diff --git a/app/app.go b/app/app.go
index 84cf3828..e4b4e4c6 100644
--- a/app/app.go
+++ b/app/app.go
@@ -4,66 +4,14 @@ package app
 
 import (
 	"errors"
-	"image"
 	"math"
 	"os"
 	"strings"
 	"time"
 
-	"gioui.org/op"
 	"gioui.org/unit"
 )
 
-// A FrameEvent asks for a new frame in the form of a list of
-// operations.
-type FrameEvent struct {
-	Config Config
-	// Size is the dimensions of the window.
-	Size image.Point
-	// Insets is the insets to apply.
-	Insets Insets
-	// Frame replaces the window's frame with the new
-	// frame.
-	Frame func(frame *op.Ops)
-	// Whether this draw is system generated and needs a complete
-	// frame before proceeding.
-	sync bool
-}
-
-// DestroyEvent is the last event sent through
-// a window event channel.
-type DestroyEvent struct {
-	// Err is nil for normal window closures. If a
-	// window is prematurely closed, Err is the cause.
-	Err error
-}
-
-// Insets is the space taken up by
-// system decoration such as translucent
-// system bars and software keyboards.
-type Insets struct {
-	Top, Bottom, Left, Right unit.Value
-}
-
-// A StageEvent is generated whenever the stage of a
-// Window changes.
-type StageEvent struct {
-	Stage Stage
-}
-
-// CommandEvent is a system event.
-type CommandEvent struct {
-	Type CommandType
-	// Suppress the default action of the command.
-	Cancel bool
-}
-
-// Stage of a Window.
-type Stage uint8
-
-// CommandType is the type of a CommandEvent.
-type CommandType uint8
-
 type windowRendezvous struct {
 	in   chan windowAndOptions
 	out  chan windowAndOptions
@@ -75,20 +23,6 @@ type windowAndOptions struct {
 	opts   *windowOptions
 }
 
-const (
-	// StagePaused is the Stage for inactive Windows.
-	// Inactive Windows don't receive FrameEvents.
-	StagePaused Stage = iota
-	// StateRunning is for active Windows.
-	StageRunning
-)
-
-const (
-	// CommandBack is the command for a back action
-	// such as the Android back button.
-	CommandBack CommandType = iota
-)
-
 const (
 	inchPrDp = 1.0 / 160
 	mmPrDp   = 25.4 / 160
@@ -109,17 +43,6 @@ const (
 // Set with the go linker flag -X.
 var extraArgs string
 
-func (l Stage) String() string {
-	switch l {
-	case StagePaused:
-		return "StagePaused"
-	case StageRunning:
-		return "StageRunning"
-	default:
-		panic("unexpected Stage value")
-	}
-}
-
 func init() {
 	if extraArgs != "" {
 		args := strings.Split(extraArgs, "|")
@@ -149,8 +72,8 @@ func Main() {
 	main()
 }
 
-// Config implements the layout.Config interface.
-type Config struct {
+// config implements the system.Config interface.
+type config struct {
 	// Device pixels per dp.
 	pxPerDp float32
 	// Device pixels per sp.
@@ -158,11 +81,11 @@ type Config struct {
 	now     time.Time
 }
 
-func (c *Config) Now() time.Time {
+func (c *config) Now() time.Time {
 	return c.now
 }
 
-func (c *Config) Px(v unit.Value) int {
+func (c *config) Px(v unit.Value) int {
 	var r float32
 	switch v.U {
 	case unit.UnitPx:
@@ -202,8 +125,3 @@ func newWindowRendezvous() *windowRendezvous {
 	}()
 	return wr
 }
-
-func (_ FrameEvent) ImplementsEvent()    {}
-func (_ StageEvent) ImplementsEvent()    {}
-func (_ *CommandEvent) ImplementsEvent() {}
-func (_ DestroyEvent) ImplementsEvent()  {}
diff --git a/app/os_android.go b/app/os_android.go
index 34820e96..5646cc2f 100644
--- a/app/os_android.go
+++ b/app/os_android.go
@@ -27,6 +27,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 	"gioui.org/unit"
 )
 
@@ -37,9 +38,9 @@ type window struct {
 
 	dpi       int
 	fontScale float32
-	insets    Insets
+	insets    system.Insets
 
-	stage   Stage
+	stage   system.Stage
 	started bool
 
 	mu        sync.Mutex
@@ -112,7 +113,7 @@ func onCreateView(env *C.JNIEnv, class C.jclass, view C.jobject) C.jlong {
 	handle := C.jlong(view)
 	views[handle] = w
 	w.loadConfig(env, class)
-	w.setStage(StagePaused)
+	w.setStage(system.StagePaused)
 	return handle
 }
 
@@ -129,7 +130,7 @@ func onDestroyView(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 func onStopView(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 	w := views[handle]
 	w.started = false
-	w.setStage(StagePaused)
+	w.setStage(system.StagePaused)
 }
 
 //export onStartView
@@ -147,7 +148,7 @@ func onSurfaceDestroyed(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 	w.mu.Lock()
 	w.win = nil
 	w.mu.Unlock()
-	w.setStage(StagePaused)
+	w.setStage(system.StagePaused)
 }
 
 //export onSurfaceChanged
@@ -171,7 +172,7 @@ func onLowMemory() {
 func onConfigurationChanged(env *C.JNIEnv, class C.jclass, view C.jlong) {
 	w := views[view]
 	w.loadConfig(env, class)
-	if w.stage >= StageRunning {
+	if w.stage >= system.StageRunning {
 		w.draw(true)
 	}
 }
@@ -182,7 +183,7 @@ func onFrameCallback(env *C.JNIEnv, class C.jclass, view C.jlong, nanos C.jlong)
 	if !exist {
 		return
 	}
-	if w.stage < StageRunning {
+	if w.stage < system.StageRunning {
 		return
 	}
 	w.mu.Lock()
@@ -199,7 +200,7 @@ func onFrameCallback(env *C.JNIEnv, class C.jclass, view C.jlong, nanos C.jlong)
 //export onBack
 func onBack(env *C.JNIEnv, class C.jclass, view C.jlong) C.jboolean {
 	w := views[view]
-	ev := &CommandEvent{Type: CommandBack}
+	ev := &system.CommandEvent{Type: system.CommandBack}
 	w.event(ev)
 	if ev.Cancel {
 		return C.JNI_TRUE
@@ -216,13 +217,13 @@ func onFocusChange(env *C.JNIEnv, class C.jclass, view C.jlong, focus C.jboolean
 //export onWindowInsets
 func onWindowInsets(env *C.JNIEnv, class C.jclass, view C.jlong, top, right, bottom, left C.jint) {
 	w := views[view]
-	w.insets = Insets{
+	w.insets = system.Insets{
 		Top:    unit.Px(float32(top)),
 		Right:  unit.Px(float32(right)),
 		Bottom: unit.Px(float32(bottom)),
 		Left:   unit.Px(float32(left)),
 	}
-	if w.stage >= StageRunning {
+	if w.stage >= system.StageRunning {
 		w.draw(true)
 	}
 }
@@ -233,16 +234,16 @@ func (w *window) setVisible() {
 	if width == 0 || height == 0 {
 		return
 	}
-	w.setStage(StageRunning)
+	w.setStage(system.StageRunning)
 	w.draw(true)
 }
 
-func (w *window) setStage(stage Stage) {
+func (w *window) setStage(stage system.Stage) {
 	if stage == w.stage {
 		return
 	}
 	w.stage = stage
-	w.event(StageEvent{stage})
+	w.event(system.StageEvent{stage})
 }
 
 func (w *window) nativeWindow(visID int) (*C.ANativeWindow, int, int) {
@@ -296,16 +297,18 @@ func (w *window) draw(sync bool) {
 		return
 	}
 	ppdp := float32(w.dpi) * inchPrDp
-	w.event(FrameEvent{
-		Size: image.Point{
-			X: int(width),
-			Y: int(height),
-		},
-		Insets: w.insets,
-		Config: Config{
-			pxPerDp: ppdp,
-			pxPerSp: w.fontScale * ppdp,
-			now:     time.Now(),
+	w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: int(width),
+				Y: int(height),
+			},
+			Insets: w.insets,
+			Config: &config{
+				pxPerDp: ppdp,
+				pxPerSp: w.fontScale * ppdp,
+				now:     time.Now(),
+			},
 		},
 		sync: sync,
 	})
diff --git a/app/os_ios.go b/app/os_ios.go
index 2eca3144..84e2f883 100644
--- a/app/os_ios.go
+++ b/app/os_ios.go
@@ -25,6 +25,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 	"gioui.org/unit"
 )
 
@@ -61,7 +62,7 @@ func onCreate(view C.CFTypeRef) {
 	w.layer = C.CFTypeRef(layerFactory())
 	C.gio_addLayerToView(view, w.layer)
 	views[view] = w
-	w.w.event(StageEvent{StagePaused})
+	w.w.event(system.StageEvent{Stage: system.StagePaused})
 }
 
 //export onDraw
@@ -74,27 +75,29 @@ func onDraw(view C.CFTypeRef, dpi, sdpi, width, height C.CGFloat, sync C.int, to
 	w.visible.Store(true)
 	C.gio_updateView(view, w.layer)
 	if !wasVisible {
-		w.w.event(StageEvent{StageRunning})
+		w.w.event(system.StageEvent{Stage: system.StageRunning})
 	}
 	isSync := false
 	if sync != 0 {
 		isSync = true
 	}
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: int(width + .5),
-			Y: int(height + .5),
-		},
-		Insets: Insets{
-			Top:    unit.Px(float32(top)),
-			Right:  unit.Px(float32(right)),
-			Bottom: unit.Px(float32(bottom)),
-			Left:   unit.Px(float32(left)),
-		},
-		Config: Config{
-			pxPerDp: float32(dpi) * inchPrDp,
-			pxPerSp: float32(sdpi) * inchPrDp,
-			now:     time.Now(),
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: int(width + .5),
+				Y: int(height + .5),
+			},
+			Insets: system.Insets{
+				Top:    unit.Px(float32(top)),
+				Right:  unit.Px(float32(right)),
+				Bottom: unit.Px(float32(bottom)),
+				Left:   unit.Px(float32(left)),
+			},
+			Config: &config{
+				pxPerDp: float32(dpi) * inchPrDp,
+				pxPerSp: float32(sdpi) * inchPrDp,
+				now:     time.Now(),
+			},
 		},
 		sync: isSync,
 	})
@@ -104,14 +107,14 @@ func onDraw(view C.CFTypeRef, dpi, sdpi, width, height C.CGFloat, sync C.int, to
 func onStop(view C.CFTypeRef) {
 	w := views[view]
 	w.visible.Store(false)
-	w.w.event(StageEvent{StagePaused})
+	w.w.event(system.StageEvent{Stage: system.StagePaused})
 }
 
 //export onDestroy
 func onDestroy(view C.CFTypeRef) {
 	w := views[view]
 	delete(views, view)
-	w.w.event(DestroyEvent{})
+	w.w.event(system.DestroyEvent{})
 	C.gio_removeLayer(w.layer)
 	C.CFRelease(w.layer)
 	w.layer = 0
diff --git a/app/os_js.go b/app/os_js.go
index d3fbaa63..0432089b 100644
--- a/app/os_js.go
+++ b/app/os_js.go
@@ -11,6 +11,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 )
 
 type window struct {
@@ -53,7 +54,7 @@ func createWindow(win *Window, opts *windowOptions) error {
 	go func() {
 		w.w.setDriver(w)
 		w.focus()
-		w.w.event(StageEvent{StageRunning})
+		w.w.event(system.StageEvent{Stage: system.StageRunning})
 		w.draw(true)
 		select {}
 		w.cleanup()
@@ -338,24 +339,26 @@ func (w *window) showTextInput(show bool) {
 
 func (w *window) draw(sync bool) {
 	width, height, scale, cfg := w.config()
-	if cfg == (Config{}) {
+	if cfg == (config{}) {
 		return
 	}
 	w.mu.Lock()
 	w.scale = float32(scale)
 	w.mu.Unlock()
 	cfg.now = time.Now()
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: width,
-			Y: height,
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: width,
+				Y: height,
+			},
+			Config: &cfg,
 		},
-		Config: cfg,
-		sync:   sync,
+		sync: sync,
 	})
 }
 
-func (w *window) config() (int, int, float32, Config) {
+func (w *window) config() (int, int, float32, config) {
 	rect := w.cnv.Call("getBoundingClientRect")
 	width, height := rect.Get("width").Float(), rect.Get("height").Float()
 	scale := w.window.Get("devicePixelRatio").Float()
@@ -368,7 +371,7 @@ func (w *window) config() (int, int, float32, Config) {
 		w.cnv.Set("height", ih)
 	}
 	const ppdp = 96 * inchPrDp * monitorScale
-	return iw, ih, float32(scale), Config{
+	return iw, ih, float32(scale), config{
 		pxPerDp: ppdp * float32(scale),
 		pxPerSp: ppdp * float32(scale),
 	}
diff --git a/app/os_macos.go b/app/os_macos.go
index e4103f14..8d125225 100644
--- a/app/os_macos.go
+++ b/app/os_macos.go
@@ -4,13 +4,6 @@
 
 package app
 
-/*
-#cgo CFLAGS: -DGL_SILENCE_DEPRECATION -Werror -Wno-deprecated-declarations -fmodules -fobjc-arc -x objective-c
-
-#include <AppKit/AppKit.h>
-#include "os_macos.h"
-*/
-import "C"
 import (
 	"errors"
 	"image"
@@ -22,8 +15,17 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 )
 
+/*
+#cgo CFLAGS: -DGL_SILENCE_DEPRECATION -Werror -Wno-deprecated-declarations -fmodules -fobjc-arc -x objective-c
+
+#include <AppKit/AppKit.h>
+#include "os_macos.h"
+*/
+import "C"
+
 func init() {
 	// Darwin requires that UI operations happen on the main thread only.
 	runtime.LockOSThread()
@@ -32,7 +34,7 @@ func init() {
 type window struct {
 	view  C.CFTypeRef
 	w     *Window
-	stage Stage
+	stage system.Stage
 	ppdp  float32
 	scale float32
 }
@@ -89,12 +91,12 @@ func (w *window) setAnimating(anim bool) {
 	C.gio_setAnimating(w.view, animb)
 }
 
-func (w *window) setStage(stage Stage) {
+func (w *window) setStage(stage system.Stage) {
 	if stage == w.stage {
 		return
 	}
 	w.stage = stage
-	w.w.event(StageEvent{stage})
+	w.w.event(system.StageEvent{Stage: stage})
 }
 
 // Use a top level func for onFrameCallback to avoid
@@ -197,14 +199,16 @@ func (w *window) draw(sync bool) {
 	height := int(hf*w.scale + .5)
 	cfg := configFor(w.ppdp, w.scale)
 	cfg.now = time.Now()
-	w.setStage(StageRunning)
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: width,
-			Y: height,
+	w.setStage(system.StageRunning)
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: width,
+				Y: height,
+			},
+			Config: &cfg,
 		},
-		Config: cfg,
-		sync:   sync,
+		sync: sync,
 	})
 }
 
@@ -217,9 +221,9 @@ func getPixelsPerDp(scale float32) float32 {
 	return ppdp / scale
 }
 
-func configFor(ppdp, scale float32) Config {
+func configFor(ppdp, scale float32) config {
 	ppdp = ppdp * scale
-	return Config{
+	return config{
 		pxPerDp: ppdp,
 		pxPerSp: ppdp,
 	}
@@ -230,7 +234,7 @@ func gio_onTerminate(view C.CFTypeRef) {
 	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		delete(views, view)
-		w.w.event(DestroyEvent{})
+		w.w.event(system.DestroyEvent{})
 	})
 }
 
@@ -238,7 +242,7 @@ func gio_onTerminate(view C.CFTypeRef) {
 func gio_onHide(view C.CFTypeRef) {
 	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
-		w.setStage(StagePaused)
+		w.setStage(system.StagePaused)
 	})
 }
 
@@ -246,7 +250,7 @@ func gio_onHide(view C.CFTypeRef) {
 func gio_onShow(view C.CFTypeRef) {
 	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
-		w.setStage(StageRunning)
+		w.setStage(system.StageRunning)
 	})
 }
 
diff --git a/app/os_wayland.go b/app/os_wayland.go
index 5cf77168..1019791e 100644
--- a/app/os_wayland.go
+++ b/app/os_wayland.go
@@ -21,6 +21,7 @@ import (
 	"gioui.org/internal/fling"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 	syscall "golang.org/x/sys/unix"
 )
 
@@ -116,7 +117,7 @@ type window struct {
 		dir            f32.Point
 	}
 
-	stage             Stage
+	stage             system.Stage
 	dead              bool
 	pendingErr        error
 	lastFrameCallback *C.struct_wl_callback
@@ -302,7 +303,7 @@ func gio_onXdgSurfaceConfigure(data unsafe.Pointer, wmSurf *C.struct_xdg_surface
 	w.serial = serial
 	w.needAck = true
 	w.mu.Unlock()
-	w.setStage(StageRunning)
+	w.setStage(system.StageRunning)
 	w.draw(true)
 }
 
@@ -772,7 +773,7 @@ loop:
 			break
 		}
 		if w.dead {
-			w.w.event(DestroyEvent{Err: w.pendingErr})
+			w.w.event(system.DestroyEvent{Err: w.pendingErr})
 			break
 		}
 		// Clear poll events.
@@ -979,16 +980,16 @@ func (w *window) updateOutputs() {
 	}
 	w.mu.Unlock()
 	if !found {
-		w.setStage(StagePaused)
+		w.setStage(system.StagePaused)
 	} else {
-		w.setStage(StageRunning)
+		w.setStage(system.StageRunning)
 		w.draw(true)
 	}
 }
 
-func (w *window) config() (int, int, Config) {
+func (w *window) config() (int, int, config) {
 	width, height := w.width*w.scale, w.height*w.scale
-	return width, height, Config{
+	return width, height, config{
 		pxPerDp: w.ppdp * float32(w.scale),
 		pxPerSp: w.ppsp * float32(w.scale),
 	}
@@ -1015,7 +1016,7 @@ func (w *window) draw(sync bool) {
 		return
 	}
 	width, height, cfg := w.config()
-	if cfg == (Config{}) {
+	if cfg == (config{}) {
 		return
 	}
 	if animating && w.lastFrameCallback == nil {
@@ -1024,22 +1025,24 @@ func (w *window) draw(sync bool) {
 		C.gio_wl_callback_add_listener(w.lastFrameCallback, unsafe.Pointer(w.surf))
 	}
 	cfg.now = time.Now()
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: width,
-			Y: height,
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: width,
+				Y: height,
+			},
+			Config: &cfg,
 		},
-		Config: cfg,
-		sync:   sync,
+		sync: sync,
 	})
 }
 
-func (w *window) setStage(s Stage) {
+func (w *window) setStage(s system.Stage) {
 	if s == w.stage {
 		return
 	}
 	w.stage = s
-	w.w.event(StageEvent{s})
+	w.w.event(system.StageEvent{s})
 }
 
 func (w *window) display() *C.struct_wl_display {
diff --git a/app/os_windows.go b/app/os_windows.go
index 0f9e24ee..7520d7ae 100644
--- a/app/os_windows.go
+++ b/app/os_windows.go
@@ -17,6 +17,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 )
 
 var winMap = make(map[syscall.Handle]*window)
@@ -60,7 +61,7 @@ type window struct {
 	w      *Window
 	width  int
 	height int
-	stage  Stage
+	stage  system.Stage
 	dead   bool
 
 	mu        sync.Mutex
@@ -183,7 +184,7 @@ func createWindow(window *Window, opts *windowOptions) error {
 		defer delete(winMap, w.hwnd)
 		w.w = window
 		w.w.setDriver(w)
-		defer w.w.event(DestroyEvent{})
+		defer w.w.event(system.DestroyEvent{})
 		showWindow(w.hwnd, _SW_SHOWDEFAULT)
 		setForegroundWindow(w.hwnd)
 		setFocus(w.hwnd)
@@ -326,9 +327,9 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 	case _WM_SIZE:
 		switch wParam {
 		case _SIZE_MINIMIZED:
-			w.setStage(StagePaused)
+			w.setStage(system.StagePaused)
 		case _SIZE_MAXIMIZED, _SIZE_RESTORED:
-			w.setStage(StageRunning)
+			w.setStage(system.StageRunning)
 			w.draw(true)
 		}
 	}
@@ -395,9 +396,9 @@ func (w *window) postRedraw() {
 	}
 }
 
-func (w *window) setStage(s Stage) {
+func (w *window) setStage(s system.Stage) {
 	w.stage = s
-	w.w.event(StageEvent{s})
+	w.w.event(system.StageEvent{Stage: s})
 }
 
 func (w *window) draw(sync bool) {
@@ -407,13 +408,15 @@ func (w *window) draw(sync bool) {
 	w.height = int(r.bottom - r.top)
 	cfg := configForDC(w.hdc)
 	cfg.now = time.Now()
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: w.width,
-			Y: w.height,
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: w.width,
+				Y: w.height,
+			},
+			Config: &cfg,
 		},
-		Config: cfg,
-		sync:   sync,
+		sync: sync,
 	})
 }
 
@@ -474,14 +477,14 @@ func convertKeyCode(code uintptr) (rune, bool) {
 	return r, true
 }
 
-func configForDC(hdc syscall.Handle) Config {
+func configForDC(hdc syscall.Handle) config {
 	dpi := getDeviceCaps(hdc, _LOGPIXELSX)
 	ppdp := float32(dpi) * inchPrDp * monitorScale
 	// Force a minimum density to keep text legible and to handle bogus output geometry.
 	if ppdp < minDensity {
 		ppdp = minDensity
 	}
-	return Config{
+	return config{
 		pxPerDp: ppdp,
 		pxPerSp: ppdp,
 	}
diff --git a/app/window.go b/app/window.go
index ac4a275a..42ac61cd 100644
--- a/app/window.go
+++ b/app/window.go
@@ -12,6 +12,7 @@ import (
 	"gioui.org/app/internal/input"
 	"gioui.org/io/event"
 	"gioui.org/io/profile"
+	"gioui.org/io/system"
 	"gioui.org/op"
 	"gioui.org/unit"
 )
@@ -24,6 +25,12 @@ type windowOptions struct {
 	Title         string
 }
 
+type frameEvent struct {
+	system.FrameEvent
+
+	sync bool
+}
+
 // Window represents an operating system window.
 type Window struct {
 	driver    *window
@@ -37,7 +44,7 @@ type Window struct {
 	invalidates chan struct{}
 	frames      chan *op.Ops
 
-	stage        Stage
+	stage        system.Stage
 	animating    bool
 	hasNextFrame bool
 	nextFrame    time.Time
@@ -170,7 +177,7 @@ func (w *Window) updateAnimation() {
 		w.delayedDraw.Stop()
 		w.delayedDraw = nil
 	}
-	if w.stage >= StageRunning && w.hasNextFrame {
+	if w.stage >= system.StageRunning && w.hasNextFrame {
 		if dt := time.Until(w.nextFrame); dt <= 0 {
 			animate = true
 		} else {
@@ -210,10 +217,10 @@ func (w *Window) waitAck() {
 func (w *Window) destroy(err error) {
 	// Ack the current event.
 	w.ack <- struct{}{}
-	w.out <- DestroyEvent{err}
+	w.out <- system.DestroyEvent{Err: err}
 	for e := range w.in {
 		w.ack <- struct{}{}
-		if _, ok := e.(DestroyEvent); ok {
+		if _, ok := e.(system.DestroyEvent); ok {
 			return
 		}
 	}
@@ -223,7 +230,7 @@ func (w *Window) run(opts *windowOptions) {
 	defer close(w.in)
 	defer close(w.out)
 	if err := createWindow(w, opts); err != nil {
-		w.out <- DestroyEvent{err}
+		w.out <- system.DestroyEvent{Err: err}
 		return
 	}
 	for {
@@ -240,9 +247,9 @@ func (w *Window) run(opts *windowOptions) {
 			w.updateAnimation()
 		case e := <-w.in:
 			switch e2 := e.(type) {
-			case StageEvent:
+			case system.StageEvent:
 				if w.gpu != nil {
-					if e2.Stage < StageRunning {
+					if e2.Stage < system.StageRunning {
 						w.gpu.Release()
 						w.gpu = nil
 					} else {
@@ -253,18 +260,18 @@ func (w *Window) run(opts *windowOptions) {
 				w.updateAnimation()
 				w.out <- e
 				w.waitAck()
-			case FrameEvent:
+			case frameEvent:
 				if e2.Size == (image.Point{}) {
 					panic(errors.New("internal error: zero-sized Draw"))
 				}
-				if w.stage < StageRunning {
+				if w.stage < system.StageRunning {
 					// No drawing if not visible.
 					break
 				}
 				w.drawStart = time.Now()
 				w.hasNextFrame = false
 				e2.Frame = w.update
-				w.out <- e2
+				w.out <- e2.FrameEvent
 				var frame *op.Ops
 				// Wait for either a frame or the ack event,
 				// which meant that the client didn't draw.
@@ -303,12 +310,12 @@ func (w *Window) run(opts *windowOptions) {
 						return
 					}
 				}
-			case *CommandEvent:
+			case *system.CommandEvent:
 				w.out <- e
 				w.waitAck()
 			case driverEvent:
 				w.driver = e2.driver
-			case DestroyEvent:
+			case system.DestroyEvent:
 				w.out <- e2
 				w.ack <- struct{}{}
 				return
diff --git a/io/system/system.go b/io/system/system.go
new file mode 100644
index 00000000..c2d8f168
--- /dev/null
+++ b/io/system/system.go
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// Package system contains events usually handled at the top-level
+// program level.
+package system
+
+import (
+	"image"
+	"time"
+
+	"gioui.org/op"
+	"gioui.org/unit"
+)
+
+// A FrameEvent asks for a new frame in the form of a list of
+// operations.
+type FrameEvent struct {
+	Config Config
+	// Size is the dimensions of the window.
+	Size image.Point
+	// Insets is the insets to apply.
+	Insets Insets
+	// Frame replaces the window's frame with the new
+	// frame.
+	Frame func(frame *op.Ops)
+	// Whether this draw is system generated and needs a complete
+	// frame before proceeding.
+	sync bool
+}
+
+// Config define the essential properties of
+// the environment.
+type Config interface {
+	// Now returns the current animation time.
+	Now() time.Time
+
+	unit.Converter
+}
+
+// DestroyEvent is the last event sent through
+// a window event channel.
+type DestroyEvent struct {
+	// Err is nil for normal window closures. If a
+	// window is prematurely closed, Err is the cause.
+	Err error
+}
+
+// Insets is the space taken up by
+// system decoration such as translucent
+// system bars and software keyboards.
+type Insets struct {
+	Top, Bottom, Left, Right unit.Value
+}
+
+// A StageEvent is generated whenever the stage of a
+// Window changes.
+type StageEvent struct {
+	Stage Stage
+}
+
+// CommandEvent is a system event.
+type CommandEvent struct {
+	Type CommandType
+	// Suppress the default action of the command.
+	Cancel bool
+}
+
+// Stage of a Window.
+type Stage uint8
+
+// CommandType is the type of a CommandEvent.
+type CommandType uint8
+
+const (
+	// StagePaused is the Stage for inactive Windows.
+	// Inactive Windows don't receive FrameEvents.
+	StagePaused Stage = iota
+	// StateRunning is for active Windows.
+	StageRunning
+)
+
+const (
+	// CommandBack is the command for a back action
+	// such as the Android back button.
+	CommandBack CommandType = iota
+)
+
+func (l Stage) String() string {
+	switch l {
+	case StagePaused:
+		return "StagePaused"
+	case StageRunning:
+		return "StageRunning"
+	default:
+		panic("unexpected Stage value")
+	}
+}
+
+func (_ FrameEvent) ImplementsEvent()    {}
+func (_ StageEvent) ImplementsEvent()    {}
+func (_ *CommandEvent) ImplementsEvent() {}
+func (_ DestroyEvent) ImplementsEvent()  {}
diff --git a/layout/layout.go b/layout/layout.go
index 3ace2667..f5160893 100644
--- a/layout/layout.go
+++ b/layout/layout.go
@@ -4,9 +4,9 @@ package layout
 
 import (
 	"image"
-	"time"
 
 	"gioui.org/io/event"
+	"gioui.org/io/system"
 	"gioui.org/op"
 	"gioui.org/unit"
 )
@@ -53,20 +53,11 @@ type Context struct {
 	// operation.
 	Dimensions Dimensions
 
-	Config
+	system.Config
 	event.Queue
 	*op.Ops
 }
 
-// Config define the essential properties of
-// the environment.
-type Config interface {
-	// Now returns the current animation time.
-	Now() time.Time
-
-	unit.Converter
-}
-
 const (
 	Start Alignment = iota
 	End
@@ -104,7 +95,7 @@ func (s *Context) Layout(cs Constraints, w Widget) Dimensions {
 
 // Reset the context. The constraints' minimum and maximum values are
 // set to the size.
-func (c *Context) Reset(cfg Config, size image.Point) {
+func (c *Context) Reset(cfg system.Config, size image.Point) {
 	c.Constraints = RigidConstraints(size)
 	c.Dimensions = Dimensions{}
 	c.Config = cfg