ui: Refactoring: theUIContext is always non-nil

run.go

@@ -207,11 +207,11 @@ func RunGame(game Game) error {
 	if uiDriver().CanHaveWindow() {
 		fixWindowPosition(WindowSize())
 	}
-	return runGame(game, 1)
+	return runGame(game, 0)
 }
 
 func runGame(game Game, scale float64) error {
-	theUIContext = newUIContext(game, scale)
+	theUIContext.set(game, scale)
 	if err := uiDriver().Run(theUIContext, graphicsDriver()); err != nil {
 		if err == driver.RegularTermination {
 			return nil
@@ -232,8 +232,7 @@ func RunWithoutMainLoop(f func(*Image) error, width, height int, scale float64,
 		width:  width,
 		height: height,
 	}
-
-	theUIContext = newUIContext(game, scale)
+	theUIContext.set(game, scale)
 	return uiDriver().RunWithoutMainLoop(width, height, scale, title, theUIContext, graphicsDriver())
 }
 
@@ -252,9 +251,6 @@ func SetScreenSize(width, height int) {
 	if width <= 0 || height <= 0 {
 		panic("ebiten: width and height must be positive")
 	}
-	if theUIContext == nil {
-		panic("ebiten: SetScreenSize can't be called before the main loop starts")
-	}
 	theUIContext.SetScreenSize(width, height)
 }
 
@@ -263,17 +259,11 @@ func SetScreenScale(scale float64) {
 	if scale <= 0 {
 		panic("ebiten: scale must be positive")
 	}
-	if theUIContext == nil {
-		panic("ebiten: SetScreenScale can't be called before the main loop starts")
-	}
 	theUIContext.setScaleForWindow(scale)
 }
 
 // ScreenScale is deprecated as of 1.11.0-alpha. Use WindowSize instead.
 func ScreenScale() float64 {
-	if theUIContext == nil {
-		panic("ebiten: ScreenScale can't be called before the main loop starts")
-	}
 	return theUIContext.getScaleForWindow()
 }
 

uicontext.go

@@ -51,17 +51,6 @@ func (d *defaultGame) Layout(outsideWidth, outsideHeight int) (screenWidth, scre
 	return w, h
 }
 
-func newUIContext(game Game, scaleForWindow float64) *uiContext {
-	u := &uiContext{
-		game:           game,
-		scaleForWindow: scaleForWindow,
-	}
-	if g, ok := game.(*defaultGame); ok {
-		g.context = u
-	}
-	return u
-}
-
 type uiContext struct {
 	game      Game
 	offscreen *Image
@@ -81,30 +70,49 @@ type uiContext struct {
 	m sync.Mutex
 }
 
-var theUIContext *uiContext
+var theUIContext = &uiContext{}
+
+func (c *uiContext) set(game Game, scaleForWindow float64) {
+	c.m.Lock()
+	defer c.m.Unlock()
+	c.game = game
+
+	if g, ok := game.(*defaultGame); ok {
+		c.scaleForWindow = scaleForWindow
+		g.context = c
+	}
+}
 
 func (c *uiContext) setScaleForWindow(scale float64) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	if c.game == nil {
+		panic("ebiten: setScaleForWindow can be called only after the main loop starts")
+	}
+
 	g, ok := c.game.(*defaultGame)
 	if !ok {
 		panic("ebiten: setScaleForWindow can be called only when Run is used")
 	}
 
-	c.m.Lock()
-	defer c.m.Unlock()
-
 	w, h := g.width, g.height
 	c.scaleForWindow = scale
 	uiDriver().SetWindowSize(int(float64(w)*scale), int(float64(h)*scale))
 }
 
 func (c *uiContext) getScaleForWindow() float64 {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	if c.game == nil {
+		panic("ebiten: getScaleForWindow can be called only after the main loop starts")
+	}
+
 	if _, ok := c.game.(*defaultGame); !ok {
 		panic("ebiten: getScaleForWindow can be called only when Run is used")
 	}
-
-	c.m.Lock()
 	s := c.scaleForWindow
-	c.m.Unlock()
 	return s
 }
 
@@ -113,14 +121,18 @@ func (c *uiContext) getScaleForWindow() float64 {
 // SetScreenSize is for backward compatibility. This is called from ebiten.SetScreenSize and
 // uidriver/mobile.UserInterface.
 func (c *uiContext) SetScreenSize(width, height int) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	if c.game == nil {
+		panic("ebiten: SetScreenSize can be called only after the main loop starts")
+	}
+
 	g, ok := c.game.(*defaultGame)
 	if !ok {
 		panic("ebiten: SetScreenSize can be called only when Run is used")
 	}
 
-	c.m.Lock()
-	defer c.m.Unlock()
-
 	g.width = width
 	g.height = height
 	s := c.scaleForWindow