize
 		w.out <- ConfigEvent{Config: cnf}
 	}
-	return appSize
+	return appSize, decSize
 }
 
 // Perform the actions on the window.

io/system/system.go

@@ -24,6 +24,8 @@ type FrameEvent struct {
 	Metric unit.Metric
 	// Size is the dimensions of the window.
 	Size image.Point
+	// Decoration size is the dimensions of the window's decoration.
+	DecorationSize image.Point
 	// Insets is the insets to apply.
 	Insets Insets
 	// Frame completes the FrameEvent by drawing the graphical operations