Fix painting with root transform and a root element background image

Background images are painted by ViewPainter via a call to
PaintFillLayer, passing a |paint_rect|. PaintFillLayer assumes that
any offset from (0, 0) of |paint_rect| is the paint offset in the local
transform space. This was not the case the root element has a transform.
In those cases, remove the offset.

Bug: 988446

Change-Id: I74439771ade6c9c7a54131a84b40ea9a0df5e25c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2018451Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735029}

third_party/blink/renderer/core/paint/background_image_geometry.cc

@@ -442,13 +442,13 @@ LayoutRect FixedAttachmentPositioningArea(const LayoutBoxModelObject& obj,
 
 }  // Anonymous namespace
 
-BackgroundImageGeometry::BackgroundImageGeometry(const LayoutView& view)
+BackgroundImageGeometry::BackgroundImageGeometry(
+    const LayoutView& view,
+    bool root_elemnet_has_transform)
     : box_(view),
       positioning_box_(view.RootBox()),
-      has_non_local_geometry_(false),
       painting_view_(true),
-      painting_table_cell_(false),
-      cell_using_container_background_(false) {
+      root_element_has_transform_(root_elemnet_has_transform) {
   // The background of the box generated by the root element covers the
   // entire canvas and will be painted by the view object, but the we should
   // still use the root element box for positioning.
@@ -457,12 +457,7 @@ BackgroundImageGeometry::BackgroundImageGeometry(const LayoutView& view)
 
 BackgroundImageGeometry::BackgroundImageGeometry(
     const LayoutBoxModelObject& obj)
-    : box_(obj),
-      positioning_box_(obj),
-      has_non_local_geometry_(false),
-      painting_view_(false),
-      painting_table_cell_(false),
-      cell_using_container_background_(false) {
+    : box_(obj), positioning_box_(obj) {
   // Specialized constructor should be used for LayoutView.
   DCHECK(!obj.IsLayoutView());
 }
@@ -474,8 +469,6 @@ BackgroundImageGeometry::BackgroundImageGeometry(
       positioning_box_(background_object && !background_object->IsTableCell()
                            ? ToLayoutBoxModelObject(*background_object)
                            : cell),
-      has_non_local_geometry_(false),
-      painting_view_(false),
       painting_table_cell_(true) {
   cell_using_container_background_ =
       background_object && !background_object->IsTableCell();
@@ -729,6 +722,17 @@ void BackgroundImageGeometry::ComputePositioningArea(
     snapped_box_offset =
         LayoutPoint(snapped_box_outset.Left() - snapped_dest_adjust.Left(),
                     snapped_box_outset.Top() - snapped_dest_adjust.Top());
+
+    // |paint_rect|'s location is usually assumed by BackgroundImageGeometry
+    // to encode paint offset in the local transform space. The one case in
+    // which this is not true is painting the background of the LayoutView
+    // canvas when the HTML element has a transform. In that case, the
+    // paint offset is zero, and the offset gets applied later by a
+    // PaintOffsetTranslation.
+    if (painting_view_ && root_element_has_transform_) {
+      unsnapped_box_offset -= paint_rect.Location();
+      snapped_box_offset -= paint_rect.Location();
+    }
   }
 }
 

third_party/blink/renderer/core/paint/background_image_geometry.h

@@ -31,7 +31,7 @@ class BackgroundImageGeometry {
 
  public:
   // Constructor for LayoutView where the coordinate space is different.
-  BackgroundImageGeometry(const LayoutView&);
+  BackgroundImageGeometry(const LayoutView&, bool root_elemnet_has_transform);
 
   // Constructor for table cells where background_object may be the row or
   // column the background image is attached to.
@@ -181,10 +181,11 @@ class BackgroundImageGeometry {
   FloatPoint phase_;
   LayoutSize tile_size_;
   LayoutSize repeat_spacing_;
-  bool has_non_local_geometry_;
-  bool painting_view_;
-  bool painting_table_cell_;
-  bool cell_using_container_background_;
+  bool has_non_local_geometry_ = false;
+  bool painting_view_ = false;
+  bool painting_table_cell_ = false;
+  bool cell_using_container_background_ = false;
+  bool root_element_has_transform_ = false;
 };
 
 }  // namespace blink

third_party/blink/renderer/core/paint/view_painter.cc

@@ -272,10 +272,12 @@ void ViewPainter::PaintRootElementGroup(
   // the pixel_snapped_background_rect and context to documentElement visual
   // space.
   bool background_renderable = true;
+  bool root_element_has_transform = false;
   IntRect paint_rect = pixel_snapped_background_rect;
   if (!root_object || !root_object->IsBox()) {
     background_renderable = false;
   } else {
+    root_element_has_transform = root_object->StyleRef().HasTransform();
     TransformationMatrix transform;
     root_object->GetTransformFromContainer(root_object->View(),
                                            PhysicalOffset(), transform);
@@ -362,23 +364,18 @@ void ViewPainter::PaintRootElementGroup(
     context.FillRect(paint_rect, Color(), SkBlendMode::kClear);
   }
 
-  BackgroundImageGeometry geometry(layout_view_);
+  BackgroundImageGeometry geometry(layout_view_, root_element_has_transform);
   BoxModelObjectPainter box_model_painter(layout_view_);
   for (const auto* fill_layer : base::Reversed(reversed_paint_list)) {
     DCHECK(fill_layer->Clip() == EFillBox::kBorder);
 
-    if (BackgroundImageGeometry::ShouldUseFixedAttachment(*fill_layer)) {
-      box_model_painter.PaintFillLayer(
-          paint_info, Color(), *fill_layer,
-          PhysicalRect(pixel_snapped_background_rect), kBackgroundBleedNone,
-          geometry);
-    } else {
-      PhysicalRect painting_rect(paint_rect);
+    PhysicalRect painting_rect(paint_rect);
+    if (!BackgroundImageGeometry::ShouldUseFixedAttachment(*fill_layer))
       painting_rect.Move(root_object->FirstFragment().PaintOffset());
-      box_model_painter.PaintFillLayer(paint_info, Color(), *fill_layer,
-                                       painting_rect, kBackgroundBleedNone,
-                                       geometry);
-    }
+
+    box_model_painter.PaintFillLayer(paint_info, Color(), *fill_layer,
+                                     painting_rect, kBackgroundBleedNone,
+                                     geometry);
   }
 
   if (should_draw_background_in_separate_buffer && !painted_separate_backdrop)

third_party/blink/web_tests/TestExpectations

@@ -380,7 +380,6 @@ crbug.com/1042453 [ Mac ] external/wpt/css/filter-effects/idlharness.any.worker.
 crbug.com/1042783 external/wpt/css/css-backgrounds/background-size/background-size-near-zero-png.html [ Failure ]
 crbug.com/1042783 external/wpt/css/css-backgrounds/background-size/background-size-near-zero-svg.html [ Failure ]
 
-crbug.com/898293 external/wpt/css/css-transforms/transform-translate-background-001.html [ Failure ]
 
 # ====== Paint team owned tests to here ======