From 7ec63acd1dc5d05c47c1915fe491df56bab7e0a2 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Wed, 19 Aug 2020 01:23:27 +0900
Subject: [PATCH] ebiten: Bug fix: Set the state of being volatile on
 SetClearingScreenSkipped

Fixes #1309
---
 examples/contextlost/main.go | 11 ++++++++++-
 run.go                       |  1 +
 uicontext.go                 | 11 ++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/examples/contextlost/main.go b/examples/contextlost/main.go
index 2d06d84a0..e8b799542 100644
--- a/examples/contextlost/main.go
+++ b/examples/contextlost/main.go
@@ -93,6 +93,10 @@ func (g *Game) Update(screen *ebiten.Image) error {
 		return nil
 	}
 
+	if inpututil.IsKeyJustPressed(ebiten.KeyS) {
+		ebiten.SetClearingScreenSkipped(!ebiten.IsClearingScreenSkipped())
+	}
+
 	g.count++
 	return nil
 }
@@ -107,7 +111,12 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	op.GeoM.Translate(screenWidth/2, screenHeight/2)
 	screen.DrawImage(gophersImage, op)
 
-	ebitenutil.DebugPrint(screen, "Press Space to force to lose/restore the GL context!\n(Browser only)")
+	msg := `Press Space to force to lose/restore the GL context!
+(Browser only)
+
+Press S to switch clearing the screen
+at the beginning of each frame.`
+	ebitenutil.DebugPrint(screen, msg)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
diff --git a/run.go b/run.go
index b8698050a..f64eb5751 100644
--- a/run.go
+++ b/run.go
@@ -112,6 +112,7 @@ func SetClearingScreenSkipped(skipped bool) {
 		v = 1
 	}
 	atomic.StoreInt32(&isClearingScreenSkipped, v)
+	theUIContext.setClearingScreenSkipped(skipped)
 }
 
 // IsClearingScreenSkipped returns true if the frame isn't cleared at the beginning.
diff --git a/uicontext.go b/uicontext.go
index 57986100b..ede097e8c 100644
--- a/uicontext.go
+++ b/uicontext.go
@@ -176,7 +176,7 @@ func (c *uiContext) updateOffscreen() {
 	}
 	if c.offscreen == nil {
 		c.offscreen = newImage(sw, sh, FilterDefault)
-		c.offscreen.mipmap.SetVolatile(true)
+		c.offscreen.mipmap.SetVolatile(!IsClearingScreenSkipped())
 	}
 
 	// The window size is automatically adjusted when Run is used.
@@ -193,6 +193,15 @@ func (c *uiContext) updateOffscreen() {
 	// scale. This is fine since ebiten.ScreenScale will be deprecated.
 }
 
+func (c *uiContext) setClearingScreenSkipped(skipped bool) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	if c.offscreen != nil {
+		c.offscreen.mipmap.SetVolatile(!skipped)
+	}
+}
+
 func (c *uiContext) setWindowResizable(resizable bool) {
 	c.m.Lock()
 	defer c.m.Unlock()