Compose render-to-texture widgets through QRhi

QPlatformTextureList holds a QRhiTexture instead of GLuint. A
QPlatformBackingStore now optionally can own a QRhi and a
QRhiSwapChain for the associated window.  Non-GL rendering must use
this QRhi everywhere, whereas GL (QOpenGLWidget) can choose to still
rely on resource sharing between contexts. A widget tells that it
wants QRhi and the desired configuration in a new virtual function in
QWidgetPrivate returning a QPlatformBackingStoreRhiConfig. This is
evaluated (among a top-level's all children) upon create() before
creating the repaint manager and the QWidgetWindow.

In QOpenGLWidget what do request is obvious: it will request an
OpenGL-based QRhi. QQuickWidget (or a potential future QRhiWidget)
will be more interesting: it needs to honor the standard Qt Quick
env.vars. and QQuickWindow APIs (or, in whatever way the user
configured the QRhiWidget), and so will set up the config struct
accordingly.

In addition, the rhiconfig and surface type is (re)evaluated when
(re)parenting a widget to a new tlw. If needed, this will now trigger
a destroy - create on the tlw. This should be be safe to do in
setParent. When multiple child widgets report an enabled rhiconfig,
the first one (the first child encountered) wins. So e.g. attempting
to have a QOpenGLWidget and a Vulkan-based QQuickWidget in the same
top-level window will fail one of the widgets (it likely won't
render).

RasterGLSurface is no longer used by widgets. Rather, the appropriate
surface type is chosen.

The rhi support in the backingstore is usable without widgets as well.
To make rhiFlush() functional, one needs to call setRhiConfig() after
creating the QBackingStore. (like QWidget does to top-level windows)

Most of the QT_NO_OPENGL ifdefs are eliminated all over the place.
Everything with QRhi is unconditional code at compile time, except the
actual initialization.

Having to plumb the widget tlw's shareContext (or, now, the QRhi)
through QWindowPrivate is no longer needed.  The old approach does not
scale: to implement composeAndFlush (now rhiFlush) we need more than
just a QRhi object, and this way we no longer pollute everything
starting from the widget level (QWidget's topextra -> QWidgetWindow ->
QWindowPrivate) just to send data around.

The BackingStoreOpenGLSupport interface and the QtGui - QtOpenGL split
is all gone. Instead, there is a QBackingStoreDefaultCompositor in
QtGui which is what the default implementations of composeAndFlush and
toTexture call. (overriding composeAndFlush and co. f.ex. in eglfs
should continue working mostly as-is, apart from adapting to the
texture list changes and getting the native OpenGL texture id out of
the QRhiTexture)

As QQuickWidget is way too complicated to just port as-is, an rhi
manual test (rhiwidget) is introduced as a first step, in ordewr to
exercise a simple, custom render-to-texture widget that does something
using a (not necessarily OpenGL-backed) QRhi and acts as fully
functional QWidget (modeled after QOpenGLWidget). This can also form
the foundation of a potential future QRhiWidget.

It is also possible to force the QRhi-based flushing always,
regardless of the presence of render-to-texture widgets. To exercise
this, set the env.var. QT_WIDGETS_RHI=1. This picks a
platform-specific default, and can be overridden with
QT_WIDGETS_RHI_BACKEND. (in sync with Qt Quick) This can eventually be
extended to query the platform plugin as well to check if the platform
plugin prefers to always do flushes with a 3D API.

QOpenGLWidget should work like before from the user's perspective, while
internally it has to do some things differently to play nice and prevent
regressions with the new rendering architecture. To exercise this
better, the qopenglwidget example gets a new tab-based view (that could
perhaps replace the example's main window later on?). The openglwidget
manual test is made compatible with Qt 6, and gets a counterpart in form
of the dockedopenglwidget manual test, which is a modified version of
the cube example that features dock widgets. This is relevant in
particular because render-to-texture widgets within a QDockWidget has
its own specific quirks, with logic taking this into account, hence
testing is essential.

For existing applications there are two important consequences with
this patch in place:

- Once the rhi-based composition is enabled, it stays active for the
lifetime of the top-level window.

- Dynamically creating and parenting the first render-to-texture
widget to an already created tlw will destroy and recreate the tlw
(and the underlying window). The visible effects of this depend on the
platform.  (e.g. the window may disappear and reappear on some,
whereas with other windowing systems it is not noticeable at all -
this is not really different from similar situtions with reparenting
or when moving windows between screens, so should be acceptable in
practice)

- On iOS raster windows are flushed with Metal (and rhi) from now on
(previously this was through OpenGL by making flush() call
composeAndFlush().

Change-Id: Id05bd0f7a26fa845f8b7ad8eedda3b0e78ab7a4e
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 80 insertions, 61 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 0a0957bf5e..1527ec679f 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -77,9 +77,6 @@
 #include "qscopeguard.h"
 #include <QtGui/private/qhighdpiscaling_p.h>
 #include <QtGui/qinputmethod.h>
-#include <QtGui/qopenglcontext.h>
-#include <QtGui/private/qopenglcontext_p.h>
-#include <QtGui/qoffscreensurface.h>
 
 #if QT_CONFIG(graphicseffect)
 #include <private/qgraphicseffect_p.h>
@@ -178,10 +175,8 @@ QWidgetPrivate::QWidgetPrivate(int version)
 #ifndef QT_NO_IM
       , inheritsInputMethodHints(0)
 #endif
-#ifndef QT_NO_OPENGL
       , renderToTextureReallyDirty(1)
-      , renderToTextureComposeActive(0)
-#endif
+      , usesRhiFlush(0)
       , childrenHiddenByWState(0)
       , childrenShownByExpose(0)
 #if defined(Q_OS_WIN)
@@ -1114,6 +1109,47 @@ QScreen *QWidgetPrivate::associatedScreen() const
     return nullptr;
 }
 
+// finds the first rhiconfig in the hierarchy that has enable==true
+static bool q_evaluateRhiConfigRecursive(const QWidget *w, QPlatformBackingStoreRhiConfig *outConfig, QSurface::SurfaceType *outType)
+{
+    QPlatformBackingStoreRhiConfig config = QWidgetPrivate::get(w)->rhiConfig();
+    if (config.isEnabled()) {
+        if (outConfig)
+            *outConfig = config;
+        if (outType)
+            *outType = QBackingStoreRhiSupport::surfaceTypeForConfig(config);
+        return true;
+    }
+    QObjectList children = w->children();
+    for (int i = 0; i < children.size(); i++) {
+        if (children.at(i)->isWidgetType()) {
+            const QWidget *childWidget = qobject_cast<const QWidget *>(children.at(i));
+            if (childWidget) {
+                if (q_evaluateRhiConfigRecursive(childWidget, outConfig, outType))
+                    return true;
+            }
+        }
+    }
+    return false;
+}
+
+// First tries q_evaluateRhiConfigRecursive, then if that did not indicate that rhi is wanted,
+// then checks env.vars or something else to see if we need to force using rhi-based composition.
+bool q_evaluateRhiConfig(const QWidget *w, QPlatformBackingStoreRhiConfig *outConfig, QSurface::SurfaceType *outType)
+{
+    if (q_evaluateRhiConfigRecursive(w, outConfig, outType)) {
+        qCDebug(lcWidgetPainting) << "Tree with root" << w << "evaluates to flushing with QRhi";
+        return true;
+    }
+
+    if (QBackingStoreRhiSupport::checkForceRhi(outConfig, outType)) {
+        qCDebug(lcWidgetPainting) << "Tree with root" << w << "evaluated to forced flushing with QRhi";
+        return true;
+    }
+
+    return false;
+}
+
 // ### fixme: Qt 6: Remove parameter window from QWidget::create()
 
 /*!
@@ -1336,14 +1372,21 @@ void QWidgetPrivate::create()
 #endif
 
     QBackingStore *store = q->backingStore();
+    usesRhiFlush = false;
 
     if (!store) {
         if (q->windowType() != Qt::Desktop) {
-            if (q->isWindow())
+            if (q->isWindow()) {
                 q->setBackingStore(new QBackingStore(win));
+                QPlatformBackingStoreRhiConfig rhiConfig;
+                usesRhiFlush = q_evaluateRhiConfig(q, &rhiConfig, nullptr);
+                topData()->backingStore->handle()->setRhiConfig(rhiConfig);
+            }
         } else {
             q->setAttribute(Qt::WA_PaintOnScreen, true);
         }
+    } else if (win->handle()) {
+        usesRhiFlush = q_evaluateRhiConfig(q, nullptr, nullptr);
     }
 
     setWindowModified_helper();
@@ -1685,10 +1728,7 @@ void QWidgetPrivate::deleteTLSysExtra()
 
         extra->topextra->repaintManager.reset(nullptr);
         deleteBackingStore(this);
-#ifndef QT_NO_OPENGL
         extra->topextra->widgetTextures.clear();
-        extra->topextra->shareContext.reset();
-#endif
 
         //the toplevel might have a context with a "qglcontext associated with it. We need to
         //delete the qglcontext before we delete the qplatformopenglcontext.
@@ -5538,30 +5578,22 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                 //paint the background
                 if ((asRoot || q->autoFillBackground() || onScreen || q->testAttribute(Qt::WA_StyledBackground))
                     && !q->testAttribute(Qt::WA_OpaquePaintEvent) && !q->testAttribute(Qt::WA_NoSystemBackground)) {
-#ifndef QT_NO_OPENGL
                     beginBackingStorePainting();
-#endif
                     QPainter p(q);
                     paintBackground(&p, toBePainted, (asRoot || onScreen) ? (flags | DrawAsRoot) : DrawWidgetFlags());
-#ifndef QT_NO_OPENGL
                     endBackingStorePainting();
-#endif
                 }
 
                 if (!sharedPainter)
                     setSystemClip(pdev->paintEngine(), pdev->devicePixelRatio(), toBePainted.translated(offset));
 
                 if (!onScreen && !asRoot && !isOpaque && q->testAttribute(Qt::WA_TintedBackground)) {
-#ifndef QT_NO_OPENGL
                     beginBackingStorePainting();
-#endif
                     QPainter p(q);
                     QColor tint = q->palette().window().color();
                     tint.setAlphaF(.6f);
                     p.fillRect(toBePainted.boundingRect(), tint);
-#ifndef QT_NO_OPENGL
                     endBackingStorePainting();
-#endif
                 }
             }
 
@@ -5572,7 +5604,6 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
 #endif
 
             bool skipPaintEvent = false;
-#ifndef QT_NO_OPENGL
             if (renderToTexture) {
                 // This widget renders into a texture which is composed later. We just need to
                 // punch a hole in the backingstore, so the texture will be visible.
@@ -5598,7 +5629,6 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                 else
                     skipPaintEvent = true;
             }
-#endif // QT_NO_OPENGL
 
             if (!skipPaintEvent) {
                 //actually send the paint event
@@ -5654,10 +5684,8 @@ void QWidgetPrivate::sendPaintEvent(const QRegion &toBePainted)
     QPaintEvent e(toBePainted);
     QCoreApplication::sendSpontaneousEvent(q, &e);
 
-#ifndef QT_NO_OPENGL
     if (renderToTexture)
         resolveSamples();
-#endif // QT_NO_OPENGL
 }
 
 void QWidgetPrivate::render(QPaintDevice *target, const QPoint &targetOffset,
@@ -9232,9 +9260,7 @@ bool QWidget::event(QEvent *event)
         }
         if (d->data.fnt.d->dpi != logicalDpiY())
             d->updateFont(d->data.fnt);
-#ifndef QT_NO_OPENGL
         d->renderToTextureReallyDirty = 1;
-#endif
         break;
     case QEvent::DynamicPropertyChange: {
         const QByteArray &propName = static_cast<QDynamicPropertyChangeEvent *>(event)->propertyName();
@@ -10511,22 +10537,20 @@ void QWidget::setParent(QWidget *parent)
     setParent((QWidget*)parent, windowFlags() & ~Qt::WindowType_Mask);
 }
 
-#ifndef QT_NO_OPENGL
-static void sendWindowChangeToTextureChildrenRecursively(QWidget *widget)
+static void sendWindowChangeToTextureChildrenRecursively(QWidget *widget, QEvent::Type eventType)
 {
     QWidgetPrivate *d = QWidgetPrivate::get(widget);
     if (d->renderToTexture) {
-        QEvent e(QEvent::WindowChangeInternal);
+        QEvent e(eventType);
         QCoreApplication::sendEvent(widget, &e);
     }
 
     for (int i = 0; i < d->children.size(); ++i) {
         QWidget *w = qobject_cast<QWidget *>(d->children.at(i));
         if (w && !w->isWindow() && QWidgetPrivate::get(w)->textureChildSeen)
-            sendWindowChangeToTextureChildrenRecursively(w);
+            sendWindowChangeToTextureChildrenRecursively(w, eventType);
     }
 }
-#endif
 
 /*!
     \overload
@@ -10582,6 +10606,12 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
             QCoreApplication::sendEvent(this, &e);
         }
     }
+
+    // texture-based widgets need a pre-notification when their associated top-level window changes
+    // This is not under the wasCreated/newParent conditions above in order to also play nice with QDockWidget.
+    if (d->textureChildSeen && ((!parent && parentWidget()) || (parent && parent->window() != oldtlw)))
+        sendWindowChangeToTextureChildrenRecursively(this, QEvent::WindowAboutToChangeInternal);
+
     // If we get parented into another window, children will be folded
     // into the new parent's focus chain, so clear focus now.
     if (newParent && isAncestorOf(focusWidget()) && !(f & Qt::Window))
@@ -10592,12 +10622,10 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
     if (desktopWidget)
         parent = nullptr;
 
-#ifndef QT_NO_OPENGL
     if (d->textureChildSeen && parent) {
         // set the textureChildSeen flag up the whole parent chain
         QWidgetPrivate::get(parent)->setTextureChildSeen();
     }
-#endif
 
     if (QWidgetRepaintManager *oldPaintManager = oldtlw->d_func()->maybeRepaintManager()) {
         if (newParent)
@@ -10659,12 +10687,11 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
         QEvent e(QEvent::ParentChange);
         QCoreApplication::sendEvent(this, &e);
     }
-#ifndef QT_NO_OPENGL
-    //renderToTexture widgets also need to know when their top-level window changes
-    if (d->textureChildSeen && oldtlw != window()) {
-        sendWindowChangeToTextureChildrenRecursively(this);
-    }
-#endif
+
+    // texture-based widgets need another event when their top-level window
+    // changes (more precisely, has already changed at this point)
+    if (d->textureChildSeen && oldtlw != window())
+        sendWindowChangeToTextureChildrenRecursively(this, QEvent::WindowChangeInternal);
 
     if (!wasCreated) {
         if (isWindow() || parentWidget()->isVisible())
@@ -10690,6 +10717,20 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
 
     if (d->extra && d->extra->hasWindowContainer)
         QWindowContainer::parentWasChanged(this);
+
+    QWidget *newtlw = window();
+    if (oldtlw != newtlw) {
+        QSurface::SurfaceType surfaceType = QSurface::RasterSurface;
+        if (q_evaluateRhiConfig(this, nullptr, &surfaceType)) {
+            newtlw->d_func()->usesRhiFlush = true;
+            if (QWindow *w = newtlw->windowHandle()) {
+                if (w->surfaceType() != surfaceType) {
+                    newtlw->destroy();
+                    newtlw->create();
+                }
+            }
+        }
+    }
 }
 
 void QWidgetPrivate::setParent_sys(QWidget *newparent, Qt::WindowFlags f)
@@ -10947,7 +10988,7 @@ void QWidgetPrivate::repaint(T r)
         return;
 
     QTLWExtra *tlwExtra = q->window()->d_func()->maybeTopData();
-    if (tlwExtra && tlwExtra->backingStore)
+    if (tlwExtra && tlwExtra->backingStore && tlwExtra->repaintManager)
         tlwExtra->repaintManager->markDirty(r, q, QWidgetRepaintManager::UpdateNow);
 }
 
@@ -11022,7 +11063,7 @@ void QWidgetPrivate::update(T r)
     }
 
     QTLWExtra *tlwExtra = q->window()->d_func()->maybeTopData();
-    if (tlwExtra && tlwExtra->backingStore)
+    if (tlwExtra && tlwExtra->backingStore && tlwExtra->repaintManager)
         tlwExtra->repaintManager->markDirty(clipped, q);
 }
 
@@ -12158,27 +12199,6 @@ void QWidgetPrivate::adjustQuitOnCloseAttribute()
     }
 }
 
-QOpenGLContext *QWidgetPrivate::shareContext() const
-{
-#ifdef QT_NO_OPENGL
-    return nullptr;
-#else
-    if (!extra || !extra->topextra || !extra->topextra->window)
-        return nullptr;
-
-    if (!extra->topextra->shareContext) {
-        auto ctx = std::make_unique<QOpenGLContext>();
-        ctx->setShareContext(qt_gl_global_share_context());
-        ctx->setFormat(extra->topextra->window->format());
-        ctx->setScreen(extra->topextra->window->screen());
-        ctx->create();
-        extra->topextra->shareContext = std::move(ctx);
-    }
-    return extra->topextra->shareContext.get();
-#endif // QT_NO_OPENGL
-}
-
-#ifndef QT_NO_OPENGL
 void QWidgetPrivate::sendComposeStatus(QWidget *w, bool end)
 {
     QWidgetPrivate *wd = QWidgetPrivate::get(w);
@@ -12194,7 +12214,6 @@ void QWidgetPrivate::sendComposeStatus(QWidget *w, bool end)
             sendComposeStatus(w, end);
     }
 }
-#endif // QT_NO_OPENGL
 
 Q_WIDGETS_EXPORT QWidgetData *qt_qwidget_data(QWidget *widget)
 {