internal/ui: bug fix: need to sleep when swapping buffers is skipped

Closes #2890

internal/graphicsdriver/metal/graphics_darwin.go

@@ -20,7 +20,6 @@ import (
 	"math"
 	"runtime"
 	"sort"
-	"time"
 	"unsafe"
 
 	"github.com/ebitengine/purego/objc"
@@ -62,8 +61,6 @@ type Graphics struct {
 	maxImageSize int
 	tmpTextures  []mtl.Texture
 
-	lastFlush time.Time
-
 	pool cocoa.NSAutoreleasePool
 }
 
@@ -230,25 +227,12 @@ func (g *Graphics) flushIfNeeded(present bool) {
 		return
 	}
 
-	now := time.Now()
-	defer func() {
-		g.lastFlush = now
-	}()
-
 	g.flushRenderCommandEncoderIfNeeded()
 
 	if present {
 		// This check is necessary when skipping to render the screen (SetScreenClearedEveryFrame(false)).
-		if g.screenDrawable == (ca.MetalDrawable{}) {
-			if g.cb != (mtl.CommandBuffer{}) {
-				g.screenDrawable = g.view.nextDrawable()
-			} else {
-				if delta := time.Second/60 - now.Sub(g.lastFlush); delta > 0 {
-					// nextDrawable can return immediately when the command buffer is empty.
-					// To avoid high CPU usage, sleep instead (#2520).
-					time.Sleep(delta)
-				}
-			}
+		if g.screenDrawable == (ca.MetalDrawable{}) && g.cb != (mtl.CommandBuffer{}) {
+			g.screenDrawable = g.view.nextDrawable()
 		}
 		if g.screenDrawable != (ca.MetalDrawable{}) {
 			g.cb.PresentDrawable(g.screenDrawable)

internal/ui/context.go

@@ -17,6 +17,7 @@ package ui
 import (
 	"math"
 	"sync"
+	"time"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
 	"github.com/hajimehoshi/ebiten/v2/internal/buffered"
@@ -56,6 +57,7 @@ type context struct {
 	offscreenHeight float64
 
 	isOffscreenModified bool
+	lastDrawTime        time.Time
 
 	skipCount int
 
@@ -203,6 +205,11 @@ func (c *context) drawGame(graphicsDriver graphicsdriver.Graphics, forceDraw boo
 		c.skipCount = 0
 	}
 
+	now := time.Now()
+	defer func() {
+		c.lastDrawTime = now
+	}()
+
 	if c.skipCount < maxSkipCount {
 		if graphicsDriver.NeedsClearingScreen() {
 			// This clear is needed for fullscreen mode or some mobile platforms (#622).
@@ -214,6 +221,9 @@ func (c *context) drawGame(graphicsDriver graphicsdriver.Graphics, forceDraw boo
 		// The final screen is never used as the rendering source.
 		// Flush its buffer here just in case.
 		c.screen.flushBufferIfNeeded()
+	} else if delta := time.Second/60 - now.Sub(c.lastDrawTime); 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)
 	}
 
 	return nil