cmd/ebitenmobile: use setPreserveEGLContextOnPause(true)

setPreserveEGLContextOnPause(true) suppresses context losts, and
basically we will no longer need our restoring logic.

Updates #805

cmd/ebitenmobile/_files/EbitenSurfaceView.java

@@ -33,12 +33,17 @@ class EbitenSurfaceView extends GLSurfaceView implements RenderRequester {
     private class EbitenRenderer implements GLSurfaceView.Renderer {
 
         private boolean errored_ = false;
+        private boolean onceSurfaceCreated_ = false;
+        private boolean contextLost_ = false;
 
         @Override
         public void onDrawFrame(GL10 gl) {
             if (errored_) {
                 return;
             }
+            if (contextLost_) {
+                return;
+            }
             try {
                 Ebitenmobileview.update();
             } catch (final Exception e) {
@@ -54,7 +59,17 @@ class EbitenSurfaceView extends GLSurfaceView implements RenderRequester {
 
         @Override
         public void onSurfaceCreated(GL10 gl, EGLConfig config) {
-            Ebitenmobileview.onContextLost();
+            if (!onceSurfaceCreated_) {
+                onceSurfaceCreated_ = true;
+                return;
+            }
+            contextLost_ = true;
+            new Handler(Looper.getMainLooper()).post(new Runnable() {
+                @Override
+                public void run() {
+                    onContextLost();
+                }
+            });
         }
 
         @Override
@@ -76,6 +91,7 @@ class EbitenSurfaceView extends GLSurfaceView implements RenderRequester {
         setEGLContextClientVersion(3);
         setEGLConfigChooser(8, 8, 8, 8, 0, 0);
         setRenderer(new EbitenRenderer());
+        setPreserveEGLContextOnPause(true);
         Ebitenmobileview.setRenderRequester(this);
     }
 
@@ -83,6 +99,12 @@ class EbitenSurfaceView extends GLSurfaceView implements RenderRequester {
         ((EbitenView)getParent()).onErrorOnGameUpdate(e);
     }
 
+    private void onContextLost() {
+        Log.v("Go", "Kill the application due to a context lost");
+        // TODO: Relaunch this application for better UX (#805).
+        Runtime.getRuntime().exit(0);
+    }
+
     @Override
     public synchronized void setExplicitRenderingMode(boolean explicitRendering) {
         if (explicitRendering) {

internal/graphicsdriver/opengl/graphics.go

@@ -315,6 +315,12 @@ func (g *Graphics) NeedsRestoring() bool {
 	if runtime.GOOS == "js" {
 		return false
 	}
+	// On Android, `setPreserveEGLContextOnPause(true)` is called and then context loss unlikely happens.
+	// If this happens, Ebitengine tries to relaunch the app (#805).
+	if runtime.GOOS == "android" {
+		return false
+	}
+	// TODO: Remove the entire logic of the restoring (#805).
 	return g.context.ctx.IsES()
 }
 

internal/restorable/images.go

@@ -15,8 +15,6 @@
 package restorable
 
 import (
-	"runtime"
-
 	"github.com/hajimehoshi/ebiten/v2/internal/debug"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicscommand"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
@@ -47,7 +45,6 @@ type images struct {
 	images     map[*Image]struct{}
 	shaders    map[*Shader]struct{}
 	lastTarget *Image
-	contextLost bool
 }
 
 // theImages represents the images for the current process.
@@ -91,9 +88,6 @@ func RestoreIfNeeded(graphicsDriver graphicsdriver.Graphics) error {
 	if !forceRestoring {
 		var r bool
 
-		if canDetectContextLostExplicitly {
-			r = theImages.contextLost
-		} else {
 		// As isInvalidated() is expensive, call this only for one image.
 		// This assumes that if there is one image that is invalidated, all images are invalidated.
 		for img := range theImages.images {
@@ -108,7 +102,6 @@ func RestoreIfNeeded(graphicsDriver graphicsdriver.Graphics) error {
 			}
 			break
 		}
-		}
 
 		if !r {
 			return nil
@@ -265,8 +258,6 @@ func (i *images) restore(graphicsDriver graphicsdriver.Graphics) error {
 		}
 	}
 
-	i.contextLost = false
-
 	return nil
 }
 
@@ -283,14 +274,3 @@ func InitializeGraphicsDriverState(graphicsDriver graphicsdriver.Graphics) error
 func MaxImageSize(graphicsDriver graphicsdriver.Graphics) int {
 	return graphicscommand.MaxImageSize(graphicsDriver)
 }
-
-// OnContextLost is called when the context lost is detected in an explicit way.
-func OnContextLost() {
-	canDetectContextLostExplicitly = true
-	theImages.contextLost = true
-}
-
-// canDetectContextLostExplicitly reports whether Ebitengine can detect a context lost in an explicit way.
-// On Android, a context lost can be detected via GLSurfaceView.Renderer.onSurfaceCreated.
-// On iOS w/ OpenGL ES, this can be detected only when gomobile-build is used.
-var canDetectContextLostExplicitly = runtime.GOOS == "android"

mobile/ebitenmobileview/mobile.go

@@ -30,7 +30,6 @@ import (
 	"sync"
 
 	"github.com/hajimehoshi/ebiten/v2"
-	"github.com/hajimehoshi/ebiten/v2/internal/restorable"
 	"github.com/hajimehoshi/ebiten/v2/internal/ui"
 )
 
@@ -113,10 +112,6 @@ func Resume() error {
 	return ui.Get().SetForeground(true)
 }
 
-func OnContextLost() {
-	restorable.OnContextLost()
-}
-
 func DeviceScale() float64 {
 	return ui.Get().DeviceScaleFactor()
 }