Fix bounding box of zero-width entities in QFontEngineFT

Freetype can give us non empty bounds for zero-width characters,
this change just makes us skip metrics of characters already found to
not contribute to text advance. The coretext and windows
font-engines already uses the already calculated advance.

Change-Id: I82b3521a4fb92614be509be5982cd5ab9c1eb7de
Fixes: QTBUG-58854
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

3 files changed, 30 insertions, 0 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 403a0510fa..2ed0f21d3e 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -663,6 +663,9 @@ glyph_metrics_t QFontEngine::tightBoundingBox(const QGlyphLayout &glyphs)
     QFixed ymax = 0;
     QFixed xmax = 0;
     for (int i = 0; i < glyphs.numGlyphs; i++) {
+        // If shaping has found this should be ignored, ignore it.
+        if (!glyphs.advances[i] || glyphs.attributes[i].dontPrint)
+            continue;
         glyph_metrics_t bb = boundingBox(glyphs.glyphs[i]);
         QFixed x = overall.xoff + glyphs.offsets[i].x + bb.x;
         QFixed y = overall.yoff + glyphs.offsets[i].y + bb.y;
diff --git a/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp b/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
index 8c6cc8fbc1..d176f60d10 100644
--- a/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
+++ b/src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
@@ -1672,6 +1672,9 @@ glyph_metrics_t QFontEngineFT::boundingBox(const QGlyphLayout &glyphs)
     QFixed ymax = 0;
     QFixed xmax = 0;
     for (int i = 0; i < glyphs.numGlyphs; i++) {
+        // If shaping has found this should be ignored, ignore it.
+        if (!glyphs.advances[i] || glyphs.attributes[i].dontPrint)
+            continue;
         Glyph *g = cacheEnabled ? defaultGlyphSet.getGlyph(glyphs.glyphs[i]) : 0;
         if (!g) {
             if (!face)
diff --git a/tests/auto/gui/text/qfontmetrics/tst_qfontmetrics.cpp b/tests/auto/gui/text/qfontmetrics/tst_qfontmetrics.cpp
index a0e8525268..6fe3e20083 100644
--- a/tests/auto/gui/text/qfontmetrics/tst_qfontmetrics.cpp
+++ b/tests/auto/gui/text/qfontmetrics/tst_qfontmetrics.cpp
@@ -59,6 +59,7 @@ private slots:
     void mnemonicTextWidth();
     void leadingBelowLine();
     void elidedMetrics();
+    void zeroWidthMetrics();
 };
 
 void tst_QFontMetrics::same()
@@ -358,5 +359,28 @@ void tst_QFontMetrics::elidedMetrics()
     QFontDatabase::removeApplicationFont(id);
 }
 
+void tst_QFontMetrics::zeroWidthMetrics()
+{
+    QString zwnj(QChar(0x200c));
+    QString zwsp(QChar(0x200b));
+
+    QFont font;
+    QFontMetricsF fm(font);
+    QCOMPARE(fm.horizontalAdvance(zwnj), 0);
+    QCOMPARE(fm.horizontalAdvance(zwsp), 0);
+    QCOMPARE(fm.boundingRect(zwnj).width(), 0);
+    QCOMPARE(fm.boundingRect(zwsp).width(), 0);
+
+    QString string1 = QStringLiteral("(") + zwnj + QStringLiteral(")");
+    QString string2 = QStringLiteral("(") + zwnj + zwnj + QStringLiteral(")");
+    QString string3 = QStringLiteral("(") + zwsp + QStringLiteral(")");
+    QString string4 = QStringLiteral("(") + zwsp + zwsp + QStringLiteral(")");
+
+    QCOMPARE(fm.horizontalAdvance(string1), fm.horizontalAdvance(string2));
+    QCOMPARE(fm.horizontalAdvance(string3), fm.horizontalAdvance(string4));
+    QCOMPARE(fm.boundingRect(string1).width(), fm.boundingRect(string2).width());
+    QCOMPARE(fm.boundingRect(string3).width(), fm.boundingRect(string4).width());
+}
+
 QTEST_MAIN(tst_QFontMetrics)
 #include "tst_qfontmetrics.moc"