Cherry-pick 1be1a3f. rdar://123854414

text-wrap: balance, prefering longer lines at the beginning of block https://bugs.webkit.org/show_bug.cgi?id=268780 rdar://122338948 Reviewed by Alan Baradlay. When balancing, there are different results that produce the same score, i.e.: the overall deviation to the ideal line is the same for different layout configurations. The current implementation prefers to keep longer lines at the end of the block, rather than at the beginning. Although this is not a bug, since specification doesn't dictates the shape of balancing, this might look a bit weird for some authors, as we are used to the Greedy behavior of "wrap", which will have a shorter line at the end. Also, other UAs prefers to have longer lines at the beginning, so, although it is not a bug, it would make the feature less confusing for authors if we would match the same behavior. We are introducing a new test to track the behavior of WebKit shape, but since this is not dictate by specification, this should not be WPT test. * LayoutTests/fast/text/whitespace/text-wrap-balance-shape-expected.html: Added. * LayoutTests/fast/text/whitespace/text-wrap-balance-shape.html: Added. * Source/WebCore/layout/formattingContexts/inline/InlineContentBalancer.cpp: (WebCore::Layout::InlineContentBalancer::balanceRangeWithLineRequirement): Canonical link: https://commits.webkit.org/274125@main Canonical link: https://commits.webkit.org/272448.663@safari-7618-branch
WebKit · Mar 1, 2024 · b36c04b · b36c04b
1 parent a7d6999
commit b36c04b
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diff --git a/LayoutTests/fast/text/whitespace/text-wrap-balance-shape-expected.html b/LayoutTests/fast/text/whitespace/text-wrap-balance-shape-expected.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/css-text-4/#valdef-text-wrap-balance">
+<!-- This tests that we prefer to accumulate longer lines at the beginning of the block, rather than at the end.
+Since specification (see href) doesn't dictates the shape itself, this should not be a general web-platform test, since other UAs might prefer to shape it on a different way. -->
+<style>
+.container {
+  font-family: monospace;
+  font-size: 20px;
+  width: 20ch;
+}
+</style>
+<div class="container">
+  123 567 901 345 789
+  123 567 901 345 789
+  123 123 567 901<br>
+  345 789 123 567<br>
+  901 345 789 123
+</div>
diff --git a/LayoutTests/fast/text/whitespace/text-wrap-balance-shape.html b/LayoutTests/fast/text/whitespace/text-wrap-balance-shape.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/css-text-4/#valdef-text-wrap-balance">
+<!-- This tests that we prefer to accumulate longer lines at the beginning of the block, rather than at the end.
+Since specification (see href) doesn't dictates the shape itself, this should not be a general web-platform test, since other UAs might prefer to shape it on a different way. -->
+<style>
+.container {
+  font-family: monospace;
+  font-size: 20px;
+  width: 20ch;
+  text-wrap: balance;
+}
+</style>
+<div class="container">
+  123 567 901 345 789
+  123 567 901 345 789 123
+  123 567 901 345 789
+  123 567 901 345 789
+  123
+</div>
diff --git a/Source/WebCore/layout/formattingContexts/inline/InlineContentBalancer.cpp b/Source/WebCore/layout/formattingContexts/inline/InlineContentBalancer.cpp
@@ -29,6 +29,7 @@
 #include "InlineLineBuilder.h"
 #include "RenderStyleInlines.h"
 #include <limits>
+#include <wtf/MathExtras.h>
 
 namespace WebCore {
 namespace Layout {
@@ -292,7 +293,8 @@ std::optional<Vector<LayoutUnit>> InlineContentBalancer::balanceRangeWithLineReq
             // Compute the cost of this line based on the line index
             for (size_t lineIndex = 1; lineIndex <= numberOfLines; lineIndex++) {
                 auto accumulatedCost = candidateLineCost + state[startIndex][lineIndex - 1].accumulatedCost;
-                if (accumulatedCost < state[breakIndex][lineIndex].accumulatedCost) {
+                auto currentAccumulatedCost = state[breakIndex][lineIndex].accumulatedCost;
+                if (accumulatedCost < currentAccumulatedCost || WTF::areEssentiallyEqual(accumulatedCost, currentAccumulatedCost)) {
                     state[breakIndex][lineIndex].accumulatedCost = accumulatedCost;
                     state[breakIndex][lineIndex].previousBreakIndex = startIndex;
                 }