Add Selection Mode

The selection mode action is a checkable toggle action named
"Select Files and Folders" which has "Space" as the default
shortcut.

In selection mode a bottom bar with contextual actions is shown.
These should mostly mirror the actions which are available through
the right-click context menu aka DolphinContextMenu.

Resizing of the window might make a overflow button appear in the
bottom selection mode bar.

This commit makes press and hold in the view activate selection
mode. This behaviour is not triggered if the press and hold is
used to either start a rubberband selection or a drag operation
within a short time. The length of the short timeframe is defined
by a QStyleHint. This is currently not implemented in touch
because I can't test it.

Mix the selection mode bars' background colors using a nice
combination of colors from the current color scheme

BUG: 427202

1 files changed, 45 insertions, 0 deletions

diff --git a/src/selectionmode/backgroundcolorhelper.h b/src/selectionmode/backgroundcolorhelper.h
new file mode 100644
index 000000000..0e8a61b34
--- /dev/null
+++ b/src/selectionmode/backgroundcolorhelper.h
@@ -0,0 +1,45 @@
+/*
+    This file is part of the KDE project
+    SPDX-FileCopyrightText: 2022 Felix Ernst <[email protected]>
+
+    SPDX-License-Identifier: LGPL-2.1-only OR LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL
+*/
+
+#ifndef BACKGROUNDCOLORHELPER_H
+#define BACKGROUNDCOLORHELPER_H
+
+#include <QColor>
+#include <QPointer>
+
+#include <memory>
+
+class QWidget;
+
+/**
+ * @brief A Singleton class for managing the colors of selection mode widgets.
+ */
+class BackgroundColorHelper
+{
+public:
+    static BackgroundColorHelper *instance();
+
+    /**
+     * Changes the background color of @p widget to a distinct color scheme matching color which makes it clear that the widget belongs to the selection mode.
+     */
+    void controlBackgroundColor(QWidget *widget);
+
+private:
+    BackgroundColorHelper();
+
+    void slotPaletteChanged();
+
+    void updateBackgroundColor();
+
+private:
+    std::vector<QPointer<QWidget>> m_colorControlledWidgets;
+    QColor m_backgroundColor;
+
+    static BackgroundColorHelper *s_instance;
+};
+
+#endif // BACKGROUNDCOLORHELPER_H