Support dragging panels to stack and snap.

chrome/browser/ui/panels/stacked_panel_drag_handler.cc

Index: chrome/browser/ui/panels/stacked_panel_drag_handler.cc
diff --git a/chrome/browser/ui/panels/stacked_panel_drag_handler.cc b/chrome/browser/ui/panels/stacked_panel_drag_handler.cc
index ede20012ebf22ad8c7c3e4a5f9e8e488b6ab1336..e09b65a840525fb456c1c7104edf007ec976d838 100644
--- a/chrome/browser/ui/panels/stacked_panel_drag_handler.cc
+++ b/chrome/browser/ui/panels/stacked_panel_drag_handler.cc
@@ -7,13 +7,76 @@
 #include "base/logging.h"
 #include "chrome/browser/ui/panels/panel.h"
 #include "chrome/browser/ui/panels/panel_collection.h"
+#include "chrome/browser/ui/panels/stacked_panel_collection.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/rect.h"
 
 // static
 void StackedPanelDragHandler::HandleDrag(Panel* panel,
-                                         const gfx::Point& target_position) {
+                                         const gfx::Point& target_position,
+                                         bool in_orginal_collection) {
   DCHECK_EQ(PanelCollection::STACKED, panel->collection()->type());
 
-  // TODO(jianli): to be implemented.
+  StackedPanelCollection* stack = panel->stack();
+  DCHECK(stack);
+
+  // If the panel is in its original stack, only top panel is allowed to drag.
+  if (in_orginal_collection && panel != stack->top_panel())
+    return;
+
+  // Find out if all panels in the stack are being dragged.
+  bool all_panels_under_drag = true;
+  for (StackedPanelCollection::Panels::const_iterator iter =
+           stack->panels().begin();
+       iter != stack->panels().end(); ++iter) {
+    if (!(*iter)->in_preview_mode()) {
+      all_panels_under_drag = false;
+      break;
+    }
+  }
+
+  gfx::Vector2d delta_origin = target_position - panel->GetBounds().origin();
+
+  // If not all panels in the stack are being dragged, it means that these
+  // panels being dragged have just been added to this stack. Dragging these
+  // panels should only cause the horizontal movement due to that y position
+  // of these panels have already aligned.
+  if (!all_panels_under_drag)
+    delta_origin.set_y(0);
+
+  stack->MoveAllDraggingPanelsInstantly(delta_origin);
+}
+
+// static
+void StackedPanelDragHandler::FinalizeDrag(Panel* panel) {
+  DCHECK_EQ(PanelCollection::STACKED, panel->collection()->type());
+
+  StackedPanelCollection* stack = panel->stack();
+  DCHECK(stack);
+
+  // It is only needed when dragging a panel/stack to stack to the top of
+  // another panel/stack.
+  if (stack->top_panel() != panel)
+    return;
+
+  // Find the first non-dragging panel that is used to align all dragging panels
+  // above it to have the same x position. This is because all dragging panels
+  // are only aligned vertically when the stacking occurs.
+  Panel* first_non_dragging_panel = NULL;
+  for (StackedPanelCollection::Panels::const_iterator iter =
+           stack->panels().begin();
+       iter != stack->panels().end(); ++iter) {
+    Panel* panel = *iter;
+    if (!panel->in_preview_mode()) {
+      first_non_dragging_panel = panel;
+      break;
+    }
+  }
+  if (!first_non_dragging_panel)
+    return;
+
+  gfx::Vector2d delta_origin(
+      first_non_dragging_panel->GetBounds().x() - panel->GetBounds().x(),
+      0);
+  stack->MoveAllDraggingPanelsInstantly(delta_origin);
 }