Merge commit 'origin/4.5'

Conflicts:
	src/gui/graphicsview/qgraphicsitem.cpp
	src/gui/graphicsview/qgraphicsitem_p.h
	src/gui/graphicsview/qgraphicsscene.cpp
	src/gui/painting/qtransform.cpp

2 files changed, 26 insertions, 2 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index dc236e4..c7a20db 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -3607,6 +3607,9 @@ int QImage::pixelIndex(int x, int y) const
 
     If the \a position is not valid, the results are undefined.
 
+    \warning This function is expensive when used for massive pixel
+    manipulations.
+
     \sa setPixel(), valid(), {QImage#Pixel Manipulation}{Pixel
     Manipulation}
 */
@@ -5581,6 +5584,8 @@ bool QImage::isDetached() const
 
     Use one of the composition mods in QPainter::CompositionMode instead.
 
+    \warning This function is expensive.
+
     \sa alphaChannel(), {QImage#Image Transformations}{Image
     Transformations}, {QImage#Image Formats}{Image Formats}
 */
@@ -5663,6 +5668,11 @@ void QImage::setAlphaChannel(const QImage &alphaChannel)
     \l{QPixmap::}{alphaChannel()}, which works in the same way as
     this function on QPixmaps.
 
+    Most usecases for this function can be replaced with QPainter and
+    using composition modes.
+
+    \warning This is an expensive function.
+
     \sa setAlphaChannel(), hasAlphaChannel(),
     {QPixmap#Pixmap Information}{Pixmap},
     {QImage#Image Transformations}{Image Transformations}
diff --git a/src/gui/image/qpixmap.cpp b/src/gui/image/qpixmap.cpp
index e563fc9..3b82da8 100644
--- a/src/gui/image/qpixmap.cpp
+++ b/src/gui/image/qpixmap.cpp
@@ -724,7 +724,7 @@ void QPixmap::resize_helper(const QSize &s)
     pixels black. The effect of this function is undefined when the pixmap is
     being painted on.
 
-    This is potentially an expensive operation.
+    \warning This is potentially an expensive operation.
 
     \sa mask(), {QPixmap#Pixmap Transformations}{Pixmap Transformations},
     QBitmap
@@ -1430,6 +1430,12 @@ void QPixmap::deref()
     If the given \a size is empty, this function returns a null
     pixmap.
 
+
+    In some cases it can be more beneficial to draw the pixmap to a
+    painter with a scale set rather than scaling the pixmap. This is
+    the case when the painter is for instance based on OpenGL or when
+    the scale factor changes rapidly.
+
     \sa isNull(), {QPixmap#Pixmap Transformations}{Pixmap
     Transformations}
 
@@ -1801,6 +1807,10 @@ int QPixmap::metric(PaintDeviceMetric metric) const
     The effect of this function is undefined when the pixmap is being
     painted on.
 
+    \warning This is potentially an expensive operation. Most usecases
+    for this function are covered by QPainter and compositionModes
+    which will normally execute faster.
+
     \sa alphaChannel(), {QPixmap#Pixmap Transformations}{Pixmap
     Transformations}
  */
@@ -1843,6 +1853,9 @@ void QPixmap::setAlphaChannel(const QPixmap &alphaChannel)
 
     \image alphachannelimage.png The pixmap and channelImage QPixmaps
 
+    \warning This is an expensive operation. The alpha channel of the
+    pixmap is extracted dynamically from the pixeldata.
+
     \sa setAlphaChannel(), {QPixmap#Pixmap Information}{Pixmap
     Information}
 */
@@ -1864,7 +1877,8 @@ QPaintEngine *QPixmap::paintEngine() const
 
     Extracts a bitmap mask from the pixmap's alphachannel.
 
-    This is potentially an expensive operation.
+    \warning This is potentially an expensive operation. The mask of
+    the pixmap is extracted dynamically from the pixeldata.
 
     \sa setMask(), {QPixmap#Pixmap Information}{Pixmap Information}
 */