LibGUI: Keep scrolling while drag-selecting outside a TextEditor

If you start selecting text and move the cursor outside the TextEditor
widget area without letting go of the mouse button, we will now keep
scrolling a little bit every 100ms.

Libraries/LibGUI/TextEditor.cpp

@@ -27,6 +27,7 @@
 #include <AK/QuickSort.h>
 #include <AK/StringBuilder.h>
 #include <Kernel/KeyCode.h>
+#include <LibCore/Timer.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/Clipboard.h>
 #include <LibGUI/FontDatabase.h>
@@ -60,6 +61,10 @@ TextEditor::TextEditor(Type type)
     // FIXME: Recompute vertical scrollbar step size on font change.
     vertical_scrollbar().set_step(line_height());
     m_cursor = { 0, 0 };
+    m_automatic_selection_scroll_timer = add<Core::Timer>(100, [this] {
+        automatic_selection_scroll_timer_fired();
+    });
+    m_automatic_selection_scroll_timer->stop();
     create_actions();
 }
 
@@ -261,6 +266,7 @@ void TextEditor::mousedown_event(MouseEvent& event)
     }
 
     m_in_drag_select = true;
+    m_automatic_selection_scroll_timer->start();
 
     set_cursor(text_position_at(event.position()));
 
@@ -289,6 +295,7 @@ void TextEditor::mouseup_event(MouseEvent& event)
 
 void TextEditor::mousemove_event(MouseEvent& event)
 {
+    m_last_mousemove_position = event.position();
     if (m_in_drag_select) {
         set_cursor(text_position_at(event.position()));
         m_selection.set_end(m_cursor);
@@ -298,6 +305,18 @@ void TextEditor::mousemove_event(MouseEvent& event)
     }
 }
 
+void TextEditor::automatic_selection_scroll_timer_fired()
+{
+    if (!m_in_drag_select) {
+        m_automatic_selection_scroll_timer->stop();
+        return;
+    }
+    set_cursor(text_position_at(m_last_mousemove_position));
+    m_selection.set_end(m_cursor);
+    did_update_selection();
+    update();
+}
+
 int TextEditor::ruler_width() const
 {
     if (!m_ruler_visible)
@@ -1189,12 +1208,17 @@ void TextEditor::enter_event(Core::Event&)
 {
     ASSERT(window());
     window()->set_override_cursor(StandardCursor::IBeam);
+
+    m_automatic_selection_scroll_timer->stop();
 }
 
 void TextEditor::leave_event(Core::Event&)
 {
     ASSERT(window());
     window()->set_override_cursor(StandardCursor::None);
+
+    if (m_in_drag_select)
+        m_automatic_selection_scroll_timer->start();
 }
 
 void TextEditor::did_change()

Libraries/LibGUI/TextEditor.h

@@ -200,6 +200,8 @@ private:
     size_t visual_line_containing(size_t line_index, size_t column) const;
     void recompute_visual_lines(size_t line_index);
 
+    void automatic_selection_scroll_timer_fired();
+
     template<class T, class... Args>
     inline void execute(Args&&... args)
     {
@@ -247,6 +249,9 @@ private:
     NonnullOwnPtrVector<LineVisualData> m_line_visual_data;
 
     OwnPtr<SyntaxHighlighter> m_highlighter;
+
+    RefPtr<Core::Timer> m_automatic_selection_scroll_timer;
+    Gfx::Point m_last_mousemove_position;
 };
 
 }