ebiten: add RunGameOptions.SingleThread and deprecate ebitenginesinglethread build tag

Closes #2830

doc.go

@@ -109,7 +109,8 @@
 // `ebitenginesinglethread` disables Ebitengine's thread safety to unlock maximum performance. If you use this you will have
 // to manage threads yourself. Functions like IsKeyPressed will no longer be concurrent-safe with this build tag.
 // They must be called from the main thread or the same goroutine as the given game's callback functions like Update
-// to RunGame. `ebitenginesinglethread` works only with desktops.
+// `ebitenginesinglethread` works only with desktops.
+// `ebitenginesinglethread` was deprecated as of v2.7. Use RunGameOptions.SingleThread instead.
 //
 // `microsoftgdk` is for Microsoft GDK (e.g. Xbox).
 //

internal/ui/run_notsinglethread.go

@@ -12,55 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build !android && !ios && !js && !ebitenginesinglethread && !ebitensinglethread
+//go:build !ebitenginesinglethread && !ebitensinglethread
 
 package ui
 
-import (
+const buildTagSingleThread = false
-	stdcontext "context"
-
-	"golang.org/x/sync/errgroup"
-
-	"github.com/hajimehoshi/ebiten/v2/internal/graphicscommand"
-	"github.com/hajimehoshi/ebiten/v2/internal/thread"
-)
-
-func (u *UserInterface) run(game Game, options *RunOptions) error {
-	u.mainThread = thread.NewOSThread()
-	u.renderThread = thread.NewOSThread()
-	graphicscommand.SetRenderThread(u.renderThread)
-
-	// Set the running state true after the main thread is set, and before initOnMainThread is called (#2742).
-	// TODO: As the existance of the main thread is the same as the value of `running`, this is redundant.
-	// Make `mainThread` atomic and remove `running` if possible.
-	u.setRunning(true)
-	defer u.setRunning(false)
-
-	u.context = newContext(game)
-
-	if err := u.initOnMainThread(options); err != nil {
-		return err
-	}
-
-	ctx, cancel := stdcontext.WithCancel(stdcontext.Background())
-	defer cancel()
-
-	var wg errgroup.Group
-
-	// Run the render thread.
-	wg.Go(func() error {
-		defer cancel()
-		_ = u.renderThread.Loop(ctx)
-		return nil
-	})
-
-	// Run the game thread.
-	wg.Go(func() error {
-		defer cancel()
-		return u.loopGame()
-	})
-
-	// Run the main thread.
-	_ = u.mainThread.Loop(ctx)
-	return wg.Wait()
-}

internal/ui/run_singlethread.go

@@ -12,33 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build js || (!android && !ios && (ebitenginesinglethread || ebitensinglethread))
+//go:build ebitenginesinglethread || ebitensinglethread
 
 package ui
 
-import (
+const buildTagSingleThread = true
-	"github.com/hajimehoshi/ebiten/v2/internal/graphicscommand"
-	"github.com/hajimehoshi/ebiten/v2/internal/thread"
-)
-
-func (u *UserInterface) run(game Game, options *RunOptions) error {
-	// Initialize the main thread first so the thread is available at u.run (#809).
-	u.mainThread = thread.NewNoopThread()
-	u.renderThread = thread.NewNoopThread()
-	graphicscommand.SetRenderThread(u.renderThread)
-
-	u.setRunning(true)
-	defer u.setRunning(false)
-
-	u.context = newContext(game)
-
-	if err := u.initOnMainThread(options); err != nil {
-		return err
-	}
-
-	if err := u.loopGame(); err != nil {
-		return err
-	}
-
-	return nil
-}

internal/ui/ui.go

@@ -15,12 +15,16 @@
 package ui
 
 import (
+	stdcontext "context"
 	"errors"
 	"image"
 	"sync"
 	"sync/atomic"
 
+	"golang.org/x/sync/errgroup"
+
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicscommand"
 	"github.com/hajimehoshi/ebiten/v2/internal/mipmap"
 	"github.com/hajimehoshi/ebiten/v2/internal/thread"
 )
@@ -142,6 +146,7 @@ type RunOptions struct {
 	InitUnfocused     bool
 	ScreenTransparent bool
 	SkipTaskbar       bool
+	SingleThread      bool
 }
 
 // InitialWindowPosition returns the position for centering the given second width/height pair within the first width/height pair.
@@ -202,3 +207,65 @@ func (u *UserInterface) isTerminated() bool {
 func (u *UserInterface) setTerminated() {
 	atomic.StoreInt32(&u.terminated, 1)
 }
+
+func (u *UserInterface) runMultiThread(game Game, options *RunOptions) error {
+	u.mainThread = thread.NewOSThread()
+	u.renderThread = thread.NewOSThread()
+	graphicscommand.SetRenderThread(u.renderThread)
+
+	// Set the running state true after the main thread is set, and before initOnMainThread is called (#2742).
+	// TODO: As the existance of the main thread is the same as the value of `running`, this is redundant.
+	// Make `mainThread` atomic and remove `running` if possible.
+	u.setRunning(true)
+	defer u.setRunning(false)
+
+	u.context = newContext(game)
+
+	if err := u.initOnMainThread(options); err != nil {
+		return err
+	}
+
+	ctx, cancel := stdcontext.WithCancel(stdcontext.Background())
+	defer cancel()
+
+	var wg errgroup.Group
+
+	// Run the render thread.
+	wg.Go(func() error {
+		defer cancel()
+		_ = u.renderThread.Loop(ctx)
+		return nil
+	})
+
+	// Run the game thread.
+	wg.Go(func() error {
+		defer cancel()
+		return u.loopGame()
+	})
+
+	// Run the main thread.
+	_ = u.mainThread.Loop(ctx)
+	return wg.Wait()
+}
+
+func (u *UserInterface) runSingleThread(game Game, options *RunOptions) error {
+	// Initialize the main thread first so the thread is available at u.run (#809).
+	u.mainThread = thread.NewNoopThread()
+	u.renderThread = thread.NewNoopThread()
+	graphicscommand.SetRenderThread(u.renderThread)
+
+	u.setRunning(true)
+	defer u.setRunning(false)
+
+	u.context = newContext(game)
+
+	if err := u.initOnMainThread(options); err != nil {
+		return err
+	}
+
+	if err := u.loopGame(); err != nil {
+		return err
+	}
+
+	return nil
+}

internal/ui/ui_glfw.go

@@ -121,7 +121,10 @@ func init() {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	return u.run(game, options)
+	if options.SingleThread || buildTagSingleThread {
+		return u.runSingleThread(game, options)
+	}
+	return u.runMultiThread(game, options)
 }
 
 func (u *UserInterface) init() error {

internal/ui/ui_js.go

@@ -741,7 +741,7 @@ func (u *UserInterface) forceUpdateOnMinimumFPSMode() {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	return u.run(game, options)
+	return u.runSingleThread(game, options)
 }
 
 func (u *UserInterface) initOnMainThread(options *RunOptions) error {

internal/ui/ui_nintendosdk.go

@@ -76,7 +76,10 @@ func (u *UserInterface) init() error {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	return u.run(game, options)
+	if options.SingleThread || buildTagSingleThread {
+		return u.runSingleThread(game, options)
+	}
+	return u.runMultiThread(game, options)
 }
 
 func (u *UserInterface) initOnMainThread(options *RunOptions) error {

internal/ui/ui_playstation5.go

@@ -70,7 +70,10 @@ func (u *UserInterface) init() error {
 }
 
 func (u *UserInterface) Run(game Game, options *RunOptions) error {
-	return u.run(game, options)
+	if options.SingleThread || buildTagSingleThread {
+		return u.runSingleThread(game, options)
+	}
+	return u.runMultiThread(game, options)
 }
 
 func (u *UserInterface) initOnMainThread(options *RunOptions) error {

run.go

@@ -253,6 +253,20 @@ type RunGameOptions struct {
 	//
 	// The default (zero) value is false, which means that an icon is shown on a taskbar.
 	SkipTaskbar bool
+
+	// SingleThread indicates whether the single thread mode is used explicitly or not.
+	// The single thread mode disables Ebitengine's thread safety to unlock maximum performance.
+	// If you use this you will have to manage threads yourself.
+	// Functions like IsKeyPressed will no longer be concurrent-safe with this build tag.
+	// They must be called from the main thread or the same goroutine as the given game's callback functions like Update.
+	//
+	// SingleThread works only with desktops.
+	//
+	// If SingleThread is false, and if the build tag `ebitenginesinglethread` is specified,
+	// the single thread mode is used.
+	//
+	// The default (zero) value is false, which means that the single thread mode is disabled.
+	SingleThread bool
 }
 
 // RunGameWithOptions starts the main loop and runs the game with the specified options.
@@ -672,6 +686,7 @@ func toUIRunOptions(options *RunGameOptions) *ui.RunOptions {
 		InitUnfocused:     options.InitUnfocused,
 		ScreenTransparent: options.ScreenTransparent,
 		SkipTaskbar:       options.SkipTaskbar,
+		SingleThread:      options.SingleThread,
 	}
 }