tor-browser

commit 878d1288a77241ee489677b28a2d8799bc8627fc
parent 2a1d70136b8cdd09919940f398782660742b7236
Author: Jonathan Kew <jkew@mozilla.com>
Date:   Thu,  2 Oct 2025 10:02:01 +0000

Bug 1991943 - Try to skip some text-autospace work if no CJK glyph runs are present. r=layout-reviewers,dshin,TYLin

For the GlyphRuns in a given gfxTextRun, we already track whether they are
associated with a CJK script, so we can use this knowledge to potentially
avoid some auto-spacing work when the textrun is known to be CJK-free. This
extends the previous idea of checking whether the character buffer is 2-byte,
and should let us skip the character-class processing in more cases.

Differential Revision: https://phabricator.services.mozilla.com/D267050

Diffstat:
M
layout/generic/nsTextFrame.cpp
 | 
42
++++++++++++++++++++++++++++++------------

1 file changed, 30 insertions(+), 12 deletions(-)
diff --git a/layout/generic/nsTextFrame.cpp b/layout/generic/nsTextFrame.cpp
@@ -4054,6 +4054,18 @@ static Maybe<TextAutospace::CharClass> GetPrecedingCharClassFromFrameTree(
   return Nothing();
 }
 
+static bool HasCJKGlyphRun(const gfxTextRun* aTextRun) {
+  uint32_t numGlyphRuns;
+  const gfxTextRun::GlyphRun* run = aTextRun->GetGlyphRuns(&numGlyphRuns);
+  while (numGlyphRuns-- > 0) {
+    if (run->mIsCJK) {
+      return true;
+    }
+    run++;
+  }
+  return false;
+}
+
 void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
                                                        Spacing* aSpacing,
                                                        bool aIgnoreTabs) const {
@@ -4065,16 +4077,9 @@ void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
     return;
   }
 
-  // Find our offset into the original+transformed string
-  gfxSkipCharsIterator start(mStart);
-  start.SetSkippedOffset(aRange.start);
-
   // First, compute the word spacing, letter spacing, and text-autospace
   // spacing.
   if (mWordSpacing || mLetterSpacing || mTextAutospace) {
-    // Iterate over non-skipped characters
-    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
@@ -4101,6 +4106,10 @@ void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
         after = mLetterSpacing - before;
         break;
     }
+
+    // Find our offset into the original+transformed string
+    gfxSkipCharsIterator start(mStart);
+    start.SetSkippedOffset(aRange.start);
     bool atStart = mStartOfLineOffset == start.GetSkippedOffset() &&
                    !mFrame->IsInSVGTextSubtree();
 
@@ -4143,6 +4152,14 @@ void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
       return prevClass.valueOr(CharClass::Other);
     };
 
+    // If text-autospace is enabled, we may be able to skip some processing if
+    // there are no CJK glyphs in the textrun, so check for their presence.
+    bool textIncludesCJK = mTextAutospace && mCharacterDataBuffer.Is2b() &&
+                           HasCJKGlyphRun(mTextRun);
+
+    // Iterate over non-skipped characters
+    nsSkipCharsRunIterator run(
+        start, nsSkipCharsRunIterator::LENGTH_UNSKIPPED_ONLY, aRange.Length());
     while (run.NextRun()) {
       uint32_t runOffsetInSubstring = run.GetSkippedOffset() - aRange.start;
       gfxSkipCharsIterator iter = run.GetPos();
@@ -4169,18 +4186,19 @@ void nsTextFrame::PropertyProvider::GetSpacingInternal(Range aRange,
           uint32_t runOffset = iter.GetSkippedOffset() - aRange.start;
           aSpacing[runOffset].mAfter += mWordSpacing;
         }
-        // Add text-autospace spacing only at cluster starts. Always check
-        // 2-byte text; for 1-byte, check only at the frame start (a preceding
-        // content might be an ideograph requiring autospacing).
+        // Add text-autospace spacing only at cluster starts. Always check the
+        // character classes if the textrun includes CJK; otherwise, check only
+        // at the frame start (as preceding content might be an ideograph
+        // requiring autospacing).
         if (mTextAutospace &&
-            (mCharacterDataBuffer.Is2b() ||
+            (textIncludesCJK ||
              run.GetOriginalOffset() + i == mFrame->GetContentOffset()) &&
             mTextRun->IsClusterStart(run.GetSkippedOffset() + i)) {
           const char32_t currScalar =
               mCharacterDataBuffer.ScalarValueAt(run.GetOriginalOffset() + i);
           const auto currClass = TextAutospace::GetCharClass(currScalar);
 
-          // It is rare for the current class to be is a combining mark, as
+          // It is rare for the current class to be a combining mark, as
           // combining marks are not cluster starts. We still check in case a
           // stray mark appears at the start of a frame.
           if (currClass != CharClass::CombiningMark) {