c# generate data matrix code 5: Doing More with Qt in Visual C#.NET

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CHAPTER 5: Doing More with Qt
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transformation (linear transformation followed by a translation) of its coordinate system. You can use the following methods to adjust the coordinate system used by QPainter scale to scale the coordinate system by an offset. rotate to rotate the coordinate system clockwise around its origin. translate to translate (shift by an offset) the coordinate system. shear to twist a coordinate system around the origin. Another common operation you may want to perform is off-screen drawing. While Qt double-buffers drawing to prevent flickering, sometimes you need to perform off-screen drawing for other reasons, such as to composite multiple bitmaps to create a specific bitmap, or decorate a bitmap with text to be draw in multiple locations. Qt provides the QImage class and its subclasses as other concrete implementations of QPaintDevice. So you can create a QPainter using a QImage instance, and then drawing on the image using the QPainter. Qt provides four implementations of QImage: QImage class, optimized for fast input/output and direct pixel manipulation. QPixmap class, optimized for on-screen drawing. QBitmap class, an optimized QPixmap with a bitdepth of 1. QPicture class, a paint device that records and replays QPainter commands in a manner similar to QPainterPath. Interestingly, QImage and its subclasses are Qt value classes like QString; because they use implicit data sharing, you can pass them around freely as you would other implicitly shared data classes like QString and QList. Under the hood, Qt s implicit data sharing handles one shared block for multiple instances, using copy-on-write to create multiple copies of the data only when necessary. To read about how Qt s implicit data sharing works under the hood, see Qt s documentation at http://doc.qt.nokia.com/implicitsharing.html.
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Integrating Qt Objects with Web Content
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In the previous chapter we used Qt s WebKit integration to show HTML, but neither said much about its capabilities, nor took advantage of those capabilities. As it happens, Qt and WebKit are quite well-integrated through the QtWebKit implementation, which lets you not just render web content but enhance it by embedding QObject instances in the web content. QtWebKit is a full port of the open source WebKit engine, including rendering for HTML and XHTML, as well as Scalable Vector Graphics (SVG) documents, all styled using CSS and scripted using JavaScript. The most obvious use for QtWebKit is displaying web content or web-styled content in your application, but there are other things you can do, too, such as process web content into bitmaps for placement in your application (think of a wall in a platform game showing real-time data from a web-based news feed).
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CHAPTER 5: Doing More with Qt
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Linking Your Application with QtWebKit
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Linking against QtWebKit in your application is easy just be sure that WebKit is in your PRO file s QT variable, like this:
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QT += webkit
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Of course, C++ classes that access QtWebKit classes need to have access to QtWebkit s interfaces. The easiest way to do this is to include QtWebKit s headers any place you need them, like this:
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#include <QtWebKit>
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For faster compilation, you can always forward-declare the classes you re going to use in your header files, and include just the definitions you require, although there s no guarantee that under-the-hood QtWebKit headers are doing the same thing.
Displaying Web Content with QtWebKit
For most purposes, the first class in QtWebKit you use is QWebView. It s a descendant of QWidget that you first encountered in the last chapter when we used it to display the HTML content associated with an earthShake report in the USGS Really Simple Syndication (RSS) feed using the setHtml method. You could just as easily have it load web content from a remote server using its load method, like this:
QWebView* view = new QWebView(parent); view->load(QUrl("http://www.apress.com/")); view->show();
NOTE: If you find yourself using Qt s graphics scene architecture and need to render Web content, use QGraphicsWebView instead. It inherits from QGraphicsItem and renders correctly in a QGraphicsScene. The QWebView load method takes a QUrl, representing a URL; there are type coercion functions that let you supply a string and it ll be coerced to a URL at runtime, but it s better to be specific instead of relying on compiler magic to say what you mean. QtWebKit s content loading is asynchronous, so it doesn t block the user thread. It signals its progress so that you can notify the user or take other action. It emits the loadStarted signal when the view begins loading, and periodically emits loadProgress whenever a web element of the page (such as an image or JavaScript segment) is fully loaded. When the entire page is loaded, the QWebView emits the loadFinished signal, passing true if the page is successfully loaded, or false if there is a failure. You can control a QWebView s behavior using an instance of QWebSettings, available by calling QWebView::settings. You can change the font family and font size, but the most important things you can adjust are the web attributes that determine how QtWebKit behaves. The attributes include:
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