ebiten: Add IsWindowBeingClosed / SetWindowClosingHandled / IsWindowClosingHandled

IsWindowBeingClosed reports whether the window is being closed by
the user.

SetWindowClosingHandled sets whether the window closing is handled
or not. If the state is true, the window is not closed immediately
by the user and the game can handle the closing state. In this case,
the Update function should return an error in order to end the game.

This change also adds examples/windowclosing.

Closes #1574

examples/windowclosing/main.go

@@ -0,0 +1,67 @@
+// Copyright 2021 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build example
+
+package main
+
+import (
+	"errors"
+	"log"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
+	"github.com/hajimehoshi/ebiten/v2/inpututil"
+)
+
+var regularTermination = errors.New("regular termination")
+
+type Game struct {
+	windowClosingHandled bool
+}
+
+func (g *Game) Update() error {
+	if ebiten.IsWindowBeingClosed() {
+		g.windowClosingHandled = true
+	}
+	if g.windowClosingHandled {
+		if inpututil.IsKeyJustPressed(ebiten.KeyY) {
+			return regularTermination
+		}
+		if inpututil.IsKeyJustPressed(ebiten.KeyN) {
+			g.windowClosingHandled = false
+		}
+	}
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	if !g.windowClosingHandled {
+		ebitenutil.DebugPrint(screen, "Try to close this window.")
+		return
+	}
+	ebitenutil.DebugPrint(screen, "Do you really want to close this window? [y/n]")
+}
+
+func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
+	return outsideWidth, outsideHeight
+}
+
+func main() {
+	ebiten.SetWindowClosingHandled(true)
+	ebiten.SetWindowTitle("Window Closing (Ebiten Demo)")
+	if err := ebiten.RunGame(&Game{}); err != nil && err != regularTermination {
+		log.Fatal(err)
+	}
+}

internal/driver/ui.go

@@ -93,4 +93,8 @@ type Window interface {
 	SetIcon(iconImages []image.Image)
 	SetTitle(title string)
 	Restore()
+
+	IsBeingClosed() bool
+	SetClosingHandled(handled bool)
+	IsClosingHandled() bool
 }

internal/glfw/callback_notwindows.go

@@ -23,6 +23,7 @@ import (
 
 var (
 	charModsCallbacks        = map[CharModsCallback]glfw.CharModsCallback{}
+	closeCallbacks           = map[CloseCallback]glfw.CloseCallback{}
 	framebufferSizeCallbacks = map[FramebufferSizeCallback]glfw.FramebufferSizeCallback{}
 	scrollCallbacks          = map[ScrollCallback]glfw.ScrollCallback{}
 	sizeCallbacks            = map[SizeCallback]glfw.SizeCallback{}
@@ -40,6 +41,18 @@ func ToCharModsCallback(cb func(window *Window, char rune, mods ModifierKey)) Ch
 	return id
 }
 
+func ToCloseCallback(cb func(window *Window)) CloseCallback {
+	if cb == nil {
+		return 0
+	}
+	id := CloseCallback(len(closeCallbacks) + 1)
+	var gcb glfw.CloseCallback = func(window *glfw.Window) {
+		cb(theWindows.get(window))
+	}
+	closeCallbacks[id] = gcb
+	return id
+}
+
 func ToFramebufferSizeCallback(cb func(window *Window, width int, height int)) FramebufferSizeCallback {
 	if cb == nil {
 		return 0

internal/glfw/callback_windows.go

@@ -28,6 +28,16 @@ func ToCharModsCallback(cb func(window *Window, char rune, mods ModifierKey)) Ch
 	}))
 }
 
+func ToCloseCallback(cb func(window *Window)) CloseCallback {
+	if cb == nil {
+		return 0
+	}
+	return CloseCallback(windows.NewCallbackCDecl(func(window uintptr) uintptr {
+		cb(theGLFWWindows.get(window))
+		return 0
+	}))
+}
+
 func ToFramebufferSizeCallback(cb func(window *Window, width int, height int)) FramebufferSizeCallback {
 	if cb == nil {
 		return 0

internal/glfw/glfw_notwindows.go

@@ -174,6 +174,11 @@ func (w *Window) SetCursor(cursor *Cursor) {
 	w.w.SetCursor(c)
 }
 
+func (w *Window) SetCloseCallback(cbfun CloseCallback) (previous CloseCallback) {
+	w.w.SetCloseCallback(closeCallbacks[cbfun])
+	return ToCloseCallback(nil) // TODO
+}
+
 func (w *Window) SetFramebufferSizeCallback(cbfun FramebufferSizeCallback) (previous FramebufferSizeCallback) {
 	w.w.SetFramebufferSizeCallback(framebufferSizeCallbacks[cbfun])
 	return ToFramebufferSizeCallback(nil) // TODO
@@ -184,6 +189,10 @@ func (w *Window) SetScrollCallback(cbfun ScrollCallback) (previous ScrollCallbac
 	return ToScrollCallback(nil) // TODO
 }
 
+func (w *Window) SetShouldClose(value bool) {
+	w.w.SetShouldClose(value)
+}
+
 func (w *Window) SetSizeCallback(cbfun SizeCallback) (previous SizeCallback) {
 	w.w.SetSizeCallback(sizeCallbacks[cbfun])
 	prev := w.prevSizeCallback

internal/glfw/glfw_windows.go

@@ -201,6 +201,12 @@ func (w *Window) SetCharModsCallback(cbfun CharModsCallback) (previous CharModsC
 	return ToCharModsCallback(nil) // TODO
 }
 
+func (w *Window) SetCloseCallback(cbfun CloseCallback) (previous CloseCallback) {
+	glfwDLL.call("glfwSetWindowCloseCallback", w.w, uintptr(cbfun))
+	panicError()
+	return ToCloseCallback(nil) // TODO
+}
+
 func (w *Window) SetCursor(cursor *Cursor) {
 	var c uintptr
 	if cursor != nil {
@@ -221,6 +227,15 @@ func (w *Window) SetScrollCallback(cbfun ScrollCallback) (previous ScrollCallbac
 	return ToScrollCallback(nil) // TODO
 }
 
+func (w *Window) SetShouldClose(value bool) {
+	var v uintptr = False
+	if value {
+		v = True
+	}
+	glfwDLL.call("glfwSetWindowShouldClose", w.w, v)
+	panicError()
+}
+
 func (w *Window) SetSizeCallback(cbfun SizeCallback) (previous SizeCallback) {
 	glfwDLL.call("glfwSetWindowSizeCallback", w.w, uintptr(cbfun))
 	panicError()

internal/glfw/type.go

@@ -19,6 +19,7 @@ package glfw
 
 type (
 	CharModsCallback        uintptr
+	CloseCallback           uintptr
 	FramebufferSizeCallback uintptr
 	ScrollCallback          uintptr
 	SizeCallback            uintptr

internal/uidriver/glfw/ui.go

@@ -64,14 +64,16 @@ type UserInterface struct {
 	maxWindowWidthInDP  int
 	maxWindowHeightInDP int
 
-	running             uint32
-	toChangeSize        bool
-	origPosX            int
-	origPosY            int
-	runnableOnUnfocused bool
-	vsync               bool
-	iconImages          []image.Image
-	cursorShape         driver.CursorShape
+	running              uint32
+	toChangeSize         bool
+	origPosX             int
+	origPosY             int
+	runnableOnUnfocused  bool
+	vsync                bool
+	iconImages           []image.Image
+	cursorShape          driver.CursorShape
+	windowClosingHandled bool
+	windowBeingClosed    bool
 
 	// setSizeCallbackEnabled must be accessed from the main thread.
 	setSizeCallbackEnabled bool
@@ -108,6 +110,7 @@ type UserInterface struct {
 	iwindow window
 
 	sizeCallback              glfw.SizeCallback
+	closeCallback             glfw.CloseCallback
 	framebufferSizeCallback   glfw.FramebufferSizeCallback
 	framebufferSizeCallbackCh chan struct{}
 
@@ -476,6 +479,26 @@ func (u *UserInterface) setInitWindowMaximized(maximized bool) {
 	u.m.Unlock()
 }
 
+func (u *UserInterface) isWindowClosingHandled() bool {
+	u.m.Lock()
+	v := u.windowClosingHandled
+	u.m.Unlock()
+	return v
+}
+
+func (u *UserInterface) setWindowClosingHandled(handled bool) {
+	u.m.Lock()
+	u.windowClosingHandled = handled
+	u.m.Unlock()
+}
+
+func (u *UserInterface) isWindowBeingClosed() bool {
+	u.m.Lock()
+	v := u.windowBeingClosed
+	u.m.Unlock()
+	return v
+}
+
 func (u *UserInterface) isInitFocused() bool {
 	u.m.Lock()
 	v := u.initFocused
@@ -724,6 +747,7 @@ func (u *UserInterface) createWindow() error {
 	// TODO: Set icons
 
 	u.registerWindowSetSizeCallback()
+	u.registerWindowCloseCallback()
 
 	return nil
 }
@@ -776,6 +800,23 @@ func (u *UserInterface) registerWindowSetSizeCallback() {
 	u.window.SetSizeCallback(u.sizeCallback)
 }
 
+// registerWindowCloseCallback must be called from the main thread.
+func (u *UserInterface) registerWindowCloseCallback() {
+	if u.closeCallback == 0 {
+		u.closeCallback = glfw.ToCloseCallback(func(_ *glfw.Window) {
+			u.m.Lock()
+			u.windowBeingClosed = true
+			u.m.Unlock()
+
+			if !u.isWindowClosingHandled() {
+				return
+			}
+			u.window.SetShouldClose(false)
+		})
+	}
+	u.window.SetCloseCallback(u.closeCallback)
+}
+
 func (u *UserInterface) init() error {
 	if u.Graphics().IsGL() {
 		glfw.WindowHint(glfw.ClientAPI, glfw.OpenGLAPI)
@@ -1347,6 +1388,10 @@ func (u *UserInterface) ResetForFrame() {
 		u.context.Layout(w, h)
 	}
 	u.input.resetForFrame()
+
+	u.m.Lock()
+	u.windowBeingClosed = false
+	u.m.Unlock()
 }
 
 func (u *UserInterface) MonitorPosition() (int, int) {

internal/uidriver/glfw/window.go

@@ -264,3 +264,15 @@ func (w *window) SetTitle(title string) {
 		return nil
 	})
 }
+
+func (w *window) IsBeingClosed() bool {
+	return w.ui.isWindowBeingClosed()
+}
+
+func (w *window) SetClosingHandled(handled bool) {
+	w.ui.setWindowClosingHandled(handled)
+}
+
+func (w *window) IsClosingHandled() bool {
+	return w.ui.isWindowClosingHandled()
+}

window.go

@@ -315,3 +315,46 @@ func RestoreWindow() {
 		w.Restore()
 	}
 }
+
+// IsWindowBeingClosed returns true when the user is trying to close the window on desktops.
+// As the window is closed immediately by default,
+// you might want to call SetWindowClosingHandled(true) to prevent the window is automatically closed.
+//
+// IsWindowBeingClosed always returns false on other platforms.
+//
+// IsWindowBeingClosed is concurrent-safe.
+func IsWindowBeingClosed() bool {
+	if w := uiDriver().Window(); w != nil {
+		return w.IsBeingClosed()
+	}
+	return false
+}
+
+// SetWindowClosingHandled sets whether the window closing is handled or not on desktops. The default state is false.
+//
+// If the window closing is handled, the window is not closed immediately and
+// the game can know whether the window is begin closed or not by IsWindowBeingClosed.
+// In this case, the window is not closed automatically.
+// To end the game, you have to return an error value at the Game's Update function.
+//
+// SetWindowClosingHandled works only on desktops.
+// SetWindowClosingHandled does nothing on other platforms.
+//
+// SetWindowClosingHandled is concurrent-safe.
+func SetWindowClosingHandled(handled bool) {
+	if w := uiDriver().Window(); w != nil {
+		w.SetClosingHandled(handled)
+	}
+}
+
+// IsWindowClosingHandled reports whether the window closing is handled or not on desktops by SetWindowClosingHandled.
+//
+// IsWindowClosingHandled always returns false on other platforms.
+//
+// IsWindowClosingHandled is concurrent-safe.
+func IsWindowClosingHandled() bool {
+	if w := uiDriver().Window(); w != nil {
+		return w.IsClosingHandled()
+	}
+	return false
+}