| 1 | /****************************************************************************
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| 2 | **
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| 3 | ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
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| 4 | ** All rights reserved.
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| 5 | ** Contact: Nokia Corporation ([email protected])
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| 6 | **
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| 7 | ** This file is part of the documentation of the Qt Toolkit.
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| 8 | **
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| 9 | ** $QT_BEGIN_LICENSE:FDL$
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| 10 | ** Commercial Usage
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| 11 | ** Licensees holding valid Qt Commercial licenses may use this file in
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| 12 | ** accordance with the Qt Commercial License Agreement provided with the
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| 13 | ** Software or, alternatively, in accordance with the terms contained in a
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| 14 | ** written agreement between you and Nokia.
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| 15 | **
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| 16 | ** GNU Free Documentation License
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| 17 | ** Alternatively, this file may be used under the terms of the GNU Free
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| 18 | ** Documentation License version 1.3 as published by the Free Software
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| 20 | ** file.
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| 22 | ** If you have questions regarding the use of this file, please contact
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| 23 | ** Nokia at [email protected].
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| 24 | ** $QT_END_LICENSE$
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| 26 | ****************************************************************************/
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| 27 |
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| 28 | /*!
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| 29 | \example painting/concentriccircles
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| 30 | \title Concentric Circles Example
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| 31 |
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| 32 | The Concentric Circles example shows the improved rendering
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| 33 | quality that can be obtained using floating point precision and
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| 34 | anti-aliasing when drawing custom widgets. The example also shows
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| 35 | how to do simple animations.
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| 36 |
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| 37 | The application's main window displays several widgets which are
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| 38 | drawn using the various combinations of precision and
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| 39 | anti-aliasing.
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| 40 |
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| 41 | \image concentriccircles-example.png
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| 42 |
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| 43 | Anti-aliasing is one of QPainter's render hints. The
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| 44 | QPainter::RenderHints are used to specify flags to QPainter that
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| 45 | may, or may not, be respected by any given
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| 46 | engine. QPainter::Antialiasing indicates that the engine should
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| 47 | anti-alias the edges of primitives if possible, i.e. put
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| 48 | additional pixels around the original ones to smooth the edges.
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| 49 |
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| 50 | The difference between floating point precision and integer
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| 51 | precision is a matter of accuracy, and is visible in the
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| 52 | application's main window: Even though the logic that is
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| 53 | calculating the circles' geometry is the same, floating points
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| 54 | ensure that the white spaces between each circle are of the same
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| 55 | size, while integers make two and two circles appear as if they
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| 56 | belong together. The reason is that the integer based precision
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| 57 | rely on rounding off non-integer calculations.
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| 58 |
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| 59 | The example consists of two classes:
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| 60 |
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| 61 | \list
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| 62 | \o \c CircleWidget is a custom widget which renders several animated
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| 63 | concentric circles.
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| 64 | \o \c Window is the application's main window displaying four \c
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| 65 | {CircleWidget}s drawn using different combinations of precision
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| 66 | and aliasing.
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| 67 | \endlist
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| 68 |
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| 69 | First we will review the CircleWidget class, then we will take a
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| 70 | look at the Window class.
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| 71 |
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| 72 | \section1 CircleWidget Class Definition
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