From 41c08151f3815af843491d1659f9770c4c115e6d Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 23 Sep 2018 19:41:36 -0700
Subject: [PATCH] Qt: Fix tearing issues

---
 src/platform/qt/CoreController.cpp | 12 +++++-------
 src/platform/qt/CoreController.h   |  4 ++--
 src/platform/qt/DisplayQt.cpp      |  2 +-
 3 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/platform/qt/CoreController.cpp b/src/platform/qt/CoreController.cpp
index f81eb6c9b..b8ac73de5 100644
--- a/src/platform/qt/CoreController.cpp
+++ b/src/platform/qt/CoreController.cpp
@@ -46,6 +46,7 @@ CoreController::CoreController(mCore* core, QObject* parent)
 	m_buffers[0].fill(0xFF);
 	m_buffers[1].fill(0xFF);
 	m_activeBuffer = &m_buffers[0];
+	m_completeBuffer = m_buffers[0];
 
 	m_threadContext.core->setVideoBuffer(m_threadContext.core, reinterpret_cast<color_t*>(m_activeBuffer->data()), size.width());
 
@@ -209,12 +210,9 @@ CoreController::~CoreController() {
 	m_threadContext.core->deinit(m_threadContext.core);
 }
 
-color_t* CoreController::drawContext() {
+const color_t* CoreController::drawContext() {
 	QMutexLocker locker(&m_mutex);
-	if (!m_completeBuffer) {
-		return nullptr;
-	}
-	return reinterpret_cast<color_t*>(m_completeBuffer->data());
+	return reinterpret_cast<const color_t*>(m_completeBuffer.constData());
 }
 
 bool CoreController::isPaused() {
@@ -790,7 +788,7 @@ int CoreController::updateAutofire() {
 
 void CoreController::finishFrame() {
 	QMutexLocker locker(&m_mutex);
-	m_completeBuffer = m_activeBuffer;
+	memcpy(m_completeBuffer.data(), m_activeBuffer->constData(), m_activeBuffer->size());
 
 	// TODO: Generalize this to triple buffering?
 	m_activeBuffer = &m_buffers[0];
@@ -798,7 +796,7 @@ void CoreController::finishFrame() {
 		m_activeBuffer = &m_buffers[1];
 	}
 	// Copy contents to avoid issues when doing frameskip
-	memcpy(m_activeBuffer->data(), m_completeBuffer->data(), m_activeBuffer->size());
+	memcpy(m_activeBuffer->data(), m_completeBuffer.constData(), m_activeBuffer->size());
 	m_threadContext.core->setVideoBuffer(m_threadContext.core, reinterpret_cast<color_t*>(m_activeBuffer->data()), screenDimensions().width());
 
 	for (auto& action : m_frameActions) {
diff --git a/src/platform/qt/CoreController.h b/src/platform/qt/CoreController.h
index 4ea647402..ec6b7d998 100644
--- a/src/platform/qt/CoreController.h
+++ b/src/platform/qt/CoreController.h
@@ -58,7 +58,7 @@ public:
 
 	mCoreThread* thread() { return &m_threadContext; }
 
-	color_t* drawContext();
+	const color_t* drawContext();
 
 	bool isPaused();
 	bool hasStarted();
@@ -174,7 +174,7 @@ private:
 
 	QByteArray m_buffers[2];
 	QByteArray* m_activeBuffer;
-	QByteArray* m_completeBuffer = nullptr;
+	QByteArray m_completeBuffer;
 
 	std::unique_ptr<mCacheSet> m_cacheSet;
 	std::unique_ptr<Override> m_override;
diff --git a/src/platform/qt/DisplayQt.cpp b/src/platform/qt/DisplayQt.cpp
index 846382f3a..6043a7399 100644
--- a/src/platform/qt/DisplayQt.cpp
+++ b/src/platform/qt/DisplayQt.cpp
@@ -51,7 +51,7 @@ void DisplayQt::filter(bool filter) {
 
 void DisplayQt::framePosted() {
 	update();
-	color_t* buffer = m_context->drawContext();
+	const color_t* buffer = m_context->drawContext();
 	if (const_cast<const QImage&>(m_backing).bits() == reinterpret_cast<const uchar*>(buffer)) {
 		return;
 	}