Changeset 239330 in webkit

Timestamp:

Dec 18, 2018 7:19:21 AM (5 years ago)

Author:

Alan Bujtas

Message:

[LFC][BFC][MarginCollapsing] Expand marginAfterCollapsesWithParentMarginAfter and marginBeforeCollapsesWithParentMarginBefore collapsing logic
​https://bugs.webkit.org/show_bug.cgi?id=192787

Reviewed by Antti Koivisto.

• layout/blockformatting/BlockFormattingContext.h:
• layout/blockformatting/BlockMarginCollapse.cpp:

(WebCore::Layout::hasClearance):
(WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginBeforeCollapsesWithParentMarginBefore):
(WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithSiblingMarginBeforeWithClearance):
(WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginBefore):
(WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginAfter):

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• layout/blockformatting/BlockFormattingContext.h (modified) (1 diff)
• layout/blockformatting/BlockMarginCollapse.cpp (modified) (6 diffs)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2018-12-18  Zalan Bujtas  <zalan@apple.com>
+
+        [LFC][BFC][MarginCollapsing] Expand marginAfterCollapsesWithParentMarginAfter and marginBeforeCollapsesWithParentMarginBefore collapsing logic
+        https://bugs.webkit.org/show_bug.cgi?id=192787
+
+        Reviewed by Antti Koivisto.
+
+        * layout/blockformatting/BlockFormattingContext.h:
+        * layout/blockformatting/BlockMarginCollapse.cpp:
+        (WebCore::Layout::hasClearance):
+        (WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginBeforeCollapsesWithParentMarginBefore):
+        (WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithSiblingMarginBeforeWithClearance):
+        (WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginBefore):
+        (WebCore::Layout::BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginAfter):
+
 2018-12-17  Fujii Hironori  <Hironori.Fujii@sony.com>
 

trunk/Source/WebCore/layout/blockformatting/BlockFormattingContext.h

@@ -106 +106 @@
             static bool marginBeforeCollapsesWithPreviousSibling(const Box&);
             static bool marginAfterCollapsesWithNextSibling(const Box&);
+            static bool marginAfterCollapsesWithSiblingMarginBeforeWithClearance(const Box&);
+            static bool marginAfterCollapsesWithParentMarginBefore(const Box&);
             static bool marginsCollapseThrough(const Box&);
         };

trunk/Source/WebCore/layout/blockformatting/BlockMarginCollapse.cpp

@@ -70 +70 @@
 }
 
+static bool hasClearance(const Box& layoutBox)
+{
+    if (!layoutBox.hasFloatClear())
+        return false;
+    // FIXME
+    return false;
+}
+
 static bool establishesBlockFormattingContext(const Box& layoutBox)
 {
@@ -180 +188 @@
     ASSERT(layoutBox.isBlockLevelBox());
 
-    if (layoutBox.isFloatingOrOutOfFlowPositioned())
+    // Margins between a floated box and any other box do not collapse.
+    if (layoutBox.isFloatingPositioned())
+        return false;
+
+    // Margins of absolutely positioned boxes do not collapse.
+    if (layoutBox.isOutOfFlowPositioned())
+        return false;
+
+    // Margins of inline-block boxes do not collapse.
+    if (layoutBox.isInlineBlockBox())
         return false;
 
@@ -198 +215 @@
         return false;
 
+    // ...and the child has no clearance.
+    if (hasClearance(layoutBox))
+        return false;
+
     if (BlockFormattingContext::Quirks::shouldIgnoreMarginBefore(layoutState, layoutBox))
         return false;
@@ -204 +225 @@
 }
 
+bool BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithSiblingMarginBeforeWithClearance(const Box&)
+{
+    return false;
+}
+
+bool BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginBefore(const Box&)
+{
+    return false;
+}
+
 bool BlockFormattingContext::Geometry::MarginCollapse::marginAfterCollapsesWithParentMarginAfter(const Box& layoutBox)
 {
-    // last inflow box to parent.
-    // https://www.w3.org/TR/CSS21/box.html#collapsing-margins
     if (layoutBox.isAnonymous())
         return false;
@@ -213 +242 @@
     ASSERT(layoutBox.isBlockLevelBox());
 
-    if (layoutBox.isFloatingOrOutOfFlowPositioned())
-        return false;
-
-    if (marginsCollapseThrough(layoutBox))
+    // Margins between a floated box and any other box do not collapse.
+    if (layoutBox.isFloatingPositioned())
+        return false;
+
+    // Margins of absolutely positioned boxes do not collapse.
+    if (layoutBox.isOutOfFlowPositioned())
+        return false;
+
+    // Margins of inline-block boxes do not collapse.
+    if (layoutBox.isInlineBlockBox())
         return false;
 
@@ -224 +259 @@
 
     auto& parent = *layoutBox.parent();
-    // Margins of elements that establish new block formatting contexts do not collapse with their in-flow children
+    // Margins of elements that establish new block formatting contexts do not collapse with their in-flow children.
     if (establishesBlockFormattingContext(parent))
         return false;
 
+    // The bottom margin of an in-flow block box with a 'height' of 'auto' collapses with its last in-flow block-level child's bottom margin, if:
+    if (!parent.style().height().isAuto())
+        return false;
+
+    // the box has no bottom padding, and
+    if (hasPaddingBefore(parent))
+        return false;
+
+    // the box has no bottom border, and
     if (hasBorderBefore(parent))
         return false;
 
-    if (hasPaddingBefore(parent))
-        return false;
-
-    if (!parent.style().height().isAuto())
+    // the child's bottom margin neither collapses with a top margin that has clearance...
+    if (marginAfterCollapsesWithSiblingMarginBeforeWithClearance(layoutBox))
+        return false;
+
+    // nor (if the box's min-height is non-zero) with the box's top margin.
+    auto computedMinHeight = parent.style().logicalMinHeight();
+    if (!computedMinHeight.isAuto() && computedMinHeight.value() && marginAfterCollapsesWithParentMarginBefore(layoutBox))
         return false;