LibGUI: Implement IconView auto-scrolling when trying to select items out of view

If selecting in a large icon view, and dragging the mouse outside
of the widget, or close to the border of it, start scrolling
automatically. This allows for selecting large amount of items
that exceed the amount that can be displayed.

Libraries/LibGUI/IconView.cpp

@@ -25,6 +25,7 @@
  */
 
 #include <AK/StringBuilder.h>
+#include <LibCore/Timer.h>
 #include <LibGUI/DragOperation.h>
 #include <LibGUI/IconView.h>
 #include <LibGUI/Model.h>
@@ -128,7 +129,7 @@ ModelIndex IconView::index_at_event_position(const Gfx::IntPoint& position) cons
     ASSERT(model());
     // FIXME: Since all items are the same size, just compute the clicked item index
     //        instead of iterating over everything.
-    auto adjusted_position = this->adjusted_position(position);
+    auto adjusted_position = to_content_position(position);
     for (int item_index = 0; item_index < item_count(); ++item_index) {
         Gfx::IntRect item_rect;
         Gfx::IntRect icon_rect;
@@ -142,11 +143,6 @@ ModelIndex IconView::index_at_event_position(const Gfx::IntPoint& position) cons
     return {};
 }
 
-Gfx::IntPoint IconView::adjusted_position(const Gfx::IntPoint& position) const
-{
-    return position.translated(0, vertical_scrollbar().value());
-}
-
 void IconView::mousedown_event(MouseEvent& event)
 {
     if (!model())
@@ -171,7 +167,7 @@ void IconView::mousedown_event(MouseEvent& event)
         selection().clear();
     }
 
-    auto adjusted_position = this->adjusted_position(event.position());
+    auto adjusted_position = to_content_position(event.position());
 
     m_might_drag = false;
     m_rubber_banding = true;
@@ -184,6 +180,8 @@ void IconView::mouseup_event(MouseEvent& event)
     if (m_rubber_banding && event.button() == MouseButton::Left) {
         m_rubber_banding = false;
         m_rubber_band_remembered_selection.clear();
+        if (m_out_of_view_timer)
+            m_out_of_view_timer->stop();
         update();
     }
     AbstractView::mouseup_event(event);
@@ -208,33 +206,86 @@ void IconView::drag_move_event(DragEvent& event)
     event.accept();
 }
 
+bool IconView::update_rubber_banding(const Gfx::IntPoint& position)
+{
+    auto adjusted_position = to_content_position(position);
+    if (m_rubber_band_current != adjusted_position) {
+        m_rubber_band_current = adjusted_position;
+        auto rubber_band_rect = Gfx::IntRect::from_two_points(m_rubber_band_origin, m_rubber_band_current);
+        selection().clear();
+        for (auto item_index : items_intersecting_rect(rubber_band_rect)) {
+            selection().add(model()->index(item_index, model_column()));
+        }
+        if (m_rubber_banding_store_selection) {
+            for (auto stored_item : m_rubber_band_remembered_selection) {
+                selection().add(stored_item);
+            }
+        }
+        update();
+        return true;
+    }
+    return false;
+}
+
+#define SCROLL_OUT_OF_VIEW_HOT_MARGIN 20
+
 void IconView::mousemove_event(MouseEvent& event)
 {
     if (!model())
         return AbstractView::mousemove_event(event);
 
     if (m_rubber_banding) {
-        auto adjusted_position = this->adjusted_position(event.position());
+        m_rubber_banding_store_selection = (event.modifiers() & Mod_Ctrl);
-        if (m_rubber_band_current != adjusted_position) {
+
-            m_rubber_band_current = adjusted_position;
+        auto in_view_rect = widget_inner_rect();
-            auto rubber_band_rect = Gfx::IntRect::from_two_points(m_rubber_band_origin, m_rubber_band_current);
+        in_view_rect.shrink(SCROLL_OUT_OF_VIEW_HOT_MARGIN, SCROLL_OUT_OF_VIEW_HOT_MARGIN);
-            selection().clear();
+        if (!in_view_rect.contains(event.position())) {
-            for (auto item_index : items_intersecting_rect(rubber_band_rect)) {
+            if (!m_out_of_view_timer) {
-                selection().add(model()->index(item_index, model_column()));
+                m_out_of_view_timer = add<Core::Timer>();
+                m_out_of_view_timer->set_interval(100);
+                m_out_of_view_timer->on_timeout = [this] {
+                    scroll_out_of_view_timer_fired();
+                };
             }
-            if (event.modifiers() & Mod_Ctrl) {
+            
-                for (auto stored_item : m_rubber_band_remembered_selection) {
+            m_out_of_view_position = event.position();
-                    selection().add(stored_item);
+            if (!m_out_of_view_timer->is_active())
-                }
+                m_out_of_view_timer->start();
-            }
+        } else {
-            update();
+            if (m_out_of_view_timer)
-            return;
+                m_out_of_view_timer->stop();
         }
+        if (update_rubber_banding(event.position()))
+            return;
     }
 
     AbstractView::mousemove_event(event);
 }
 
+void IconView::scroll_out_of_view_timer_fired()
+{
+    auto scroll_to = to_content_position(m_out_of_view_position);
+    // Adjust the scroll-to position by SCROLL_OUT_OF_VIEW_HOT_MARGIN / 2
+    // depending on which direction we're scrolling. This allows us to
+    // start scrolling before we actually leave the visible area, which
+    // is important when there is no space to further move the mouse. The
+    // speed of scrolling is determined by the distance between the mouse
+    // pointer and the widget's inner rect shrunken by the hot margin
+    auto in_view_rect = widget_inner_rect().shrunken(SCROLL_OUT_OF_VIEW_HOT_MARGIN, SCROLL_OUT_OF_VIEW_HOT_MARGIN);
+    int adjust_x = 0, adjust_y = 0;
+    if (m_out_of_view_position.y() > in_view_rect.bottom())
+        adjust_y = (SCROLL_OUT_OF_VIEW_HOT_MARGIN / 2) + min(SCROLL_OUT_OF_VIEW_HOT_MARGIN, m_out_of_view_position.y() - in_view_rect.bottom());
+    else if (m_out_of_view_position.y() < in_view_rect.top())
+        adjust_y = -(SCROLL_OUT_OF_VIEW_HOT_MARGIN / 2) + max(-SCROLL_OUT_OF_VIEW_HOT_MARGIN, m_out_of_view_position.y() - in_view_rect.top());
+    if (m_out_of_view_position.x() > in_view_rect.right())
+        adjust_x = (SCROLL_OUT_OF_VIEW_HOT_MARGIN / 2) + min(SCROLL_OUT_OF_VIEW_HOT_MARGIN, m_out_of_view_position.x() - in_view_rect.right());
+    else if (m_out_of_view_position.x() < in_view_rect.left())
+        adjust_x = -(SCROLL_OUT_OF_VIEW_HOT_MARGIN / 2) + max(-SCROLL_OUT_OF_VIEW_HOT_MARGIN, m_out_of_view_position.x() - in_view_rect.left());
+    
+    ScrollableWidget::scroll_into_view({scroll_to.translated(adjust_x, adjust_y), {1, 1}}, true, true);
+    update_rubber_banding(m_out_of_view_position);
+}
+
 void IconView::get_item_rects(int item_index, const Gfx::Font& font, const Variant& item_text, Gfx::IntRect& item_rect, Gfx::IntRect& icon_rect, Gfx::IntRect& text_rect) const
 {
     item_rect = this->item_rect(item_index);

Libraries/LibGUI/IconView.h

@@ -46,7 +46,6 @@ public:
     void set_model_column(int column) { m_model_column = column; }
 
     virtual ModelIndex index_at_event_position(const Gfx::IntPoint&) const override;
-    Gfx::IntPoint adjusted_position(const Gfx::IntPoint&) const;
 
     virtual void select_all() override;
 private:
@@ -67,6 +66,8 @@ private:
     Vector<int> items_intersecting_rect(const Gfx::IntRect&) const;
     void update_content_size();
     void get_item_rects(int item_index, const Gfx::Font&, const Variant& item_text, Gfx::IntRect& item_rect, Gfx::IntRect& icon_rect, Gfx::IntRect& text_rect) const;
+    bool update_rubber_banding(const Gfx::IntPoint&);
+    void scroll_out_of_view_timer_fired();
 
     int m_horizontal_padding { 5 };
     int m_model_column { 0 };
@@ -76,6 +77,9 @@ private:
     Gfx::IntSize m_effective_item_size { 80, 80 };
 
     bool m_rubber_banding { false };
+    bool m_rubber_banding_store_selection { false };
+    RefPtr<Core::Timer> m_out_of_view_timer;
+    Gfx::IntPoint m_out_of_view_position;
     Gfx::IntPoint m_rubber_band_origin;
     Gfx::IntPoint m_rubber_band_current;
     Vector<ModelIndex> m_rubber_band_remembered_selection;