source: trunk/doc/src/painting-and-printing/printing.qdoc@ 860

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/*!
  \group printing
  \title Printer and Printing APIs
  \brief Classes for producing printed output
  \ingroup groups
*/

/*!
  \page printing.html
  \title Printing with Qt
  \ingroup qt-graphics

  \previouspage Styling
  \contentspage The Paint System

  \brief A guide to producing printed output with Qt's paint system and widgets.

  Qt provides extensive cross-platform support for printing. Using the printing
  systems on each platform, Qt applications can print to attached printers and
  across networks to remote printers. Qt's printing system also enables PostScript
  and PDF files to be generated, providing the foundation for basic report
  generation facilities.

  \tableofcontents
  
  \section1 Classes Supporting Printing

  The following classes support the selecting and setting up of printers and
  printing output.
  
  \annotatedlist printing

  \section1 Paint Devices and Printing

  In Qt, printers are represented by QPrinter, a paint device that provides
  functionality specific to printing, such as support for multiple pages and
  double-sided output. As a result, printing involves using a QPainter to paint
  onto a series of pages in the same way that you would paint onto a custom
  widget or image.

  \section2 Creating a QPrinter

  Although QPrinter objects can be constructed and set up without requiring user
  input, printing is often performed as a result of a request by the user;
  for example, when the user selects the \gui{File|Print...} menu item in a GUI
  application. In such cases, a newly-constructed QPrinter object is supplied to
  a QPrintDialog, allowing the user to specify the printer to use, paper size, and
  other printing properties.

  \snippet examples/richtext/orderform/mainwindow.cpp 18

  It is also possible to set certain default properties by modifying the QPrinter
  before it is supplied to the print dialog. For example, applications that
  generate batches of reports for printing may set up the QPrinter to
  \l{QPrinter::setOutputFileName()}{write to a local file} by default rather than
  to a printer.

  \section2 Painting onto a Page

  Once a QPrinter object has been constructed and set up, a QPainter can be used
  to perform painting operations on it. We can construct and set up a painter in
  the following way:

  \snippet doc/src/snippets/printing-qprinter/object.cpp 0

  Since the QPrinter starts with a blank page, we only need to call the
  \l{QPrinter::}{newPage()} function after drawing each page, except for the
  last page.

  The document is sent to the printer, or written to a local file, when we call
  \l{QPainter::}{end()}.

  \section2 Coordinate Systems

  QPrinter provides functions that can be used to obtain information about the
  dimensions of the paper (the paper rectangle) and the dimensions of the
  printable area (the page rectangle). These are given in logical device
  coordinates that may differ from the physical coordinates used by the device
  itself, indicating that the printer is able to render text and graphics at a
  (typically higher) resolution than the user's display.

  Although we do not need to handle the conversion between logical and physical
  coordinates ourselves, we still need to apply transformations to painting
  operations because the pixel measurements used to draw on screen are often
  too small for the higher resolutions of typical printers.

  \table
  \row \o \bold{Printer and Painter Coordinate Systems}

  The \l{QPrinter::}{paperRect()} and \l{QPrinter::}{pageRect()} functions
  provide information about the size of the paper used for printing and the
  area on it that can be painted on.

  The rectangle returned by \l{QPrinter::}{pageRect()} usually lies inside
  the rectangle returned by \l{QPrinter::}{paperRect()}. You do not need to
  take the positions and sizes of these area into account when using a QPainter
  with a QPrinter as the underlying paint device; the origin of the painter's
  coordinate system will coincide with the top-left corner of the page
  rectangle, and painting operations will be clipped to the bounds of the
  drawable part of the page.

  \o \inlineimage printer-rects.png
  \endtable

  The paint system automatically uses the correct device metrics when painting
  text but, if you need to position text using information obtained from
  font metrics, you need to ensure that the print device is specified when
  you construct QFontMetrics and QFontMetricsF objects, or ensure that each QFont
  used is constructed using the form of the constructor that accepts a
  QPaintDevice argument.

  \section1 Printing Widgets

  To print a widget, you can use the QWidget::render() function. As mentioned,
  the printer's resolution is usually higher than the screen resolution, so you
  will have to scale the painter. You may also want to position the widget on the
  page. The following code sample shows how this may look.

  \snippet doc/src/snippets/widgetprinting.cpp 0

  This will center the widget on the page and scale it so that it fits the page.

  \section1 Printing from Complex Widgets

  Certain widgets, such as QTextEdit and QGraphicsView, display rich content
  that is typically managed by instances of other classes, such as QTextDocument
  and QGraphicsScene. As a result, it is these content handling classes that
  usually provide printing functionality, either via a function that can be used
  to perform the complete task, or via a function that accepts an existing
  QPainter object. Some widgets provide convenience functions to expose underlying
  printing features, avoiding the need to obtain the content handler just to call
  a single function.

  The following table shows which class and function are responsible for
  printing from a selection of different widgets. For widgets that do not expose
  printing functionality directly, the content handling classes containing this
  functionality can be obtained via a function in the corresponding widget's API.

  \table
  \header \o Widget         \o Printing function        \o Accepts
  \row    \o QGraphicsView  \o QGraphicsView::render()  \o QPainter
  \row    \o QSvgWidget     \o QSvgRenderer::render()   \o QPainter
  \row    \o QTextEdit      \o QTextDocument::print()   \o QPrinter
  \row    \o QTextLayout    \o QTextLayout::draw()      \o QPainter
  \row    \o QTextLine      \o QTextLine::draw()        \o QPainter
  \endtable

  QTextEdit requires a QPrinter rather than a QPainter because it uses information
  about the configured page dimensions in order to insert page breaks at the most
  appropriate places in printed documents.
*/

/*!
  \page pdf-licensing.html
  \title Notes about PDF Licensing
  \ingroup licensing
  \brief Details of restrictions on the use of PDF-related trademarks.

  Please note that Adobe\reg places restrictions on the use of its trademarks
  (including logos) in conjunction with PDF; e.g. "Adobe PDF". Please refer
  to \l{http://www.adobe.com}{www.adobe.com} for guidelines.
*/