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.

1 files changed, 72 insertions, 21 deletions

diff --git a/Libraries/LibGUI/IconView.cpp b/Libraries/LibGUI/IconView.cpp
index b96fc68b46..1cebea04a5 100644
--- a/Libraries/LibGUI/IconView.cpp
+++ b/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());
-        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 (event.modifiers() & Mod_Ctrl) {
-                for (auto stored_item : m_rubber_band_remembered_selection) {
-                    selection().add(stored_item);
-                }
+        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())) {
+            if (!m_out_of_view_timer) {
+                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();
+                };
             }
-            update();
-            return;
+            
+            m_out_of_view_position = event.position();
+            if (!m_out_of_view_timer->is_active())
+                m_out_of_view_timer->start();
+        } else {
+            if (m_out_of_view_timer)
+                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);