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Bug 1890773 - Create a pref to control how letter-spacing is inserted around characters. r=layout-reviewers,emilio

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With the pref set to 0 by default, this does not change any existing behavior.

My intention is that a following patch will set it to 2 in Nightly. This will affect
a bunch of reftests, and so test/expectation adjustments will also be needed.

Differential Revision: https://phabricator.services.mozilla.com/D207150
This commit is contained in:
Jonathan Kew
2024-04-11 18:41:37 +00:00
parent ae8bec2d03
commit 10169b1937
3 changed files with 59 additions and 3 deletions
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49
layout/generic/nsTextFrame.cpp
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@@ -3611,6 +3611,20 @@ void nsTextFrame::PropertyProvider::GetSpacing(Range aRange,
!(mTextRun->GetFlags2() & nsTextFrameUtils::Flags::HasTab));
}
static bool CanAddSpacingBefore(const gfxTextRun* aTextRun, uint32_t aOffset,
bool aNewlineIsSignificant) {
const auto* g = aTextRun->GetCharacterGlyphs();
MOZ_ASSERT(aOffset < aTextRun->GetLength());
if (aNewlineIsSignificant && g[aOffset].CharIsNewline()) {
return false;
}
if (!aOffset) {
return true;
}
return g[aOffset].IsClusterStart() && g[aOffset].IsLigatureGroupStart() &&
!g[aOffset - 1].CharIsFormattingControl() && !g[aOffset].CharIsTab();
}
static bool CanAddSpacingAfter(const gfxTextRun* aTextRun, uint32_t aOffset,
bool aNewlineIsSignificant) {
const auto* g = aTextRun->GetCharacterGlyphs();
@@ -3683,14 +3697,45 @@ void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
nsSkipCharsRunIterator run(
start, nsSkipCharsRunIterator::LENGTH_UNSKIPPED_ONLY, aRange.Length());
bool newlineIsSignificant = mTextStyle->NewlineIsSignificant(mFrame);
// Which letter-spacing model are we using?
// 0 - Gecko legacy model, spacing added to trailing side of letter
// 1 - WebKit/Blink-compatible, spacing added to right-hand side
// 2 - Symmetrical spacing, half added to each side
gfxFloat before, after;
switch (StaticPrefs::layout_css_letter_spacing_model()) {
default: // use Gecko legacy behavior if pref value is unknown
case 0:
before = 0.0;
after = mLetterSpacing;
break;
case 1:
if (mTextRun->IsRightToLeft()) {
before = mLetterSpacing;
after = 0.0;
} else {
before = 0.0;
after = mLetterSpacing;
}
break;
case 2:
before = mLetterSpacing / 2.0;
after = mLetterSpacing - before;
break;
}
while (run.NextRun()) {
uint32_t runOffsetInSubstring = run.GetSkippedOffset() - aRange.start;
gfxSkipCharsIterator iter = run.GetPos();
for (int32_t i = 0; i < run.GetRunLength(); ++i) {
if (CanAddSpacingAfter(mTextRun, run.GetSkippedOffset() + i,
if (before != 0.0 &&
CanAddSpacingBefore(mTextRun, run.GetSkippedOffset() + i,
newlineIsSignificant)) {
aSpacing[runOffsetInSubstring + i].mBefore += before;
}
if (after != 0.0 &&
CanAddSpacingAfter(mTextRun, run.GetSkippedOffset() + i,
newlineIsSignificant)) {
// End of a cluster, not in a ligature: put letter-spacing after it
aSpacing[runOffsetInSubstring + i].mAfter += mLetterSpacing;
aSpacing[runOffsetInSubstring + i].mAfter += after;
}
if (IsCSSWordSpacingSpace(mFrag, i + run.GetOriginalOffset(), mFrame,
mTextStyle)) {