Re-land Catch up the spec update in CSS Rhythmic Sizing

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 203 matching lines @@
     setLineBreakInfo(0, 0, BidiStatus());
 
   for (RootInlineBox* prev = prevRootBox();
        prev && prev->lineBreakObj() == box->getLineLayoutItem();
        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;
+static inline void applyLineHeightStep(uint8_t lineHeightStep,
+                                       int& maxAscent,
+                                       int& maxDescent) {
+  // Round up to the multiple of units, by adding spaces to over/under equally.
+  // https://drafts.csswg.org/css-rhythm/#line-height-step
+  int remainder = (maxAscent + maxDescent) % lineHeightStep;
+  if (!remainder)
     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;
+  DCHECK_GT(remainder, 0);
+  int space = lineHeightStep - remainder;
+  maxDescent += space / 2;
+  maxAscent += space - space / 2;
 }
 
 LayoutUnit RootInlineBox::alignBoxesInBlockDirection(
     LayoutUnit heightOfBlock,
     GlyphOverflowAndFallbackFontsMap& textBoxDataMap,
     VerticalPositionCache& verticalPositionCache) {
   // SVG will handle vertical alignment on its own.
   if (isSVGRootInlineBox())
     return LayoutUnit();
 
@@ skipping 11 matching lines @@
 
   computeLogicalBoxHeights(this, maxPositionTop, maxPositionBottom, maxAscent,
                            maxDescent, setMaxAscent, setMaxDescent,
                            noQuirksMode, textBoxDataMap, baselineType(),
                            verticalPositionCache);
 
   if (maxAscent + maxDescent < std::max(maxPositionTop, maxPositionBottom))
     adjustMaxAscentAndDescent(maxAscent, maxDescent, maxPositionTop.toInt(),
                               maxPositionBottom.toInt());
 
-  if (getLineLayoutItem().styleRef().snapHeightUnit())
-    snapHeight(maxAscent, maxDescent, getLineLayoutItem().styleRef());
+  if (uint8_t lineHeightStep = getLineLayoutItem().styleRef().lineHeightStep())
+    applyLineHeightStep(lineHeightStep, maxAscent, maxDescent);
 
   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;
@@ skipping 495 matching lines @@
   }
   endBox = nullptr;
   return nullptr;
 }
 
 const char* RootInlineBox::boxName() const {
   return "RootInlineBox";
 }
 
 }  // namespace blink