internal/ui: add sleep for an environment where vsync doesn't work

Updates #2952

internal/ui/context.go

@@ -70,7 +70,14 @@ func newContext(game Game) *context {
 
 func (c *context) updateFrame(graphicsDriver graphicsdriver.Graphics, outsideWidth, outsideHeight float64, deviceScaleFactor float64, ui *UserInterface) error {
 	// TODO: If updateCount is 0 and vsync is disabled, swapping buffers can be skipped.
-	return c.updateFrameImpl(graphicsDriver, clock.UpdateFrame(), outsideWidth, outsideHeight, deviceScaleFactor, ui, false)
+	needsSwapBuffers, err := c.updateFrameImpl(graphicsDriver, clock.UpdateFrame(), outsideWidth, outsideHeight, deviceScaleFactor, ui, false)
+	if err != nil {
+		return err
+	}
+	if err := c.swapBuffersOrWait(needsSwapBuffers, graphicsDriver, ui.FPSMode() == FPSModeVsyncOn); err != nil {
+		return err
+	}
+	return nil
 }
 
 func (c *context) forceUpdateFrame(graphicsDriver graphicsdriver.Graphics, outsideWidth, outsideHeight float64, deviceScaleFactor float64, ui *UserInterface) error {
@@ -81,63 +88,50 @@ func (c *context) forceUpdateFrame(graphicsDriver graphicsdriver.Graphics, outsi
 		n = 2
 	}
 	for i := 0; i < n; i++ {
-		if err := c.updateFrameImpl(graphicsDriver, 1, outsideWidth, outsideHeight, deviceScaleFactor, ui, true); err != nil {
+		needsSwapBuffers, err := c.updateFrameImpl(graphicsDriver, 1, outsideWidth, outsideHeight, deviceScaleFactor, ui, true)
+		if err != nil {
+			return err
+		}
+		if err := c.swapBuffersOrWait(needsSwapBuffers, graphicsDriver, ui.FPSMode() == FPSModeVsyncOn); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-func (c *context) updateFrameImpl(graphicsDriver graphicsdriver.Graphics, updateCount int, outsideWidth, outsideHeight float64, deviceScaleFactor float64, ui *UserInterface, forceDraw bool) (err error) {
+func (c *context) updateFrameImpl(graphicsDriver graphicsdriver.Graphics, updateCount int, outsideWidth, outsideHeight float64, deviceScaleFactor float64, ui *UserInterface, forceDraw bool) (needsSwapBuffers bool, err error) {
 	// The given outside size can be 0 e.g. just after restoring from the fullscreen mode on Windows (#1589)
 	// Just ignore such cases. Otherwise, creating a zero-sized framebuffer causes a panic.
 	if outsideWidth == 0 || outsideHeight == 0 {
-		return nil
+		return false, nil
 	}
 
 	debug.FrameLogf("----\n")
 
-	var needSwapBuffers bool
-
 	if err := atlas.BeginFrame(graphicsDriver); err != nil {
-		return err
+		return false, err
 	}
 	defer func() {
 		if err1 := atlas.EndFrame(); err1 != nil && err == nil {
+			needsSwapBuffers = false
 			err = err1
 			return
 		}
-
-		if needSwapBuffers {
-			if err1 := atlas.SwapBuffers(graphicsDriver); err1 != nil && err == nil {
-				err = err1
-				return
-			}
-		} else {
-			now := time.Now()
-			defer func() {
-				c.lastSwapBufferTime = now
-			}()
-			if delta := time.Second/60 - now.Sub(c.lastSwapBufferTime); delta > 0 {
-				// When swapping buffers is skipped and Draw is called too early, sleep for a while to suppress CPU usages (#2890).
-				time.Sleep(delta)
-			}
-		}
 	}()
 
 	// Flush deferred functions, like reading pixels from GPU.
 	if err := c.processFuncsInFrame(ui); err != nil {
-		return err
+		return false, err
 	}
 
 	// ForceUpdate can be invoked even if the context is not initialized yet (#1591).
 	if w, h := c.layoutGame(outsideWidth, outsideHeight, deviceScaleFactor); w == 0 || h == 0 {
-		return nil
+		return false, nil
 	}
 
 	// Update the input state after the layout is updated as a cursor position is affected by the layout.
 	if err := ui.updateInputState(); err != nil {
-		return err
+		return false, err
 	}
 
 	// Ensure that Update is called once before Draw so that Update can be used for initialization.
@@ -155,15 +149,15 @@ func (c *context) updateFrameImpl(graphicsDriver graphicsdriver.Graphics, update
 		})
 
 		if err := hook.RunBeforeUpdateHooks(); err != nil {
-			return err
+			return false, err
 		}
 		if err := c.game.Update(); err != nil {
-			return err
+			return false, err
 		}
 
 		// Catch the error that happened at (*Image).At.
 		if err := ui.error(); err != nil {
-			return err
+			return false, err
 		}
 
 		ui.tick.Add(1)
@@ -172,13 +166,39 @@ func (c *context) updateFrameImpl(graphicsDriver graphicsdriver.Graphics, update
 	// Update window icons during a frame, since an icon might be *ebiten.Image and
 	// getting pixels from it needs to be in a frame (#1468).
 	if err := ui.updateIconIfNeeded(); err != nil {
-		return err
+		return false, err
 	}
 
 	// Draw the game.
-	needSwapBuffers, err = c.drawGame(graphicsDriver, ui, forceDraw)
-	if err != nil {
-		return err
+	return c.drawGame(graphicsDriver, ui, forceDraw)
+}
+
+func (c *context) swapBuffersOrWait(needsSwapBuffers bool, graphicsDriver graphicsdriver.Graphics, vsyncEnabled bool) error {
+	now := time.Now()
+	defer func() {
+		c.lastSwapBufferTime = now
+	}()
+
+	if needsSwapBuffers {
+		if err := atlas.SwapBuffers(graphicsDriver); err != nil {
+			return err
+		}
+	}
+
+	var waitTime time.Duration
+	if !needsSwapBuffers {
+		// When swapping buffers is skipped and Draw is called too early, sleep for a while to suppress CPU usages (#2890).
+		waitTime = time.Second / 60
+	} else if vsyncEnabled {
+		// In some environments, e.g. Linux on Parallels, SwapBuffers doesn't wait for the vsync (#2952).
+		// In the case when the display has high refresh rates like 240 [Hz], the wait time should be small.
+		waitTime = time.Millisecond
+	}
+	if waitTime > 0 {
+		if delta := waitTime - now.Sub(c.lastSwapBufferTime); delta > 0 {
+			println(waitTime.String(), now.Sub(c.lastSwapBufferTime).String())
+			time.Sleep(delta)
+		}
 	}
 
 	return nil