all: separate the rendering thread from the main thread

Updates #1704
Closes #2512

internal/graphicsdriver/metal/graphics_darwin.go

@@ -17,6 +17,7 @@ package metal
 import (
 	"fmt"
 	"math"
+	"runtime"
 	"sort"
 	"unsafe"
 
@@ -86,7 +87,15 @@ func NewGraphics() (graphicsdriver.Graphics, error) {
 		return nil, fmt.Errorf("metal: mtl.CreateSystemDefaultDevice failed")
 	}
 
-	return &Graphics{}, nil
+	g := &Graphics{}
+
+	if runtime.GOOS != "ios" {
+		// Initializing a Metal device and a layer must be done in the main thread on macOS.
+		if err := g.view.initialize(); err != nil {
+			return nil, err
+		}
+	}
+	return g, nil
 }
 
 func (g *Graphics) Begin() error {
@@ -356,9 +365,12 @@ func (g *Graphics) Initialize() error {
 		g.dsss = map[stencilMode]mtl.DepthStencilState{}
 	}
 
+	if runtime.GOOS == "ios" {
+		// Initializing a Metal device and a layer must be done in the render thread on iOS.
 		if err := g.view.initialize(); err != nil {
 			return err
 		}
+	}
 	if g.transparent {
 		g.view.ml.SetOpaque(false)
 	}

internal/graphicsdriver/metal/view_macos_darwin.go

@@ -36,6 +36,7 @@ func (v *view) update() {
 		return
 	}
 
+	// TODO: Should this be called on the main thread?
 	cocoaWindow := ns.NewWindow(v.window)
 	cocoaWindow.ContentView().SetLayer(v.ml)
 	cocoaWindow.ContentView().SetWantsLayer(true)

internal/thread/thread.go

@@ -16,6 +16,7 @@ package thread
 
 import (
 	"context"
+	"runtime"
 )
 
 // OSThread represents an OS thread.
@@ -32,12 +33,13 @@ func NewOSThread() *OSThread {
 	}
 }
 
-// Loop starts the thread loop until Stop is called.
-//
-// It is assumed that an OS thread is fixed by runtime.LockOSThread when Loop is called.
+// Loop starts the thread loop until Stop is called on the current OS thread.
 //
 // Loop must be called on the thread.
 func (t *OSThread) Loop(ctx context.Context) error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
 	for {
 		select {
 		case fn := <-t.funcs:

internal/ui/context.go

@@ -16,6 +16,7 @@ package ui
 
 import (
 	"math"
+	"sync"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
 	"github.com/hajimehoshi/ebiten/v2/internal/buffered"
@@ -57,6 +58,8 @@ type context struct {
 	isOffscreenModified bool
 
 	skipCount int
+
+	setContextOnce sync.Once
 }
 
 func newContext(game Game) *context {

internal/ui/run_glfw_notsinglethread.go

@@ -27,21 +27,24 @@ import (
 func (u *userInterfaceImpl) Run(game Game, options *RunOptions) error {
 	u.context = newContext(game)
 
-	// Initialize the main thread first so the thread is available at u.run (#809).
-	u.mainThread = thread.NewOSThread()
-
-	graphicscommand.SetRenderThread(u.mainThread)
-
 	u.setRunning(true)
 	defer u.setRunning(false)
 
-	if err := u.init(options); err != nil {
+	if err := u.initOnMainThread(options); err != nil {
 		return err
 	}
 
+	u.mainThread = thread.NewOSThread()
+	u.renderThread = thread.NewOSThread()
+	graphicscommand.SetRenderThread(u.renderThread)
+
 	ctx, cancel := stdcontext.WithCancel(stdcontext.Background())
 	defer cancel()
 
+	go func() {
+		_ = u.renderThread.Loop(ctx)
+	}()
+
 	ch := make(chan error, 1)
 	go func() {
 		defer close(ch)

internal/ui/run_glfw_singlethread.go

@@ -26,12 +26,13 @@ func (u *userInterfaceImpl) Run(game Game, options *RunOptions) error {
 
 	// Initialize the main thread first so the thread is available at u.run (#809).
 	u.mainThread = thread.NewNoopThread()
-	graphicscommand.SetRenderThread(u.mainThread)
+	u.renderThread = thread.NewNoopThread()
+	graphicscommand.SetRenderThread(u.renderThread)
 
 	u.setRunning(true)
 	defer u.setRunning(false)
 
-	if err := u.init(options); err != nil {
+	if err := u.initOnMainThread(options); err != nil {
 		return err
 	}
 

internal/ui/ui_glfw.go

@@ -111,6 +111,7 @@ type userInterfaceImpl struct {
 	glContextSetOnce sync.Once
 
 	mainThread   threadInterface
+	renderThread threadInterface
 	m            sync.RWMutex
 }
 
@@ -796,8 +797,7 @@ event:
 	u.framebufferSizeCallbackCh = nil
 }
 
-// init must be called from the main thread.
-func (u *userInterfaceImpl) init(options *RunOptions) error {
+func (u *userInterfaceImpl) initOnMainThread(options *RunOptions) error {
 	glfw.WindowHint(glfw.AutoIconify, glfw.False)
 
 	decorated := glfw.False
@@ -1004,7 +1004,8 @@ func (u *userInterfaceImpl) update() (float64, float64, error) {
 
 func (u *userInterfaceImpl) loopGame() error {
 	defer u.mainThread.Call(func() {
-		u.window.Destroy()
+		// An explicit destorying a window tries to delete a GL context on the main thread on Windows (wglDeleteContext),
+		// but this causes an error unfortunately.
 		glfw.Terminate()
 	})
 	for {
@@ -1026,7 +1027,7 @@ func (u *userInterfaceImpl) updateGame() error {
 	}
 
 	u.glContextSetOnce.Do(func() {
-		u.mainThread.Call(func() {
+		u.renderThread.Call(func() {
 			if u.graphicsDriver.IsGL() {
 				u.window.MakeContextCurrent()
 			}
@@ -1037,13 +1038,13 @@ func (u *userInterfaceImpl) updateGame() error {
 		return err
 	}
 
-	u.mainThread.Call(func() {
+	u.renderThread.Call(func() {
 		// Call updateVsync even though fpsMode is not updated.
 		// When toggling to fullscreen, vsync state might be reset unexpectedly (#1787).
-		u.updateVsync()
+		u.updateVsyncOnRenderThread()
 
 		// This works only for OpenGL.
-		u.swapBuffers()
+		u.swapBuffersOnRenderThread()
 	})
 
 	return nil
@@ -1083,8 +1084,7 @@ func (u *userInterfaceImpl) updateIconIfNeeded() {
 	})
 }
 
-// swapBuffers must be called from the main thread.
-func (u *userInterfaceImpl) swapBuffers() {
+func (u *userInterfaceImpl) swapBuffersOnRenderThread() {
 	if u.graphicsDriver.IsGL() {
 		u.window.SwapBuffers()
 	}
@@ -1260,8 +1260,7 @@ func (u *userInterfaceImpl) minimumWindowWidth() int {
 	return 1
 }
 
-// updateVsync must be called on the main thread.
-func (u *userInterfaceImpl) updateVsync() {
+func (u *userInterfaceImpl) updateVsyncOnRenderThread() {
 	if u.graphicsDriver.IsGL() {
 		// SwapInterval is affected by the current monitor of the window.
 		// This needs to be called at least after SetMonitor.

internal/ui/ui_nintendosdk.go

@@ -67,6 +67,7 @@ func (u *userInterfaceImpl) Run(game Game, options *RunOptions) error {
 	u.graphicsDriver = g
 	nintendosdk.InitializeGame()
 	for {
+		// TODO: Make a separate thread for rendering (#2512).
 		nintendosdk.BeginFrame()
 		gamepad.Update()
 		u.updateInputState()