Native style: copy QStyle from widgets, and implement ground work for creating native styles

This is the initial patch for adding native style support to controls2.

The gist of the patch is that it copies QStyle from widgets (including the
mac plugin style), remove all notions of widgets, tweak it as needed, and
make it compile inside the qtquickcontrols2 repository as a separate
QML plugin (QtQuick.NativeStyle).

The "new" QStyle is then used to draw primitives onto nine-patch-images that can
be rendered by the scene graph. Each such primitive/image will be wrapped by a
QQuickStyleItem (which is a subclass of QQuickItem). E.g a button background will
be implemented by QQuickStyleItemButton.cpp. This item can then be placed anywhere
in the QML code to draw a native-looking button background.

Controls2 has its own styling API, where a style consist of a set of QML files
that extend template controls written in C++. To enable native styling, we simply
follow the exact same approach; We create a style folder per platform alongside
the other styles in controls2. Each style will contain a set of qml files for the
controls (Button.qml, Slider.qml, etc), and inside each control, the style items
will be used to draw the default delegates. Since it's likely that each such
qml file will be implemented equal in all the desktop styles (but not always), the
native style plugin contains a set of default controls (e.g DefaultButton.qml) that
a platform style can choose to inherit from and extend as needed.

Included is also an example called "DesktopGallery" that can be used to
test and view the controls.

Change-Id: I8b45aa7d493930f552d3ad2e3e3e7184129a9d6c
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 412 insertions, 0 deletions

diff --git a/src/imports/nativestyle/qstyle/qquickstyle.cpp b/src/imports/nativestyle/qstyle/qquickstyle.cpp
new file mode 100644
index 00000000..2278fb65
--- /dev/null
+++ b/src/imports/nativestyle/qstyle/qquickstyle.cpp
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+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the Qt Quick Controls 2 module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL3$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPLv3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or later as published by the Free
+** Software Foundation and appearing in the file LICENSE.GPL included in
+** the packaging of this file. Please review the following information to
+** ensure the GNU General Public License version 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickstyle.h"
+#include "qquickstyle_p.h"
+#include "qquickstyleoption.h"
+
+#include <QtGui/qpainter.h>
+#include <QtGui/qbitmap.h>
+#include <QtGui/qpixmapcache.h>
+#include <QtGui/qpa/qplatformtheme.h>
+
+#include <QtGui/private/qguiapplication_p.h>
+
+#ifndef QT_NO_DEBUG
+#    include <QtCore/qdebug.h>
+#endif
+
+#include <limits.h>
+#include <algorithm>
+
+QT_BEGIN_NAMESPACE
+
+namespace QQC2 {
+
+/*!
+    Constructs a style object.
+*/
+QStyle::QStyle()
+    : QObject(*new QStylePrivate)
+{
+    Q_D(QStyle);
+    d->proxyStyle = this;
+}
+
+/*!
+    \internal
+
+    Constructs a style object.
+*/
+QStyle::QStyle(QStylePrivate &dd)
+    : QObject(dd)
+{
+    Q_D(QStyle);
+    d->proxyStyle = this;
+}
+
+/*!
+    Destroys the style object.
+*/
+QStyle::~QStyle()
+{
+}
+
+/*!
+    \fn QRect QStyle::itemTextRect(const QFontMetrics &metrics, const QRect &rectangle, int alignment, bool enabled, const QString &text) const
+
+    Returns the area within the given \a rectangle in which to draw
+    the provided \a text according to the specified font \a metrics
+    and \a alignment. The \a enabled parameter indicates whether or
+    not the associated item is enabled.
+
+    If the given \a rectangle is larger than the area needed to render
+    the \a text, the rectangle that is returned will be offset within
+    \a rectangle according to the specified \a alignment.  For
+    example, if \a alignment is Qt::AlignCenter, the returned
+    rectangle will be centered within \a rectangle. If the given \a
+    rectangle is smaller than the area needed, the returned rectangle
+    will be the smallest rectangle large enough to render the \a text.
+
+    \sa Qt::Alignment
+*/
+QRect QStyle::itemTextRect(const QFontMetrics &metrics, const QRect &rect, int alignment, bool enabled,
+                       const QString &text) const
+{
+    QRect result;
+    int x, y, w, h;
+    rect.getRect(&x, &y, &w, &h);
+    if (!text.isEmpty()) {
+        result = metrics.boundingRect(x, y, w, h, alignment, text);
+        if (!enabled && proxy()->styleHint(SH_EtchDisabledText)) {
+            result.setWidth(result.width()+1);
+            result.setHeight(result.height()+1);
+        }
+    } else {
+        result = QRect(x, y, w, h);
+    }
+    return result;
+}
+
+/*!
+    \fn QRect QStyle::itemPixmapRect(const QRect &rectangle, int alignment, const QPixmap &pixmap) const
+
+    Returns the area within the given \a rectangle in which to draw
+    the specified \a pixmap according to the defined \a alignment.
+*/
+QRect QStyle::itemPixmapRect(const QRect &rect, int alignment, const QPixmap &pixmap) const
+{
+    QRect result;
+    int x, y, w, h;
+    rect.getRect(&x, &y, &w, &h);
+
+    const int pixmapWidth = pixmap.width()/pixmap.devicePixelRatio();
+    const int pixmapHeight = pixmap.height()/pixmap.devicePixelRatio();
+
+    if ((alignment & Qt::AlignVCenter) == Qt::AlignVCenter)
+        y += h/2 - pixmapHeight/2;
+    else if ((alignment & Qt::AlignBottom) == Qt::AlignBottom)
+        y += h - pixmapHeight;
+    if ((alignment & Qt::AlignRight) == Qt::AlignRight)
+        x += w - pixmapWidth;
+    else if ((alignment & Qt::AlignHCenter) == Qt::AlignHCenter)
+        x += w/2 - pixmapWidth/2;
+    else if ((alignment & Qt::AlignLeft) != Qt::AlignLeft && QGuiApplication::isRightToLeft())
+        x += w - pixmapWidth;
+    result = QRect(x, y, pixmapWidth, pixmapHeight);
+    return result;
+}
+
+/*!
+    \fn void QStyle::drawItemText(QPainter *painter, const QRect &rectangle, int alignment, const QPalette &palette, bool enabled, const QString& text, QPalette::ColorRole textRole) const
+
+    Draws the given \a text in the specified \a rectangle using the
+    provided \a painter and \a palette.
+
+    The text is drawn using the painter's pen, and aligned and wrapped
+    according to the specified \a alignment. If an explicit \a
+    textRole is specified, the text is drawn using the \a palette's
+    color for the given role. The \a enabled parameter indicates
+    whether or not the item is enabled; when reimplementing this
+    function, the \a enabled parameter should influence how the item is
+    drawn.
+
+    \sa Qt::Alignment, drawItemPixmap()
+*/
+void QStyle::drawItemText(QPainter *painter, const QRect &rect, int alignment, const QPalette &pal,
+                          bool enabled, const QString& text, QPalette::ColorRole textRole) const
+{
+    if (text.isEmpty())
+        return;
+    QPen savedPen;
+    if (textRole != QPalette::NoRole) {
+        savedPen = painter->pen();
+        painter->setPen(QPen(pal.brush(textRole), savedPen.widthF()));
+    }
+    if (!enabled) {
+        if (proxy()->styleHint(SH_DitherDisabledText)) {
+            QRect br;
+            painter->drawText(rect, alignment, text, &br);
+            painter->fillRect(br, QBrush(painter->background().color(), Qt::Dense5Pattern));
+            return;
+        } else if (proxy()->styleHint(SH_EtchDisabledText)) {
+            QPen pen = painter->pen();
+            painter->setPen(pal.light().color());
+            painter->drawText(rect.adjusted(1, 1, 1, 1), alignment, text);
+            painter->setPen(pen);
+        }
+    }
+    painter->drawText(rect, alignment, text);
+    if (textRole != QPalette::NoRole)
+        painter->setPen(savedPen);
+}
+
+/*!
+    \fn void QStyle::drawItemPixmap(QPainter *painter, const QRect &rectangle, int alignment,
+                            const QPixmap &pixmap) const
+
+    Draws the given \a pixmap in the specified \a rectangle, according
+    to the specified \a alignment, using the provided \a painter.
+
+    \sa drawItemText()
+*/
+
+void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
+                            const QPixmap &pixmap) const
+{
+    qreal scale = pixmap.devicePixelRatio();
+    QRect aligned = alignedRect(QGuiApplication::layoutDirection(), QFlag(alignment), pixmap.size() / scale, rect);
+    QRect inter = aligned.intersected(rect);
+
+    painter->drawPixmap(inter.x(), inter.y(), pixmap, inter.x() - aligned.x(), inter.y() - aligned.y(), inter.width() * scale, inter.height() *scale);
+}
+
+/*!
+    \fn QRect QStyle::visualRect(Qt::LayoutDirection direction, const QRect &boundingRectangle, const QRect &logicalRectangle)
+
+    Returns the given \a logicalRectangle converted to screen
+    coordinates based on the specified \a direction. The \a
+    boundingRectangle is used when performing the translation.
+
+    This function is provided to support right-to-left desktops, and
+    is typically used in implementations of the subControlRect()
+    function.
+
+    \sa QWidget::layoutDirection
+*/
+QRect QStyle::visualRect(Qt::LayoutDirection direction, const QRect &boundingRect, const QRect &logicalRect)
+{
+    if (direction == Qt::LeftToRight)
+        return logicalRect;
+    QRect rect = logicalRect;
+    rect.translate(2 * (boundingRect.right() - logicalRect.right()) +
+                   logicalRect.width() - boundingRect.width(), 0);
+    return rect;
+}
+
+/*!
+    \fn QPoint QStyle::visualPos(Qt::LayoutDirection direction, const QRect &boundingRectangle, const QPoint &logicalPosition)
+
+    Returns the given \a logicalPosition converted to screen
+    coordinates based on the specified \a direction.  The \a
+    boundingRectangle is used when performing the translation.
+
+    \sa QWidget::layoutDirection
+*/
+QPoint QStyle::visualPos(Qt::LayoutDirection direction, const QRect &boundingRect, const QPoint &logicalPos)
+{
+    if (direction == Qt::LeftToRight)
+        return logicalPos;
+    return QPoint(boundingRect.right() - logicalPos.x(), logicalPos.y());
+}
+
+/*!
+     Returns a new rectangle of the specified \a size that is aligned to the given \a
+     rectangle according to the specified \a alignment and \a direction.
+ */
+QRect QStyle::alignedRect(Qt::LayoutDirection direction, Qt::Alignment alignment, const QSize &size, const QRect &rectangle)
+{
+    alignment = visualAlignment(direction, alignment);
+    int x = rectangle.x();
+    int y = rectangle.y();
+    int w = size.width();
+    int h = size.height();
+    if ((alignment & Qt::AlignVCenter) == Qt::AlignVCenter)
+        y += rectangle.size().height()/2 - h/2;
+    else if ((alignment & Qt::AlignBottom) == Qt::AlignBottom)
+        y += rectangle.size().height() - h;
+    if ((alignment & Qt::AlignRight) == Qt::AlignRight)
+        x += rectangle.size().width() - w;
+    else if ((alignment & Qt::AlignHCenter) == Qt::AlignHCenter)
+        x += rectangle.size().width()/2 - w/2;
+    return QRect(x, y, w, h);
+}
+
+/*!
+  Transforms an \a alignment of Qt::AlignLeft or Qt::AlignRight
+  without Qt::AlignAbsolute into Qt::AlignLeft or Qt::AlignRight with
+  Qt::AlignAbsolute according to the layout \a direction. The other
+  alignment flags are left untouched.
+
+  If no horizontal alignment was specified, the function returns the
+  default alignment for the given layout \a direction.
+
+  QWidget::layoutDirection
+*/
+Qt::Alignment QStyle::visualAlignment(Qt::LayoutDirection direction, Qt::Alignment alignment)
+{
+    return QGuiApplicationPrivate::visualAlignment(direction, alignment);
+}
+
+/*!
+    Converts the given \a logicalValue to a pixel position. The \a min
+    parameter maps to 0, \a max maps to \a span and other values are
+    distributed evenly in-between.
+
+    This function can handle the entire integer range without
+    overflow, providing that \a span is less than 4096.
+
+    By default, this function assumes that the maximum value is on the
+    right for horizontal items and on the bottom for vertical items.
+    Set the \a upsideDown parameter to true to reverse this behavior.
+
+    \sa sliderValueFromPosition()
+*/
+
+int QStyle::sliderPositionFromValue(int min, int max, int logicalValue, int span, bool upsideDown)
+{
+    if (span <= 0 || logicalValue < min || max <= min)
+        return 0;
+    if (logicalValue > max)
+        return upsideDown ? span : min;
+
+    uint range = max - min;
+    uint p = upsideDown ? max - logicalValue : logicalValue - min;
+
+    if (range > (uint)INT_MAX/4096) {
+        double dpos = (double(p))/(double(range)/span);
+        return int(dpos);
+    } else if (range > (uint)span) {
+        return (2 * p * span + range) / (2*range);
+    } else {
+        uint div = span / range;
+        uint mod = span % range;
+        return p * div + (2 * p * mod + range) / (2 * range);
+    }
+    // equiv. to (p * span) / range + 0.5
+    // no overflow because of this implicit assumption:
+    // span <= 4096
+}
+
+/*!
+    \fn int QStyle::sliderValueFromPosition(int min, int max, int position, int span, bool upsideDown)
+
+    Converts the given pixel \a position to a logical value. 0 maps to
+    the \a min parameter, \a span maps to \a max and other values are
+    distributed evenly in-between.
+
+    This function can handle the entire integer range without
+    overflow.
+
+    By default, this function assumes that the maximum value is on the
+    right for horizontal items and on the bottom for vertical
+    items. Set the \a upsideDown parameter to true to reverse this
+    behavior.
+
+    \sa sliderPositionFromValue()
+*/
+
+int QStyle::sliderValueFromPosition(int min, int max, int pos, int span, bool upsideDown)
+{
+    if (span <= 0 || pos <= 0)
+        return upsideDown ? max : min;
+    if (pos >= span)
+        return upsideDown ? min : max;
+
+    uint range = max - min;
+
+    if ((uint)span > range) {
+        int tmp = (2 * pos * range + span) / (2 * span);
+        return upsideDown ? max - tmp : tmp + min;
+    } else {
+        uint div = range / span;
+        uint mod = range % span;
+        int tmp = pos * div + (2 * pos * mod + span) / (2 * span);
+        return upsideDown ? max - tmp : tmp + min;
+    }
+    // equiv. to min + (pos*range)/span + 0.5
+    // no overflow because of this implicit assumption:
+    // pos <= span < sqrt(INT_MAX+0.0625)+0.25 ~ sqrt(INT_MAX)
+}
+
+/*!
+     Returns the style's standard palette.
+
+    Note that on systems that support system colors, the style's
+    standard palette is not used. In particular, the Windows
+    Vista and Mac styles do not use the standard palette, but make
+    use of native theme engines. With these styles, you should not set
+    the palette with QApplication::setPalette().
+
+    \sa QApplication::setPalette()
+ */
+QPalette QStyle::standardPalette() const
+{
+    QColor background = QColor(0xd4, 0xd0, 0xc8); // win 2000 grey
+
+    QColor light(background.lighter());
+    QColor dark(background.darker());
+    QColor mid(Qt::gray);
+    QPalette palette(Qt::black, background, light, dark, mid, Qt::black, Qt::white);
+    palette.setBrush(QPalette::Disabled, QPalette::WindowText, dark);
+    palette.setBrush(QPalette::Disabled, QPalette::Text, dark);
+    palette.setBrush(QPalette::Disabled, QPalette::ButtonText, dark);
+    palette.setBrush(QPalette::Disabled, QPalette::Base, background);
+    return palette;
+}
+
+//Windows and KDE allow menus to cover the taskbar, while GNOME and macOS don't
+bool QStylePrivate::useFullScreenForPopup()
+{
+    auto theme = QGuiApplicationPrivate::platformTheme();
+    return theme && theme->themeHint(QPlatformTheme::UseFullScreenForPopupMenu).toBool();
+}
+
+} // namespace QQC2
+
+QT_END_NAMESPACE
+
+#include "moc_qquickstyle.cpp"