From d5138bf8854fb77b5998d4a6907a00b51b4ce269 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 11 Apr 2021 23:31:29 -0700
Subject: [PATCH] Qt: Fix OpenGL renderer lagging behind when fast-forwarding
 (fixes #2094)

---
 CHANGES                        |  1 +
 src/platform/qt/DisplayGL.cpp  | 22 +++++++++-------------
 src/platform/qt/DisplayGL.h    |  1 -
 src/platform/qt/VideoProxy.cpp |  2 +-
 4 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/CHANGES b/CHANGES
index 6b0fedc8f..0a9123002 100644
--- a/CHANGES
+++ b/CHANGES
@@ -14,6 +14,7 @@ Other fixes:
  - GBA Video: Fix mode 5 frame 1 caching (fixes mgba.io/i/2075)
  - GBA Video: Don't attempt to copy invalid registers when switching renderer
  - Qt: Fix crash when switching from high-resolution OpenGL renderer to software
+ - Qt: Fix OpenGL renderer lagging behind when fast-forwarding (fixes mgba.io/i/2094)
 Misc:
  - Core: Truncate preloading ROMs that slightly exceed max size (fixes mgba.io/i/2093)
  - GBA: Default-enable VBA bug compat for Ruby and Emerald ROM hacks
diff --git a/src/platform/qt/DisplayGL.cpp b/src/platform/qt/DisplayGL.cpp
index c30cba9f5..c613e7afb 100644
--- a/src/platform/qt/DisplayGL.cpp
+++ b/src/platform/qt/DisplayGL.cpp
@@ -432,23 +432,16 @@ void PainterGL::draw() {
 	if (!m_active || m_queue.isEmpty()) {
 		return;
 	}
-	if (m_lagging >= 1) {
-		return;
-	}
 	mCoreSync* sync = &m_context->thread()->impl->sync;
 	if (!mCoreSyncWaitFrameStart(sync)) {
 		mCoreSyncWaitFrameEnd(sync);
-		++m_lagging;
 		if ((sync->audioWait || sync->videoFrameWait) && m_delayTimer.elapsed() < 1000 / m_surface->screen()->refreshRate()) {
 			QTimer::singleShot(1, this, &PainterGL::draw);
 		}
 		return;
 	}
 	dequeue();
-	if (m_videoProxy) {
-		// Only block on the next frame if we're trying to run at roughly 60fps via audio
-		m_videoProxy->setBlocking(sync->audioWait && std::abs(60.f - sync->fpsTarget) < 0.1f);
-	}
+	bool forceRedraw = !m_videoProxy;
 	if (!m_delayTimer.isValid()) {
 		m_delayTimer.start();
 	} else {
@@ -456,13 +449,18 @@ void PainterGL::draw() {
 			while (m_delayTimer.nsecsElapsed() + 2000000 < 1000000000 / sync->fpsTarget) {
 				QThread::usleep(500);
 			}
+			forceRedraw = true;
+		} else if (!forceRedraw) {
+			forceRedraw = m_delayTimer.nsecsElapsed() + 2000000 >= 1000000000 / m_surface->screen()->refreshRate();
 		}
-		m_delayTimer.restart();
 	}
 	mCoreSyncWaitFrameEnd(sync);
 
-	performDraw();
-	m_backend->swap(m_backend);
+	if (forceRedraw) {
+		m_delayTimer.restart();
+		performDraw();
+		m_backend->swap(m_backend);
+	}
 }
 
 void PainterGL::forceDraw() {
@@ -504,7 +502,6 @@ void PainterGL::pause() {
 }
 
 void PainterGL::unpause() {
-	m_lagging = 0;
 	m_active = true;
 }
 
@@ -538,7 +535,6 @@ void PainterGL::enqueue(const uint32_t* backing) {
 			memcpy(buffer, backing, size.width() * size.height() * BYTES_PER_PIXEL);
 		}
 	}
-	m_lagging = 0;
 	m_queue.enqueue(buffer);
 }
 
diff --git a/src/platform/qt/DisplayGL.h b/src/platform/qt/DisplayGL.h
index 111f0cc88..d0cea76cb 100644
--- a/src/platform/qt/DisplayGL.h
+++ b/src/platform/qt/DisplayGL.h
@@ -141,7 +141,6 @@ private:
 	std::array<std::array<uint32_t, 0x100000>, 3> m_buffers;
 	QList<uint32_t*> m_free;
 	QQueue<uint32_t*> m_queue;
-	QAtomicInt m_lagging = 0;
 	uint32_t* m_buffer = nullptr;
 	QPainter m_painter;
 	QMutex m_mutex;
diff --git a/src/platform/qt/VideoProxy.cpp b/src/platform/qt/VideoProxy.cpp
index 60cb938b8..7c6366229 100644
--- a/src/platform/qt/VideoProxy.cpp
+++ b/src/platform/qt/VideoProxy.cpp
@@ -14,7 +14,7 @@ using namespace QGBA;
 VideoProxy::VideoProxy() {
 	mVideoLoggerRendererCreate(&m_logger.d, false);
 	m_logger.d.block = true;
-	m_logger.d.waitOnFlush = false;
+	m_logger.d.waitOnFlush = true;
 
 	m_logger.d.init = &cbind<&VideoProxy::init>;
 	m_logger.d.reset = &cbind<&VideoProxy::reset>;