From 629c5bf76c7b7ad1133020f1a028b96e29d944c9 Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Fri, 20 Jan 2017 15:26:41 -0800
Subject: [PATCH] Qt: Fix timing issues on high refresh rate monitors

---
 CHANGES                       |  1 +
 src/platform/qt/DisplayGL.cpp | 11 +++++++++++
 src/platform/qt/DisplayGL.h   |  3 ++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index 9b62df111..6c9392ca9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5,6 +5,7 @@ Bugfixes:
  - Libretro: Fix saving in GB games (fixes mgba.io/i/486)
  - LR35902: Fix pc overflowing current region off-by-one
  - GB MBC: Fix ROM bank overflows getting set to bank 0
+ - Qt: Fix timing issues on high refresh rate monitors
 Misc:
  - Qt: Improved HiDPI support
  - Feature: Support ImageMagick 7
diff --git a/src/platform/qt/DisplayGL.cpp b/src/platform/qt/DisplayGL.cpp
index 986e6eb9a..3d30193c1 100644
--- a/src/platform/qt/DisplayGL.cpp
+++ b/src/platform/qt/DisplayGL.cpp
@@ -7,6 +7,7 @@
 
 #include <QApplication>
 #include <QResizeEvent>
+#include <QTimer>
 
 extern "C" {
 #include "core/core.h"
@@ -319,6 +320,16 @@ void PainterGL::draw() {
 	if (m_queue.isEmpty() || !mCoreThreadIsActive(m_context)) {
 		return;
 	}
+	if (!m_delayTimer.isValid()) {
+		m_delayTimer.start();
+	} else if (m_delayTimer.elapsed() < 16) {
+		QMetaObject::invokeMethod(this, "draw", Qt::QueuedConnection);
+		QThread::usleep(500);
+		return;
+	} else {
+		m_delayTimer.restart();
+	}
+
 	if (mCoreSyncWaitFrameStart(&m_context->sync) || !m_queue.isEmpty()) {
 		dequeue();
 		mCoreSyncWaitFrameEnd(&m_context->sync);
diff --git a/src/platform/qt/DisplayGL.h b/src/platform/qt/DisplayGL.h
index 5803dfd92..ec9cd7581 100644
--- a/src/platform/qt/DisplayGL.h
+++ b/src/platform/qt/DisplayGL.h
@@ -15,12 +15,12 @@
 #endif
 #endif
 
+#include <QElapsedTimer>
 #include <QGLWidget>
 #include <QList>
 #include <QMouseEvent>
 #include <QQueue>
 #include <QThread>
-#include <QTimer>
 
 extern "C" {
 #include "platform/video-backend.h"
@@ -122,6 +122,7 @@ private:
 	VideoBackend* m_backend;
 	QSize m_size;
 	MessagePainter* m_messagePainter;
+	QElapsedTimer m_delayTimer;
 };
 
 }