| 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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| 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/basicdrawing
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| 30 | \title Basic Drawing Example
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| 31 |
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| 32 | The Basic Drawing example shows how to display basic graphics
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| 33 | primitives in a variety of styles using the QPainter class.
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| 34 |
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| 35 | QPainter performs low-level painting on widgets and other paint
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| 36 | devices. The class can draw everything from simple lines to
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| 37 | complex shapes like pies and chords. It can also draw aligned text
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| 38 | and pixmaps. Normally, it draws in a "natural" coordinate system,
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| 39 | but it can in addition do view and world transformation.
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| 40 |
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| 41 | \image basicdrawing-example.png
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| 42 |
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| 43 | The example provides a render area, displaying the currently
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| 44 | active shape, and lets the user manipulate the rendered shape and
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| 45 | its appearance using the QPainter parameters: The user can change
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| 46 | the active shape (\gui Shape), and modify the QPainter's pen (\gui
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| 47 | {Pen Width}, \gui {Pen Style}, \gui {Pen Cap}, \gui {Pen Join}),
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| 48 | brush (\gui {Brush Style}) and render hints (\gui
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| 49 | Antialiasing). In addition the user can rotate a shape (\gui
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| 50 | Transformations); behind the scenes we use QPainter's ability to
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| 51 | manipulate the coordinate system to perform the rotation.
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| 52 |
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| 53 | The Basic Drawing example consists of two classes:
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| 54 |
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| 55 | \list
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| 56 | \o \c RenderArea is a custom widget that renders multiple
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| 57 | copies of the currently active shape.
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| 58 | \o \c Window is the application's main window displaying a
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| 59 | \c RenderArea widget in addition to several parameter widgets.
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| 60 | \endlist
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| 61 |
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| 62 | First we will review the \c Window class, then we will take a
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| 63 | look at the \c RenderArea class.
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| 64 |
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| 65 | \section1 Window Class Definition
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| 66 |
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| 67 | The Window class inherits QWidget, and is the application's main
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| 68 | window displaying a \c RenderArea widget in addition to several
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| 69 | parameter widgets.
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| 70 |
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| 71 | \snippet examples/painting/basicdrawing/window.h 0
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| 72 |
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| 73 | We declare the various widgets, and three private slots updating
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| 74 | the \c RenderArea widget: The \c shapeChanged() slot updates the
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| 75 | \c RenderArea widget when the user changes the currently active
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| 76 | shape. We call the \c penChanged() slot when either of the
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| 77 | QPainter's pen parameters changes. And the \c brushChanged() slot
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| 78 | updates the \c RenderArea widget when the user changes the
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| 79 | painter's brush style.
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| 80 |
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| 81 | \section1 Window Class Implementation
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| 82 |
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| 83 | In the constructor we create and initialize the various widgets
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| 84 | appearing in the main application window.
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| 85 |
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| 86 | \snippet examples/painting/basicdrawing/window.cpp 1
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| 87 |
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| 88 | First we create the \c RenderArea widget that will render the
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| 89 | currently active shape. Then we create the \gui Shape combobox,
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| 90 | and add the associated items (i.e. the different shapes a QPainter
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| 91 | can draw).
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| 92 |
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| 93 | \snippet examples/painting/basicdrawing/window.cpp 2
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| 94 |
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| 95 | QPainter's pen is a QPen object; the QPen class defines how a
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| 96 | painter should draw lines and outlines of shapes. A pen has
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| 97 | several properties: Width, style, cap and join.
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| 98 |
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| 99 | A pen's width can be \e zero or greater, but the most common width
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| 100 | is zero. Note that this doesn't mean 0 pixels, but implies that
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| 101 | the shape is drawn as smoothly as possible although perhaps not
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| 102 | mathematically correct.
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| 103 |
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| 104 | We create a QSpinBox for the \gui {Pen Width} parameter.
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| 105 |
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| 106 | \snippet examples/painting/basicdrawing/window.cpp 3
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| 107 |
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| 108 | The pen style defines the line type. The default style is solid
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| 109 | (Qt::SolidLine). Setting the style to none (Qt::NoPen) tells the
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| 110 | painter to not draw lines or outlines. The pen cap defines how
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| 111 | the end points of lines are drawn. And the pen join defines how
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| 112 | two lines join when multiple connected lines are drawn. The cap
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