From 76d6055bb0095caf57431f7250bc0e965aa49e5e Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 3 Jul 2022 05:27:15 -0700
Subject: [PATCH] Qt: Improve frame pacing, maybe

---
 src/core/sync.c               |  4 +--
 src/platform/qt/DisplayGL.cpp | 48 +++++++++++++++++++++++------------
 src/platform/qt/DisplayGL.h   |  4 ++-
 3 files changed, 37 insertions(+), 19 deletions(-)

diff --git a/src/core/sync.c b/src/core/sync.c
index b2a65493b..78b04ea3e 100644
--- a/src/core/sync.c
+++ b/src/core/sync.c
@@ -25,10 +25,10 @@ void mCoreSyncPostFrame(struct mCoreSync* sync) {
 	MutexLock(&sync->videoFrameMutex);
 	++sync->videoFramePending;
 	do {
-		ConditionWake(&sync->videoFrameAvailableCond);
 		if (sync->videoFrameWait) {
 			ConditionWait(&sync->videoFrameRequiredCond, &sync->videoFrameMutex);
 		}
+		ConditionWake(&sync->videoFrameAvailableCond);
 	} while (sync->videoFrameWait && sync->videoFramePending);
 	MutexUnlock(&sync->videoFrameMutex);
 }
@@ -54,7 +54,7 @@ bool mCoreSyncWaitFrameStart(struct mCoreSync* sync) {
 	}
 	if (sync->videoFrameWait) {
 		ConditionWake(&sync->videoFrameRequiredCond);
-		if (ConditionWaitTimed(&sync->videoFrameAvailableCond, &sync->videoFrameMutex, 50)) {
+		if (ConditionWaitTimed(&sync->videoFrameAvailableCond, &sync->videoFrameMutex, 4)) {
 			return false;
 		}
 	}
diff --git a/src/platform/qt/DisplayGL.cpp b/src/platform/qt/DisplayGL.cpp
index 740604b82..4175505b5 100644
--- a/src/platform/qt/DisplayGL.cpp
+++ b/src/platform/qt/DisplayGL.cpp
@@ -619,11 +619,12 @@ void PainterGL::start() {
 	m_buffer = nullptr;
 	m_active = true;
 	m_started = true;
+	resetTiming();
 	emit started();
 }
 
 void PainterGL::draw() {
-	if (!m_started || m_queue.isEmpty()) {
+	if (!m_started) {
 		return;
 	}
 
@@ -636,14 +637,16 @@ void PainterGL::draw() {
 	}
 
 	mCoreSync* sync = &m_context->thread()->impl->sync;
+
+	qint64 targetNsec = 1000000000 / sync->fpsTarget;
+	qint64 refreshNsec = 1000000000 / m_window->screen()->refreshRate();
+	qint64 delay = m_timerResidue;
+
 	if (!mCoreSyncWaitFrameStart(sync)) {
 		mCoreSyncWaitFrameEnd(sync);
 		if (!sync->audioWait && !sync->videoFrameWait) {
 			return;
 		}
-		if (m_delayTimer.elapsed() >= 1000 / m_window->screen()->refreshRate()) {
-			return;
-		}
 		if (!m_drawTimer.isActive()) {
 			m_drawTimer.start(1);
 		}
@@ -651,23 +654,30 @@ void PainterGL::draw() {
 	}
 	dequeue();
 	bool forceRedraw = !m_videoProxy;
-	if (!m_delayTimer.isValid()) {
-		m_delayTimer.start();
-	} else {
-		if (sync->audioWait || sync->videoFrameWait) {
-			while (m_delayTimer.nsecsElapsed() + OVERHEAD_NSEC < 1000000000 / sync->fpsTarget) {
-				QThread::usleep(500);
-			}
-			forceRedraw = sync->videoFrameWait;
-		}
-		if (!forceRedraw) {
-			forceRedraw = m_delayTimer.nsecsElapsed() + OVERHEAD_NSEC >= 1000000000 / m_window->screen()->refreshRate();
+	if (sync->audioWait || sync->videoFrameWait) {
+		while (delay + m_delayTimer.nsecsElapsed() + OVERHEAD_NSEC < targetNsec) {
+			QThread::usleep(200);
 		}
+		forceRedraw = sync->videoFrameWait;
+	}
+	if (!forceRedraw) {
+		forceRedraw = delay + m_delayTimer.nsecsElapsed() + OVERHEAD_NSEC >= refreshNsec;
 	}
 	mCoreSyncWaitFrameEnd(sync);
 
 	if (forceRedraw) {
+		delay += m_delayTimer.nsecsElapsed();
 		m_delayTimer.restart();
+
+		delay -= targetNsec;
+		m_timerResidue = (m_timerResidue + delay) / 2;
+
+		if (m_timerResidue > refreshNsec) {
+			if (!m_drawTimer.isActive()) {
+				m_drawTimer.start(1);
+			}
+		}
+
 		performDraw();
 		m_backend->swap(m_backend);
 	}
@@ -679,11 +689,16 @@ void PainterGL::forceDraw() {
 		if (m_delayTimer.elapsed() < 1000 / m_window->screen()->refreshRate()) {
 			return;
 		}
-		m_delayTimer.restart();
+		resetTiming();
 	}
 	m_backend->swap(m_backend);
 }
 
+void PainterGL::resetTiming() {
+	m_delayTimer.restart();
+	m_timerResidue = 0;
+}
+
 void PainterGL::stop() {
 	m_started = false;
 	QMetaObject::invokeMethod(this, "doStop", Qt::BlockingQueuedConnection);
@@ -721,6 +736,7 @@ void PainterGL::pause() {
 
 void PainterGL::unpause() {
 	m_active = true;
+	resetTiming();
 }
 
 void PainterGL::performDraw() {
diff --git a/src/platform/qt/DisplayGL.h b/src/platform/qt/DisplayGL.h
index 47f94157d..5b12feae0 100644
--- a/src/platform/qt/DisplayGL.h
+++ b/src/platform/qt/DisplayGL.h
@@ -176,8 +176,9 @@ private:
 	void performDraw();
 	void dequeue();
 	void dequeueAll(bool keep = false);
+	void resetTiming();
 
-	std::array<std::array<uint32_t, 0x100000>, 3> m_buffers;
+	std::array<std::array<uint32_t, 0x100000>, 8> m_buffers;
 	QList<uint32_t*> m_free;
 	QQueue<uint32_t*> m_queue;
 	uint32_t* m_buffer = nullptr;
@@ -194,6 +195,7 @@ private:
 	bool m_active = false;
 	bool m_started = false;
 	QTimer m_drawTimer;
+	qint64 m_timerResidue;
 	std::shared_ptr<CoreController> m_context;
 	CoreController::Interrupter m_interrupter;
 	bool m_supportsShaders;