Fix drag offset for holding space drag image.

The drag offset was slightly off as it didn't adequately account for
insets added for shadow rendering. If the elevation of dragged items
was increased, the drag offset could become severely off.

Now, drag offset is calculated correctly with respect to shadow margins
as well as insets added to accommodate the overflow badge (when present).

Bug: 1139113
Change-Id: I18f1aebd8818203196787c8b587ad1c2e55ecbc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485338
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818629}

ash/system/holding_space/holding_space_drag_util.cc

@@ -312,6 +312,49 @@ class DragImageView : public views::View {
   DragImageView& operator=(const DragImageView&) = delete;
   ~DragImageView() override = default;
 
+  // Paints this view to a `gfx::ImageSkia` for use as a drag image.
+  gfx::ImageSkia GetDragImage(float scale, bool is_pixel_canvas) {
+#if DCHECK_IS_ON()
+    // NOTE: This method will *not* paint `ui::Layer`s, so it is expected that
+    // all views in this view hierarchy *not* paint to layers.
+    AssertNoLayers(this);
+#endif  // DCHECK_IS_ON()
+    SkBitmap bitmap;
+    Paint(views::PaintInfo::CreateRootPaintInfo(
+        ui::CanvasPainter(&bitmap, size(), scale,
+                          /*clear_color=*/SK_ColorTRANSPARENT, is_pixel_canvas)
+            .context(),
+        size()));
+    return gfx::ImageSkia(gfx::ImageSkiaRep(bitmap, scale));
+  }
+
+  // Returns the drag offset to use when rendering this view as a drag image.
+  // This offset will position the cursor directly over the top left hand corner
+  // of the first dragged item (or flipped for RTL).
+  gfx::Vector2d GetDragOffset() const {
+    DCHECK(first_drag_image_item_view_);
+    const gfx::Rect contents_bounds =
+        first_drag_image_item_view_->GetContentsBounds();
+
+    // Use the contents origin of the first dragged item instead of its local
+    // bounds origin to exclude the region reserved for its shadow margins.
+    gfx::Point contents_origin = contents_bounds.origin();
+    views::View::ConvertPointToTarget(first_drag_image_item_view_->parent(),
+                                      /*target=*/this, &contents_origin);
+
+    gfx::Vector2d drag_offset = contents_origin.OffsetFromOrigin();
+
+    // In RTL, its necessary to offset by the contents width of the first
+    // dragged item so that the cursor is positioned over its top right hand
+    // corner. Again, contents width is used instead of local bounds width to
+    // exclude shadow margins.
+    if (base::i18n::IsRTL())
+      drag_offset += gfx::Vector2d(contents_bounds.width(), 0);
+
+    return drag_offset;
+  }
+
+ private:
   // views::View:
   gfx::Insets GetInsets() const override {
     if (!drag_image_overflow_badge_)
@@ -345,23 +388,6 @@ class DragImageView : public views::View {
         gfx::Rect(badge_origin, badge_size));
   }
 
-  // Paints this view to a `gfx::ImageSkia`.
-  gfx::ImageSkia PaintToImageSkia(float scale, bool is_pixel_canvas) {
-#if DCHECK_IS_ON()
-    // NOTE: This method will *not* paint `ui::Layer`s, so it is expected that
-    // all views in this view hierarchy *not* paint to layers.
-    AssertNoLayers(this);
-#endif  // DCHECK_IS_ON()
-    SkBitmap bitmap;
-    Paint(views::PaintInfo::CreateRootPaintInfo(
-        ui::CanvasPainter(&bitmap, size(), scale,
-                          /*clear_color=*/SK_ColorTRANSPARENT, is_pixel_canvas)
-            .context(),
-        size()));
-    return gfx::ImageSkia(gfx::ImageSkiaRep(bitmap, scale));
-  }
-
- private:
   void InitLayout(const std::vector<const HoldingSpaceItem*>& items) {
     auto* layout = SetLayoutManager(std::make_unique<views::FillLayout>());
     AddDragImageItemViews(items);
@@ -435,15 +461,8 @@ void CreateDragImage(const std::vector<const HoldingSpaceItemView*>& views,
   DragImageView drag_image_view(GetHoldingSpaceItems(views));
   drag_image_view.SetSize(drag_image_view.GetPreferredSize());
 
-  *drag_image = drag_image_view.PaintToImageSkia(scale, is_pixel_canvas);
-
-  // The `drag_offset` should correct for the extra space that may have been
-  // added to layout the overflow badge (if present). Doing so will position the
-  // cursor at the top left hand corner of the first dragged item (or flipped
-  // for RTL).
-  *drag_offset =
-      gfx::Vector2d(base::i18n::IsRTL() ? drag_image_view.width() : 0,
-                    drag_image_view.GetInsets().top());
+  *drag_image = drag_image_view.GetDragImage(scale, is_pixel_canvas);
+  *drag_offset = drag_image_view.GetDragOffset();
 }
 
 }  // namespace holding_space_util