From bfd5774fafb0e3942d418280d53bc6b4bc6a487b Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Thu, 14 Nov 2019 13:07:10 +0900
Subject: [PATCH] graphicsdriver/glfw: Bug fix: CPU was busy when the window is
 hidden

Fixes #982
---
 internal/uidriver/glfw/ui.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/internal/uidriver/glfw/ui.go b/internal/uidriver/glfw/ui.go
index 47f49422f..8818e40f4 100644
--- a/internal/uidriver/glfw/ui.go
+++ b/internal/uidriver/glfw/ui.go
@@ -823,6 +823,13 @@ func (u *UserInterface) loop(context driver.UIContext) error {
 		})
 	}()
 	for {
+		unfocused := u.window.GetAttrib(glfw.Focused) == glfw.False
+
+		var t1, t2 time.Time
+
+		if unfocused {
+			t1 = time.Now()
+		}
 		if err := u.update(context); err != nil {
 			return err
 		}
@@ -831,6 +838,19 @@ func (u *UserInterface) loop(context driver.UIContext) error {
 			u.swapBuffers()
 			return nil
 		})
+		if unfocused {
+			t2 = time.Now()
+		}
+
+		// When a window is not focused, SwapBuffers might return immediately and CPU might be busy.
+		// Mitigate this by sleeping (#982).
+		if unfocused {
+			d := t2.Sub(t1)
+			const wait = time.Second / 60
+			if d < wait {
+				time.Sleep(wait - d)
+			}
+		}
 	}
 }