ui: Update GraphicsContext every frame (#490)

internal/ui/ui_glfw.go

@@ -422,6 +422,23 @@ func (u *userInterface) pollEvents() {
 	currentInput.update(u.window, u.getScale()*glfwScale())
 }
 
+func (u *userInterface) updateGraphicsContext(g GraphicsContext) {
+	actualScale := 0.0
+	sizeChanged := false
+	_ = u.runOnMainThread(func() error {
+		if !u.sizeChanged {
+			return nil
+		}
+		u.sizeChanged = false
+		actualScale = u.actualScreenScale()
+		sizeChanged = true
+		return nil
+	})
+	if sizeChanged {
+		g.SetSize(u.width, u.height, actualScale)
+	}
+}
+
 func (u *userInterface) update(g GraphicsContext) error {
 	shouldClose := false
 	_ = u.runOnMainThread(func() error {
@@ -441,20 +458,8 @@ func (u *userInterface) update(g GraphicsContext) error {
 		return nil
 	})
 
-	actualScale := 0.0
-	sizeChanged := false
-	_ = u.runOnMainThread(func() error {
-		if !u.sizeChanged {
-			return nil
-		}
-		u.sizeChanged = false
-		actualScale = u.actualScreenScale()
-		sizeChanged = true
-		return nil
-	})
-	if sizeChanged {
-		g.SetSize(u.width, u.height, actualScale)
-	}
+	// This call is needed for initialization.
+	u.updateGraphicsContext(g)
 
 	_ = u.runOnMainThread(func() error {
 		u.pollEvents()
@@ -470,6 +475,8 @@ func (u *userInterface) update(g GraphicsContext) error {
 	})
 	if err := g.Update(func() {
 		currentInput.runeBuffer = currentInput.runeBuffer[:0]
+		// The offscreens must be updated every frame (#490).
+		u.updateGraphicsContext(g)
 	}); err != nil {
 		return err
 	}

internal/ui/ui_js.go

@@ -123,6 +123,13 @@ func (u *userInterface) actualScreenScale() float64 {
 	return u.getScale() * devicescale.DeviceScale()
 }
 
+func (u *userInterface) updateGraphicsContext(g GraphicsContext) {
+	if u.sizeChanged {
+		u.sizeChanged = false
+		g.SetSize(u.width, u.height, u.actualScreenScale())
+	}
+}
+
 func (u *userInterface) update(g GraphicsContext) error {
 	if !u.runnableInBackground && !u.windowFocus {
 		return nil
@@ -132,13 +139,11 @@ func (u *userInterface) update(g GraphicsContext) error {
 		g.Invalidate()
 	}
 	currentInput.updateGamepads()
-	if u.sizeChanged {
-		u.sizeChanged = false
-		g.SetSize(u.width, u.height, u.actualScreenScale())
-		return nil
-	}
+	u.updateGraphicsContext(g)
 	if err := g.Update(func() {
 		currentInput.runeBuffer = nil
+		// The offscreens must be updated every frame (#490).
+		u.updateGraphicsContext(g)
 	}); err != nil {
 		return err
 	}

internal/ui/ui_mobile.go

@@ -82,12 +82,7 @@ func Run(width, height int, scale float64, title string, g GraphicsContext) erro
 	}
 }
 
-func (u *userInterface) update(g GraphicsContext) error {
-	<-chRender
-	defer func() {
-		chRenderEnd <- struct{}{}
-	}()
-
+func (u *userInterface) updateGraphicsContext(g GraphicsContext) {
 	sizeChanged := false
 	width, height := 0, 0
 	actualScale := 0.0
@@ -106,8 +101,19 @@ func (u *userInterface) update(g GraphicsContext) error {
 		// Sizing also calls GL functions
 		g.SetSize(width, height, actualScale)
 	}
+}
 
-	if err := g.Update(func() {}); err != nil {
+func (u *userInterface) update(g GraphicsContext) error {
+	<-chRender
+	defer func() {
+		chRenderEnd <- struct{}{}
+	}()
+
+	u.updateGraphicsContext(g)
+
+	if err := g.Update(func() {
+		u.updateGraphicsContext(g)
+	}); err != nil {
 		return err
 	}
 	return nil