Don't commit same buffer multiple times

In Qt we call flush() when we think the window might need to be
updated. It is also possible to trigger a flush while painting.

Two fixes:

1) If there are attempted flushes between beginPaint() and endPaint,
queue them up, and do them in endPaint().

2) Make sure we only commit the buffer once: after that the
compositor owns the buffer, and it can repaint on its own.

Change-Id: Ibf61068fa95760eb67dbc0b1d0534854114ea528
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 5d658f675..b88541ad8 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -75,6 +75,8 @@ QT_BEGIN_NAMESPACE
 
 namespace QtWaylandClient {
 
+Q_LOGGING_CATEGORY(lcWaylandBackingstore, "qt.qpa.wayland.backingstore")
+
 QWaylandWindow *QWaylandWindow::mMouseGrab = nullptr;
 
 QWaylandWindow::QWaylandWindow(QWindow *window)
@@ -556,6 +558,7 @@ 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;
@@ -586,12 +589,18 @@ void QWaylandWindow::damage(const QRect &rect)
 
 void QWaylandWindow::commit(QWaylandBuffer *buffer, const QRegion &damage)
 {
+    if (buffer->committed()) {
+        qCDebug(lcWaylandBackingstore) << "Buffer already committed, ignoring.";
+        return;
+    }
     if (!isInitialized())
         return;
 
     attachOffset(buffer);
     for (const QRect &rect: damage)
         wl_surface::damage(rect.x(), rect.y(), rect.width(), rect.height());
+    Q_ASSERT(!buffer->committed());
+    buffer->setCommitted();
     wl_surface::commit();
 }