Fix for phase in background tiling.

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

Index: third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
diff --git a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
index a362e111a228bbbfbad8360d23a3cce030b54313..ff62a03b6639fbd92045a3ead9c41dba1aeeac05 100644
--- a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
+++ b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
@@ -124,7 +124,7 @@ LayoutSize calculateFillTileSize(const LayoutBoxModelObject& obj, const FillLaye
     }
     }
 
-    ASSERT_NOT_REACHED();
+    NOTREACHED();

[leviw_travelin_and_unemployed, 2016/04/01 20:16:40]

Why this change? Are we moving to using NOTREACHED() instead of
ASSERT_NOT_REACHED()?

[Stephen Chennney, 2016/04/01 20:38:36]

Yes, per an email on blink-dev we're supposed to move all Blink ASSERT related
stuff to Chromium equivalents.

     return LayoutSize();
 }
 
@@ -158,18 +158,88 @@ LayoutSize applySubPixelHeuristicToImageSize(const LayoutSize& size, const Layou
 
 } // anonymous namespace
 
-void BackgroundImageGeometry::setNoRepeatX(LayoutUnit xOffset)
+void BackgroundImageGeometry::setNoRepeatX(const LayoutUnit& xOffset)

[leviw_travelin_and_unemployed, 2016/04/01 20:16:40]

I find it weird to use const references for LayoutUnits. It shouldn't be any
cheaper than just copying.

[Stephen Chennney, 2016/04/01 20:38:36]

I'll switch them back. I was just in a const groove.

 {
     m_destRect.move(std::max(xOffset, LayoutUnit()), LayoutUnit());
     m_phase.setX(-std::min(xOffset, LayoutUnit()));
     m_destRect.setWidth(m_tileSize.width() + std::min(xOffset, LayoutUnit()));
+    setSpaceSize(LayoutSize(LayoutUnit(), spaceSize().height()));
 }
 
-void BackgroundImageGeometry::setNoRepeatY(LayoutUnit yOffset)
+void BackgroundImageGeometry::setNoRepeatY(const LayoutUnit& yOffset)

[leviw_travelin_and_unemployed, 2016/04/01 20:16:40]

Ditto.

 {
     m_destRect.move(LayoutUnit(), std::max(yOffset, LayoutUnit()));
     m_phase.setY(-std::min(yOffset, LayoutUnit()));
     m_destRect.setHeight(m_tileSize.height() + std::min(yOffset, LayoutUnit()));
+    setSpaceSize(LayoutSize(spaceSize().width(), LayoutUnit()));
+}
+
+void BackgroundImageGeometry::setRepeatX(
+    const FillLayer& fillLayer,
+    const LayoutSize& unsnappedTileSize,
+    const LayoutUnit& snappedAvailableWidth,
+    const LayoutUnit& unsnappedAvailableWidth,
+    const LayoutUnit& extraOffset)
+{
+    // We would like to identify the phase as a fraction of the image size in the absence of snapping,
+    // then re-apply it to the snapped values. This is to handle large positions.
+    if (unsnappedTileSize.width()) {

[leviw_travelin_and_unemployed, 2016/04/01 20:16:40]

This is unfortunate copy pasta.

[Stephen Chennney, 2016/04/01 20:38:36]

Yeah, but because we don't use arrays of 2 values for [x,y] we can't make them
all one method. I do only use width in this one though, and height in the next,
so it can be simplified.

+        LayoutUnit computedXPosition = roundedMinimumValueForLength(fillLayer.xPosition(), unsnappedAvailableWidth);
+        if (fillLayer.backgroundXOrigin() == RightEdge) {
+            float numberOfTilesInPosition = (snappedAvailableWidth - computedXPosition + extraOffset).toFloat() / unsnappedTileSize.width().toFloat();
+            float fractionalPositionWithinTile = numberOfTilesInPosition - truncf(numberOfTilesInPosition);
+            setPhaseX(LayoutUnit(fractionalPositionWithinTile * tileSize().width()));
+        } else {
+            float numberOfTilesInPosition = (computedXPosition + extraOffset).toFloat() / unsnappedTileSize.width().toFloat();
+            float fractionalPositionWithinTile = 1.0f - (numberOfTilesInPosition - truncf(numberOfTilesInPosition));
+            setPhaseX(LayoutUnit(fractionalPositionWithinTile * tileSize().width()));
+        }
+    } else {
+        setPhaseX(LayoutUnit());
+    }
+    setSpaceSize(LayoutSize(LayoutUnit(), spaceSize().height()));
+}
+
+void BackgroundImageGeometry::setRepeatY(
+    const FillLayer& fillLayer,
+    const LayoutSize& unsnappedTileSize,
+    const LayoutUnit& snappedAvailableHeight,
+    const LayoutUnit& unsnappedAvailableHeight,
+    const LayoutUnit& extraOffset)
+{
+    // We would like to identify the phase as a fraction of the image size in the absence of snapping,
+    // then re-apply it to the snapped values. This is to handle large positions.
+    if (unsnappedTileSize.height()) {
+        LayoutUnit computedYPosition = roundedMinimumValueForLength(fillLayer.yPosition(), unsnappedAvailableHeight);
+        if (fillLayer.backgroundYOrigin() == BottomEdge) {
+            float numberOfTilesInPosition = (snappedAvailableHeight - computedYPosition + extraOffset).toFloat() / unsnappedTileSize.height().toFloat();
+            float fractionalPositionWithinTile = numberOfTilesInPosition - truncf(numberOfTilesInPosition);
+            setPhaseY(LayoutUnit(fractionalPositionWithinTile * tileSize().height()));
+        } else {
+            float numberOfTilesInPosition = (computedYPosition + extraOffset).toFloat() / unsnappedTileSize.height().toFloat();
+            float fractionalPositionWithinTile = 1.0f - (numberOfTilesInPosition - truncf(numberOfTilesInPosition));
+            setPhaseY(LayoutUnit(fractionalPositionWithinTile * tileSize().height()));
+        }
+    } else {
+        setPhaseY(LayoutUnit());
+    }
+    setSpaceSize(LayoutSize(spaceSize().width(), LayoutUnit()));
+}
+
+void BackgroundImageGeometry::setSpaceX(const LayoutUnit& space, const LayoutUnit& availableWidth, const LayoutUnit& extraOffset)

[leviw_travelin_and_unemployed, 2016/04/01 20:16:40]

Elon Musk is gonna be pissed.

[Stephen Chennney, 2016/04/01 20:38:36]

I never saw that coming.

+{
+    LayoutUnit computedXPosition = roundedMinimumValueForLength(Length(), availableWidth);
+    setSpaceSize(LayoutSize(space.round(), spaceSize().height()));
+    LayoutUnit actualWidth = tileSize().width() + space;
+    setPhaseX(actualWidth ? LayoutUnit(actualWidth - fmodf((computedXPosition + extraOffset), actualWidth)) : LayoutUnit());
+}
+
+void BackgroundImageGeometry::setSpaceY(const LayoutUnit& space, const LayoutUnit& availableHeight, const LayoutUnit& extraOffset)
+{
+    LayoutUnit computedYPosition = roundedMinimumValueForLength(Length(), availableHeight);
+    setSpaceSize(LayoutSize(spaceSize().width(), space.round()));
+    LayoutUnit actualHeight = tileSize().height() + space;
+    setPhaseY(actualHeight ? LayoutUnit(actualHeight - fmodf((computedYPosition + extraOffset), actualHeight)) : LayoutUnit());
 }
 
 void BackgroundImageGeometry::useFixedAttachment(const LayoutPoint& attachmentPoint)
@@ -189,9 +259,9 @@ void BackgroundImageGeometry::calculate(const LayoutBoxModelObject& obj, const L
     if (isLayoutView) {
         // It is only possible reach here when root element has a box.
         Element* documentElement = obj.document().documentElement();
-        ASSERT(documentElement);
-        ASSERT(documentElement->layoutObject());
-        ASSERT(documentElement->layoutObject()->isBox());
+        DCHECK(documentElement);
+        DCHECK(documentElement->layoutObject());
+        DCHECK(documentElement->layoutObject()->isBox());
         rootBox = toLayoutBox(documentElement->layoutObject());
     }
     const LayoutBoxModelObject& positioningBox = isLayoutView ? static_cast<const LayoutBoxModelObject&>(*rootBox) : obj;
@@ -269,6 +339,8 @@ void BackgroundImageGeometry::calculate(const LayoutBoxModelObject& obj, const L
 
     EFillRepeat backgroundRepeatX = fillLayer.repeatX();
     EFillRepeat backgroundRepeatY = fillLayer.repeatY();
+    LayoutUnit unsnappedAvailableWidth = positioningAreaSize.width() - fillTileSize.width();
+    LayoutUnit unsnappedAvailableHeight = positioningAreaSize.height() - fillTileSize.height();
     positioningAreaSize = LayoutSize(snapSizeToPixel(positioningAreaSize.width(), m_destRect.x()), snapSizeToPixel(positioningAreaSize.height(), m_destRect.y()));
     LayoutUnit availableWidth = positioningAreaSize.width() - tileSize().width();
     LayoutUnit availableHeight = positioningAreaSize.height() - tileSize().height();
@@ -306,49 +378,31 @@ void BackgroundImageGeometry::calculate(const LayoutBoxModelObject& obj, const L
     }
 
     if (backgroundRepeatX == RepeatFill) {
-        LayoutUnit xOffset = fillLayer.backgroundXOrigin() == RightEdge ? availableWidth - computedXPosition : computedXPosition;
-        setPhaseX(tileSize().width() ? LayoutUnit(tileSize().width() - fmodf((xOffset + left), tileSize().width()))
-            : LayoutUnit());
-        setSpaceSize(LayoutSize());
+        setRepeatX(fillLayer, fillTileSize, availableWidth, unsnappedAvailableWidth, left);
     } else if (backgroundRepeatX == SpaceFill && tileSize().width() > LayoutUnit()) {
         LayoutUnit space = getSpaceBetweenImageTiles(positioningAreaSize.width(), tileSize().width());
-        LayoutUnit actualWidth = tileSize().width() + space;
-
-        if (space >= LayoutUnit()) {
-            computedXPosition = roundedMinimumValueForLength(Length(), availableWidth);
-            setSpaceSize(LayoutSize(space.round(), LayoutUnit()));
-            setPhaseX(actualWidth ? LayoutUnit(actualWidth - fmodf((computedXPosition + left), actualWidth)) : LayoutUnit());
-        } else {
+        if (space >= LayoutUnit())
+            setSpaceX(space, availableWidth, left);
+        else
             backgroundRepeatX = NoRepeatFill;
-        }
     }
     if (backgroundRepeatX == NoRepeatFill) {
         LayoutUnit xOffset = fillLayer.backgroundXOrigin() == RightEdge ? availableWidth - computedXPosition : computedXPosition;
         setNoRepeatX(left + xOffset);
-        setSpaceSize(LayoutSize(LayoutUnit(), spaceSize().height()));
     }
 
     if (backgroundRepeatY == RepeatFill) {
-        LayoutUnit yOffset = fillLayer.backgroundYOrigin() == BottomEdge ? availableHeight - computedYPosition : computedYPosition;
-        setPhaseY(tileSize().height() ? LayoutUnit(tileSize().height() - fmodf((yOffset + top), tileSize().height()))
-            : LayoutUnit());
-        setSpaceSize(LayoutSize(spaceSize().width(), LayoutUnit()));
+        setRepeatY(fillLayer, fillTileSize, availableHeight, unsnappedAvailableHeight, top);
     } else if (backgroundRepeatY == SpaceFill && tileSize().height() > LayoutUnit()) {
         LayoutUnit space = getSpaceBetweenImageTiles(positioningAreaSize.height(), tileSize().height());
-        LayoutUnit actualHeight = tileSize().height() + space;
-
-        if (space >= LayoutUnit()) {
-            computedYPosition = roundedMinimumValueForLength(Length(), availableHeight);
-            setSpaceSize(LayoutSize(spaceSize().width(), space.round()));
-            setPhaseY(actualHeight ? LayoutUnit(actualHeight - fmodf((computedYPosition + top), actualHeight)) : LayoutUnit());
-        } else {
+        if (space >= LayoutUnit())
+            setSpaceY(space, availableHeight, top);
+        else
             backgroundRepeatY = NoRepeatFill;
-        }
     }
     if (backgroundRepeatY == NoRepeatFill) {
         LayoutUnit yOffset = fillLayer.backgroundYOrigin() == BottomEdge ? availableHeight - computedYPosition : computedYPosition;
         setNoRepeatY(top + yOffset);
-        setSpaceSize(LayoutSize(spaceSize().width(), LayoutUnit()));
     }
 
     if (fixedAttachment)