Add layout support for the snap-height property

third_party/WebKit/Source/core/layout/line/RootInlineBox.cpp

 /*
  * Copyright (C) 2003, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 173 matching lines @@
 {
     if (box->lineLayoutItem() == m_lineBreakObj)
         setLineBreakInfo(0, 0, BidiStatus());
 
     for (RootInlineBox* prev = prevRootBox(); prev && prev->lineBreakObj() == box->lineLayoutItem(); prev = prev->prevRootBox()) {
         prev->setLineBreakInfo(0, 0, BidiStatus());
         prev->markDirty();
     }
 }
 
+static inline void snapHeight(int& maxAscent, int& maxDescent, const ComputedStyle& style)
+{
+    // If position is 0, add spaces to over/under equally.
+    // https://drafts.csswg.org/css-snap-size/#snap-height
+    int unit = style.snapHeightUnit();
+    ASSERT(unit);
+    int position = style.snapHeightPosition();
+    if (!position) {
+        int space = unit - ((maxAscent + maxDescent) % unit);
+        maxDescent += space / 2;
+        maxAscent += space - space / 2;
+        return;
+    }
+
+    // Match the baseline to the specified position.
+    // https://drafts.csswg.org/css-snap-size/#snap-baseline
+    ASSERT(position > 0 && position <= 100);
+    position = position * unit / 100;
+    int spaceOver = position - maxAscent % unit;
+    if (spaceOver < 0) {
+        spaceOver += unit;
+        ASSERT(spaceOver >= 0);
+    }
+    maxAscent += spaceOver;
+    maxDescent += unit - (maxAscent + maxDescent) % unit;
+}
+
 LayoutUnit RootInlineBox::alignBoxesInBlockDirection(LayoutUnit heightOfBlock, GlyphOverflowAndFallbackFontsMap& textBoxDataMap, VerticalPositionCache& verticalPositionCache)
 {
     // SVG will handle vertical alignment on its own.
     if (isSVGRootInlineBox())
         return LayoutUnit();
 
     LayoutUnit maxPositionTop;
     LayoutUnit maxPositionBottom;
     int maxAscent = 0;
     int maxDescent = 0;
     bool setMaxAscent = false;
     bool setMaxDescent = false;
 
     // Figure out if we're in no-quirks mode.
     bool noQuirksMode = lineLayoutItem().document().inNoQuirksMode();
 
     m_baselineType = dominantBaseline();
 
     computeLogicalBoxHeights(this, maxPositionTop, maxPositionBottom, maxAscent, maxDescent, setMaxAscent, setMaxDescent, noQuirksMode, textBoxDataMap, baselineType(), verticalPositionCache);
 
     if (maxAscent + maxDescent < std::max(maxPositionTop, maxPositionBottom))
         adjustMaxAscentAndDescent(maxAscent, maxDescent, maxPositionTop, maxPositionBottom);
 
+    if (lineLayoutItem().styleRef().snapHeightUnit())
+        snapHeight(maxAscent, maxDescent, lineLayoutItem().styleRef());
+
     LayoutUnit maxHeight = LayoutUnit(maxAscent + maxDescent);
     LayoutUnit lineTop = heightOfBlock;
     LayoutUnit lineBottom = heightOfBlock;
     LayoutUnit lineTopIncludingMargins = heightOfBlock;
     LayoutUnit lineBottomIncludingMargins = heightOfBlock;
     LayoutUnit selectionBottom = heightOfBlock;
     bool setLineTop = false;
     bool hasAnnotationsBefore = false;
     bool hasAnnotationsAfter = false;
     placeBoxesInBlockDirection(heightOfBlock, maxHeight, maxAscent, noQuirksMode, lineTop, lineBottom, selectionBottom, setLineTop, lineTopIncludingMargins, lineBottomIncludingMargins, hasAnnotationsBefore, hasAnnotationsAfter, baselineType());
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     endBox = nullptr;
     return nullptr;
 }
 
 const char* RootInlineBox::boxName() const
 {
     return "RootInlineBox";
 }
 
 } // namespace blink