Set a non-zero default cacheBuffer.

The likelihood of constant framerate when flicking is considerably
improved by having a cacheBuffer.  Since there is only a minimal cost
in having a modest cacheBuffer, it is better to have a more optimal
default value - 320 seems a good starting point.

Change-Id: Id3c8a153821573b5b08c6fbd80d34152908d358d
Reviewed-by: Bea Lam <bea.lam@nokia.com>

3 files changed, 14 insertions, 5 deletions

diff --git a/src/quick/items/qquickgridview.cpp b/src/quick/items/qquickgridview.cpp
index 331f23e4c8..fa1e96c824 100644
--- a/src/quick/items/qquickgridview.cpp
+++ b/src/quick/items/qquickgridview.cpp
@@ -1533,8 +1533,10 @@ void QQuickGridView::setHighlightFollowsCurrentItem(bool autoHighlight)
     area may be created/retained.  The buffered delegates are created asynchronously,
     allowing creation to occur across multiple frames and reducing the
     likelihood of skipping frames.  In order to improve painting performance
-    delegates outside the visible area have their \l visible property set to
-    false until they are moved into the visible area.
+    delegates outside the visible area are not painted.
+
+    The default value of this property is platform dependent, but will usually
+    be a non-zero value.
 
     Note that cacheBuffer is not a pixel buffer - it only maintains additional
     instantiated delegates.
diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index 26580e0346..8b8f9356c9 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -41,9 +41,14 @@
 
 #include "qquickitemview_p_p.h"
 #include <QtQuick/private/qquicktransition_p.h>
+#include "qplatformdefs.h"
 
 QT_BEGIN_NAMESPACE
 
+// Default cacheBuffer for all views.
+#ifndef QML_VIEW_DEFAULTCACHEBUFFER
+#define QML_VIEW_DEFAULTCACHEBUFFER 320
+#endif
 
 FxViewItem::FxViewItem(QQuickItem *i, bool own, bool trackGeometry)
     : item(i)
@@ -1410,7 +1415,7 @@ void QQuickItemView::componentComplete()
 
 QQuickItemViewPrivate::QQuickItemViewPrivate()
     : itemCount(0)
-    , buffer(0), bufferMode(BufferBefore | BufferAfter)
+    , buffer(QML_VIEW_DEFAULTCACHEBUFFER), bufferMode(BufferBefore | BufferAfter)
     , layoutDirection(Qt::LeftToRight), verticalLayoutDirection(QQuickItemView::TopToBottom)
     , moveReason(Other)
     , visibleIndex(0)
diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index 75d4933862..5401abc442 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -2094,8 +2094,10 @@ void QQuickListView::setOrientation(QQuickListView::Orientation orientation)
     area may be created/retained.  The buffered delegates are created asynchronously,
     allowing creation to occur across multiple frames and reducing the
     likelihood of skipping frames.  In order to improve painting performance
-    delegates outside the visible area have their \l visible property set to
-    false until they are moved into the visible area.
+    delegates outside the visible area are not painted.
+
+    The default value of this property is platform dependent, but will usually
+    be a non-zero value.
 
     Note that cacheBuffer is not a pixel buffer - it only maintains additional
     instantiated delegates.