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Fix invisible RTL text on Qt backend (MeasureWidths uses visual instead of logical positions) #1116

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Fix invisible RTL text on Qt backend (MeasureWidths uses visual instead of logical positions) #1116

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34 changes: 26 additions & 8 deletions thirdparty/scintilla/qt/ScintillaEditBase/PlatQt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -667,16 +667,29 @@ void SurfaceImpl::MeasureWidths(const Font *font,
QTextLine tl = tlay.createLine();
tlay.endLayout();
if (mode.codePage == SC_CP_UTF8) {
// Measure each character's advance width independently and accumulate in
// logical (document) order, rather than using QTextLine::cursorToX(), which
// returns *visual* bidi-reordered positions. Scintilla's EditView code relies
// on positions[] being monotonically non-decreasing in logical order to place
// styled runs, the caret, and selection highlights; for RTL text (e.g. Hebrew),
// cursorToX() violates that invariant and pushes glyphs outside the visible
// clip rectangle, making them appear invisible.
QFontMetricsF metrics(*FontPointer(font), GetPaintDevice());
int fit = su.size();
int ui=0;
size_t i=0;
XYPOSITION cumulativeWidth = 0;
while (ui<fit) {
const unsigned char uch = text[i];
const unsigned int byteCount = UTF8BytesOfLead[uch];
const int codeUnits = UTF16LengthFromUTF8ByteCount(byteCount);
qreal xPosition = tl.cursorToX(ui+codeUnits);
#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
cumulativeWidth += metrics.horizontalAdvance(su.mid(ui, codeUnits));
#else
cumulativeWidth += metrics.width(su.mid(ui, codeUnits));
#endif
for (size_t bytePos=0; (bytePos<byteCount) && (i<text.length()); bytePos++) {
positions[i++] = xPosition;
positions[i++] = cumulativeWidth;
}
ui += codeUnits;
}
Expand Down Expand Up @@ -765,21 +778,26 @@ void SurfaceImpl::MeasureWidthsUTF8(const Font *font,
{
if (!font)
return;
// See the comment in MeasureWidths(): measure per-character in logical order
// rather than using QTextLine::cursorToX(), which returns visual bidi-reordered
// positions and breaks position monotonicity for RTL text.
QString su = QString::fromUtf8(text.data(), static_cast<int>(text.length()));
QTextLayout tlay(su, *FontPointer(font), GetPaintDevice());
tlay.beginLayout();
QTextLine tl = tlay.createLine();
tlay.endLayout();
QFontMetricsF metrics(*FontPointer(font), GetPaintDevice());
int fit = su.size();
int ui=0;
size_t i=0;
XYPOSITION cumulativeWidth = 0;
while (ui<fit) {
const unsigned char uch = text[i];
const unsigned int byteCount = UTF8BytesOfLead[uch];
const int codeUnits = UTF16LengthFromUTF8ByteCount(byteCount);
qreal xPosition = tl.cursorToX(ui+codeUnits);
#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
cumulativeWidth += metrics.horizontalAdvance(su.mid(ui, codeUnits));
#else
cumulativeWidth += metrics.width(su.mid(ui, codeUnits));
#endif
for (size_t bytePos=0; (bytePos<byteCount) && (i<text.length()); bytePos++) {
positions[i++] = xPosition;
positions[i++] = cumulativeWidth;
}
ui += codeUnits;
}
Expand Down
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