Avoid synthesizing stretch on condensed font families

If an entire font family is condensed or stretched and we match by
family name, the default stretch factor of 100 will make the font
engine try to synthesize it back to medium stretched font.

The existing code is already made to deal with a stretch of 0 that is
no longer used. This patch reintroduces 0 stretch to indicate no
specific stretch has been requested. Specifically setting stretch to
100 on a QFont will introduce the old behavior.

[ChangeLog][QtGui][QFont] The default value of QFont::stretch() is
now 0 to indicate any default stretch is acceptable.

Task-number: QTBUG-48043
Change-Id: I574747f980fd4f9893df828818aae99a07b41623
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

1 files changed, 8 insertions, 7 deletions

diff --git a/src/gui/text/qfontdatabase.cpp b/src/gui/text/qfontdatabase.cpp
index 594d791e9c..cb1619e690 100644
--- a/src/gui/text/qfontdatabase.cpp
+++ b/src/gui/text/qfontdatabase.cpp
@@ -951,12 +951,14 @@ QFontEngine *loadSingleEngine(int script,
             }
         }
 
-        // If the font data's native stretch matches the requested stretch we need to set stretch to 100
-        // to avoid the fontengine synthesizing stretch. If they didn't match exactly we need to calculate
-        // the new stretch factor. This only done if not matched by styleName.
+        // To avoid synthesized stretch we need a matching stretch to be 100 after this point.
+        // If stretch didn't match exactly we need to calculate the new stretch factor.
+        // This only done if not matched by styleName.
         if (style->key.stretch != 0 && request.stretch != 0
             && (request.styleName.isEmpty() || request.styleName != style->styleName)) {
-            def.stretch = (request.stretch * 100 + 50) / style->key.stretch;
+            def.stretch = (request.stretch * 100 + style->key.stretch / 2) / style->key.stretch;
+        } else {
+            def.stretch = 100;
         }
 
         engine = pfdb->fontEngine(def, size->handle);
@@ -1219,7 +1221,8 @@ static int match(int script, const QFontDef &request,
     QtFontStyle::Key styleKey;
     styleKey.style = request.style;
     styleKey.weight = request.weight;
-    styleKey.stretch = request.stretch;
+    // Prefer a stretch closest to 100.
+    styleKey.stretch = request.stretch ? request.stretch : 100;
     char pitch = request.ignorePitch ? '*' : request.fixedPitch ? 'm' : 'p';
 
 
@@ -2740,8 +2743,6 @@ void QFontDatabase::load(const QFontPrivate *d, int script)
     }
     if (req.pointSize < 0)
         req.pointSize = req.pixelSize*72.0/d->dpi;
-    if (req.stretch == 0)
-        req.stretch = 100;
 
     // respect the fallback families that might be passed through the request
     const QStringList fallBackFamilies = familyList(req);