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, 94 insertions, 0 deletions

diff --git a/src/quick/items/qquickpalettecolorprovider_p.h b/src/quick/items/qquickpalettecolorprovider_p.h
new file mode 100644
index 0000000000..952c74aa0d
--- /dev/null
+++ b/src/quick/items/qquickpalettecolorprovider_p.h
@@ -0,0 +1,94 @@
+/****************************************************************************
+**
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef QQUICKPALETTECOLORPROVIDER_P_H
+#define QQUICKPALETTECOLORPROVIDER_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtGui/QPalette>
+
+#include <QtQuick/qtquickglobal.h>
+
+#include <QtQuick/private/qtquickglobal_p.h>
+#include <private/qlazilyallocated_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QQuickAbstractPaletteProvider;
+
+class Q_QUICK_PRIVATE_EXPORT QQuickPaletteColorProvider
+    : public std::enable_shared_from_this<QQuickPaletteColorProvider>
+{
+public:
+    QQuickPaletteColorProvider();
+
+    const QColor &color(QPalette::ColorGroup group, QPalette::ColorRole role) const;
+    bool setColor(QPalette::ColorGroup group, QPalette::ColorRole role, QColor color);
+    bool resetColor(QPalette::ColorGroup group, QPalette::ColorRole role);
+
+    bool fromQPalette(QPalette p);
+    QPalette palette() const;
+
+    const QQuickAbstractPaletteProvider *paletteProvider() const;
+    void setPaletteProvider(const QQuickAbstractPaletteProvider *paletteProvider);
+
+    bool copyColorGroup(QPalette::ColorGroup cg, const QQuickPaletteColorProvider &p);
+
+    bool reset();
+
+    bool inheritPalette(const QPalette &p);
+
+private:
+    QPalette m_resolvedPalette;
+    QLazilyAllocated<QPalette> m_requestedPalette;
+
+    using Deleter = std::function<void(const QQuickAbstractPaletteProvider*)>;
+    using ProviderPtr = std::unique_ptr<const QQuickAbstractPaletteProvider, Deleter>;
+    ProviderPtr m_paletteProvider;
+};
+
+QT_END_NAMESPACE
+
+#endif // QQUICKPALETTECOLORPROVIDER_P_H