source: trunk/doc/src/examples/transformations.qdoc@ 5

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41
42/*!
43 \example painting/transformations
44 \title Transformations Example
45
46 The Transformations example shows how transformations influence
47 the way that QPainter renders graphics primitives. In particular
48 it shows how the order of transformations affect the result.
49
50 \image transformations-example.png
51
52 The application allows the user to manipulate the rendering of a
53 shape by changing the translation, rotation and scale of
54 QPainter's coordinate system.
55
56 The example consists of two classes and a global enum:
57
58 \list
59 \o The \c RenderArea class controls the rendering of a given shape.
60 \o The \c Window class is the application's main window.
61 \o The \c Operation enum describes the various transformation
62 operations available in the application.
63 \endlist
64
65 First we will take a quick look at the \c Operation enum, then we
66 will review the \c RenderArea class to see how a shape is
67 rendered. Finally, we will take a look at the Transformations
68 application's features implemented in the \c Window class.
69
70 \section1 Transformation Operations
71
72 Normally, the QPainter operates on the associated device's own
73 coordinate system, but it also has good support for coordinate
74 transformations.
75
76 The default coordinate system of a paint device has its origin at
77 the top-left corner. The x values increase to the right and the y
78 values increase downwards. You can scale the coordinate system by
79 a given offset using the QPainter::scale() function, you can
80 rotate it clockwise using the QPainter::rotate() function and you
81 can translate it (i.e. adding a given offset to the points) using
82 the QPainter::translate() function. You can also twist the
83 coordinate system around the origin (called shearing) using the
84 QPainter::shear() function.
85
86 All the tranformation operations operate on QPainter's
87 tranformation matrix that you can retrieve using the
88 QPainter::matrix() function. A matrix transforms a point in the
89 plane to another point. For more information about the
90 transformation matrix, see the \l {The Coordinate System} and
91 QMatrix documentation.
92
93 \snippet examples/painting/transformations/renderarea.h 0
94
95 The global \c Operation enum is declared in the \c renderarea.h
96 file and describes the various transformation operations available
97 in the Transformations application.
98
99 \section1 RenderArea Class Definition
100
101 The \c RenderArea class inherits QWidget, and controls the
102 rendering of a given shape.