From 25a5f1dd83a6fe914feffb372a8fd278df7441ef Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 30 Sep 2018 14:43:53 +0900
Subject: [PATCH] ui: Sleep when vsync doesn't work (#692)

---
 internal/ui/ui_glfw.go | 21 +++++++++++++++++++++
 run.go                 |  3 +++
 2 files changed, 24 insertions(+)

diff --git a/internal/ui/ui_glfw.go b/internal/ui/ui_glfw.go
index be0331dec..47dd87e2d 100644
--- a/internal/ui/ui_glfw.go
+++ b/internal/ui/ui_glfw.go
@@ -625,11 +625,32 @@ func (u *userInterface) loop(g GraphicsContext) error {
 		if err := u.update(g); err != nil {
 			return err
 		}
+
+		u.m.Lock()
+		vsync := u.vsync
+		u.m.Unlock()
+
 		// The bound framebuffer must be the original screen framebuffer
 		// before swapping buffers.
 		opengl.GetContext().BindScreenFramebuffer()
+
 		_ = u.runOnMainThread(func() error {
+			if !vsync {
+				u.swapBuffers()
+				return nil
+			}
+
+			n1 := time.Now().UnixNano()
 			u.swapBuffers()
+			n2 := time.Now().UnixNano()
+			d := time.Duration(n2 - n1)
+
+			// On macOS Mojave, vsync might not work (#692).
+			// As a tempoarry fix, just wait for a millisecond not to consume CPU too much.
+			const threshold = 4 * time.Millisecond // 250 [Hz]
+			if d < threshold {
+				time.Sleep(threshold - d)
+			}
 			return nil
 		})
 	}
diff --git a/run.go b/run.go
index 7dfaed164..bc7be7c3c 100644
--- a/run.go
+++ b/run.go
@@ -38,6 +38,9 @@ const FPS = DefaultTPS
 // CurrentFPS returns the current number of FPS (frames per second), that represents
 // how many swapping buffer happens per second.
 //
+// On some environments, CurrentFPS doesn't return a reliable value since vsync doesn't work well there.
+// If you want to measure the application's speed, Use CurrentTPS.
+//
 // CurrentFPS is concurrent-safe.
 func CurrentFPS() float64 {
 	return clock.CurrentFPS()