fix getComputedStyle positioned element values

third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ skipping 144 matching lines @@
         return cssValuePool().createIdentifierValue(CSSValueLuminance);
     }
 
     ASSERT_NOT_REACHED();
 
     return nullptr;
 }
 
 static PassRefPtrWillBeRawPtr<CSSValue> valueForPositionOffset(const ComputedStyle& style, CSSPropertyID propertyID, const LayoutObject* layoutObject)
 {
-    Length offset;
+    Length offset, opposite;
     switch (propertyID) {
     case CSSPropertyLeft:
         offset = style.left();
+        opposite = style.right();
         break;
     case CSSPropertyRight:
         offset = style.right();
+        opposite = style.left();
         break;
     case CSSPropertyTop:
         offset = style.top();
+        opposite = style.bottom();
         break;
     case CSSPropertyBottom:
         offset = style.bottom();
+        opposite = style.top();
         break;
     default:
         return nullptr;
     }
 
     if (offset.hasPercent() && layoutObject && layoutObject->isBox() && layoutObject->isPositioned()) {
         LayoutUnit containingBlockSize = (propertyID == CSSPropertyLeft || propertyID == CSSPropertyRight) ?
             toLayoutBox(layoutObject)->containingBlockLogicalWidthForContent() :
             toLayoutBox(layoutObject)->containingBlockLogicalHeightForGetComputedStyle();
         return zoomAdjustedPixelValue(valueForLength(offset, containingBlockSize), style);
     }
+
     if (offset.isAuto()) {

[mstensho (USE GERRIT), 2016/04/04 09:13:26]

"if (offset.isAuto() && layoutObject)", to reduce indentation and lines of code?
:)

[Mr. Kevin, 2016/04/04 17:35:22]

It falls through at the end to handle isAuto() && !layoutObject, but it's
clearer and has less indentation to separate that condition out, so done.

-        // FIXME: It's not enough to simply return "auto" values for one offset if the other side is defined.
-        // In other words if left is auto and right is not auto, then left's computed value is negative right().
-        // So we should get the opposite length unit and see if it is auto.
+        if (layoutObject) {
+            // If the property applies to a positioned element and the resolved value of the display
+            // property is not none, the resolved value is the used value.
+            if (layoutObject->isInFlowPositioned()) {
+                // If e.g. left is auto and right is not auto, then left's computed value is negative right.
+                // So we get the opposite length unit and see if it is auto.
+                if (opposite.isAuto())
+                    return cssValuePool().createValue(0, CSSPrimitiveValue::UnitType::Pixels);
+
+                if (opposite.hasPercent()) {
+                    LayoutUnit containingBlockSize =
+                        (propertyID == CSSPropertyLeft || propertyID == CSSPropertyRight) ?
+                        toLayoutBox(layoutObject)->containingBlockLogicalWidthForContent() :

[mstensho (USE GERRIT), 2016/04/04 09:13:26]

Using logical width and height to resolve physical left/top/right/bottom is
actually wrong (if writing mode is vertical), but this is what the percentage
handling code above already does too, so, fine, better be consistent. :)

[Mr. Kevin, 2016/04/04 17:35:22]

Acknowledged.

+                        toLayoutBox(layoutObject)->containingBlockLogicalHeightForGetComputedStyle();
+                    return zoomAdjustedPixelValue(-floatValueForLength(opposite, containingBlockSize), style);
+                }
+                return zoomAdjustedPixelValue(-opposite.pixels(), style);
+            }
+
+            if (layoutObject->isOutOfFlowPositioned()) {
+                // For fixed and absolute positioned elements, the top, left, bottom, and right
+                // are defined relative to the corresponding sides of the containing block.
+                LayoutBlock* container = layoutObject->containingBlock();
+                const LayoutBox* layoutBox = toLayoutBox(layoutObject);
+
+                // clientOffset is the distance from this object's border edge to the container's
+                // padding edge. Thus it includes margins which we subtract below.
+                const LayoutSize clientOffset =
+                    layoutBox->locationOffset() - LayoutSize(container->clientLeft(), container->clientTop());
+                LayoutUnit position;
+
+                switch (propertyID) {
+                case CSSPropertyLeft:
+                    position = clientOffset.width() - layoutBox->marginLeft();
+                    break;
+                case CSSPropertyTop:
+                    position = clientOffset.height() - layoutBox->marginTop();
+                    break;
+                case CSSPropertyRight:
+                    position = container->clientWidth() - layoutBox->marginRight() -
+                        (layoutBox->offsetWidth() + clientOffset.width());
+                    break;
+                case CSSPropertyBottom:
+                    position = container->clientHeight() - layoutBox->marginBottom() -
+                        (layoutBox->offsetHeight() + clientOffset.height());
+                    break;
+                default:
+                    ASSERT_NOT_REACHED();
+                }
+                return zoomAdjustedPixelValue(position, style);
+            }
+        }
         return cssValuePool().createIdentifierValue(CSSValueAuto);
     }
 
     return zoomAdjustedPixelValueForLength(offset, style);
 }
 
 static PassRefPtrWillBeRawPtr<CSSBorderImageSliceValue> valueForNinePieceImageSlice(const NinePieceImage& image)
 {
     // Create the slices.
     RefPtrWillBeRawPtr<CSSPrimitiveValue> top = nullptr;
@@ skipping 2551 matching lines @@
     case CSSPropertyAll:
         return nullptr;
     default:
         break;
     }
     ASSERT_NOT_REACHED();
     return nullptr;
 }
 
 } // namespace blink