Tweaking how background images interact with sub pixel borders. *** NOT FOR LANDING

third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/BackgroundImageGeometry.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTableCell.h"
@@ skipping 449 matching lines @@
     fixed_attachment = false;
   }
 
   if (!fixed_attachment) {
     SetDestRect(paint_rect);
 
     LayoutUnit right;
     LayoutUnit bottom;
     // Scroll and Local.
     if (fill_layer.Origin() != kBorderFillBox) {
-      left = LayoutUnit(positioning_box.BorderLeft());
-      right = LayoutUnit(positioning_box.BorderRight());
-      top = LayoutUnit(positioning_box.BorderTop());
-      bottom = LayoutUnit(positioning_box.BorderBottom());
+      left = LayoutUnit(positioning_box.BorderLeft().Round());
+      right = LayoutUnit(positioning_box.BorderRight().Round());
+      top = LayoutUnit(positioning_box.BorderTop().Round());
+      bottom = LayoutUnit(positioning_box.BorderBottom().Round());
       if (fill_layer.Origin() == kContentFillBox) {
-        left += positioning_box.PaddingLeft();
-        right += positioning_box.PaddingRight();
-        top += positioning_box.PaddingTop();
-        bottom += positioning_box.PaddingBottom();
+        left = std::max(
+            left, positioning_box.BorderLeft() + positioning_box.PaddingLeft());
+        right = std::max(right, positioning_box.BorderRight() +
+                                    positioning_box.PaddingRight());
+        top = std::max(
+            top, positioning_box.BorderTop() + positioning_box.PaddingTop());
+        bottom = std::max(bottom, positioning_box.BorderBottom() +
+                                      positioning_box.PaddingBottom());
       }
     }
 
     if (is_layout_view) {
       // 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.
       positioning_area.SetSize(root_box->Size());
       positioning_area.ContractEdges(top, right, bottom, left);
 
@@ skipping 108 matching lines @@
     SetPhaseY(TileSize().Height()
                   ? LayoutUnit(roundf(TileSize().Height() -
                                       fmodf((computed_y_position + top),
                                             TileSize().Height())))
                   : LayoutUnit());
     SetSpaceSize(LayoutSize());
   }
 
   if (background_repeat_x == kRepeatFill) {
     SetRepeatX(fill_layer, fill_tile_size.Width(), available_width,
-               unsnapped_available_width, left, offset_in_background.X());
+               unsnapped_available_width,
+               LayoutUnit(SnapSizeToPixel(left, dest_rect_.X())),
+               offset_in_background.X());
   } else if (background_repeat_x == kSpaceFill &&
              TileSize().Width() > LayoutUnit()) {
     LayoutUnit space = GetSpaceBetweenImageTiles(positioning_area_size.Width(),
                                                  TileSize().Width());
     if (space >= LayoutUnit())
       SetSpaceX(space, available_width, left);
     else
       background_repeat_x = kNoRepeatFill;
   }
   if (background_repeat_x == kNoRepeatFill) {
     LayoutUnit x_offset = fill_layer.BackgroundXOrigin() == kRightEdge
                               ? available_width - computed_x_position
                               : computed_x_position;
     SetNoRepeatX(left + x_offset);
     if (offset_in_background.X() > TileSize().Width())
       SetDestRect(LayoutRect());
   }
 
   if (background_repeat_y == kRepeatFill) {
     SetRepeatY(fill_layer, fill_tile_size.Height(), available_height,
-               unsnapped_available_height, top, offset_in_background.Y());
+               unsnapped_available_height,
+               LayoutUnit(SnapSizeToPixel(top, dest_rect_.Y())),
+               offset_in_background.Y());
   } else if (background_repeat_y == kSpaceFill &&
              TileSize().Height() > LayoutUnit()) {
     LayoutUnit space = GetSpaceBetweenImageTiles(positioning_area_size.Height(),
                                                  TileSize().Height());
     if (space >= LayoutUnit())
       SetSpaceY(space, available_height, top);
     else
       background_repeat_y = kNoRepeatFill;
   }
   if (background_repeat_y == kNoRepeatFill) {
     LayoutUnit y_offset = fill_layer.BackgroundYOrigin() == kBottomEdge
                               ? available_height - computed_y_position
                               : computed_y_position;
     SetNoRepeatY(top + y_offset);
     if (offset_in_background.Y() > TileSize().Height())
       SetDestRect(LayoutRect());
   }
 
   if (fixed_attachment)
     UseFixedAttachment(paint_rect.Location());
 
   // Clip the final output rect to the paint rect
   dest_rect_.Intersect(paint_rect);
 
   // Snap as-yet unsnapped values.
   SetDestRect(LayoutRect(PixelSnappedIntRect(dest_rect_)));
 }
 
 }  // namespace blink