Add the graphics api independent scenegraph port

Opt in via environment variables:
QSG_RHI=1 -> enable using QRhi instead of GL
QSG_RHI_BACKEND -> set to vulkan, metal, d3d11, gl to override the default
(the default is d3d11 on Windows, metal on Mac, gl elsewhere)

Or force a given rhi backend via the existing
QQuickWindow::setSceneGraphBackend().

Otherwise the default behavior is the same as before, the rhi code path
is never active by default.

-no-opengl builds are supported in the sense that they work and default
to the software backend. However, the rhi code path cannot currently be
used in such builds, even though QRhi from qtbase is fully functional
with Vulkan, D3D, or Metal even when qtbase was configured with
-no-opengl. This cannot be utilized by Quick atm due to OpenGL usage
being all over the place in the sources corresponding to the default
backend, and those host the rhi code path as well. This will be cleaned up
hopefully in Qt 6, with the removal all direct OpenGL usage.

Other env.vars.:
QSG_RHI_DEBUG_LAYER=1 -> enable D3D debug or Vulkan validation layer
(assuming the system is set up for this)
QSG_RHI_SHADEREFFECT_DEBUG=1 -> print stuff from ShaderEffect
QSG_SAMPLES=1,2,4,... -> MSAA sample count (but QSurfaceFormat works too)
QT_D3D_ADAPTER_INDEX=0,1,... -> D3D adapter index
QT_VK_PHYSICAL_DEVICE_INDEX=0,1,... -> Vulkan physical device index
QSG_RHI_UINT32_INDEX=1 -> always use uint index data (both
merged/unmerged, convert when needed - with some rhi backends this is
implicit)
QSG_RENDER_LOOP -> to override the render loop as usual. The default
with RHI is threaded for Metal, threaded for Vulkan on Windows, basic
for Vulkan on Linux and Android (to be checked later), while the existing
rules apply for OpenGL.

Not supported when running with QRhi:
  - particles
  - compressed atlases (though this is transparent to the apps)
  - QSGRenderNode
  - QQuickRenderControl
  - QQuickFramebufferObject
  - certain QQuickWindow functionality that depends directly on OpenGL
  - anisotropic filtering for textures
  - native text may lack some gamma correction
  - QSGEngine applicability unclear
  - some QML profiler logs may be incorrect or irrelevant

Change-Id: I7822e99ad79e342e4166275da6e9e66498d76521
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 321 insertions, 61 deletions

diff --git a/src/quick/scenegraph/qsgrenderloop.cpp b/src/quick/scenegraph/qsgrenderloop.cpp
index 2e91bafa7c..f3812f474a 100644
--- a/src/quick/scenegraph/qsgrenderloop.cpp
+++ b/src/quick/scenegraph/qsgrenderloop.cpp
@@ -40,6 +40,7 @@
 #include "qsgrenderloop_p.h"
 #include "qsgthreadedrenderloop_p.h"
 #include "qsgwindowsrenderloop_p.h"
+#include "qsgrhisupport_p.h"
 #include <private/qquickanimatorcontroller_p.h>
 
 #include <QtCore/QCoreApplication>
@@ -50,6 +51,7 @@
 #include <QtGui/QOffscreenSurface>
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformintegration.h>
+#include <QPlatformSurfaceEvent>
 
 #include <QtQml/private/qqmlglobal_p.h>
 
@@ -59,23 +61,35 @@
 #include <QtQuick/private/qsgrenderer_p.h>
 #include <private/qquickprofiler_p.h>
 
+#include <private/qsgrhishadereffectnode_p.h>
+
 #if QT_CONFIG(opengl)
-# include <QtGui/QOpenGLContext>
-# include <private/qsgdefaultrendercontext_p.h>
+#include <QtGui/QOpenGLContext>
 #if QT_CONFIG(quick_shadereffect)
-# include <private/qquickopenglshadereffectnode_p.h>
+#include <private/qquickopenglshadereffectnode_p.h>
 #endif
+#include <private/qsgdefaultrendercontext_p.h>
 #endif
 
 #ifdef Q_OS_WIN
-#  include <QtCore/qt_windows.h>
+#include <QtCore/qt_windows.h>
 #endif
 
 QT_BEGIN_NAMESPACE
 
 extern bool qsg_useConsistentTiming();
 extern Q_GUI_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_format, bool include_alpha);
-#if QT_CONFIG(opengl)
+
+// ### We do not yet support using Qt Quick with QRhi (and Vulkan, D3D
+// or Metal) in -no-opengl builds as of Qt 5.14. This is due to to the
+// widespread direct OpenGL usage all over the place in qsgdefault*
+// and the related classes. To be cleaned up in Qt 6 when the direct
+// GL code path is removed.
+
+#if QT_CONFIG(opengl) /* || QT_CONFIG(vulkan) || defined(Q_OS_WIN) || defined(Q_OS_DARWIN) */
+
+#define ENABLE_DEFAULT_BACKEND
+
 /*
     expectations for this manager to work:
      - one opengl context to render multiple windows
@@ -88,17 +102,13 @@ extern Q_GUI_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_
 DEFINE_BOOL_CONFIG_OPTION(qmlNoThreadedRenderer, QML_BAD_GUI_RENDER_LOOP);
 DEFINE_BOOL_CONFIG_OPTION(qmlForceThreadedRenderer, QML_FORCE_THREADED_RENDERER); // Might trigger graphics driver threading bugs, use at own risk
 #endif
+
 QSGRenderLoop *QSGRenderLoop::s_instance = nullptr;
 
 QSGRenderLoop::~QSGRenderLoop()
 {
 }
 
-QSurface::SurfaceType QSGRenderLoop::windowSurfaceType() const
-{
-    return QSurface::OpenGLSurface;
-}
-
 void QSGRenderLoop::cleanup()
 {
     if (!s_instance)
@@ -112,18 +122,36 @@ void QSGRenderLoop::cleanup()
     }
     delete s_instance;
     s_instance = nullptr;
+
+#ifdef ENABLE_DEFAULT_BACKEND
+    QSGRhiSupport::instance()->cleanup();
+    QSGRhiProfileConnection::instance()->cleanup();
+#endif
+}
+
+QSurface::SurfaceType QSGRenderLoop::windowSurfaceType() const
+{
+#ifdef ENABLE_DEFAULT_BACKEND
+    return QSGRhiSupport::instance()->windowSurfaceType();
+#else
+    return QSurface::RasterSurface;
+#endif
 }
 
-/*!
- * Non-threaded render loops immediately run the job if there is a context.
- */
 void QSGRenderLoop::postJob(QQuickWindow *window, QRunnable *job)
 {
     Q_ASSERT(job);
-#if QT_CONFIG(opengl)
+#ifdef ENABLE_DEFAULT_BACKEND
     Q_ASSERT(window);
-    if (window->openglContext()) {
-        window->openglContext()->makeCurrent(window);
+    if (!QSGRhiSupport::instance()->isRhiEnabled()) {
+        if (window->openglContext()) {
+            window->openglContext()->makeCurrent(window);
+            job->run();
+        }
+    } else {
+        // ### needs https://codereview.qt-project.org/c/qt/qtbase/+/265231
+//        if (window->rhi())
+//            window->rhi()->makeThreadLocalNativeContextCurrent();
         job->run();
     }
 #else
@@ -132,7 +160,8 @@ void QSGRenderLoop::postJob(QQuickWindow *window, QRunnable *job)
 #endif
     delete job;
 }
-#if QT_CONFIG(opengl)
+
+#ifdef ENABLE_DEFAULT_BACKEND
 class QSGGuiThreadRenderLoop : public QSGRenderLoop
 {
     Q_OBJECT
@@ -160,6 +189,10 @@ public:
     QSGContext *sceneGraphContext() const override;
     QSGRenderContext *createRenderContext(QSGContext *) const override { return rc; }
 
+    void releaseSwapchain(QQuickWindow *window);
+
+    bool eventFilter(QObject *watched, QEvent *event) override;
+
     struct WindowData {
         bool updatePending : 1;
         bool grabOnly : 1;
@@ -167,13 +200,16 @@ public:
 
     QHash<QQuickWindow *, WindowData> m_windows;
 
-    QOpenGLContext *gl;
+    QOpenGLContext *gl = nullptr;
+    QOffscreenSurface *offscreenSurface = nullptr;
+    QRhi *rhi = nullptr;
     QSGContext *sg;
     QSGRenderContext *rc;
 
     QImage grabContent;
 };
 #endif
+
 QSGRenderLoop *QSGRenderLoop::instance()
 {
     if (!s_instance) {
@@ -183,28 +219,64 @@ QSGRenderLoop *QSGRenderLoop::instance()
             const_cast<QLoggingCategory &>(QSG_LOG_INFO()).setEnabled(QtDebugMsg, true);
 
         s_instance = QSGContext::createWindowManager();
-#if QT_CONFIG(opengl)
+#ifdef ENABLE_DEFAULT_BACKEND
         if (!s_instance) {
+            QSGRhiSupport *rhiSupport = QSGRhiSupport::instance();
 
-            enum RenderLoopType {
-                BasicRenderLoop,
-                ThreadedRenderLoop,
-                WindowsRenderLoop
-            };
-
-            RenderLoopType loopType = BasicRenderLoop;
-
-#ifdef Q_OS_WIN
-            // With desktop OpenGL (opengl32.dll), use threaded. Otherwise (ANGLE) use windows.
-            if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL
-                && QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::ThreadedOpenGL))
+            QSGRenderLoopType loopType;
+            if (rhiSupport->isRhiEnabled() && rhiSupport->rhiBackend() != QRhi::OpenGLES2) {
                 loopType = ThreadedRenderLoop;
-            else
-                loopType = WindowsRenderLoop;
+            } else {
+                loopType = BasicRenderLoop;
+#ifdef Q_OS_WIN
+                // With desktop OpenGL (opengl32.dll), use threaded. Otherwise (ANGLE) use windows.
+                if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL
+                        && QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::ThreadedOpenGL))
+                {
+                    loopType = ThreadedRenderLoop;
+                } else {
+                    loopType = WindowsRenderLoop;
+                }
 #else
-            if (QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::ThreadedOpenGL))
-                loopType = ThreadedRenderLoop;
+                if (QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::ThreadedOpenGL))
+                    loopType = ThreadedRenderLoop;
+#endif
+            }
+
+            if (rhiSupport->isRhiEnabled()) {
+                // no 'windows' because that's not yet ported to the rhi
+                if (loopType == WindowsRenderLoop)
+                    loopType = BasicRenderLoop;
+
+                switch (rhiSupport->rhiBackend()) {
+                case QRhi::Vulkan:
+#if defined(Q_OS_LINUX) && !defined(Q_OS_ANDROID)
+                    // ### to be investigated (Mesa/Gnome deadlocks on
+                    // resize with threaded+Vulkan (but not threaded+GL))
+                    loopType = BasicRenderLoop;
 #endif
+                    break;
+
+                case QRhi::D3D11:
+                    // D3D11 is forced to 'basic' always for now. The threaded loop's model may
+                    // not be suitable for DXGI due to the possibility of having the main
+                    // thread blocked while issuing a Present. To be investigated.
+                    loopType = BasicRenderLoop;
+                    break;
+
+                case QRhi::Null:
+                    loopType = BasicRenderLoop;
+                    break;
+
+                default:
+                    break;
+                }
+            }
+
+            // The environment variables can always override. This is good
+            // because in some situations it makes perfect sense to try out a
+            // render loop that is otherwise disabled by default.
+
             if (qmlNoThreadedRenderer())
                 loopType = BasicRenderLoop;
             else if (qmlForceThreadedRenderer())
@@ -275,14 +347,15 @@ void QSGRenderLoop::handleContextCreationFailure(QQuickWindow *window,
     if (!signalEmitted)
         qFatal("%s", qPrintable(untranslatedMessage));
 }
-#if QT_CONFIG(opengl)
+
+#ifdef ENABLE_DEFAULT_BACKEND
 QSGGuiThreadRenderLoop::QSGGuiThreadRenderLoop()
-    : gl(nullptr)
 {
     if (qsg_useConsistentTiming()) {
         QUnifiedTimer::instance(true)->setConsistentTiming(true);
         qCDebug(QSG_LOG_INFO, "using fixed animation steps");
     }
+
     sg = QSGContext::createDefaultContext();
     rc = sg->createRenderContext();
 }
@@ -318,38 +391,86 @@ void QSGGuiThreadRenderLoop::windowDestroyed(QQuickWindow *window)
     QQuickWindowPrivate *d = QQuickWindowPrivate::get(window);
 
     bool current = false;
-    QScopedPointer<QOffscreenSurface> offscreenSurface;
     if (gl) {
         QSurface *surface = window;
         // There may be no platform window if the window got closed.
-        if (!window->handle()) {
-            offscreenSurface.reset(new QOffscreenSurface);
-            offscreenSurface->setFormat(gl->format());
-            offscreenSurface->create();
-            surface = offscreenSurface.data();
-        }
-        current = gl->makeCurrent(surface);
+        if (!window->handle())
+            surface = offscreenSurface;
+        if (!rhi)
+            current = gl->makeCurrent(surface);
+        else
+            current = true;
     }
     if (Q_UNLIKELY(!current))
         qCDebug(QSG_LOG_RENDERLOOP, "cleanup without an OpenGL context");
 
-#if QT_CONFIG(quick_shadereffect) && QT_CONFIG(opengl)
-    if (current)
-        QQuickOpenGLShaderEffectMaterial::cleanupMaterialCache();
+#if QT_CONFIG(quick_shadereffect)
+    QSGRhiShaderEffectNode::cleanupMaterialTypeCache();
+#if QT_CONFIG(opengl)
+    QQuickOpenGLShaderEffectMaterial::cleanupMaterialCache();
+#endif
 #endif
 
+    if (d->swapchain) {
+        if (window->handle()) {
+            // We get here when exiting via QCoreApplication::quit() instead of
+            // through QWindow::close().
+            releaseSwapchain(window);
+        } else {
+            qWarning("QSGGuiThreadRenderLoop cleanup with QQuickWindow %p swapchain %p still alive, this should not happen.",
+                     window, d->swapchain);
+        }
+    }
+
     d->cleanupNodesOnShutdown();
     if (m_windows.size() == 0) {
         rc->invalidate();
+        d->rhi = nullptr;
+        delete rhi;
+        rhi = nullptr;
         delete gl;
         gl = nullptr;
+        delete offscreenSurface;
+        offscreenSurface = nullptr;
     } else if (gl && window == gl->surface() && current) {
-        gl->doneCurrent();
+        if (!rhi)
+            gl->doneCurrent();
     }
 
     delete d->animationController;
 }
 
+void QSGGuiThreadRenderLoop::releaseSwapchain(QQuickWindow *window)
+{
+    QQuickWindowPrivate *wd = QQuickWindowPrivate::get(window);
+    delete wd->rpDescForSwapchain;
+    wd->rpDescForSwapchain = nullptr;
+    delete wd->swapchain;
+    wd->swapchain = nullptr;
+    delete wd->depthStencilForSwapchain;
+    wd->depthStencilForSwapchain = nullptr;
+    wd->hasActiveSwapchain = wd->hasRenderableSwapchain = wd->swapchainJustBecameRenderable = false;
+}
+
+bool QSGGuiThreadRenderLoop::eventFilter(QObject *watched, QEvent *event)
+{
+    switch (event->type()) {
+    case QEvent::PlatformSurface:
+        // this is the proper time to tear down the swapchain (while the native window and surface are still around)
+        if (static_cast<QPlatformSurfaceEvent *>(event)->surfaceEventType() == QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed) {
+            QQuickWindow *w = qobject_cast<QQuickWindow *>(watched);
+            if (w) {
+                releaseSwapchain(w);
+                w->removeEventFilter(this);
+            }
+        }
+        break;
+    default:
+        break;
+    }
+    return QObject::eventFilter(watched, event);
+}
+
 void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
 {
     if (!m_windows.contains(window))
@@ -364,8 +485,35 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
         return;
 
     bool current = false;
-
-    if (!gl) {
+    QSGRhiSupport *rhiSupport = QSGRhiSupport::instance();
+    int rhiSampleCount = 1;
+    const bool enableRhi = rhiSupport->isRhiEnabled();
+
+    if (enableRhi && !rhi) {
+        offscreenSurface = rhiSupport->maybeCreateOffscreenSurface(window);
+        rhi = rhiSupport->createRhi(window, offscreenSurface);
+        if (rhi) {
+            if (rhiSupport->isProfilingRequested())
+                QSGRhiProfileConnection::instance()->initialize(rhi);
+
+            current = true;
+
+            // The sample count cannot vary between windows as we use the same
+            // rendercontext for all of them. Decide it here and now.
+            rhiSampleCount = rhiSupport->chooseSampleCountForWindowWithRhi(window, rhi);
+
+            cd->rhi = rhi; // set this early in case something hooked up to rc initialized() accesses it
+
+            QSGDefaultRenderContext::InitParams rcParams;
+            rcParams.rhi = rhi;
+            rcParams.sampleCount = rhiSampleCount;
+            rcParams.initialSurfacePixelSize = window->size() * window->effectiveDevicePixelRatio();
+            rcParams.maybeSurface = window;
+            cd->context->initialize(&rcParams);
+        } else {
+            handleContextCreationFailure(window, false);
+        }
+    } else if (!enableRhi && !gl) {
         gl = new QOpenGLContext();
         gl->setFormat(window->requestedFormat());
         gl->setScreen(window->screen());
@@ -377,15 +525,50 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
             gl = nullptr;
             handleContextCreationFailure(window, isEs);
         } else {
+            if (!offscreenSurface) {
+                offscreenSurface = new QOffscreenSurface;
+                offscreenSurface->setFormat(gl->format());
+                offscreenSurface->create();
+            }
             cd->fireOpenGLContextCreated(gl);
             current = gl->makeCurrent(window);
         }
         if (current) {
-            auto openglRenderContext = static_cast<QSGDefaultRenderContext *>(cd->context);
-            openglRenderContext->initialize(gl);
+            QSGDefaultRenderContext::InitParams rcParams;
+            rcParams.sampleCount = qMax(1, gl->format().samples());
+            rcParams.openGLContext = gl;
+            rcParams.initialSurfacePixelSize = window->size() * window->effectiveDevicePixelRatio();
+            rcParams.maybeSurface = window;
+            cd->context->initialize(&rcParams);
         }
     } else {
-        current = gl->makeCurrent(window);
+        if (!rhi)
+            current = gl->makeCurrent(window);
+        else
+            current = true;
+    }
+
+    if (enableRhi && rhi && !cd->swapchain) {
+        // if it's not the first window then the rhi is not yet stored to
+        // QQuickWindowPrivate, do it now
+        cd->rhi = rhi;
+
+        QRhiSwapChain::Flags flags = QRhiSwapChain::UsedAsTransferSource; // may be used in a grab
+
+        cd->swapchain = rhi->newSwapChain();
+        cd->depthStencilForSwapchain = rhi->newRenderBuffer(QRhiRenderBuffer::DepthStencil,
+                                                            QSize(),
+                                                            rhiSampleCount,
+                                                            QRhiRenderBuffer::UsedWithSwapChainOnly);
+        cd->swapchain->setWindow(window);
+        cd->swapchain->setDepthStencil(cd->depthStencilForSwapchain);
+        qDebug("MSAA sample count for the swapchain is %d", rhiSampleCount);
+        cd->swapchain->setSampleCount(rhiSampleCount);
+        cd->swapchain->setFlags(flags);
+        cd->rpDescForSwapchain = cd->swapchain->newCompatibleRenderPassDescriptor();
+        cd->swapchain->setRenderPassDescriptor(cd->rpDescForSwapchain);
+
+        window->installEventFilter(this);
     }
 
     bool lastDirtyWindow = true;
@@ -407,6 +590,17 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
         if (!m_windows.contains(window))
             return;
     }
+
+    QSize effectiveOutputSize; // always prefer what the surface tells us, not the QWindow
+    if (cd->swapchain) {
+        effectiveOutputSize = cd->swapchain->surfacePixelSize();
+        // An update request could still be delivered right before we get an
+        // unexpose. With Vulkan on Windows for example attempting to render
+        // leads to failures at this stage since the surface size is already 0.
+        if (effectiveOutputSize.isEmpty())
+            return;
+    }
+
     QElapsedTimer renderTimer;
     qint64 renderTime = 0, syncTime = 0, polishTime = 0;
     bool profileFrames = QSG_LOG_TIME_RENDERLOOP().isDebugEnabled();
@@ -424,6 +618,41 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
 
     emit window->afterAnimating();
 
+    // Begin the frame before syncing -> sync is where we may invoke
+    // updatePaintNode() on the items and they may want to do resource updates.
+    // Also relevant for applications that connect to the before/afterSynchronizing
+    // signals and want to do graphics stuff already there.
+    if (cd->swapchain) {
+        Q_ASSERT(!effectiveOutputSize.isEmpty());
+        const QSize previousOutputSize = cd->swapchain->currentPixelSize();
+        if (previousOutputSize != effectiveOutputSize || cd->swapchainJustBecameRenderable) {
+            if (cd->swapchainJustBecameRenderable)
+                qDebug("just became exposed");
+            cd->swapchainJustBecameRenderable = false;
+            cd->depthStencilForSwapchain->setPixelSize(effectiveOutputSize);
+
+            cd->depthStencilForSwapchain->build();
+            cd->hasActiveSwapchain = cd->swapchain->buildOrResize();
+
+            cd->hasRenderableSwapchain = cd->hasActiveSwapchain;
+            if (!cd->hasActiveSwapchain)
+                qWarning("Failed to build or resize swapchain");
+            else
+                qDebug() << "rhi swapchain size" << effectiveOutputSize;
+        }
+
+        Q_ASSERT(rhi == cd->rhi);
+        QRhi::FrameOpResult frameResult = rhi->beginFrame(cd->swapchain);
+        if (frameResult != QRhi::FrameOpSuccess) {
+            if (frameResult == QRhi::FrameOpDeviceLost)
+                qWarning("Device lost");
+            else if (frameResult == QRhi::FrameOpError)
+                qWarning("Failed to start frame");
+            // out of date is not worth warning about - it may happen even during resizing on some platforms
+            return;
+        }
+    }
+
     cd->syncSceneGraph();
     if (lastDirtyWindow)
         rc->endSync();
@@ -433,7 +662,7 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
     Q_QUICK_SG_PROFILE_RECORD(QQuickProfiler::SceneGraphRenderLoopFrame,
                               QQuickProfiler::SceneGraphRenderLoopSync);
 
-    cd->renderSceneGraph(window->size());
+    cd->renderSceneGraph(window->size(), effectiveOutputSize);
 
     if (profileFrames)
         renderTime = renderTimer.nsecsElapsed();
@@ -441,17 +670,27 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
                               QQuickProfiler::SceneGraphRenderLoopRender);
 
     if (data.grabOnly) {
-        bool alpha = window->format().alphaBufferSize() > 0 && window->color().alpha() != 255;
-        grabContent = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), alpha, alpha);
+        const bool alpha = window->format().alphaBufferSize() > 0 && window->color().alpha() != 255;
+        if (cd->swapchain)
+            grabContent = rhiSupport->grabAndBlockInCurrentFrame(rhi, cd->swapchain);
+        else
+            grabContent = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), alpha, alpha);
         grabContent.setDevicePixelRatio(window->effectiveDevicePixelRatio());
         data.grabOnly = false;
     }
 
-    if (alsoSwap && window->isVisible()) {
+    const bool needsPresent = alsoSwap && window->isVisible();
+    if (cd->swapchain) {
+        QRhi::EndFrameFlags flags = 0;
+        if (!needsPresent)
+            flags |= QRhi::SkipPresent;
+        rhi->endFrame(cd->swapchain, flags);
+    } else if (needsPresent) {
         if (!cd->customRenderStage || !cd->customRenderStage->swap())
             gl->swapBuffers(window);
-        cd->fireFrameSwapped();
     }
+    if (needsPresent)
+        cd->fireFrameSwapped();
 
     qint64 swapTime = 0;
     if (profileFrames)
@@ -472,6 +711,8 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
         lastFrameTime = QTime::currentTime();
     }
 
+    QSGRhiProfileConnection::instance()->send(rhi);
+
     // Might have been set during syncSceneGraph()
     if (data.updatePending)
         maybeUpdate(window);
@@ -479,7 +720,26 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
 
 void QSGGuiThreadRenderLoop::exposureChanged(QQuickWindow *window)
 {
-    if (window->isExposed()) {
+    QQuickWindowPrivate *wd = QQuickWindowPrivate::get(window);
+
+    // This is tricker than used to be. We want to detect having an empty
+    // surface size (which may be the case even when window->size() is
+    // non-empty, on some platforms with some graphics APIs!) as well as the
+    // case when the window just became "newly exposed" (e.g. after a
+    // minimize-restore on Windows, or when switching between fully obscured -
+    // not fully obscured on macOS)
+
+    if (!window->isExposed() || (wd->hasActiveSwapchain && wd->swapchain->surfacePixelSize().isEmpty()))
+        wd->hasRenderableSwapchain = false;
+
+    if (window->isExposed() && !wd->hasRenderableSwapchain && wd->hasActiveSwapchain
+            && !wd->swapchain->surfacePixelSize().isEmpty())
+    {
+        wd->hasRenderableSwapchain = true;
+        wd->swapchainJustBecameRenderable = true;
+    }
+
+    if (window->isExposed() && (!rhi || !wd->hasActiveSwapchain || wd->hasRenderableSwapchain)) {
         m_windows[window].updatePending = true;
         renderWindow(window);
     }
@@ -527,7 +787,7 @@ void QSGGuiThreadRenderLoop::handleUpdateRequest(QQuickWindow *window)
     renderWindow(window);
 }
 
-#endif
+#endif // ENABLE_DEFAULT_BACKEND
 
 #include "qsgrenderloop.moc"
 #include "moc_qsgrenderloop_p.cpp"