Introduce new mechanism to manage palette functionality in QML

Main goals of these changes:
1) Add an ability to work with disabled and inactive palettes from QML
2) Eliminate massive code duplication in qtquickcontrols2 module
3) Provide easily extensible architecture for this piece of
functionality

Architectural part.

Palette
It was decided to not change existing QPalette, but add thin wrappers
around it to provide all required functionality. These wrappers are
highly coupled with QPalette class because of using some enum values
from it.
There are two new classes QQuickPalette and QQuickColorGroup.
QQuickPalette class inherits QQuickColorGroup class and represents
Active/All color group. QQuickPalette also provides an access to three
color groups: Active, Inactive, and Disabled.
In order to access colors the special class QQuickPaletteColorProvider
is used. This is a wrapper around QPalette that provides some
convenience functions.

Interface
The private property "palette" should be exposed.

Implementation
All private parts of classes that implement
QQuickAbstractPaletteProvider have to inherit
QQuickPaletteProviderPrivateBase class. This template class implement
all functionality: create palette, resolve dependencies, connect objects
etc. This is important to mention that related data is lazily
allocatable on demand only. Hence, there is no memory overhead for
regular items.

Change-Id: I911424b730451b1ad47f68fd8007953b66eddb28
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 328 insertions, 0 deletions

diff --git a/src/quick/items/qquickpalette.cpp b/src/quick/items/qquickpalette.cpp
new file mode 100644
index 0000000000..f5c0aa8b04
--- /dev/null
+++ b/src/quick/items/qquickpalette.cpp
@@ -0,0 +1,328 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtQuick 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 "qquickpalette_p.h"
+
+#include <QtQuick/private/qquickpalettecolorprovider_p.h>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \internal
+
+    \class QQuickPalette
+    \brief The QQuickPalette class contains color groups for each QML item state.
+    \inmodule QtQuick
+    \since 6.0
+
+    This class is the wrapper around QPalette.
+
+    \sa QQuickColorGroup, QQuickAbstractPaletteProvider, QPalette
+ */
+
+/*!
+    \qmltype Palette
+    \instantiates QQuickPalette
+    \inherits QQuickColorGroup
+    \inqmlmodule QtQuick
+    \ingroup qtquick-visual
+    \brief The QQuickPalette class contains color groups for each QML item state.
+
+    A palette consists of three color groups: Active, Disabled, and Inactive.
+    Active color group is the default group, its colors are used for other groups
+    if colors of these groups aren't explicitly specified.
+
+    In the following example, color is applied for all color groups:
+    \code
+    ApplicationWindow {
+        palette.buttonText: "salmon"
+
+        ColumnLayout {
+            Button {
+                text: qsTr("Disabled button")
+                enabled: false
+            }
+
+            Button {
+                text: qsTr("Enabled button")
+            }
+        }
+    }
+    \endcode
+    It means that text color will be the same for both buttons.
+
+    In the following example, colors will be different for enabled and disabled states:
+    \code
+    ApplicationWindow {
+        palette.buttonText: "salmon"
+        palette.disabled.buttonText: "lavender"
+
+        ColumnLayout {
+            Button {
+                text: qsTr("Disabled button")
+                enabled: false
+            }
+
+            Button {
+                text: qsTr("Enabled button")
+            }
+        }
+    }
+    \endcode
+
+    It is also possible to specify colors like this:
+    \code
+    palette {
+        buttonText: "azure"
+        button: "khaki"
+
+        disabled {
+            buttonText: "lavender"
+            button: "coral"
+        }
+    }
+    \endcode
+    This approach is convenient when you need to specify a whole palette with all color groups.
+*/
+
+/*!
+    \qmlproperty QQuickColorGroup QtQuick::QQuickPalette::inactive
+
+    The Inactive group is used for windows that have no keyboard focus.
+
+    \sa QPalette::Inactive
+*/
+
+/*!
+    \qmlproperty QQuickColorGroup QtQuick::QQuickPalette::disabled
+
+    The Disabled group is used for elements that are disabled for some reason.
+
+    \sa QPalette::Disabled
+*/
+
+QQuickPalette::QQuickPalette(QObject *parent)
+    : QQuickColorGroup(parent)
+    , m_currentGroup(defaultCurrentGroup())
+{
+}
+
+QQuickColorGroup *QQuickPalette::active() const
+{
+    return colorGroup(QPalette::Active);
+}
+
+QQuickColorGroup *QQuickPalette::inactive() const
+{
+    return colorGroup(QPalette::Inactive);
+}
+
+QQuickColorGroup *QQuickPalette::disabled() const
+{
+    return colorGroup(QPalette::Disabled);
+}
+
+/*!
+    \internal
+
+    Returns the palette's current color group.
+    The default value is Active.
+ */
+QPalette::ColorGroup QQuickPalette::currentColorGroup() const
+{
+    return m_currentGroup;
+}
+
+/*!
+    \internal
+
+    Sets \a currentGroup for this palette.
+
+    The current color group is used when accessing colors of this palette.
+    For example, if color group is Disabled, color accessors will be
+    returning colors form the respective group.
+    \code
+    QQuickPalette palette;
+
+    palette.setAlternateBase(Qt::green);
+    palette.disabled()->setAlternateBase(Qt::red);
+
+    auto color = palette.alternateBase(); // Qt::green
+
+    palette.setCurrentGroup(QPalette::Disabled);
+    color = palette.alternateBase(); // Qt::red
+    \endcode
+
+    Emits QColorGroup::changed().
+ */
+void QQuickPalette::setCurrentGroup(QPalette::ColorGroup currentGroup)
+{
+    if (m_currentGroup != currentGroup) {
+        m_currentGroup = currentGroup;
+        Q_EMIT changed();
+    }
+}
+
+void QQuickPalette::fromQPalette(QPalette palette)
+{
+    if (colorProvider().fromQPalette(std::move(palette))) {
+        Q_EMIT changed();
+    }
+}
+
+QPalette QQuickPalette::toQPalette() const
+{
+    return colorProvider().palette();
+}
+
+const QQuickAbstractPaletteProvider *QQuickPalette::paletteProvider() const
+{
+    return colorProvider().paletteProvider();
+}
+
+void QQuickPalette::setPaletteProvider(const QQuickAbstractPaletteProvider *paletteProvider)
+{
+    colorProvider().setPaletteProvider(paletteProvider);
+}
+
+void QQuickPalette::reset()
+{
+    if (colorProvider().reset()) {
+        Q_EMIT changed();
+    }
+}
+
+void QQuickPalette::inheritPalette(const QPalette &palette)
+{
+    if (colorProvider().inheritPalette(palette)) {
+        Q_EMIT changed();
+    }
+}
+
+void QQuickPalette::setActive(QQuickColorGroup *active)
+{
+    setColorGroup(QPalette::Active, active, &QQuickPalette::activeChanged);
+}
+
+void QQuickPalette::setInactive(QQuickColorGroup *inactive)
+{
+    setColorGroup(QPalette::Inactive, inactive, &QQuickPalette::inactiveChanged);
+}
+
+void QQuickPalette::setDisabled(QQuickColorGroup *disabled)
+{
+    setColorGroup(QPalette::Disabled, disabled, &QQuickPalette::disabledChanged);
+}
+
+
+void QQuickPalette::setColorGroup(QPalette::ColorGroup groupTag,
+                                  const QQuickColorGroup::GroupPtr &group,
+                                  void (QQuickPalette::*notifier)())
+{
+    if (isValidColorGroup(groupTag, group)) {
+        if (colorProvider().copyColorGroup(groupTag, group->colorProvider())) {
+            Q_EMIT (this->*notifier)();
+            Q_EMIT changed();
+        }
+    }
+}
+
+QQuickColorGroup::GroupPtr QQuickPalette::colorGroup(QPalette::ColorGroup groupTag) const
+{
+    if (auto group = findColorGroup(groupTag)) {
+        return group;
+    }
+
+    auto group = QQuickColorGroup::createWithParent(*const_cast<QQuickPalette*>(this));
+    const_cast<QQuickPalette*>(this)->registerColorGroup(group, groupTag);
+    return group;
+}
+
+QQuickColorGroup::GroupPtr QQuickPalette::findColorGroup(QPalette::ColorGroup groupTag) const
+{
+    if (auto it = m_colorGroups.find(groupTag); it != m_colorGroups.end()) {
+        return it->second;
+    }
+
+    return nullptr;
+}
+
+void QQuickPalette::registerColorGroup(QQuickColorGroup *group, QPalette::ColorGroup groupTag)
+{
+    if (auto it = m_colorGroups.find(groupTag); it != m_colorGroups.end() && it->second) {
+        it->second->deleteLater();
+    }
+
+    m_colorGroups[groupTag] = group;
+
+    group->setGroupTag(groupTag);
+
+    QQuickColorGroup::connect(group, &QQuickColorGroup::changed, this, &QQuickPalette::changed);
+}
+
+bool QQuickPalette::isValidColorGroup(QPalette::ColorGroup groupTag,
+                                      const QQuickColorGroup::GroupPtr &colorGroup) const
+{
+    if (!colorGroup) {
+        qWarning("Color group cannot be null.");
+        return false;
+    }
+
+    if (!colorGroup->parent()) {
+        qWarning("Color group should have a parent.");
+        return false;
+    }
+
+    if (colorGroup->parent() && !qobject_cast<QQuickPalette*>(colorGroup->parent())) {
+        qWarning("Color group should be a part of QQuickPalette.");
+        return false;
+    }
+
+    if (groupTag == defaultGroupTag()) {
+        qWarning("Register %i color group is not allowed."
+                 " QQuickPalette is %i color group itself.", groupTag, groupTag);
+        return false;
+    }
+
+    if (findColorGroup(groupTag) == colorGroup) {
+        qWarning("The color group is already a part of the current palette.");
+        return false;
+    }
+
+    return true;
+}
+
+QT_END_NAMESPACE