LibGUI: Improve IconView performance with large selections

This implements the following optimizations:

* Rather than clearing a HashTable of selected items and re-populating
  it every time the selection rectangle changes, determine the delta
  by only examining the items that might be in the area where the
  selection may have changed compared to the previous area. Then
  only add/remove selection items as needed.

* When painting, only query and paint the items actually visible.
  Also, keep a local cache of item information such as calculated
  rectangles and selection state, so it doesn't have to be calculated
  over and over again.

Libraries/LibGUI/AbstractView.cpp

@@ -65,12 +65,37 @@ void AbstractView::did_update_model(unsigned flags)
     m_edit_index = {};
     m_hovered_index = {};
     if (!model() || (flags & GUI::Model::InvalidateAllIndexes)) {
-        selection().clear();
+        clear_selection();
     } else {
         selection().remove_matching([this](auto& index) { return !model()->is_valid(index); });
     }
 }
 
+void AbstractView::clear_selection()
+{
+    m_selection.clear();
+}
+
+void AbstractView::set_selection(const ModelIndex& new_index)
+{
+    m_selection.set(new_index);
+}
+
+void AbstractView::add_selection(const ModelIndex& new_index)
+{
+    m_selection.add(new_index);
+}
+
+void AbstractView::remove_selection(const ModelIndex& new_index)
+{
+    m_selection.remove(new_index);
+}
+
+void AbstractView::toggle_selection(const ModelIndex& new_index)
+{
+    m_selection.toggle(new_index);
+}
+
 void AbstractView::did_update_selection()
 {
     if (!model() || selection().first() != m_edit_index)
@@ -182,14 +207,14 @@ void AbstractView::mousedown_event(MouseEvent& event)
     m_might_drag = false;
 
     if (!index.is_valid()) {
-        m_selection.clear();
+        clear_selection();
     } else if (event.modifiers() & Mod_Ctrl) {
-        m_selection.toggle(index);
+        toggle_selection(index);
     } else if (event.button() == MouseButton::Left && m_selection.contains(index) && !m_model->drag_data_type().is_null()) {
         // We might be starting a drag, so don't throw away other selected items yet.
         m_might_drag = true;
     } else {
-        m_selection.set(index);
+        set_selection(index);
     }
 
     update();
@@ -294,9 +319,9 @@ void AbstractView::mouseup_event(MouseEvent& event)
         // Since we're here, it was not that; so fix up the selection now.
         auto index = index_at_event_position(event.position());
         if (index.is_valid())
-            m_selection.set(index);
+            set_selection(index);
         else
-            m_selection.clear();
+            clear_selection();
         m_might_drag = false;
         update();
     }
@@ -315,9 +340,9 @@ void AbstractView::doubleclick_event(MouseEvent& event)
     auto index = index_at_event_position(event.position());
 
     if (!index.is_valid())
-        m_selection.clear();
+        clear_selection();
     else if (!m_selection.contains(index))
-        m_selection.set(index);
+        set_selection(index);
 
     activate_selected();
 }
@@ -330,9 +355,9 @@ void AbstractView::context_menu_event(ContextMenuEvent& event)
     auto index = index_at_event_position(event.position());
 
     if (index.is_valid())
-        m_selection.add(index);
+        add_selection(index);
     else
-        selection().clear();
+        clear_selection();
 
     if (on_context_menu_request)
         on_context_menu_request(index, event);

Libraries/LibGUI/AbstractView.h

@@ -83,6 +83,12 @@ protected:
     virtual void drop_event(DropEvent&) override;
     virtual void leave_event(Core::Event&) override;
 
+    virtual void clear_selection();
+    virtual void set_selection(const ModelIndex&);
+    virtual void add_selection(const ModelIndex&);
+    virtual void remove_selection(const ModelIndex&);
+    virtual void toggle_selection(const ModelIndex&);
+
     virtual void did_scroll() override;
     void set_hovered_index(const ModelIndex&);
     void activate(const ModelIndex&);

Libraries/LibGUI/IconView.cpp

@@ -51,10 +51,14 @@ IconView::~IconView()
 
 void IconView::select_all()
 {
-    selection().clear();
     for (int item_index = 0; item_index < item_count(); ++item_index) {
-        auto index = model()->index(item_index, model_column());
-        selection().add(index);
+        auto& item_data = m_item_data_cache[item_index];
+        if (!item_data.selected) {
+            if (item_data.is_valid())
+                add_selection(item_data);
+            else
+                add_selection(model()->index(item_index, model_column()));
+        }
     }
 }
 
@@ -69,9 +73,75 @@ void IconView::resize_event(ResizeEvent& event)
     update_content_size();
 }
 
+void IconView::reinit_item_cache() const
+{
+    auto prev_item_count = m_item_data_cache.size();
+    size_t new_item_count = item_count();
+    auto items_to_invalidate = min(prev_item_count, new_item_count);
+
+    // if the new number of items is less, check if any of the
+    // ones not in the list anymore was selected
+    for (size_t i = new_item_count; i < m_item_data_cache.size(); i++) {
+        auto& item_data = m_item_data_cache[i];
+        if (item_data.selected) {
+            ASSERT(m_selected_count_cache > 0);
+            m_selected_count_cache--;
+        }
+    }
+    if ((size_t)m_first_selected_hint >= new_item_count)
+        m_first_selected_hint = 0;
+    m_item_data_cache.resize(new_item_count);
+    for (size_t i = 0; i < items_to_invalidate; i++) {
+        auto& item_data = m_item_data_cache[i];
+        // TODO: It's unfortunate that we have no way to know whether any
+        // data actually changed, so we have to invalidate *everyone*
+        if (item_data.is_valid()/* && !model()->is_valid(item_data.index)*/)
+            item_data.invalidate();
+        if (item_data.selected && i < (size_t)m_first_selected_hint)
+            m_first_selected_hint = (int)i;
+    }
+
+    m_item_data_cache_valid = true;
+}
+
+auto IconView::get_item_data(int item_index) const -> ItemData&
+{
+    if (!m_item_data_cache_valid)
+        reinit_item_cache();
+
+    auto& item_data = m_item_data_cache[item_index];
+    if (item_data.is_valid())
+        return item_data;
+
+    item_data.index = model()->index(item_index, model_column());
+    item_data.data = model()->data(item_data.index);
+    get_item_rects(item_index, item_data, font_for_index(item_data.index));
+    item_data.valid = true;
+    return item_data;
+}
+
+auto IconView::item_data_from_content_position(const Gfx::IntPoint& content_position) const -> ItemData*
+{
+    if (!m_visual_row_count || !m_visual_column_count)
+        return nullptr;
+    int row, column;
+    column_row_from_content_position(content_position, row, column);
+    int item_index = row * m_visual_column_count + column;
+    if (item_index < 0 || item_index >= item_count())
+        return nullptr;
+    return &get_item_data(item_index);
+}
+
 void IconView::did_update_model(unsigned flags)
 {
     AbstractView::did_update_model(flags);
+    if (!model() || (flags & GUI::Model::InvalidateAllIndexes)) {
+        m_item_data_cache.clear();
+        AbstractView::clear_selection();
+        m_selected_count_cache = 0;
+        m_first_selected_hint = 0;
+    }
+    m_item_data_cache_valid = false;
     update_content_size();
     update();
 }
@@ -81,7 +151,7 @@ void IconView::update_content_size()
     if (!model())
         return set_content_size({});
 
-    m_visual_column_count = available_size().width() / effective_item_size().width();
+    m_visual_column_count = max(1, available_size().width() / effective_item_size().width());
     if (m_visual_column_count)
         m_visual_row_count = ceil_div(model()->row_count(), m_visual_column_count);
     else
@@ -91,6 +161,15 @@ void IconView::update_content_size()
     int content_height = m_visual_row_count * effective_item_size().height();
 
     set_content_size({ content_width, content_height });
+
+    if (!m_item_data_cache_valid)
+        reinit_item_cache();
+
+    for (int item_index = 0; item_index < item_count(); item_index++) {
+        auto& item_data = m_item_data_cache[item_index];
+        if (item_data.is_valid())
+            update_item_rects(item_index, item_data);
+    }
 }
 
 Gfx::IntRect IconView::item_rect(int item_index) const
@@ -107,38 +186,13 @@ Gfx::IntRect IconView::item_rect(int item_index) const
     };
 }
 
-Vector<int> IconView::items_intersecting_rect(const Gfx::IntRect& rect) const
-{
-    ASSERT(model());
-    Vector<int> item_indexes;
-    for (int item_index = 0; item_index < item_count(); ++item_index) {
-        Gfx::IntRect item_rect;
-        Gfx::IntRect icon_rect;
-        Gfx::IntRect text_rect;
-        auto index = model()->index(item_index, model_column());
-        auto item_text = model()->data(index);
-        get_item_rects(item_index, font_for_index(index), item_text, item_rect, icon_rect, text_rect);
-        if (icon_rect.intersects(rect) || text_rect.intersects(rect))
-            item_indexes.append(item_index);
-    }
-    return item_indexes;
-}
-
 ModelIndex IconView::index_at_event_position(const Gfx::IntPoint& position) const
 {
     ASSERT(model());
-    // FIXME: Since all items are the same size, just compute the clicked item index
-    //        instead of iterating over everything.
     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;
-        Gfx::IntRect text_rect;
-        auto index = model()->index(item_index, model_column());
-        auto item_text = model()->data(index);
-        get_item_rects(item_index, font_for_index(index), item_text, item_rect, icon_rect, text_rect);
-        if (icon_rect.contains(adjusted_position) || text_rect.contains(adjusted_position))
-            return index;
+    if (auto item_data = item_data_from_content_position(adjusted_position)) {
+        if (item_data->is_containing(adjusted_position))
+            return item_data->index;
     }
     return {};
 }
@@ -157,14 +211,11 @@ void IconView::mousedown_event(MouseEvent& event)
         return AbstractView::mousedown_event(event);
     }
 
-    ASSERT(m_rubber_band_remembered_selection.is_empty());
-
     if (event.modifiers() & Mod_Ctrl) {
-        selection().for_each_index([&](auto& index) {
-            m_rubber_band_remembered_selection.append(index);
-        });
+        m_rubber_banding_store_selection = true;
     } else {
-        selection().clear();
+        clear_selection();
+        m_rubber_banding_store_selection = false;
     }
 
     auto adjusted_position = to_content_position(event.position());
@@ -179,7 +230,6 @@ 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();
@@ -210,17 +260,58 @@ bool IconView::update_rubber_banding(const Gfx::IntPoint& position)
 {
     auto adjusted_position = to_content_position(position);
     if (m_rubber_band_current != adjusted_position) {
+        auto prev_rect = Gfx::IntRect::from_two_points(m_rubber_band_origin, m_rubber_band_current);
         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);
+
+        // If the rectangle width or height is 0, we still want to be able
+        // to match the items in the path. An easy work-around for this
+        // is to simply set the width or height to 1
+        auto ensure_rect = [](Gfx::IntRect& rect) {
+            if (rect.width() <= 0)
+                rect.set_width(1);
+            if (rect.height() <= 0)
+                rect.set_height(1);
+        };
+        ensure_rect(prev_rect);
+        ensure_rect(rubber_band_rect);
+
+        // Clearing the entire selection every time is very expensive,
+        // determine what items may need to be deselected and what new
+        // items may need to be selected. Avoid a ton of allocations.
+
+        auto deselect_area = prev_rect.shatter(rubber_band_rect);
+        auto select_area = rubber_band_rect.shatter(prev_rect);
+
+        // Initialize all candidate's toggle flag. We need to know which
+        // items we touched because the various rectangles likely will
+        // contain the same item more than once
+        for_each_item_intersecting_rects(deselect_area, [](ItemData& item_data) -> IterationDecision {
+            item_data.selection_toggled = false;
+            return IterationDecision::Continue;
+        });
+        for_each_item_intersecting_rects(select_area, [](ItemData& item_data) -> IterationDecision {
+            item_data.selection_toggled = false;
+            return IterationDecision::Continue;
+        });
+
+        // Now toggle all items that are no longer in the selected area, once only
+        for_each_item_intersecting_rects(deselect_area, [&](ItemData& item_data) -> IterationDecision {
+            if (!item_data.selection_toggled && item_data.is_intersecting(prev_rect) && !item_data.is_intersecting(rubber_band_rect)) {
+                item_data.selection_toggled = true;
+                toggle_selection(item_data);
             }
-        }
+            return IterationDecision::Continue;
+        });
+        // Now toggle all items that are in the new selected area, once only
+        for_each_item_intersecting_rects(select_area, [&](ItemData& item_data) -> IterationDecision {
+            if (!item_data.selection_toggled && !item_data.is_intersecting(prev_rect) && item_data.is_intersecting(rubber_band_rect)) {
+                item_data.selection_toggled = true;
+                toggle_selection(item_data);
+            }
+            return IterationDecision::Continue;
+        });
+
         update();
         return true;
     }
@@ -235,8 +326,6 @@ void IconView::mousemove_event(MouseEvent& event)
         return AbstractView::mousemove_event(event);
 
     if (m_rubber_banding) {
-        m_rubber_banding_store_selection = (event.modifiers() & Mod_Ctrl);
-
         auto in_view_rect = widget_inner_rect();
         in_view_rect.shrink(SCROLL_OUT_OF_VIEW_HOT_MARGIN, SCROLL_OUT_OF_VIEW_HOT_MARGIN);
         if (!in_view_rect.contains(event.position())) {
@@ -281,21 +370,32 @@ void IconView::scroll_out_of_view_timer_fired()
         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
+void IconView::update_item_rects(int item_index, ItemData& item_data) const
 {
-    item_rect = this->item_rect(item_index);
-    icon_rect = { 0, 0, 32, 32 };
-    icon_rect.center_within(item_rect);
-    icon_rect.move_by(0, -font.glyph_height() - 6);
-    text_rect = { 0, icon_rect.bottom() + 6 + 1, font.width(item_text.to_string()), font.glyph_height() };
-    text_rect.center_horizontally_within(item_rect);
-    text_rect.inflate(6, 4);
-    text_rect.intersect(item_rect);
+    auto item_rect = this->item_rect(item_index);
+    item_data.icon_rect.center_within(item_rect);
+    item_data.icon_rect.move_by(0, item_data.icon_offset_y);
+    item_data.text_rect.center_horizontally_within(item_rect);
+    item_data.text_rect.set_top(item_rect.y() + item_data.text_offset_y);
+}
+
+void IconView::get_item_rects(int item_index, ItemData& item_data, const Gfx::Font& font) const
+{
+    auto item_rect = this->item_rect(item_index);
+    item_data.icon_rect = { 0, 0, 32, 32 };
+    item_data.icon_rect.center_within(item_rect);
+    item_data.icon_offset_y = -font.glyph_height() - 6;
+    item_data.icon_rect.move_by(0, item_data.icon_offset_y);
+    item_data.text_rect = { 0, item_data.icon_rect.bottom() + 6 + 1, font.width(item_data.data.to_string()), font.glyph_height() };
+    item_data.text_rect.center_horizontally_within(item_rect);
+    item_data.text_rect.inflate(6, 4);
+    item_data.text_rect.intersect(item_rect);
+    item_data.text_offset_y = item_data.text_rect.y() - item_rect.y();
 }
 
 void IconView::second_paint_event(PaintEvent& event)
@@ -321,35 +421,30 @@ void IconView::paint_event(PaintEvent& event)
     Painter painter(*this);
     painter.add_clip_rect(widget_inner_rect());
     painter.add_clip_rect(event.rect());
+    
     if (fill_with_background_color())
         painter.fill_rect(event.rect(), widget_background_color);
     painter.translate(frame_thickness(), frame_thickness());
     painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
 
-    for (int item_index = 0; item_index < model()->row_count(); ++item_index) {
-        auto model_index = model()->index(item_index, m_model_column);
-        bool is_selected_item = selection().contains(model_index);
+    auto translation = painter.translation().translated(-relative_position().x(), -relative_position().y());
+    for_each_item_intersecting_rect(painter.clip_rect().translated(-translation.x(), -translation.y()), [&](auto& item_data) -> IterationDecision {
         Color background_color;
-        if (is_selected_item) {
+        if (item_data.selected) {
             background_color = is_focused() ? palette().selection() : palette().inactive_selection();
         } else {
             background_color = widget_background_color;
         }
 
-        auto icon = model()->data(model_index, Model::Role::Icon);
-        auto item_text = model()->data(model_index, Model::Role::Display);
-
-        Gfx::IntRect item_rect;
-        Gfx::IntRect icon_rect;
-        Gfx::IntRect text_rect;
-        get_item_rects(item_index, font_for_index(model_index), item_text, item_rect, icon_rect, text_rect);
+        auto icon = model()->data(item_data.index, Model::Role::Icon);
+        auto item_text = model()->data(item_data.index, Model::Role::Display);
 
         if (icon.is_icon()) {
-            if (auto bitmap = icon.as_icon().bitmap_for_size(icon_rect.width())) {
+            if (auto bitmap = icon.as_icon().bitmap_for_size(item_data.icon_rect.width())) {
                 Gfx::IntRect destination = bitmap->rect();
-                destination.center_within(icon_rect);
+                destination.center_within(item_data.icon_rect);
 
-                if (m_hovered_index.is_valid() && m_hovered_index == model_index) {
+                if (m_hovered_index.is_valid() && m_hovered_index == item_data.index) {
                     painter.blit_brightened(destination.location(), *bitmap, bitmap->rect());
                 } else {
                     painter.blit(destination.location(), *bitmap, bitmap->rect());
@@ -358,18 +453,19 @@ void IconView::paint_event(PaintEvent& event)
         }
 
         Color text_color;
-        if (is_selected_item)
+        if (item_data.selected)
             text_color = is_focused() ? palette().selection_text() : palette().inactive_selection_text();
         else
-            text_color = model()->data(model_index, Model::Role::ForegroundColor).to_color(palette().color(foreground_role()));
-        painter.fill_rect(text_rect, background_color);
-        painter.draw_text(text_rect, item_text.to_string(), font_for_index(model_index), Gfx::TextAlignment::Center, text_color, Gfx::TextElision::Right);
+            text_color = model()->data(item_data.index, Model::Role::ForegroundColor).to_color(palette().color(foreground_role()));
+        painter.fill_rect(item_data.text_rect, background_color);
+        painter.draw_text(item_data.text_rect, item_text.to_string(), font_for_index(item_data.index), Gfx::TextAlignment::Center, text_color, Gfx::TextElision::Right);
 
-        if (model_index == m_drop_candidate_index) {
+        if (item_data.index == m_drop_candidate_index) {
             // FIXME: This visualization is not great, as it's also possible to drop things on the text label..
-            painter.draw_rect(icon_rect.inflated(8, 8), palette().selection(), true);
+            painter.draw_rect(item_data.icon_rect.inflated(8, 8), palette().selection(), true);
         }
-    };
+        return IterationDecision::Continue;
+    });
 }
 
 int IconView::item_count() const
@@ -379,6 +475,122 @@ int IconView::item_count() const
     return model()->row_count();
 }
 
+void IconView::did_update_selection()
+{
+    AbstractView::did_update_selection();
+    if (m_changing_selection)
+        return;
+    
+    // Selection was modified externally, we need to synchronize our cache
+    do_clear_selection();
+    selection().for_each_index([&](const ModelIndex& index) {
+        if (index.is_valid()) {
+            auto item_index = model_index_to_item_index(index);
+            if ((size_t)item_index < m_item_data_cache.size())
+                do_add_selection(get_item_data(item_index));
+        }
+    });
+}
+
+void IconView::do_clear_selection()
+{
+    for (size_t item_index = m_first_selected_hint; item_index < m_item_data_cache.size(); item_index++) {
+        if (m_selected_count_cache == 0)
+            break;
+        auto& item_data = m_item_data_cache[item_index];
+        if (!item_data.selected)
+            continue;
+        item_data.selected = false;
+        m_selected_count_cache--;
+    }
+    m_first_selected_hint = 0;
+    ASSERT(m_selected_count_cache == 0);
+}
+
+void IconView::clear_selection()
+{
+    TemporaryChange change(m_changing_selection, true);
+    AbstractView::clear_selection();
+    do_clear_selection();
+}
+
+bool IconView::do_add_selection(ItemData& item_data)
+{
+    if (!item_data.selected) {
+        item_data.selected = true;
+        m_selected_count_cache++;
+        int item_index = &item_data - &m_item_data_cache[0];
+        if (m_first_selected_hint > item_index)
+            m_first_selected_hint = item_index;
+        return true;
+    }
+    return false;
+}
+
+void IconView::add_selection(ItemData& item_data)
+{
+    if (do_add_selection(item_data))
+        AbstractView::add_selection(item_data.index);
+}
+
+void IconView::add_selection(const ModelIndex& new_index)
+{
+    TemporaryChange change(m_changing_selection, true);
+    auto item_index = model_index_to_item_index(new_index);
+    add_selection(get_item_data(item_index));
+}
+
+void IconView::toggle_selection(ItemData& item_data)
+{
+    if (!item_data.selected)
+        add_selection(item_data);
+    else
+        remove_selection(item_data);
+}
+
+void IconView::toggle_selection(const ModelIndex& new_index)
+{
+    TemporaryChange change(m_changing_selection, true);
+    auto item_index = model_index_to_item_index(new_index);
+    toggle_selection(get_item_data(item_index));
+}
+
+void IconView::remove_selection(ItemData& item_data)
+{
+    if (!item_data.selected)
+        return;
+
+    TemporaryChange change(m_changing_selection, true);
+    item_data.selected = false;
+    ASSERT(m_selected_count_cache > 0);
+    m_selected_count_cache--;
+    int item_index = &item_data - &m_item_data_cache[0];
+    if (m_first_selected_hint == item_index) {
+        m_first_selected_hint = 0;
+        while ((size_t)item_index < m_item_data_cache.size()) {
+            if (m_item_data_cache[item_index].selected) {
+                m_first_selected_hint = item_index;
+                break;
+            }
+            item_index++;
+        }
+    }
+    AbstractView::remove_selection(item_data.index);
+}
+
+void IconView::set_selection(const ModelIndex& new_index)
+{
+    TemporaryChange change(m_changing_selection, true);
+    do_clear_selection();
+    auto item_index = model_index_to_item_index(new_index);
+    auto& item_data = get_item_data(item_index);
+    item_data.selected = true;
+    m_selected_count_cache = 1;
+    if (item_index < m_first_selected_hint)
+        m_first_selected_hint = item_index;
+    AbstractView::set_selection(new_index);
+}
+
 void IconView::keydown_event(KeyEvent& event)
 {
     if (!model())
@@ -394,7 +606,7 @@ void IconView::keydown_event(KeyEvent& event)
     if (event.key() == KeyCode::Key_Home) {
         auto new_index = model.index(0, 0);
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -403,7 +615,7 @@ void IconView::keydown_event(KeyEvent& event)
     if (event.key() == KeyCode::Key_End) {
         auto new_index = model.index(model.row_count() - 1, 0);
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -418,7 +630,7 @@ void IconView::keydown_event(KeyEvent& event)
             new_index = model.index(0, 0);
         }
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -433,7 +645,7 @@ void IconView::keydown_event(KeyEvent& event)
             new_index = model.index(0, 0);
         }
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -448,7 +660,7 @@ void IconView::keydown_event(KeyEvent& event)
             new_index = model.index(0, 0);
         }
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -463,7 +675,7 @@ void IconView::keydown_event(KeyEvent& event)
             new_index = model.index(0, 0);
         }
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -474,7 +686,7 @@ void IconView::keydown_event(KeyEvent& event)
         auto old_index = selection().first();
         auto new_index = model.index(max(0, old_index.row() - items_per_page), old_index.column());
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }
@@ -485,7 +697,7 @@ void IconView::keydown_event(KeyEvent& event)
         auto old_index = selection().first();
         auto new_index = model.index(min(model.row_count() - 1, old_index.row() + items_per_page), old_index.column());
         if (model.is_valid(new_index)) {
-            selection().set(new_index);
+            set_selection(new_index);
             scroll_into_view(new_index, Orientation::Vertical);
             update();
         }

Libraries/LibGUI/IconView.h

@@ -26,8 +26,10 @@
 
 #pragma once
 
+#include <AK/IterationDecision.h>
 #include <LibGUI/AbstractView.h>
 #include <LibGUI/Forward.h>
+#include <LibGUI/Variant.h>
 
 namespace GUI {
 
@@ -48,6 +50,7 @@ public:
     virtual ModelIndex index_at_event_position(const Gfx::IntPoint&) const override;
 
     virtual void select_all() override;
+
 private:
     IconView();
 
@@ -61,14 +64,110 @@ private:
     virtual void keydown_event(KeyEvent&) override;
     virtual void drag_move_event(DragEvent&) override;
 
+    struct ItemData {
+        Gfx::IntRect text_rect;
+        Gfx::IntRect icon_rect;
+        int icon_offset_y;
+        int text_offset_y;
+        Variant data;
+        ModelIndex index;
+        bool valid { false };
+        bool selected { false }; // always valid
+        bool selection_toggled;  // only used as a temporary marker
+
+        bool is_valid() const { return valid; }
+        void invalidate()
+        {
+            valid = false;
+            data.clear();
+        }
+
+        bool is_intersecting(const Gfx::IntRect& rect) const
+        {
+            ASSERT(valid);
+            return icon_rect.intersects(rect) || text_rect.intersects(rect);
+        }
+
+        bool is_containing(const Gfx::IntPoint& point) const
+        {
+            ASSERT(valid);
+            return icon_rect.contains(point) || text_rect.contains(point);
+        }
+    };
+
+    template<typename Function>
+    IterationDecision for_each_item_intersecting_rect(const Gfx::IntRect& rect, Function f) const
+    {
+        ASSERT(model());
+        if (rect.is_empty())
+            return IterationDecision::Continue;
+        int begin_row, begin_column;
+        column_row_from_content_position(rect.top_left(), begin_row, begin_column);
+        int end_row, end_column;
+        column_row_from_content_position(rect.bottom_right(), end_row, end_column);
+        int items_per_column = end_column - begin_column + 1;
+        int item_index = max(0, begin_row * m_visual_column_count + begin_column);
+        int last_index = min(item_count(), end_row * m_visual_column_count + end_column + 1);
+        while (item_index < last_index) {
+            for (int i = item_index; i < min(item_index + items_per_column, last_index); i++) {
+                auto& item_data = get_item_data(i);
+                if (item_data.is_intersecting(rect)) {
+                    auto decision = f(item_data);
+                    if (decision != IterationDecision::Continue)
+                        return decision;
+                }
+            }
+            item_index += m_visual_column_count;
+        };
+        return IterationDecision::Continue;
+    }
+
+    template<typename Function>
+    IterationDecision for_each_item_intersecting_rects(const Vector<Gfx::IntRect>& rects, Function f) const
+    {
+        for (auto& rect : rects) {
+            auto decision = for_each_item_intersecting_rect(rect, f);
+            if (decision != IterationDecision::Continue)
+                return decision;
+        }
+        return IterationDecision::Continue;
+    }
+
+    void column_row_from_content_position(const Gfx::IntPoint& content_position, int& row, int& column) const
+    {
+        row = max(0, min(m_visual_row_count - 1, content_position.y() / effective_item_size().height()));
+        column = max(0, min(m_visual_column_count - 1, content_position.x() / effective_item_size().width()));
+    }
+
     int item_count() const;
     Gfx::IntRect item_rect(int item_index) const;
-    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;
+    void update_item_rects(int item_index, ItemData& item_data) const;
+    void get_item_rects(int item_index, ItemData& item_data, const Gfx::Font&) const;
     bool update_rubber_banding(const Gfx::IntPoint&);
     void scroll_out_of_view_timer_fired();
 
+    void reinit_item_cache() const;
+    int model_index_to_item_index(const ModelIndex& model_index) const
+    {
+        ASSERT(model_index.row() < item_count());
+        return model_index.row();
+    }
+
+    virtual void did_update_selection() override;
+    virtual void clear_selection() override;
+    virtual void add_selection(const ModelIndex& new_index) override;
+    virtual void set_selection(const ModelIndex& new_index) override;
+    virtual void toggle_selection(const ModelIndex& new_index) override;
+
+    ItemData& get_item_data(int) const;
+    ItemData* item_data_from_content_position(const Gfx::IntPoint&) const;
+    void do_clear_selection();
+    bool do_add_selection(ItemData&);
+    void add_selection(ItemData&);
+    void remove_selection(ItemData&);
+    void toggle_selection(ItemData&);
+
     int m_horizontal_padding { 5 };
     int m_model_column { 0 };
     int m_visual_column_count { 0 };
@@ -82,9 +181,15 @@ private:
     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;
 
     ModelIndex m_drop_candidate_index;
+
+    mutable Vector<ItemData> m_item_data_cache;
+    mutable int m_selected_count_cache { 0 };
+    mutable int m_first_selected_hint { 0 };
+    mutable bool m_item_data_cache_valid { false };
+
+    bool m_changing_selection { false };
 };
 
 }