app,io/system,layout: [API] move FrameEvent and Insets to package app

In the early days of Gio, FrameEvent was part of package app. It was
moved to package system to enable layout.NewContext be a convenient
short-hand for constructing a layout.

However, it seems the better design to leave FrameEvent (and Insets) in
package app, and move layout.NewContext there as well. More importantly,
the move allows us to replace the event.Queue interface with a concrete
type.

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

app/app.go

@@ -3,9 +3,16 @@
 package app
 
 import (
+	"image"
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
+
+	"gioui.org/io/event"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/unit"
 )
 
 // extraArgs contains extra arguments to append to
@@ -30,13 +37,68 @@ var extraArgs string
 // is not supported. Default value of ID is filepath.Base(os.Args[0]).
 var ID = ""
 
-func init() {
-	if extraArgs != "" {
-		args := strings.Split(extraArgs, "|")
-		os.Args = append(os.Args, args...)
+// A FrameEvent requests a new frame in the form of a list of
+// operations that describes what to display and how to handle
+// input.
+type FrameEvent struct {
+	// Now is the current animation. Use Now instead of time.Now to
+	// synchronize animation and to avoid the time.Now call overhead.
+	Now time.Time
+	// Metric converts device independent dp and sp to device pixels.
+	Metric unit.Metric
+	// Size is the dimensions of the window.
+	Size image.Point
+	// Insets represent the space occupied by system decorations and controls.
+	Insets Insets
+	// Frame completes the FrameEvent by drawing the graphical operations
+	// from ops into the window.
+	Frame func(frame *op.Ops)
+	// Queue supplies the events for event handlers.
+	Queue event.Queue
+}
+
+// Insets is the space taken up by
+// system decoration such as translucent
+// system bars and software keyboards.
+type Insets struct {
+	// Values are in pixels.
+	Top, Bottom, Left, Right unit.Dp
+}
+
+// NewContext is a shorthand for
+//
+//	layout.Context{
+//	  Ops: ops,
+//	  Now: e.Now,
+//	  Queue: e.Queue,
+//	  Config: e.Config,
+//	  Constraints: layout.Exact(e.Size),
+//	}
+//
+// NewContext calls ops.Reset and adjusts ops for e.Insets.
+func NewContext(ops *op.Ops, e FrameEvent) layout.Context {
+	ops.Reset()
+
+	size := e.Size
+
+	if e.Insets != (Insets{}) {
+		left := e.Metric.Dp(e.Insets.Left)
+		top := e.Metric.Dp(e.Insets.Top)
+		op.Offset(image.Point{
+			X: left,
+			Y: top,
+		}).Add(ops)
+
+		size.X -= left + e.Metric.Dp(e.Insets.Right)
+		size.Y -= top + e.Metric.Dp(e.Insets.Bottom)
 	}
-	if ID == "" {
-		ID = filepath.Base(os.Args[0])
+
+	return layout.Context{
+		Ops:         ops,
+		Now:         e.Now,
+		Queue:       e.Queue,
+		Metric:      e.Metric,
+		Constraints: layout.Exact(size),
 	}
 }
 
@@ -63,3 +125,15 @@ func DataDir() (string, error) {
 func Main() {
 	osMain()
 }
+
+func (FrameEvent) ImplementsEvent() {}
+
+func init() {
+	if extraArgs != "" {
+		args := strings.Split(extraArgs, "|")
+		os.Args = append(os.Args, args...)
+	}
+	if ID == "" {
+		ID = filepath.Base(os.Args[0])
+	}
+}

app/doc.go

@@ -17,12 +17,10 @@ FrameEvent that prompts an update of the window contents.
 
 For example:
 
-	import "gioui.org/unit"
-
 	w := app.NewWindow()
 	for {
 		e := w.NextEvent()
-		if e, ok := e.(system.FrameEvent); ok {
+		if e, ok := e.(app.FrameEvent); ok {
 			ops.Reset()
 			// Add operations to ops.
 			...

app/os.go

@@ -132,7 +132,7 @@ func (o Orientation) String() string {
 }
 
 type frameEvent struct {
-	system.FrameEvent
+	FrameEvent
 
 	Sync bool
 }

app/os_android.go

@@ -836,14 +836,14 @@ func (w *window) draw(env *C.JNIEnv, sync bool) {
 	const inchPrDp = 1.0 / 160
 	ppdp := float32(w.dpi) * inchPrDp
 	dppp := unit.Dp(1.0 / ppdp)
-	insets := system.Insets{
+	insets := Insets{
 		Top:    unit.Dp(w.insets.top) * dppp,
 		Bottom: unit.Dp(w.insets.bottom) * dppp,
 		Left:   unit.Dp(w.insets.left) * dppp,
 		Right:  unit.Dp(w.insets.right) * dppp,
 	}
 	w.callbacks.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now:    time.Now(),
 			Size:   w.config.Size,
 			Insets: insets,

app/os_ios.go

@@ -156,13 +156,13 @@ func (w *window) draw(sync bool) {
 	}
 	dppp := unit.Dp(1. / m.PxPerDp)
 	w.w.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now: time.Now(),
 			Size: image.Point{
 				X: int(params.width + .5),
 				Y: int(params.height + .5),
 			},
-			Insets: system.Insets{
+			Insets: Insets{
 				Top:    unit.Dp(params.top) * dppp,
 				Bottom: unit.Dp(params.bottom) * dppp,
 				Left:   unit.Dp(params.left) * dppp,

app/os_js.go

@@ -666,7 +666,7 @@ func (w *window) draw(sync bool) {
 	}
 
 	w.w.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now:    time.Now(),
 			Size:   size,
 			Insets: insets,
@@ -676,10 +676,10 @@ func (w *window) draw(sync bool) {
 	})
 }
 
-func (w *window) getConfig() (image.Point, system.Insets, unit.Metric) {
+func (w *window) getConfig() (image.Point, Insets, unit.Metric) {
 	invscale := unit.Dp(1. / w.scale)
 	return image.Pt(w.config.Size.X, w.config.Size.Y),
-		system.Insets{
+		Insets{
 			Bottom: unit.Dp(w.inset.Y) * invscale,
 			Right:  unit.Dp(w.inset.X) * invscale,
 		}, unit.Metric{

app/os_macos.go

@@ -777,7 +777,7 @@ func (w *window) draw() {
 	cfg := configFor(w.scale)
 	w.setStage(system.StageRunning)
 	w.w.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now:    time.Now(),
 			Size:   w.config.Size,
 			Metric: cfg,

app/os_wayland.go

@@ -1712,7 +1712,7 @@ func (w *window) draw() {
 		C.wl_callback_add_listener(w.lastFrameCallback, &C.gio_callback_listener, unsafe.Pointer(w.surf))
 	}
 	w.w.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now:    time.Now(),
 			Size:   w.config.Size,
 			Metric: cfg,

app/os_windows.go

@@ -621,7 +621,7 @@ func (w *window) draw(sync bool) {
 	dpi := windows.GetWindowDPI(w.hwnd)
 	cfg := configForDPI(dpi)
 	w.w.Event(frameEvent{
-		FrameEvent: system.FrameEvent{
+		FrameEvent: FrameEvent{
 			Now:    time.Now(),
 			Size:   w.config.Size,
 			Metric: cfg,

app/os_x11.go

@@ -458,7 +458,7 @@ loop:
 
 		if (anim || syn) && w.config.Size.X != 0 && w.config.Size.Y != 0 {
 			w.w.Event(frameEvent{
-				FrameEvent: system.FrameEvent{
+				FrameEvent: FrameEvent{
 					Now:    time.Now(),
 					Size:   w.config.Size,
 					Metric: w.metric,

app/window.go

@@ -994,7 +994,7 @@ 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) (size, offset image.Point) {
+func (w *Window) decorate(d driver, e FrameEvent, o *op.Ops) (size, offset image.Point) {
 	if !w.fallbackDecorate() {
 		return e.Size, image.Pt(0, 0)
 	}