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, 12 insertions, 5 deletions

diff --git a/src/client/qwaylandshmbackingstore.cpp b/src/client/qwaylandshmbackingstore.cpp
index dde01357..ecb03c0d 100644
--- a/src/client/qwaylandshmbackingstore.cpp
+++ b/src/client/qwaylandshmbackingstore.cpp
@@ -48,7 +48,6 @@
 #include <QtCore/qtemporaryfile.h>
 #include <QtGui/QPainter>
 #include <QMutexLocker>
-#include <QLoggingCategory>
 
 #include <wayland-client.h>
 #include <wayland-client-protocol.h>
@@ -68,10 +67,6 @@ QT_BEGIN_NAMESPACE
 
 namespace QtWaylandClient {
 
-Q_DECLARE_LOGGING_CATEGORY(lcWaylandBackingstore)
-
-Q_LOGGING_CATEGORY(lcWaylandBackingstore, "qt.qpa.wayland.backingstore")
-
 QWaylandShmBuffer::QWaylandShmBuffer(QWaylandDisplay *display,
                      const QSize &size, QImage::Format format, int scale)
 {
@@ -199,6 +194,8 @@ void QWaylandShmBackingStore::beginPaint(const QRegion &region)
 void QWaylandShmBackingStore::endPaint()
 {
     mPainting = false;
+    if (mPendingFlush)
+        flush(window(), mPendingRegion, QPoint());
     waylandWindow()->setCanResize(true);
 }
 
@@ -218,9 +215,19 @@ void QWaylandShmBackingStore::flush(QWindow *window, const QRegion &region, cons
     // called instead. The default implementation from QPlatformBackingStore is sufficient
     // however so no need to reimplement that.
 
+
     Q_UNUSED(window);
     Q_UNUSED(offset);
 
+    if (mPainting) {
+        mPendingRegion |= region;
+        mPendingFlush = true;
+        return;
+    }
+
+    mPendingFlush = false;
+    mPendingRegion = QRegion();
+
     if (windowDecoration() && windowDecoration()->isDirty())
         updateDecorations();