internal/graphicsdriver/opengl: Give up restorign on browsers

Using restorable images is expensive as this sometimes requires to
load pixels from GPU. On browsers, just reloading the application
should be fine when the context lost happens.

Closes #1603

examples/contextlost/context_js.go

@@ -20,7 +20,6 @@ package main
 import (
 	"fmt"
 	"syscall/js"
-	"time"
 )
 
 func (g *Game) loseAndRestoreContext() {
@@ -48,17 +47,5 @@ func (g *Game) loseAndRestoreContext() {
 
 	ext.Call("loseContext")
 	fmt.Println("Lost the context!")
-	fmt.Println("The context is automatically restored after 3 seconds.")
 	g.lost = true
-
-	// If and only if the context is lost by loseContext, you need to call restoreContext. Note that in usual
-	// case of context lost, you cannot call restoreContext but the context should be restored automatically.
-	//
-	// After the context is lost, update will not be called. Instead, fire the goroutine to restore the context.
-	go func() {
-		time.Sleep(3 * time.Second)
-		ext.Call("restoreContext")
-		fmt.Println("Restored the context!")
-		g.lost = false
-	}()
 }

internal/graphicsdriver/opengl/context_js.go

@@ -23,7 +23,6 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl/gles"
 	"github.com/hajimehoshi/ebiten/v2/internal/jsutil"
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
-	"github.com/hajimehoshi/ebiten/v2/internal/web"
 )
 
 type (
@@ -85,7 +84,6 @@ const (
 
 var (
 	isWebGL2Available = !forceWebGL1 && (js.Global().Get("WebGL2RenderingContext").Truthy() || js.Global().Get("go2cpp").Truthy())
-	needsRestoring    = !web.IsMobileBrowser() && !js.Global().Get("go2cpp").Truthy()
 )
 
 type contextImpl struct {
@@ -526,7 +524,8 @@ func (c *context) flush() {
 }
 
 func (c *context) needsRestoring() bool {
-	return needsRestoring
+	// Though it is possible to have a logic to restore the graphics data for GPU, do not use it for performance (#1603).
+	return false
 }
 
 func (c *context) canUsePBO() bool {

internal/uidriver/js/ui_js.go

@@ -22,7 +22,6 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/driver"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl"
 	"github.com/hajimehoshi/ebiten/v2/internal/hooks"
-	"github.com/hajimehoshi/ebiten/v2/internal/restorable"
 )
 
 var (
@@ -58,7 +57,6 @@ type UserInterface struct {
 	cursorShape         driver.CursorShape
 
 	sizeChanged bool
-	contextLost bool
 
 	lastDeviceScaleFactor float64
 
@@ -290,11 +288,6 @@ func (u *UserInterface) loop(context driver.UIContext) <-chan error {
 
 	var cf js.Func
 	f := func() {
-		if u.contextLost {
-			requestAnimationFrame.Invoke(cf)
-			return
-		}
-
 		if err := u.update(); err != nil {
 			close(reqStopAudioCh)
 			<-resStopAudioCh
@@ -545,12 +538,7 @@ func setCanvasEventHandlers(v js.Value) {
 	v.Call("addEventListener", "webglcontextlost", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		e := args[0]
 		e.Call("preventDefault")
-		theUI.contextLost = true
+		window.Get("location").Call("reload")
-		restorable.OnContextLost()
-		return nil
-	}))
-	v.Call("addEventListener", "webglcontextrestored", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
-		theUI.contextLost = false
 		return nil
 	}))
 }