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/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtquick2-performance.html
\inqmlmodule QtQuick 2
\title QML Performance
\section1 Opaque Items
Items hidden behind an opaque item incur a cost. If an item will be enitrely
obscured by an opaque item, set its opacity to 0. One common example of
this is when a "details" page is shown over the main application view.
\section1 Clipping
\i clip is set to false by default. Enable clipping only when necessary.
\section1 Anchors vs. Binding
It is more efficient to use anchors rather than bindings to position items
relative to each other. Consider this use of bindings to position rect2
relative to rect1:
\code
Rectangle {
id: rect1
x: 20
width: 200; height: 200
}
Rectangle {
id: rect2
x: rect1.x
y: rect1.y + rect1.height
width: rect1.width - 20
height: 200
}
\endcode
This is achieved more efficiently using anchors:
\code
Rectangle {
id: rect1
x: 20
width: 200; height: 200
}
Rectangle {
id: rect2
height: 200
anchors.left: rect1.left
anchors.top: rect1.bottom
anchors.right: rect1.right
anchors.rightMargin: 20
}
\endcode
\section1 Images
Images consume a great deal of memory and may also be costly to load. In order
to deal with large images efficiently it is recommended that the Image::sourceSize
property be set to a size no greater than that necessary to render it. Beware that
changing the sourceSize will cause the image to be reloaded.
Images on the local filesystem are usually loaded synchronously. This is usually
the desired behavior for user interface elements, however for large images that
do not necessarily need to be visible immediately, set the Image::asynchronous
property to true. This will load the image in a low priority thread.
\section1 View Delegates
Delegates must be created quickly as the view is flicked. There are two important
aspects to maintaining a smooth view:
\list
\o Small delegates - keep the amount of QML to a minimum. Have just enough
QML in the delegate to display the necessary information. Any additional functionality
that is only needed when the delegate is clicked, for example, should be created by
a Loader as needed.
\o Fast data access - ensure the data model is as fast as possible.
\endlist
\section1 Image resources over composition
If possible, provide a single image resource, rather than using composition
of a number of elements. For example, a frame with a shadow could be created using
a Rectangle placed over an Image providing the shadow. It is more efficient to
provide an image that includes the frame and the shadow.
\section1 Limit JavaScript
Avoid running JavaScript during animation. For example, running a complex
JavaScript expression for each frame of an x property animation.
\section1 Loading later
Startup time is influenced by the amount of QML that must be loaded. Breaking your
application into components which can be loaded when needed will allow faster startup time.
This allows better runtime memory management by unloading the components when no
longer needed.
This may be achieved by using either \l Loader or creating components
\l {Dynamic Object Management in QML}{dynamically}.
\section1 Property Types
When possible use a specific type, rather than variant, when declaring properties.
\code
Item {
property variant foo: 10
property real bar: 10
x: foo * 2
y: bar *3
}
\endcode
bar is faster than foo.
*/
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