author | Eckhart Koeppen <eckhart.koppen@nokia.com> |
Thu, 08 Apr 2010 14:19:33 +0300 | |
branch | RCL_3 |
changeset 7 | 3f74d0d4af4c |
permissions | -rw-r--r-- |
7
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/**************************************************************************** |
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** |
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** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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** All rights reserved. |
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** Contact: Nokia Corporation (qt-info@nokia.com) |
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** |
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** This file is part of the documentation of the Qt Toolkit. |
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** |
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** $QT_BEGIN_LICENSE:LGPL$ |
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** No Commercial Usage |
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** This file contains pre-release code and may not be distributed. |
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** You may use this file in accordance with the terms and conditions |
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** contained in the Technology Preview License Agreement accompanying |
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** this package. |
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** |
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** GNU Lesser General Public License Usage |
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** Alternatively, this file may be used under the terms of the GNU Lesser |
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** General Public License version 2.1 as published by the Free Software |
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** Foundation and appearing in the file LICENSE.LGPL included in the |
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** packaging of this file. Please review the following information to |
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** ensure the GNU Lesser General Public License version 2.1 requirements |
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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** |
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** In addition, as a special exception, Nokia gives you certain additional |
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** rights. These rights are described in the Nokia Qt LGPL Exception |
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. |
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** |
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** If you have questions regarding the use of this file, please contact |
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** Nokia at qt-info@nokia.com. |
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** |
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** |
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** |
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** |
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** |
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** |
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** |
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** |
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** $QT_END_LICENSE$ |
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** |
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****************************************************************************/ |
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|
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/*! |
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\example richtext/textobject |
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\title Text Object Example |
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|
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The Text Object example shows how to insert an SVG file into a |
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QTextDocument. |
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|
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\image textobject-example.png |
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|
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A QTextDocument consists of a hierarchy of elements, such as text blocks and |
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frames. A text object describes the structure or format of one or more of these |
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elements. For instance, images imported from HTML are implemented using text |
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objects. Text objects are used by the document's |
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\l{QAbstractTextDocumentLayout}{layout} to lay out and render (paint) the |
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document. Each object knows how to paint the elements they govern, and |
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calculates their size. |
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|
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To be able to insert an SVG image into a text document, we create |
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a text object, and implement painting for that object. This object |
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can then be \l{QTextCharFormat::setObjectType()}{set} on a |
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QTextCharFormat. We also register the text object with the layout |
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of the document, enabling it to draw \l{QTextCharFormat}s governed |
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by our text object. We can summarize the procedure with the |
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following steps: |
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|
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\list |
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\o Implement the text object. |
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\o Register the text object with the layout of the text |
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document. |
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\o Set the text object on a QTextCharFormat. |
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\o Insert a QChar::ObjectReplacementCharacter with that |
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text char format into the document. |
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\endlist |
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The example consists of the following classes: |
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\list |
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\o \c{SvgTextObject} implements the text object. |
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\o \c{Window} shows a QTextEdit into which SVG images can be |
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inserted. |
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\endlist |
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\section1 SvgTextObject Class Definition |
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Let's take a look at the header file of \c {SvgTextObject}: |
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\snippet examples/richtext/textobject/svgtextobject.h 0 |
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A text object is a QObject that implements QTextObjectInterface. |
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Note that the first class inherited must be QObject, and that |
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you must use Q_INTERFACES to let Qt know that your class |
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implements QTextObjectInterface. |
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94 |
|
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The document layout keeps a collection of text objects stored as |
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\l{QObject}s, each of which has an associated object type. The |
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layout casts the QObject for the associated object type into the |
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QTextObjectInterface. |
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99 |
|
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The \l{QTextObjectInterface::}{intrinsicSize()} and |
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\l{QTextObjectInterface::}{drawObject()} functions are then used |
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to calculate the size of the text object and draw it. |
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103 |
|
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\section1 SvgTextObject Class Implementation |
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105 |
|
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106 |
We start of by taking a look at the |
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\l{QTextObjectInterface::}{intrinsicSize()} function: |
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108 |
|
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\snippet examples/richtext/textobject/svgtextobject.cpp 0 |
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110 |
|
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\c intrinsicSize() is called by the layout to calculate the size |
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of the text object. Notice that we have drawn the SVG image on a |
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QImage. This is because SVG rendering is quite expensive. The |
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example would lag seriously for large images if we drew them |
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with a QSvgRenderer each time. |
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116 |
|
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\snippet examples/richtext/textobject/svgtextobject.cpp 1 |
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118 |
|
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In \c drawObject(), we paint the SVG image using the QPainter |
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provided by the layout. |
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121 |
|
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\section1 Window Class Definition |
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123 |
|
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The \c Window class is a self-contained window that has a |
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QTextEdit in which SVG images can be inserted. |
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126 |
|
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\snippet examples/richtext/textobject/window.h 0 |
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128 |
|
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The \c insertTextObject() slot inserts an SVG image at the current |
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cursor position, while \c setupTextObject() creates and registers |
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the SvgTextObject with the layout of the text edit's document. |
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|
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The constructor simply calls \c setupTextObject() and \c |
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setupGui(), which creates and lays out the widgets of the \c |
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135 |
Window. |
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136 |
|
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\section1 Window Class Implementation |
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138 |
|
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We will now take a closer look at the functions that are relevant |
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to our text object, starting with the \c setupTextObject() |
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141 |
function. |
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142 |
|
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\snippet examples/richtext/textobject/window.cpp 3 |
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144 |
|
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\c {SvgTextFormat}'s value is the number of our object type. It is |
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used to identify object types by the document layout. |
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147 |
|
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Note that we only create one SvgTextObject instance; it will be |
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used for all QTextCharFormat's with the \c SvgTextFormat object |
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150 |
type. |
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|
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Let's move on to the \c insertTextObject() function: |
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|
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\snippet examples/richtext/textobject/window.cpp 1 |
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First, the \c .svg file is opened and its contents are read |
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into the \c svgData array. |
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\snippet examples/richtext/textobject/window.cpp 2 |
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|
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To speed things up, we buffer the SVG image in a QImage. We use |
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162 |
\l{QTextFormat::}{setProperty()} to store the QImage in the in the |
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QTextCharFormat. We can retrieve it later with |
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\l{QTextCharFormat::}{property()}. |
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165 |
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We insert the char format in the standard way - using a |
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QTextCursor. Notice that we use the special QChar |
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\l{QChar::}{ObjectReplacementCharacter}. |
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*/ |
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170 |