QWaylandShmBackingStore: Split buffer preparation into dedicated method

Drop "resize(QRect)" since it is ambiguous with the resize coming from
QPlatformBackingStore.

This allows to ensure a back buffer from multiple places, such as the
upcoming "scroll" support.

Change-Id: I43a5ece2d0e25e64b41335ba59b2b8c4ffcfff74
Reviewed-by: David Edmundson <davidedmundson@kde.org>

3 files changed, 11 insertions, 15 deletions

diff --git a/src/client/qwaylandshmbackingstore.cpp b/src/client/qwaylandshmbackingstore.cpp
index 723b264d5..a1e9e0e4a 100644
--- a/src/client/qwaylandshmbackingstore.cpp
+++ b/src/client/qwaylandshmbackingstore.cpp
@@ -144,9 +144,9 @@ QWaylandShmBackingStore::QWaylandShmBackingStore(QWindow *window, QWaylandDispla
         // contents from the back buffer
         mBuffers.clear();
         mFrontBuffer = nullptr;
-        // resize always resets mBackBuffer
+        // ensureBackBuffer always resets mBackBuffer
         if (mRequestedSize.isValid() && waylandWindow())
-            resize(mRequestedSize);
+            ensureBackBuffer();
         qDeleteAll(copy);
     });
 }
@@ -180,7 +180,8 @@ void QWaylandShmBackingStore::updateDirtyStates(const QRegion &region)
 void QWaylandShmBackingStore::beginPaint(const QRegion &region)
 {
     mPainting = true;
-    ensureSize();
+    waylandWindow()->setBackingStore(this);
+    ensureBackBuffer();
 
     const QMargins margins = windowDecorationMargins();
     updateDirtyStates(region.translated(margins.left(), margins.top()));
@@ -201,12 +202,6 @@ void QWaylandShmBackingStore::endPaint()
         flush(window(), mPendingRegion, QPoint());
 }
 
-void QWaylandShmBackingStore::ensureSize()
-{
-    waylandWindow()->setBackingStore(this);
-    resize(mRequestedSize);
-}
-
 void QWaylandShmBackingStore::flush(QWindow *window, const QRegion &region, const QPoint &offset)
 {
     // Invoked when the window is of type RasterSurface or when the window is
@@ -269,11 +264,11 @@ QWaylandShmBuffer *QWaylandShmBackingStore::getBuffer(const QSize &size)
     return nullptr;
 }
 
-void QWaylandShmBackingStore::resize(const QSize &size)
+void QWaylandShmBackingStore::ensureBackBuffer()
 {
     QMargins margins = windowDecorationMargins();
     qreal scale = waylandWindow()->scale();
-    QSize sizeWithMargins = (size + QSize(margins.left()+margins.right(),margins.top()+margins.bottom())) * scale;
+    const QSize sizeWithMargins = (mRequestedSize + QSize(margins.left() + margins.right(), margins.top() + margins.bottom())) * scale;
 
     // We look for a free buffer to draw into. If the buffer is not the last buffer we used,
     // that is mBackBuffer, and the size is the same we copy the damaged content into the new
diff --git a/src/client/qwaylandshmbackingstore_p.h b/src/client/qwaylandshmbackingstore_p.h
index 8c7b83dbb..788893360 100644
--- a/src/client/qwaylandshmbackingstore_p.h
+++ b/src/client/qwaylandshmbackingstore_p.h
@@ -61,7 +61,6 @@ public:
     QPaintDevice *paintDevice() override;
     void flush(QWindow *window, const QRegion &region, const QPoint &offset) override;
     void resize(const QSize &size, const QRegion &staticContents) override;
-    void resize(const QSize &size);
     void beginPaint(const QRegion &region) override;
     void endPaint() override;
 
@@ -70,7 +69,7 @@ public:
     QMargins windowDecorationMargins() const;
     QImage *entireSurface() const;
     QImage *contentSurface() const;
-    void ensureSize();
+    void ensureBackBuffer();
 
     QWaylandWindow *waylandWindow() const;
     void iterateBuffer();
diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 7bc79eb8a..bb33a747f 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -90,8 +90,10 @@ QWaylandWindow::~QWaylandWindow()
 
 void QWaylandWindow::ensureSize()
 {
-    if (mBackingStore)
-        mBackingStore->ensureSize();
+    if (mBackingStore) {
+        setBackingStore(mBackingStore);
+        mBackingStore->ensureBackBuffer();
+    }
 }
 
 void QWaylandWindow::initWindow()