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/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
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** This file is part of the documentation of the Qt Toolkit.
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** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
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** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** If you have questions regarding the use of this file, please contact
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** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qdeclarativeperformance.html
\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
\e 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
}
Rectange {
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
}
Rectange {
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.
*/
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