- Revision
- 226180
- Author
- [email protected]
- Date
- 2017-12-20 08:34:43 -0800 (Wed, 20 Dec 2017)
Log Message
Split layout of RenderMathMLRow into smaller steps
https://bugs.webkit.org/show_bug.cgi?id=180348
Patch by Frederic Wang <[email protected]> on 2017-12-20
Reviewed by Manuel Rego Casasnovas.
Source/WebCore:
Currently, RenderMathMLRow mixes too many steps in the same layout functions: layout children,
calculate stretch size, stretch vertical operators, calculate final ascent/descent, handle
out-of-flow positioned children, set logical height, set logical width for non-display
<math> tag, center display <math> tag etc This situation is inherited from the old flexbox
implementation but it makes difficult to read the code and to re-use layout & metrics
calculation for follow-up work on <mrow>-like elements (<menclose>, <mapdded>, <msqrt> or
<math>). See for example bug 160547 for <math> or bug 161126 for <menclose>.
This patch rewrites RenderMathMLRow into smaller steps:
- stretchVerticalOperatorsAndLayoutChildren() which calls layoutIfNeeded() or
insertPositionedObject() on children and stretch vertical operators.
- getContentBoundingBox() to determine the metrics of the mrow-like element without calling
layout on children or positioning them, so that we can improve mrow-like element in the
future.
- layoutRowItems() which sets the position of children.
Setting the logical width/height or centering children is now moved into layoutBlock() since
derived class overriding layoutBlock() will do their own adjustment for width, height and
positions.
Test: mathml/mrow-preferred-width-with-out-of-flow-child.html
The rest of the behavior is unchanged and already covered by existing tests.
* rendering/mathml/RenderMathMLMenclose.cpp:
(WebCore::RenderMathMLMenclose::layoutBlock): Use the new function and get contentWidth
directly from getContentBoundingBox().
* rendering/mathml/RenderMathMLPadded.cpp:
(WebCore::RenderMathMLPadded::layoutBlock): Ditto.
* rendering/mathml/RenderMathMLRoot.cpp:
(WebCore::RenderMathMLRoot::layoutBlock): Ditto, also remove useless statement
baseAscent = baseDescent.
* rendering/mathml/RenderMathMLRow.cpp:
(WebCore::toVerticalStretchyOperator): New helper function to cast to a vertical stretchy
operator.
(WebCore::RenderMathMLRow::stretchVerticalOperatorsAndLayoutChildren): New helper function
to ensure layoutIfNeeded()/insertPositionedObject() is called on children and that the
vertical operators are stretched.
(WebCore::RenderMathMLRow::getContentBoundingBox const): New helper function to determine
the width/ascent/descent to use for the mrow content.
(WebCore::RenderMathMLRow::computePreferredLogicalWidths): Skip out-of-flow children in the
preferred width calculation. This is verified by the new test.
(WebCore::RenderMathMLRow::layoutRowItems): Only keep the positioning of children with the
specified width and ascent.
(WebCore::RenderMathMLRow::layoutBlock): Center children for <math display="block"> tag and
set the logical width in other cases. Also set the logical height here.
(WebCore::RenderMathMLRow::computeLineVerticalStretch): Deleted. This work is included in
stretchVerticalOperatorsAndLayoutChildren() now.
* rendering/mathml/RenderMathMLRow.h: Update declaration of functions.
LayoutTests:
New test to verify that out-of-flow positioned children are not taken into account in the
calculation of the preferred width of the mrow element.
* mathml/mrow-preferred-width-with-out-of-flow-child-expected.html: Added.
* mathml/mrow-preferred-width-with-out-of-flow-child.html: Added.
Modified Paths
Added Paths
Diff
Modified: trunk/LayoutTests/ChangeLog (226179 => 226180)
--- trunk/LayoutTests/ChangeLog 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/LayoutTests/ChangeLog 2017-12-20 16:34:43 UTC (rev 226180)
@@ -1,3 +1,16 @@
+2017-12-20 Frederic Wang <[email protected]>
+
+ Split layout of RenderMathMLRow into smaller steps
+ https://bugs.webkit.org/show_bug.cgi?id=180348
+
+ Reviewed by Manuel Rego Casasnovas.
+
+ New test to verify that out-of-flow positioned children are not taken into account in the
+ calculation of the preferred width of the mrow element.
+
+ * mathml/mrow-preferred-width-with-out-of-flow-child-expected.html: Added.
+ * mathml/mrow-preferred-width-with-out-of-flow-child.html: Added.
+
2017-12-20 Ms2ger <[email protected]>
Make fast/css-generated-content/quotes-lang.html pass on GTK
Added: trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child-expected.html (0 => 226180)
--- trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child-expected.html (rev 0)
+++ trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child-expected.html 2017-12-20 16:34:43 UTC (rev 226180)
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<html>
+ <head>
+ <title>mrow preferred width with out-of-flow child</title>
+ </head>
+ <body>
+
+ <p>This test passes if the absolute positioned child is not taken in account in the preferred width computation. You'll see a blue rectangle of about 100px width.</p>
+
+ <table>
+ <tr>
+ <td style="background: blue">
+ <math>
+ <mspace width="100px"></mspace>
+ </math>
+ </td>
+ </tr>
+ </table>
+
+ </body>
+</html>
Added: trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child.html (0 => 226180)
--- trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child.html (rev 0)
+++ trunk/LayoutTests/mathml/mrow-preferred-width-with-out-of-flow-child.html 2017-12-20 16:34:43 UTC (rev 226180)
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html>
+ <head>
+ <title>mrow preferred width with out-of-flow child</title>
+ </head>
+ <body>
+
+ <p>This test passes if the absolute positioned child is not taken in account in the preferred width computation. You'll see a blue rectangle of about 100px width.</p>
+
+ <table>
+ <tr>
+ <td style="background: blue">
+ <math>
+ <mspace style="position: absolute;" width="100px"></mspace>
+ <mspace width="100px"></mspace>
+ </math>
+ </td>
+ </tr>
+ </table>
+
+ </body>
+</html>
Modified: trunk/Source/WebCore/ChangeLog (226179 => 226180)
--- trunk/Source/WebCore/ChangeLog 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/ChangeLog 2017-12-20 16:34:43 UTC (rev 226180)
@@ -1,3 +1,58 @@
+2017-12-20 Frederic Wang <[email protected]>
+
+ Split layout of RenderMathMLRow into smaller steps
+ https://bugs.webkit.org/show_bug.cgi?id=180348
+
+ Reviewed by Manuel Rego Casasnovas.
+
+ Currently, RenderMathMLRow mixes too many steps in the same layout functions: layout children,
+ calculate stretch size, stretch vertical operators, calculate final ascent/descent, handle
+ out-of-flow positioned children, set logical height, set logical width for non-display
+ <math> tag, center display <math> tag etc This situation is inherited from the old flexbox
+ implementation but it makes difficult to read the code and to re-use layout & metrics
+ calculation for follow-up work on <mrow>-like elements (<menclose>, <mapdded>, <msqrt> or
+ <math>). See for example bug 160547 for <math> or bug 161126 for <menclose>.
+ This patch rewrites RenderMathMLRow into smaller steps:
+ - stretchVerticalOperatorsAndLayoutChildren() which calls layoutIfNeeded() or
+ insertPositionedObject() on children and stretch vertical operators.
+ - getContentBoundingBox() to determine the metrics of the mrow-like element without calling
+ layout on children or positioning them, so that we can improve mrow-like element in the
+ future.
+ - layoutRowItems() which sets the position of children.
+
+ Setting the logical width/height or centering children is now moved into layoutBlock() since
+ derived class overriding layoutBlock() will do their own adjustment for width, height and
+ positions.
+
+ Test: mathml/mrow-preferred-width-with-out-of-flow-child.html
+ The rest of the behavior is unchanged and already covered by existing tests.
+
+ * rendering/mathml/RenderMathMLMenclose.cpp:
+ (WebCore::RenderMathMLMenclose::layoutBlock): Use the new function and get contentWidth
+ directly from getContentBoundingBox().
+ * rendering/mathml/RenderMathMLPadded.cpp:
+ (WebCore::RenderMathMLPadded::layoutBlock): Ditto.
+ * rendering/mathml/RenderMathMLRoot.cpp:
+ (WebCore::RenderMathMLRoot::layoutBlock): Ditto, also remove useless statement
+ baseAscent = baseDescent.
+ * rendering/mathml/RenderMathMLRow.cpp:
+ (WebCore::toVerticalStretchyOperator): New helper function to cast to a vertical stretchy
+ operator.
+ (WebCore::RenderMathMLRow::stretchVerticalOperatorsAndLayoutChildren): New helper function
+ to ensure layoutIfNeeded()/insertPositionedObject() is called on children and that the
+ vertical operators are stretched.
+ (WebCore::RenderMathMLRow::getContentBoundingBox const): New helper function to determine
+ the width/ascent/descent to use for the mrow content.
+ (WebCore::RenderMathMLRow::computePreferredLogicalWidths): Skip out-of-flow children in the
+ preferred width calculation. This is verified by the new test.
+ (WebCore::RenderMathMLRow::layoutRowItems): Only keep the positioning of children with the
+ specified width and ascent.
+ (WebCore::RenderMathMLRow::layoutBlock): Center children for <math display="block"> tag and
+ set the logical width in other cases. Also set the logical height here.
+ (WebCore::RenderMathMLRow::computeLineVerticalStretch): Deleted. This work is included in
+ stretchVerticalOperatorsAndLayoutChildren() now.
+ * rendering/mathml/RenderMathMLRow.h: Update declaration of functions.
+
2017-12-20 Antti Koivisto <[email protected]>
Move list and multicolumn building code from RenderTreeUpdater to RenderTreeBuilder
Modified: trunk/Source/WebCore/rendering/mathml/RenderMathMLMenclose.cpp (226179 => 226180)
--- trunk/Source/WebCore/rendering/mathml/RenderMathMLMenclose.cpp 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/rendering/mathml/RenderMathMLMenclose.cpp 2017-12-20 16:34:43 UTC (rev 226180)
@@ -173,11 +173,10 @@
if (!relayoutChildren && simplifiedLayout())
return;
- LayoutUnit contentAscent = 0;
- LayoutUnit contentDescent = 0;
- RenderMathMLRow::computeLineVerticalStretch(contentAscent, contentDescent);
- RenderMathMLRow::layoutRowItems(contentAscent, contentDescent);
- LayoutUnit contentWidth = logicalWidth();
+ LayoutUnit contentWidth, contentAscent, contentDescent;
+ stretchVerticalOperatorsAndLayoutChildren();
+ getContentBoundingBox(contentWidth, contentAscent, contentDescent);
+ layoutRowItems(contentWidth, contentAscent);
SpaceAroundContent space = spaceAroundContent(contentWidth, contentAscent + contentDescent);
setLogicalWidth(space.left + contentWidth + space.right);
Modified: trunk/Source/WebCore/rendering/mathml/RenderMathMLPadded.cpp (226179 => 226180)
--- trunk/Source/WebCore/rendering/mathml/RenderMathMLPadded.cpp 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/rendering/mathml/RenderMathMLPadded.cpp 2017-12-20 16:34:43 UTC (rev 226180)
@@ -90,11 +90,10 @@
return;
// We first layout our children as a normal <mrow> element.
- LayoutUnit contentAscent, contentDescent, contentWidth;
- contentAscent = contentDescent = 0;
- RenderMathMLRow::computeLineVerticalStretch(contentAscent, contentDescent);
- RenderMathMLRow::layoutRowItems(contentAscent, contentDescent);
- contentWidth = logicalWidth();
+ LayoutUnit contentWidth, contentAscent, contentDescent;
+ stretchVerticalOperatorsAndLayoutChildren();
+ getContentBoundingBox(contentWidth, contentAscent, contentDescent);
+ layoutRowItems(contentWidth, contentAscent);
// We parse the mpadded attributes using the content metrics as the default value.
LayoutUnit width = mpaddedWidth(contentWidth);
Modified: trunk/Source/WebCore/rendering/mathml/RenderMathMLRoot.cpp (226179 => 226180)
--- trunk/Source/WebCore/rendering/mathml/RenderMathMLRoot.cpp 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/rendering/mathml/RenderMathMLRoot.cpp 2017-12-20 16:34:43 UTC (rev 226180)
@@ -201,10 +201,9 @@
LayoutUnit baseAscent, baseDescent;
recomputeLogicalWidth();
if (rootType() == RootType::SquareRoot) {
- baseAscent = baseDescent;
- RenderMathMLRow::computeLineVerticalStretch(baseAscent, baseDescent);
- RenderMathMLRow::layoutRowItems(baseAscent, baseDescent);
- m_baseWidth = logicalWidth();
+ stretchVerticalOperatorsAndLayoutChildren();
+ getContentBoundingBox(m_baseWidth, baseAscent, baseDescent);
+ layoutRowItems(m_baseWidth, baseAscent);
} else {
getBase().layoutIfNeeded();
m_baseWidth = getBase().logicalWidth();
Modified: trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.cpp (226179 => 226180)
--- trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.cpp 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.cpp 2017-12-20 16:34:43 UTC (rev 226180)
@@ -61,29 +61,66 @@
return std::optional<int>(static_cast<int>(lroundf(ascentForChild(*baselineChild) + baselineChild->logicalTop())));
}
-void RenderMathMLRow::computeLineVerticalStretch(LayoutUnit& ascent, LayoutUnit& descent)
+static RenderMathMLOperator* toVerticalStretchyOperator(RenderBox* box)
{
+ if (is<RenderMathMLBlock>(box)) {
+ auto* renderOperator = downcast<RenderMathMLBlock>(*box).unembellishedOperator();
+ if (renderOperator && renderOperator->isStretchy() && renderOperator->isVertical())
+ return renderOperator;
+ }
+ return nullptr;
+}
+
+void RenderMathMLRow::stretchVerticalOperatorsAndLayoutChildren()
+{
+ // First calculate stretch ascent and descent.
+ LayoutUnit stretchAscent, stretchDescent;
for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
- if (is<RenderMathMLBlock>(child)) {
- auto* renderOperator = downcast<RenderMathMLBlock>(child)->unembellishedOperator();
- if (renderOperator && renderOperator->isStretchy())
- continue;
+ if (child->isOutOfFlowPositioned()) {
+ child->containingBlock()->insertPositionedObject(*child);
+ continue;
}
-
+ if (toVerticalStretchyOperator(child))
+ continue;
child->layoutIfNeeded();
+ LayoutUnit childAscent = ascentForChild(*child);
+ LayoutUnit childDescent = child->logicalHeight() - childAscent;
+ stretchAscent = std::max(stretchAscent, childAscent);
+ stretchDescent = std::max(stretchDescent, childDescent);
+ }
+ if (stretchAscent + stretchDescent <= 0) {
+ // We ensure a minimal stretch size.
+ stretchAscent = style().computedFontPixelSize();
+ stretchDescent = 0;
+ }
- LayoutUnit childHeightAboveBaseline = ascentForChild(*child);
- LayoutUnit childDepthBelowBaseline = child->logicalHeight() - childHeightAboveBaseline;
-
- ascent = std::max(ascent, childHeightAboveBaseline);
- descent = std::max(descent, childDepthBelowBaseline);
+ // Next, we stretch the vertical operators.
+ for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
+ if (child->isOutOfFlowPositioned())
+ continue;
+ if (auto renderOperator = toVerticalStretchyOperator(child)) {
+ renderOperator->stretchTo(stretchAscent, stretchDescent);
+ renderOperator->layoutIfNeeded();
+ }
}
+}
- // We ensure a minimal stretch size.
- if (ascent + descent <= 0) {
- ascent = style().computedFontPixelSize();
- descent = 0;
+void RenderMathMLRow::getContentBoundingBox(LayoutUnit& width, LayoutUnit& ascent, LayoutUnit& descent) const
+{
+ ascent = 0;
+ descent = 0;
+ width = borderAndPaddingStart();
+ for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
+ if (child->isOutOfFlowPositioned())
+ continue;
+
+ width += child->marginStart() + child->logicalWidth() + child->marginEnd();
+ LayoutUnit childAscent = ascentForChild(*child);
+ LayoutUnit childDescent = child->logicalHeight() - childAscent;
+ ascent = std::max(ascent, childAscent + child->marginTop());
+ descent = std::max(descent, childDescent + child->marginBottom());
}
+ width += borderEnd() + paddingEnd();
}
void RenderMathMLRow::computePreferredLogicalWidths()
@@ -93,8 +130,11 @@
m_minPreferredLogicalWidth = m_maxPreferredLogicalWidth = 0;
LayoutUnit preferredWidth = 0;
- for (auto* child = firstChildBox(); child; child = child->nextSiblingBox())
+ for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
+ if (child->isOutOfFlowPositioned())
+ continue;
preferredWidth += child->maxPreferredLogicalWidth() + child->marginLogicalWidth();
+ }
m_minPreferredLogicalWidth = m_maxPreferredLogicalWidth = preferredWidth + borderAndPaddingLogicalWidth();
@@ -101,71 +141,20 @@
setPreferredLogicalWidthsDirty(false);
}
-void RenderMathMLRow::layoutRowItems(LayoutUnit& ascent, LayoutUnit& descent)
+void RenderMathMLRow::layoutRowItems(LayoutUnit width, LayoutUnit ascent)
{
- // We first stretch the vertical operators.
- // For inline formulas, we can then calculate the logical width.
- LayoutUnit width = borderAndPaddingStart();
+ LayoutUnit horizontalOffset = borderAndPaddingStart();
for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
if (child->isOutOfFlowPositioned())
continue;
-
- if (is<RenderMathMLBlock>(child)) {
- auto renderOperator = downcast<RenderMathMLBlock>(child)->unembellishedOperator();
- if (renderOperator && renderOperator->isStretchy() && renderOperator->isVertical())
- renderOperator->stretchTo(ascent, descent);
- }
-
- child->layoutIfNeeded();
-
- width += child->marginStart() + child->logicalWidth() + child->marginEnd();
- }
-
- width += borderEnd() + paddingEnd();
- if ((!isRenderMathMLMath() || style().display() == INLINE))
- setLogicalWidth(width);
-
- LayoutUnit verticalOffset = borderTop() + paddingTop();
- LayoutUnit maxAscent = 0, maxDescent = 0; // Used baseline alignment.
- LayoutUnit horizontalOffset = borderAndPaddingStart();
- bool shouldFlipHorizontal = !style().isLeftToRightDirection();
- for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
- if (child->isOutOfFlowPositioned()) {
- child->containingBlock()->insertPositionedObject(*child);
- continue;
- }
- LayoutUnit childHorizontalExtent = child->logicalWidth();
- LayoutUnit ascent = ascentForChild(*child);
- LayoutUnit descent = child->verticalMarginExtent() + child->logicalHeight() - ascent;
- maxAscent = std::max(maxAscent, ascent);
- maxDescent = std::max(maxDescent, descent);
- LayoutUnit childVerticalMarginBoxExtent = maxAscent + maxDescent;
-
horizontalOffset += child->marginStart();
-
- setLogicalHeight(std::max(logicalHeight(), verticalOffset + borderBottom() + paddingBottom() + childVerticalMarginBoxExtent + horizontalScrollbarHeight()));
-
- LayoutPoint childLocation(shouldFlipHorizontal ? logicalWidth() - horizontalOffset - childHorizontalExtent : horizontalOffset, verticalOffset + child->marginTop());
- child->setLocation(childLocation);
-
- horizontalOffset += childHorizontalExtent + child->marginEnd();
+ LayoutUnit childAscent = ascentForChild(*child);
+ LayoutUnit childVerticalOffset = borderTop() + paddingTop() + child->marginTop() + ascent - childAscent;
+ LayoutUnit childWidth = child->logicalWidth();
+ LayoutUnit childHorizontalOffset = style().isLeftToRightDirection() ? horizontalOffset : width - horizontalOffset - childWidth;
+ child->setLocation(LayoutPoint(childHorizontalOffset, childVerticalOffset));
+ horizontalOffset += childWidth + child->marginEnd();
}
-
- LayoutUnit centerBlockOffset = 0;
- if (style().display() == BLOCK)
- centerBlockOffset = std::max<LayoutUnit>(0, (logicalWidth() - (horizontalOffset + borderEnd() + paddingEnd())) / 2);
-
- if (shouldFlipHorizontal && centerBlockOffset > 0)
- centerBlockOffset = -centerBlockOffset;
-
- for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
- LayoutUnit ascent = ascentForChild(*child);
- LayoutUnit startOffset = maxAscent - ascent;
- child->setLocation(child->location() + LayoutPoint(centerBlockOffset, startOffset));
- }
-
- ascent = maxAscent;
- descent = maxDescent;
}
void RenderMathMLRow::layoutBlock(bool relayoutChildren, LayoutUnit)
@@ -175,16 +164,30 @@
if (!relayoutChildren && simplifiedLayout())
return;
- LayoutUnit ascent = 0;
- LayoutUnit descent = 0;
- computeLineVerticalStretch(ascent, descent);
-
recomputeLogicalWidth();
setLogicalHeight(borderAndPaddingLogicalHeight() + scrollbarLogicalHeight());
- layoutRowItems(ascent, descent);
+ LayoutUnit width, ascent, descent;
+ stretchVerticalOperatorsAndLayoutChildren();
+ getContentBoundingBox(width, ascent, descent);
+ if (isRenderMathMLMath() && style().display() == BLOCK) {
+ // Display formulas must be centered horizontally.
+ layoutRowItems(logicalWidth(), ascent);
+ LayoutUnit centerBlockOffset = std::max<LayoutUnit>(0, logicalWidth() - width) / 2;
+ if (!style().isLeftToRightDirection())
+ centerBlockOffset = -centerBlockOffset;
+ for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
+ if (!child->isOutOfFlowPositioned())
+ child->setLocation(child->location() + LayoutPoint(centerBlockOffset, 0));
+ }
+ } else {
+ layoutRowItems(width, ascent);
+ setLogicalWidth(width);
+ }
+
+ setLogicalHeight(borderTop() + paddingTop() + ascent + descent + borderBottom() + paddingBottom() + horizontalScrollbarHeight());
updateLogicalHeight();
layoutPositionedObjects(relayoutChildren);
Modified: trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.h (226179 => 226180)
--- trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.h 2017-12-20 16:33:36 UTC (rev 226179)
+++ trunk/Source/WebCore/rendering/mathml/RenderMathMLRow.h 2017-12-20 16:34:43 UTC (rev 226180)
@@ -44,8 +44,9 @@
void layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeight = 0) override;
std::optional<int> firstLineBaseline() const override;
- void layoutRowItems(LayoutUnit& ascent, LayoutUnit& descent);
- void computeLineVerticalStretch(LayoutUnit& ascent, LayoutUnit& descent);
+ void stretchVerticalOperatorsAndLayoutChildren();
+ void getContentBoundingBox(LayoutUnit& width, LayoutUnit& ascent, LayoutUnit& descent) const;
+ void layoutRowItems(LayoutUnit width, LayoutUnit ascent);
void computePreferredLogicalWidths() override;
private:
