[css-grid] Implementation of Baseline Self-Alignment

third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 2471 matching lines @@
   int count = 0;
   for (const RootInlineBox* box = firstRootBox(); box;
        box = box->nextRootBox()) {
     count++;
     if (box == stopRootInlineBox)
       break;
   }
   return count;
 }
 
+bool LayoutBlockFlow::isDescentBaseline() const {
+  if (isOrthogonalWritingModeRoot())
+    return !styleRef().isHorizontalWritingMode();

[kojii, 2016/11/16 17:18:06]

Just curious, since I don't understand, why do we need this? I thought just
isFlippedLinesWritingMode() does the work, but if not, having a comment would
help.

[jfernandez, 2016/11/16 18:50:07]

In the general case, we don't compute baselines for orthogonal boxes; that's why
the fitstLineBoxBaseline returns -1 when isWritingModeRoot(). However, we
allow that for grid items, since we can use baseline alignment for orthogonal
grid items along the grid's column axis.

When the grid container is horizontal, then both vertical-lr and vertical-rl
will
be placed at the left edge. In case of a vertical grid container, grid items
will
be horizontal, hence we should use always the font ascent to determine
the baseline.

Perhaps a comment in the code could make this clearer. However, I still have
the feeling that perhaps this logic should be better implemented in the
specific layout models. So far, I can't do it because of what you commented
about using always logicalTop(). 

In any case, once I get a valid patch I'll rethink the whole issue to see
whether I can find a more general and solution. 

[kojii, 2016/11/18 04:14:53]

Oh I think I understand this. I think the missing piece is that this function
lacks an argument to compute "first baseline for whom", and you assume it is for
its parent, so the baseline is -1 if orthogonal root. I was thinking about using
this function for non-parents, so the logic is fine.
Sounds great, thank you for working on this again.

+  return parent() ? parent()->styleRef().isFlippedLinesWritingMode()
+                  : styleRef().isFlippedLinesWritingMode();
+}
+
 int LayoutBlockFlow::firstLineBoxBaseline() const {
-  if (isWritingModeRoot() && !isRubyRun())
+  if (isWritingModeRoot() && !isRubyRun() && !isGridItem())
     return -1;
   if (!childrenInline())
     return LayoutBlock::firstLineBoxBaseline();
   if (firstLineBox()) {
     const SimpleFontData* fontData = style(true)->font().primaryFont();
     DCHECK(fontData);
     if (!fontData)
       return -1;
     return (firstLineBox()->logicalTop() +
-            fontData->getFontMetrics().ascent(firstRootBox()->baselineType()))
+            (!isDescentBaseline()
+                 ? fontData->getFontMetrics().ascent(
+                       firstRootBox()->baselineType())
+                 : fontData->getFontMetrics().descent(
+                       firstRootBox()->baselineType())))
         .toInt();
   }
   return -1;
 }
 
 int LayoutBlockFlow::inlineBlockBaseline(
     LineDirectionMode lineDirection) const {
   // CSS2.1 states that the baseline of an 'inline-block' is:
   // the baseline of the last line box in the normal flow, unless it has
   // either no in-flow line boxes or if its 'overflow' property has a computed
@@ skipping 2030 matching lines @@
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(
     PaintInvalidationReason invalidationReason) const {
   BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
       invalidationReason);
 }
 
 }  // namespace blink