1 files changed, 117 insertions, 0 deletions
diff --git a/src/ui/widget/scrollprotected.h b/src/ui/widget/scrollprotected.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef SEEN_INKSCAPE_UI_WIDGET_SCROLLPROTECTED_H
+#define SEEN_INKSCAPE_UI_WIDGET_SCROLLPROTECTED_H
+
+/* Authors:
+ *   Thomas Holder
+ *   Anshudhar Kumar Singh <anshudhar2001@gmail.com>
+ *
+ * Copyright (C) 2020-2021 Authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include <gtkmm.h>
+
+#include "scroll-utils.h"
+
+namespace Inkscape {
+namespace UI {
+namespace Widget {
+
+/**
+ * A class decorator which blocks the scroll event if the widget does not have
+ * focus and any ancestor is a scrollable window, and SHIFT is not pressed.
+ *
+ * For custom scroll event handlers, derived classes must implement
+ * on_safe_scroll_event instead of on_scroll_event. Directly connecting to
+ * signal_scroll_event() will bypass the scroll protection.
+ *
+ * @tparam Base A subclass of Gtk::Widget
+ */
+template <typename Base>
+class ScrollProtected : public Base
+{
+public:
+    using Base::Base;
+    using typename Base::BaseObjectType;
+    ScrollProtected()
+        : Base()
+    {}
+    ScrollProtected(BaseObjectType *cobject, const Glib::RefPtr<Gtk::Builder> &refGlade)
+        : Base(cobject){};
+    ~ScrollProtected() override{};
+
+protected:
+    /**
+     * Event handler for "safe" scroll events which are only triggered if:
+     * - the widget has focus
+     * - or the widget has no scrolled window ancestor
+     * - or the Shift key is pressed
+     */
+    virtual bool on_safe_scroll_event(GdkEventScroll *event)
+    { //
+        return Base::on_scroll_event(event);
+    }
+
+    bool on_scroll_event(GdkEventScroll *event) final
+    {
+        if (!scrolling_allowed(this, event)) {
+            return false;
+        }
+        return on_safe_scroll_event(event);
+    }
+};
+
+/**
+ * A class decorator for scroll widgets like scrolled window to transfer scroll to
+ * any ancestor which is is a scrollable window when scroll reached end.
+ *
+ * For custom scroll event handlers, derived classes must implement
+ * on_safe_scroll_event instead of on_scroll_event. Directly connecting to
+ * signal_scroll_event() will bypass the scroll protection.
+ *
+ * @tparam Base A subclass of Gtk::Widget
+ */
+template <typename Base>
+class ScrollTransfer : public Base
+{
+public:
+    using Base::Base;
+    using typename Base::BaseObjectType;
+    ScrollTransfer()
+        : Base()
+    {}
+    ScrollTransfer(BaseObjectType *cobject, const Glib::RefPtr<Gtk::Builder> &refGlade)
+        : Base(cobject){};
+    ~ScrollTransfer() override{};
+protected:
+    /**
+     * Event handler for "safe" scroll events
+     */
+    virtual bool on_safe_scroll_event(GdkEventScroll *event)
+    { //
+        return Base::on_scroll_event(event);
+    }
+
+    bool on_scroll_event(GdkEventScroll *event) final
+    {
+        auto scrollable = dynamic_cast<Gtk::Widget *>(Inkscape::UI::Widget::get_scrollable_ancestor(this));
+        auto adj = this->get_vadjustment();
+        auto before = adj->get_value();
+        bool result = on_safe_scroll_event(event);
+        auto after = adj->get_value();
+        if (scrollable && before == after) {
+            return false;
+        }
+
+        return result;
+    }
+};
+
+} // namespace Widget
+} // namespace UI
+} // namespace Inkscape
+
+#endif
+// vim: filetype=cpp:expandtab:shiftwidth=4:softtabstop=4:fileencoding=utf-8:textwidth=99 :