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[web] Improve line breaker test exceptions #37244

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merged 5 commits into from
Nov 4, 2022
Merged

[web] Improve line breaker test exceptions #37244

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175922f
[web] Improve line breaker test exceptions
mdebbar Nov 1, 2022
8e02e08
always break after spaces
mdebbar Nov 2, 2022
cb1abcf
Merge branch 'main' into line_break_test_helper
mdebbar Nov 3, 2022
8084f2b
Merge branch 'main' into line_break_test_helper
mdebbar Nov 4, 2022
56022c3
explain reason for modifications
mdebbar Nov 4, 2022
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56 changes: 29 additions & 27 deletions lib/web_ui/lib/src/engine/text/line_breaker.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -127,10 +127,6 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
int? codePoint = getCodePoint(text, 0);
LineCharProperty? curr = lineLookup.findForChar(codePoint);

// When there's a sequence of spaces, this variable contains the base property
// i.e. the property of the character preceding the sequence.
LineCharProperty baseOfSpaceSequence = LineCharProperty.WJ;

// When there's a sequence of combining marks, this variable contains the base
// property i.e. the property of the character preceding the sequence.
LineCharProperty baseOfCombiningMarks = LineCharProperty.AL;
Expand All @@ -146,6 +142,9 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
type == LineBreakType.endOfText ? text.length : index;
assert(fragmentEnd >= fragmentStart);

// Uncomment the following line to help debug line breaking.
// print('{$fragmentStart:$fragmentEnd} [$debugRuleNumber] -- $type');

if (prev1 == LineCharProperty.SP) {
trailingSpaces++;
} else if (_isHardBreak(prev1) || prev1 == LineCharProperty.CR) {
Expand Down Expand Up @@ -244,13 +243,6 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
break;
}

// Establish the base for the space sequence.
if (prev1 != LineCharProperty.SP) {
// When the text/line starts with SP, we should treat the beginning of text/line
// as if it were a WJ (word joiner).
baseOfSpaceSequence = prev1 ?? LineCharProperty.WJ;
}

// Do not break before spaces or zero width space.
// LB7: × SP
// × ZW
Expand All @@ -259,11 +251,17 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
continue;
}

// Break after spaces.
// LB18: SP ÷
if (prev1 == LineCharProperty.SP) {
setBreak(LineBreakType.opportunity, 18);
continue;
}

// Break before any character following a zero-width space, even if one or
// more spaces intervene.
// LB8: ZW SP* ÷
if (prev1 == LineCharProperty.ZW ||
baseOfSpaceSequence == LineCharProperty.ZW) {
if (prev1 == LineCharProperty.ZW) {
setBreak(LineBreakType.opportunity, 8);
continue;
}
Expand Down Expand Up @@ -343,6 +341,8 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
// The above is a quote from unicode.org. In our implementation, we did the
// following modification: When there are spaces present, we consider it a
// line break opportunity.
//
// We made this modification to match the browser behavior.
if (prev1 != LineCharProperty.SP &&
(curr == LineCharProperty.CL ||
curr == LineCharProperty.CP ||
Expand All @@ -358,6 +358,8 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
//
// The above is a quote from unicode.org. In our implementation, we did the
// following modification: Allow breaks when there are spaces.
//
// We made this modification to match the browser behavior.
if (prev1 == LineCharProperty.OP) {
setBreak(LineBreakType.prohibited, 14);
continue;
Expand All @@ -368,6 +370,8 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
//
// The above is a quote from unicode.org. In our implementation, we did the
// following modification: Allow breaks when there are spaces.
//
// We made this modification to match the browser behavior.
if (prev1 == LineCharProperty.QU && curr == LineCharProperty.OP) {
setBreak(LineBreakType.prohibited, 15);
continue;
Expand All @@ -376,31 +380,29 @@ List<LineBreakFragment> _computeLineBreakFragments(String text) {
// Do not break between closing punctuation and a nonstarter, even with
// intervening spaces.
// LB16: (CL | CP) SP* × NS
if ((prev1 == LineCharProperty.CL ||
baseOfSpaceSequence == LineCharProperty.CL ||
prev1 == LineCharProperty.CP ||
baseOfSpaceSequence == LineCharProperty.CP) &&
//
// The above is a quote from unicode.org. In our implementation, we did the
// following modification: Allow breaks when there are spaces.
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Do we have details about why we modified it documented anywhere? Maybe expand on it here a bit?

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Good point. We modified it to match Chrome's behavior (which makes more sense to me than the unicode spec in these cases). I'll explain it in the comment.

//
// We made this modification to match the browser behavior.
if ((prev1 == LineCharProperty.CL || prev1 == LineCharProperty.CP) &&
curr == LineCharProperty.NS) {
setBreak(LineBreakType.prohibited, 16);
continue;
}

// Do not break within ‘——’, even with intervening spaces.
// LB17: B2 SP* × B2
if ((prev1 == LineCharProperty.B2 ||
baseOfSpaceSequence == LineCharProperty.B2) &&
curr == LineCharProperty.B2) {
//
// The above is a quote from unicode.org. In our implementation, we did the
// following modification: Allow breaks when there are spaces.
//
// We made this modification to match the browser behavior.
if (prev1 == LineCharProperty.B2 && curr == LineCharProperty.B2) {
setBreak(LineBreakType.prohibited, 17);
continue;
}

// Break after spaces.
// LB18: SP ÷
if (prev1 == LineCharProperty.SP) {
setBreak(LineBreakType.opportunity, 18);
continue;
}

// Do not break before or after quotation marks, such as ‘”’.
// LB19: × QU
// QU ×
Expand Down
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