[IFC][truncation] Content gets truncated too early caused by subpixel…

… flooring

https://bugs.webkit.org/show_bug.cgi?id=255991

Reviewed by Antti Koivisto.

This is caused by using LayoutUnit on block level to set the constraint value on the inline content,
while using InlineLayoutUnit (float) to accumulate inline content on the line.
e.g. <div width="10ch"> with ch length of 7.82px -> 78.2px which gets turned into a LayoutUnit : 5004.8 -> floored to 5004 raw value.

This is similar to what we do for regular line breaking at LineBuilder:availableWidth.

* LayoutTests/TestExpectations:
* LayoutTests/imported/w3c/web-platform-tests/css/css-ui/text-overflow-028.html:
* Source/WebCore/layout/formattingContexts/inline/display/InlineDisplayLineBuilder.cpp:
(WebCore::Layout::truncateOverflowingDisplayBoxes):

Canonical link: https://commits.webkit.org/263428@main

LayoutTests/TestExpectations

@@ -3303,8 +3303,6 @@ imported/w3c/web-platform-tests/css/css-display/run-in/run-in-table-cell-between
 imported/w3c/web-platform-tests/css/css-display/run-in/run-in-table-row-between-003.xht [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-display/run-in/run-in-text-between-004.xht [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/css/css-display/run-in/run-in-text-between-005.xht [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/css/css-ui/text-overflow-027.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/css/css-ui/text-overflow-028.html [ ImageOnlyFailure ]
 
 imported/w3c/web-platform-tests/css/mediaqueries/viewport-script-dynamic.html [ ImageOnlyFailure ]
 

LayoutTests/imported/w3c/web-platform-tests/css/css-ui/text-overflow-028.html

@@ -6,6 +6,7 @@
 <link rel="help" href="http://www.w3.org/TR/css-ui-4/#text-overflow">
 <link rel="match" href="reference/text-overflow-028-ref.html">
 <meta name="assert" content="text-overflow is a visual operation that occurs after layout, and therfore ellides text from the visual end of the line, even in bidi situations">
+<meta name="fuzzy" content="maxDifference=86; totalPixels=58" />
 <style>
 div {
   font-family: monospace;

Source/WebCore/layout/formattingContexts/inline/display/InlineDisplayLineBuilder.cpp

@@ -241,6 +241,10 @@ static float truncateOverflowingDisplayBoxes(const InlineDisplay::Line& displayL
     auto isFirstContentRun = true;
     if (rootStyle.isLeftToRightDirection()) {
         auto visualRightForContentEnd = std::max(0.f, right(displayLine) - ellipsisWidth);
+#if USE_FLOAT_AS_INLINE_LAYOUT_UNIT
+        if (visualRightForContentEnd)
+            visualRightForContentEnd += LayoutUnit::epsilon();
+#endif
         auto truncateRight = std::optional<float> { };
         for (auto& displayBox : boxes) {
             if (displayBox.isInlineBox())
@@ -258,6 +262,10 @@ static float truncateOverflowingDisplayBoxes(const InlineDisplay::Line& displayL
 
     auto truncateLeft = std::optional<float> { };
     auto visualLeftForContentEnd = std::max(0.f, left(displayLine) + ellipsisWidth);
+#if USE_FLOAT_AS_INLINE_LAYOUT_UNIT
+    if (visualLeftForContentEnd)
+        visualLeftForContentEnd -= LayoutUnit::epsilon();
+#endif
     for (auto& displayBox : makeReversedRange(boxes)) {
         if (displayBox.isInlineBox())
             continue;