Revert "Client: Full implementation for frame callbacks"

This caused regressions because QtQuick depends on swapBuffers for throttling
animations. We probably need to emulate a blocking swapBuffers and continue
after a timeout, but until we have a patch for this, revert this to avoid
releasing a regression.

This brings back the bug with a frozen event loop when a surface is waiting for
a frame callback, but this is preferable to a regression.

This reverts commit 1dc85b95ab0adc1e805d059e2c35c671ef790011.

Fixes: QTBUG-72578
Change-Id: If6435a947aae5e9fd775404649a392bfafe9130a
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

3 files changed, 35 insertions, 103 deletions

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 470ae0091..282179efb 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -358,8 +358,6 @@ void QWaylandWindow::sendExposeEvent(const QRect &rect)
 {
     if (!(mShellSurface && mShellSurface->handleExpose(rect)))
         QWindowSystemInterface::handleExposeEvent(window(), rect);
-    else
-        qCDebug(lcQpaWayland) << "sendExposeEvent: intercepted by shell extension, not sending";
     mLastExposeGeometry = rect;
 }
 
@@ -544,11 +542,18 @@ void QWaylandWindow::handleScreenRemoved(QScreen *qScreen)
 void QWaylandWindow::attach(QWaylandBuffer *buffer, int x, int y)
 {
     Q_ASSERT(!buffer->committed());
+    if (mFrameCallback) {
+        wl_callback_destroy(mFrameCallback);
+        mFrameCallback = nullptr;
+    }
+
     if (buffer) {
-        handleUpdate();
+        mFrameCallback = frame();
+        wl_callback_add_listener(mFrameCallback, &QWaylandWindow::callbackListener, this);
+        mWaitingForFrameSync = true;
         buffer->setBusy();
 
-        QtWayland::wl_surface::attach(buffer->buffer(), x, y);
+        attach(buffer->buffer(), x, y);
     } else {
         QtWayland::wl_surface::attach(nullptr, 0, 0);
     }
@@ -613,9 +618,11 @@ void QWaylandWindow::frameCallback(void *data, struct wl_callback *callback, uin
     Q_UNUSED(callback);
     QWaylandWindow *self = static_cast<QWaylandWindow*>(data);
 
-    self->mWaitingForFrameCallback = false;
-    if (self->mUpdateRequested)
+    self->mWaitingForFrameSync = false;
+    if (self->mUpdateRequested) {
+        self->mUpdateRequested = false;
         self->deliverUpdateRequest();
+    }
 }
 
 QMutex QWaylandWindow::mFrameSyncMutex;
@@ -623,10 +630,10 @@ QMutex QWaylandWindow::mFrameSyncMutex;
 void QWaylandWindow::waitForFrameSync()
 {
     QMutexLocker locker(&mFrameSyncMutex);
-    if (!mWaitingForFrameCallback)
+    if (!mWaitingForFrameSync)
         return;
     mDisplay->flushRequests();
-    while (mWaitingForFrameCallback)
+    while (mWaitingForFrameSync)
         mDisplay->blockingReadEvents();
 }
 
@@ -1027,88 +1034,12 @@ QVariant QWaylandWindow::property(const QString &name, const QVariant &defaultVa
     return m_properties.value(name, defaultValue);
 }
 
-void QWaylandWindow::timerEvent(QTimerEvent *event)
-{
-    if (event->timerId() == mFallbackUpdateTimerId) {
-        killTimer(mFallbackUpdateTimerId);
-        mFallbackUpdateTimerId = -1;
-
-        if (!isExposed()) {
-            qCDebug(lcWaylandBackingstore) << "Fallback update timer: Window not exposed,"
-                                           << "not delivering update request.";
-            return;
-        }
-
-        if (mWaitingForUpdate && mUpdateRequested && !mWaitingForFrameCallback) {
-            qCWarning(lcWaylandBackingstore) << "Delivering update request through fallback timer,"
-                                             << "may not be in sync with display";
-            deliverUpdateRequest();
-        }
-    }
-}
-
 void QWaylandWindow::requestUpdate()
 {
-    if (mUpdateRequested)
-        return;
-
-    mUpdateRequested = true;
-
-    // If we have a frame callback all is good and will be taken care of there
-    if (mWaitingForFrameCallback)
-        return;
-
-    // If we've already called deliverUpdateRequest(), but haven't seen any attach+commit/swap yet
-    if (mWaitingForUpdate) {
-        // Ideally, we should just have returned here, but we're not guaranteed that the client
-        // will actually update, so start this timer to deliver another request update after a while
-        // *IF* the client doesn't update.
-        int fallbackTimeout = 100;
-        mFallbackUpdateTimerId = startTimer(fallbackTimeout);
-        return;
-    }
-
-    // Some applications (such as Qt Quick) depend on updates being delivered asynchronously,
-    // so use invokeMethod to delay the delivery a bit.
-    QMetaObject::invokeMethod(this, [this] {
-        // Things might have changed in the meantime
-        if (mUpdateRequested && !mWaitingForUpdate && !mWaitingForFrameCallback)
-            deliverUpdateRequest();
-    }, Qt::QueuedConnection);
-}
-
-// Should be called whenever we commit a buffer (directly through wl_surface.commit or indirectly
-// with eglSwapBuffers) to know when it's time to commit the next one.
-// Can be called from the render thread (without locking anything) so make sure to not make races in this method.
-void QWaylandWindow::handleUpdate()
-{
-    // TODO: Should sync subsurfaces avoid requesting frame callbacks?
-
-    if (mFrameCallback) {
-        wl_callback_destroy(mFrameCallback);
-        mFrameCallback = nullptr;
-    }
-
-    if (mFallbackUpdateTimerId != -1) {
-        // Ideally, we would stop the fallback timer here, but since we're on another thread,
-        // it's not allowed. Instead we set mFallbackUpdateTimer to -1 here, so we'll just
-        // ignore it if it times out before it's cleaned up by the invokeMethod call.
-        int id = mFallbackUpdateTimerId;
-        mFallbackUpdateTimerId = -1;
-        QMetaObject::invokeMethod(this, [=] { killTimer(id); }, Qt::QueuedConnection);
-    }
-
-    mFrameCallback = frame();
-    wl_callback_add_listener(mFrameCallback, &QWaylandWindow::callbackListener, this);
-    mWaitingForFrameCallback = true;
-    mWaitingForUpdate = false;
-}
-
-void QWaylandWindow::deliverUpdateRequest()
-{
-    mUpdateRequested = false;
-    mWaitingForUpdate = true;
-    QPlatformWindow::deliverUpdateRequest();
+    if (!mWaitingForFrameSync)
+        QPlatformWindow::requestUpdate();
+    else
+        mUpdateRequested = true;
 }
 
 void QWaylandWindow::addAttachOffset(const QPoint point)
diff --git a/src/client/qwaylandwindow_p.h b/src/client/qwaylandwindow_p.h
index e5838d231..56ebd3cc6 100644
--- a/src/client/qwaylandwindow_p.h
+++ b/src/client/qwaylandwindow_p.h
@@ -191,10 +191,7 @@ public:
 
     bool startSystemMove(const QPoint &pos) override;
 
-    void timerEvent(QTimerEvent *event) override;
     void requestUpdate() override;
-    void handleUpdate();
-    void deliverUpdateRequest() override;
 
 public slots:
     void applyConfigure();
@@ -214,14 +211,10 @@ protected:
     Qt::MouseButtons mMousePressedInContentArea = Qt::NoButton;
 
     WId mWindowId;
-    bool mWaitingForFrameCallback = false;
+    bool mWaitingForFrameSync = false;
     struct ::wl_callback *mFrameCallback = nullptr;
     QWaitCondition mFrameSyncWait;
 
-    // True when we have called deliverRequestUpdate, but the client has not yet attached a new buffer
-    bool mWaitingForUpdate = false;
-    int mFallbackUpdateTimerId = -1;
-
     QMutex mResizeLock;
     bool mWaitingToApplyConfigure = false;
     bool mCanResize = true;
diff --git a/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp b/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
index 0cbbe5389..e58403ad0 100644
--- a/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
+++ b/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
@@ -315,9 +315,7 @@ QWaylandGLContext::QWaylandGLContext(EGLDisplay eglDisplay, QWaylandDisplay *dis
        mSupportNonBlockingSwap = false;
     }
     if (!mSupportNonBlockingSwap) {
-        qWarning(lcQpaWayland) << "Non-blocking swap buffers not supported."
-                               << "Subsurface rendering can be affected."
-                               << "It may also cause the event loop to freeze in some situations";
+        qWarning() << "Non-blocking swap buffers not supported. Subsurface rendering can be affected.";
     }
 
     updateGLFormat();
@@ -552,10 +550,20 @@ void QWaylandGLContext::swapBuffers(QPlatformSurface *surface)
         m_blitter->blit(window);
     }
 
-    window->handleUpdate();
-    int swapInterval = mSupportNonBlockingSwap ? 0 : m_format.swapInterval();
-    eglSwapInterval(m_eglDisplay, swapInterval);
-    eglSwapBuffers(m_eglDisplay, eglSurface);
+
+    QWaylandSubSurface *sub = window->subSurfaceWindow();
+    if (sub) {
+        QMutexLocker l(sub->syncMutex());
+
+        int si = (sub->isSync() && mSupportNonBlockingSwap) ? 0 : m_format.swapInterval();
+
+        eglSwapInterval(m_eglDisplay, si);
+        eglSwapBuffers(m_eglDisplay, eglSurface);
+    } else {
+        eglSwapInterval(m_eglDisplay, m_format.swapInterval());
+        eglSwapBuffers(m_eglDisplay, eglSurface);
+    }
+
 
     window->setCanResize(true);
 }