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Bug 1098417 part 1.5: Ignore computed anchor-point if 'object-fit' and 'object-position' are at their initial values, for backwards compat. r=seth

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This commit is contained in:
Daniel Holbert 2014-11-25 16:46:14 -08:00
parent c7ce74a52e
commit baf1513be2
1 changed files with 38 additions and 1 deletions
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39
layout/base/nsLayoutUtils.cpp
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@ -3624,6 +3624,29 @@ ComputeConcreteObjectSize(const nsSize& aConstraintSize,
}
}
// (Helper for HasInitialObjectFitAndPosition, to check
// each "object-position" coord.)
typedef nsStyleBackground::Position::PositionCoord PositionCoord;
static bool
IsCoord50Pct(const PositionCoord& aCoord)
{
return (aCoord.mLength == 0 &&
aCoord.mHasPercent &&
aCoord.mPercent == 0.5f);
}
// Indicates whether the given nsStylePosition has the initial values
// for the "object-fit" and "object-position" properties.
static bool
HasInitialObjectFitAndPosition(const nsStylePosition* aStylePos)
{
const nsStyleBackground::Position& objectPos = aStylePos->mObjectPosition;
return aStylePos->mObjectFit == NS_STYLE_OBJECT_FIT_FILL &&
IsCoord50Pct(objectPos.mXPosition) &&
IsCoord50Pct(objectPos.mYPosition);
}
/* static */ nsRect
nsLayoutUtils::ComputeObjectDestRect(const nsRect& aConstraintRect,
const IntrinsicSize& aIntrinsicSize,
@ -3650,7 +3673,21 @@ nsLayoutUtils::ComputeObjectDestRect(const nsRect& aConstraintRect,
imageAnchorPt += aConstraintRect.TopLeft();
if (aAnchorPoint) {
*aAnchorPoint = imageAnchorPt;
// Special-case: if our "object-fit" and "object-position" properties have
// their default values ("object-fit: fill; object-position:50% 50%"), then
// we'll override the calculated imageAnchorPt, and instead use the
// object's top-left corner.
//
// This special case is partly for backwards compatibility (since
// traditionally we've pixel-aligned the top-left corner of e.g. <img>
// elements), and partly because ComputeSnappedDrawingParameters produces
// less error if the anchor point is at the top-left corner. So, all other
// things being equal, we prefer that code path with less error.
if (HasInitialObjectFitAndPosition(aStylePos)) {
*aAnchorPoint = imageTopLeftPt;
} else {
*aAnchorPoint = imageAnchorPt;
}
}
return nsRect(imageTopLeftPt, concreteObjectSize);
}