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, 90 insertions, 0 deletions

diff --git a/src/selectionmode/backgroundcolorhelper.cpp b/src/selectionmode/backgroundcolorhelper.cpp
new file mode 100644
index 000000000..8a7d69758
--- /dev/null
+++ b/src/selectionmode/backgroundcolorhelper.cpp
@@ -0,0 +1,90 @@
+/*
+    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
+*/
+
+#include "backgroundcolorhelper.h"
+
+#include <KColorScheme>
+
+#include <QGuiApplication>
+#include <QPalette>
+#include <QtGlobal>
+#include <QWidget>
+
+BackgroundColorHelper *BackgroundColorHelper::instance()
+{
+    if (!s_instance) {
+        s_instance = new BackgroundColorHelper;
+    }
+    return s_instance;
+}
+
+
+void setBackgroundColorForWidget(QWidget *widget, QColor color)
+{
+    QPalette palette;
+    palette.setBrush(QPalette::Active,   QPalette::Window, color);
+    palette.setBrush(QPalette::Inactive, QPalette::Window, color);
+    palette.setBrush(QPalette::Disabled, QPalette::Window, color);
+    widget->setAutoFillBackground(true);
+    widget->setPalette(palette);
+}
+
+void BackgroundColorHelper::controlBackgroundColor(QWidget *widget)
+{
+    setBackgroundColorForWidget(widget, m_backgroundColor);
+
+    Q_ASSERT_X(std::find(m_colorControlledWidgets.begin(), m_colorControlledWidgets.end(), widget) == m_colorControlledWidgets.end(), "controlBackgroundColor",
+               "Duplicate insertion is not necessary because the background color should already automatically update itself on paletteChanged");
+    m_colorControlledWidgets.emplace_back(widget);
+}
+
+BackgroundColorHelper::BackgroundColorHelper()
+{
+    updateBackgroundColor();
+    QObject::connect(qApp, &QGuiApplication::paletteChanged, [=](){ slotPaletteChanged(); });
+}
+
+void BackgroundColorHelper::slotPaletteChanged()
+{
+    updateBackgroundColor();
+    for (auto i = m_colorControlledWidgets.begin(); i != m_colorControlledWidgets.end(); ++i) {
+        if (!*i) {
+            i = m_colorControlledWidgets.erase(i);
+            continue;
+        }
+        setBackgroundColorForWidget(*i, m_backgroundColor);
+    }
+}
+
+void BackgroundColorHelper::updateBackgroundColor()
+{
+    // We use colors from the color scheme for mixing so it fits the theme.
+    const auto colorScheme = KColorScheme(QPalette::Normal, KColorScheme::Window);
+    const auto activeBackgroundColor = colorScheme.background(KColorScheme::BackgroundRole::ActiveBackground).color();
+    // We use the positive color for mixing so the end product doesn't look like a warning or error.
+    const auto positiveBackgroundColor = colorScheme.background(KColorScheme::BackgroundRole::PositiveBackground).color();
+
+    // Make sure the new background color has a meaningfully different hue than the activeBackgroundColor.
+    const int hueDifference = positiveBackgroundColor.hue() - activeBackgroundColor.hue();
+    int newHue;
+    if (std::abs(hueDifference) > 80) {
+        newHue = (activeBackgroundColor.hue() + positiveBackgroundColor.hue()) / 2;
+    } else {
+        newHue = hueDifference > 0 ?
+            activeBackgroundColor.hue() + 40 :
+            activeBackgroundColor.hue() - 40;
+        newHue %= 360; // hue needs to be between 0 and 359 per Qt documentation.
+    }
+
+    m_backgroundColor = QColor::fromHsv(newHue,
+                                        // Saturation should be closer to the active color because otherwise the selection mode color might overpower it.
+                                        .7 * activeBackgroundColor.saturation() + .3 * positiveBackgroundColor.saturation(),
+                                        (activeBackgroundColor.value() + positiveBackgroundColor.value()) / 2,
+                                        (activeBackgroundColor.alpha() + positiveBackgroundColor.alpha()) / 2);
+}
+
+BackgroundColorHelper *BackgroundColorHelper::s_instance = nullptr;