ebiten: add RunGameOptions.DisableHiDPI

Closes #2987

examples/highdpi/main.go

@@ -15,9 +15,11 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	_ "image/jpeg"
 	"log"
+	"runtime"
 
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
@@ -93,7 +95,16 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	op.Filter = ebiten.FilterLinear
 	screen.DrawImage(g.highDPIImage, op)
 
-	ebitenutil.DebugPrint(screen, fmt.Sprintf("(Init) Device Scale Ratio: %0.2f", scale))
+	msg := fmt.Sprintf("Device Scale Ratio: %0.2f", scale)
+	if runtime.GOOS == "js" {
+		if !*flagDisable {
+			msg += "\nHiDPI rendering is enabled. You can disable HiDPI by -disable flag."
+		} else {
+			msg += "\nHiDPI rendering is disabled."
+		}
+	}
+	// TODO: The texts might be too small. Improve legibility.
+	ebitenutil.DebugPrint(screen, msg)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
@@ -103,10 +114,16 @@ func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
 	return int(float64(outsideWidth) * s), int(float64(outsideHeight) * s)
 }
 
+var flagDisable = flag.Bool("disable", false, "disables HiDPI rendering (only on browsers)")
+
 func main() {
+	flag.Parse()
+
 	ebiten.SetWindowSize(640, 480)
 	ebiten.SetWindowTitle("High DPI (Ebitengine Demo)")
-	if err := ebiten.RunGame(NewGame()); err != nil {
+	op := &ebiten.RunGameOptions{}
+	op.DisableHiDPI = *flagDisable
+	if err := ebiten.RunGameWithOptions(NewGame(), op); err != nil {
 		log.Fatal(err)
 	}
 }

internal/ui/ui.go

@@ -175,6 +175,7 @@ type RunOptions struct {
 	ScreenTransparent bool
 	SkipTaskbar       bool
 	SingleThread      bool
+	DisableHiDPI      bool
 	X11ClassName      string
 	X11InstanceName   string
 }

internal/ui/ui_js.go

@@ -96,6 +96,7 @@ type userInterfaceImpl struct {
 	cursorShape         CursorShape
 	onceUpdateCalled    bool
 	lastCaptureExitTime time.Time
+	hiDPIEnabled        bool
 
 	context                   *context
 	inputState                InputState
@@ -465,6 +466,7 @@ func (u *UserInterface) init() error {
 		runnableOnUnfocused: true,
 		savedCursorX:        math.NaN(),
 		savedCursorY:        math.NaN(),
+		hiDPIEnabled:        true,
 	}
 
 	// document is undefined on node.js
@@ -762,6 +764,8 @@ func (u *UserInterface) shouldFocusFirst(options *RunOptions) bool {
 func (u *UserInterface) initOnMainThread(options *RunOptions) error {
 	u.setRunning(true)
 
+	u.hiDPIEnabled = !options.DisableHiDPI
+
 	if u.shouldFocusFirst(options) {
 		canvas.Call("focus")
 	}
@@ -815,6 +819,10 @@ func (m *Monitor) Name() string {
 }
 
 func (m *Monitor) DeviceScaleFactor() float64 {
+	if !theUI.hiDPIEnabled {
+		return 1
+	}
+
 	if m.deviceScaleFactor != 0 {
 		return m.deviceScaleFactor
 	}

run.go

@@ -274,6 +274,15 @@ type RunGameOptions struct {
 	// The default (zero) value is false, which means that the single thread mode is disabled.
 	SingleThread bool
 
+	// DisableHiDPI indicates whether the rendering for HiDPI is disabled or not.
+	// If HiDPI is disabled, the device scale factor is always 1 i.e. Monitor's DeviceScaleFactor always returns 1.
+	// This is useful to get a better performance on HiDPI displays, in the expense of rendering quality.
+	//
+	// DisableHiDPI is available only on browsers.
+	//
+	// The default (zero) value is false, which means that HiDPI is enabled.
+	DisableHiDPI bool
+
 	// X11DisplayName is a class name in the ICCCM WM_CLASS window property.
 	X11ClassName string
 
@@ -703,6 +712,7 @@ func toUIRunOptions(options *RunGameOptions) *ui.RunOptions {
 		ScreenTransparent: options.ScreenTransparent,
 		SkipTaskbar:       options.SkipTaskbar,
 		SingleThread:      options.SingleThread,
+		DisableHiDPI:      options.DisableHiDPI,
 		X11ClassName:      options.X11ClassName,
 		X11InstanceName:   options.X11InstanceName,
 	}