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+/****************************************************************************
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+****************************************************************************/
+
+/*!
+ \page qt4-styles.html
+ \title The Qt 4 Style API
+
+ \contentspage {What's New in Qt 4}{Home}
+ \previouspage The Network Module in Qt 4
+ \nextpage Thread Support in Qt 4
+
+ Qt's style API is responsible for performing the widget drawing
+ for built-in widgets. The Qt 4 style API has been revised to make
+ it possible for a style to draw widgets without calling any
+ functions on the widget.
+
+ Because Qt 4 is split across multiple libraries, Qt needed this
+ update to be able to draw widgets from other libraries than
+ QtGui. For application developers, this has other benefits, such
+ as more managable parameter lists and the possibility of drawing
+ any graphical element without having a widget of a specific
+ type.
+
+ \section1 General Overview
+
+ The QStyle class is an abstract base class that encapsulates
+ the look and feel of a GUI. Qt's built-in widgets use it to
+ perform nearly all of their drawing, ensuring that they look
+ exactly like the equivalent native widgets.
+
+ Most draw functions now take four arguments:
+
+ \list
+ \o an enum value specifying which graphical element to draw
+ \o a QStyleOption specifying how and where to render that element
+ \o a QPainter that should be used to draw the element
+ \o a QWidget on which the drawing is performed (optional)
+ \endlist
+
+ The style gets all the information it needs to render the
+ graphical element from QStyleOption. The widget is passed as the
+ last argument in case the style needs it to perform special
+ effects (such as animated default buttons on Mac OS X), but it
+ isn't mandatory. In fact, QStyle can be used to draw on any
+ paint device, not just widgets, by setting the QPainter properly.
+
+ Thanks to QStyleOption, it is now possible to make QStyle draw
+ widgets without linking in any code for the widget. This is how
+ Qt's built-in styles can draw Qt 3 widgets such as
+ Q3ListView without necessarily linking against the Qt3Support
+ library. Another significant benefit of the new approach is that
+ it's now possible to use \l{QStyle}'s draw functions on other
+ widgets than the built-in widgets; for example, you can draw a
+ combobox on any widget, not just on a QComboBox.
+
+ QStyleOption has various subclasses for the various types of
+ graphical elements that can be drawn, and it's possible to create
+ custom subclasses. For example, the QStyle::PE_FrameFocusRect
+ element expects a QStyleOptionFocusRect argument. This is
+ documented for each enum value.
+
+ When reimplementing QStyle functions that take a
+ QStyleOption parameter, you often need to cast the
+ QStyleOption to a subclass (e.g., QStyleOptionFocusRect). For
+ safety, you can use qstyleoption_cast() to ensure that the
+ pointer type is correct. If the object isn't of the right type,
+ qstyleoption_cast() returns 0. For example:
+
+ \snippet doc/src/snippets/code/doc_src_qt4-styles.qdoc 0
+
+ For performance reasons, there are few member functions and the
+ access to the variables is direct. This "low-level" feel makes
+ the structures use straightforward and emphasizes that these are
+ simply parameters used by the style functions. In addition, the
+ caller of a QStyle function usually creates QStyleOption
+ objects on the stack. This combined with Qt's extensive use of
+ \l{implicit sharing} for types such as QString, QPalette, and
+ QColor ensures that no memory allocation needlessly takes place.
+ (Dynamic memory allocation can be an expensive operation,
+ especially when drawing very often in a short time.)
+
+ \section1 Example Code
+
+ The following code snippet illustrates how to use QStyle to
+ draw the focus rectangle from a custom widget's paintEvent():
+
+ \snippet doc/src/snippets/code/doc_src_qt4-styles.qdoc 1
+
+ The next example shows how to derive from an existing style to
+ customize the look of a graphical element:
+
+ \snippet doc/src/snippets/customstyle/customstyle.h 0
+ \codeline
+ \snippet doc/src/snippets/customstyle/customstyle.cpp 2
+ \snippet doc/src/snippets/customstyle/customstyle.cpp 3
+ \snippet doc/src/snippets/customstyle/customstyle.cpp 4
+
+ See also the \l{Styles Example} for a more detailed description of
+ how custom styles can be created.
+
+ \section1 Comparison with Qt 3
+
+ The QStyle class has a similar API in Qt 4 as in Qt 3, with
+ more or less the same functions. What has changed is the
+ signature of the functions and the role played by QStyleOption.
+ For example, here's the signature of the QStyle::drawControl()
+ function in Qt 3:
+
+ \snippet doc/src/snippets/code/doc_src_qt4-styles.qdoc 2
+
+ Here's the signature of the same function in Qt 4:
+
+ \snippet doc/src/snippets/code/doc_src_qt4-styles.qdoc 3
+
+ In Qt 3, some of the information required to draw a graphical
+ element was stored in a QStyleOption parameter, while the rest
+ was deduced by querying the widget. In Qt 4, everything is stored
+ in the QStyleOption parameter.
+*/