From 18d344609fc15c15110fd629a4b1d33b35ab0f85 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Wed, 5 May 2021 22:15:09 +0200
Subject: [PATCH] LibGUI: Add ScrollableContainerWidget :^)

This widget provides a scrollable view onto another (child) widget.
If the child is larger than the parent, scrollbars are provided for
panning around the child.
---
 Userland/Libraries/LibGUI/CMakeLists.txt      |  1 +
 .../LibGUI/ScrollableContainerWidget.cpp      | 74 +++++++++++++++++++
 .../LibGUI/ScrollableContainerWidget.h        | 36 +++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 Userland/Libraries/LibGUI/ScrollableContainerWidget.cpp
 create mode 100644 Userland/Libraries/LibGUI/ScrollableContainerWidget.h

diff --git a/Userland/Libraries/LibGUI/CMakeLists.txt b/Userland/Libraries/LibGUI/CMakeLists.txt
index 84f32ff05f..65362b1184 100644
--- a/Userland/Libraries/LibGUI/CMakeLists.txt
+++ b/Userland/Libraries/LibGUI/CMakeLists.txt
@@ -74,6 +74,7 @@ set(SOURCES
     RegularEditingEngine.cpp
     ResizeCorner.cpp
     RunningProcessesModel.cpp
+    ScrollableContainerWidget.cpp
     Scrollbar.cpp
     SeparatorWidget.cpp
     Shortcut.cpp
diff --git a/Userland/Libraries/LibGUI/ScrollableContainerWidget.cpp b/Userland/Libraries/LibGUI/ScrollableContainerWidget.cpp
new file mode 100644
index 0000000000..d3b4c4728f
--- /dev/null
+++ b/Userland/Libraries/LibGUI/ScrollableContainerWidget.cpp
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGUI/Layout.h>
+#include <LibGUI/ScrollableContainerWidget.h>
+
+namespace GUI {
+
+ScrollableContainerWidget::ScrollableContainerWidget()
+{
+}
+
+ScrollableContainerWidget::~ScrollableContainerWidget()
+{
+}
+
+void ScrollableContainerWidget::did_scroll()
+{
+    AbstractScrollableWidget::did_scroll();
+    update_widget_position();
+}
+
+void ScrollableContainerWidget::update_widget_position()
+{
+    if (!m_widget)
+        return;
+    m_widget->move_to(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+}
+
+void ScrollableContainerWidget::update_widget_size()
+{
+    if (!m_widget)
+        return;
+    m_widget->do_layout();
+    if (m_widget->is_shrink_to_fit() && m_widget->layout()) {
+        auto new_size = frame_inner_rect().size();
+        auto preferred_size = m_widget->layout()->preferred_size();
+        if (preferred_size.width() != -1)
+            new_size.set_width(preferred_size.width());
+        if (preferred_size.height() != -1)
+            new_size.set_height(preferred_size.height());
+        m_widget->resize(new_size);
+        set_content_size(new_size);
+    }
+}
+
+void ScrollableContainerWidget::resize_event(GUI::ResizeEvent& event)
+{
+    AbstractScrollableWidget::resize_event(event);
+    update_widget_size();
+}
+
+void ScrollableContainerWidget::set_widget(GUI::Widget* widget)
+{
+    if (m_widget == widget)
+        return;
+
+    if (m_widget)
+        remove_child(*m_widget);
+
+    m_widget = widget;
+
+    if (m_widget) {
+        add_child(*m_widget);
+        m_widget->move_to_back();
+    }
+    update_widget_size();
+    update_widget_position();
+}
+
+}
diff --git a/Userland/Libraries/LibGUI/ScrollableContainerWidget.h b/Userland/Libraries/LibGUI/ScrollableContainerWidget.h
new file mode 100644
index 0000000000..0d2410a7a3
--- /dev/null
+++ b/Userland/Libraries/LibGUI/ScrollableContainerWidget.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/AbstractScrollableWidget.h>
+
+namespace GUI {
+
+class ScrollableContainerWidget : public GUI::AbstractScrollableWidget {
+    C_OBJECT(ScrollableContainerWidget);
+
+public:
+    virtual ~ScrollableContainerWidget();
+
+    void set_widget(GUI::Widget*);
+    GUI::Widget* widget() { return m_widget; }
+    GUI::Widget const* widget() const { return m_widget; }
+
+protected:
+    virtual void did_scroll() override;
+    virtual void resize_event(GUI::ResizeEvent&) override;
+
+private:
+    void update_widget_size();
+    void update_widget_position();
+
+    ScrollableContainerWidget();
+
+    RefPtr<GUI::Widget> m_widget;
+};
+
+}