22e3111127
This eliminates seven EXAMPLE PATH DOES NOT EXIST warnings. Change-Id: Iaa6267138a1799fb775f0034805d5691bfa40d7c Reviewed-by: Christian Stenger <christian.stenger@digia.com> Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
139 lines
5.3 KiB
Plaintext
139 lines
5.3 KiB
Plaintext
/****************************************************************************
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**
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** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the documentation of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:FDL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and Digia. For licensing terms and
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** conditions see http://qt.digia.com/licensing. For further information
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** use the contact form at http://qt.digia.com/contact-us.
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**
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** GNU Free Documentation License Usage
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** Alternatively, this file may be used under the terms of the GNU Free
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** Documentation License version 1.3 as published by the Free Software
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** Foundation and appearing in the file included in the packaging of
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** this file. Please review the following information to ensure
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** the GNU Free Documentation License version 1.3 requirements
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** will be met: http://www.gnu.org/copyleft/fdl.html.
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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/*!
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\example analogclock
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\title Analog Clock Window Example
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\brief The Analog Clock Window example shows how to draw the contents of
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a custom window.
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\image analogclock-window-example.png Screenshot of the Analog
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Clock Window example
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This example demonstrates how the transformation and scaling
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features of QPainter can be used to make drawing easier.
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\section1 AnalogClockWindow Class Definition
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The \c AnalogClockWindow class provides a clock with hour and
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minute hands that is automatically updated every few seconds. We
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make use of the RasterWindow from the \l {Raster Window Example}
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and reimplement the \c render function to draw the clock face:
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\snippet analogclock/main.cpp 5
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\section1 AnalogClock Class Implementation
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\snippet analogclock/main.cpp 6
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We set a title on the window and resize to a reasonable size. Then
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we start a timer which we will use to redraw the clock every
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second.
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\snippet analogclock/main.cpp 7
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The timerEvent function is called every second as a result of
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our startTimer call. Making use of the convenience in the base
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class, we schedule the window to be repainted.
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Checking the timer's id is not strictly needed as we only have
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one active timer in this instance, but it is good practice to do
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so.
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\snippet analogclock/main.cpp 14
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\snippet analogclock/main.cpp 8
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Before we set up the painter and draw the clock, we first define
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two lists of \l {QPoint}s and two \l{QColor}s that will be used
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for the hour and minute hands. The minute hand's color has an
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alpha component of 191, meaning that it's 75% opaque.
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\snippet analogclock/main.cpp 9
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We call QPainter::setRenderHint() with QPainter::Antialiasing to
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turn on antialiasing. This makes drawing of diagonal lines much
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smoother.
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\snippet analogclock/main.cpp 10
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The translation moves the origin to the center of the window, and
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the scale operation ensures that the following drawing operations
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are scaled to fit within the window. We use a scale factor that
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let's us use x and y coordinates between -100 and 100, and that
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ensures that these lie within the length of the window's shortest
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side.
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To make our code simpler, we will draw a fixed size clock face that will
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be positioned and scaled so that it lies in the center of the window.
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We also determine the length of the window's shortest side so that we
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can fit the clock face inside the window.
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The painter takes care of all the transformations made during the
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rendering, and ensures that everything is drawn correctly. Letting
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the painter handle transformations is often easier than performing
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manual calculations.
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\image analogclockwindow-viewport.png
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We draw the hour hand first, using a formula that rotates the coordinate
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system counterclockwise by a number of degrees determined by the current
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hour and minute. This means that the hand will be shown rotated clockwise
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by the required amount.
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\snippet analogclock/main.cpp 11
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We set the pen to be Qt::NoPen because we don't want any outline,
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and we use a solid brush with the color appropriate for
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displaying hours. Brushes are used when filling in polygons and
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other geometric shapes.
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\snippet analogclock/main.cpp 2
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We save and restore the transformation matrix before and after the
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rotation because we want to place the minute hand without having to
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take into account any previous rotations.
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\snippet analogclock/main.cpp 12
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We draw markers around the edge of the clock for each hour. We
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draw each marker then rotate the coordinate system so that the
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painter is ready for the next one.
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\snippet analogclock/main.cpp 13
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\snippet analogclock/main.cpp 3
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The minute hand is rotated in a similar way to the hour hand.
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\snippet analogclock/main.cpp 4
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Again, we draw markers around the edge of the clock, but this
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time to indicate minutes. We skip multiples of 5 to avoid drawing
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minute markers on top of hour markers.
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*/
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