Comment 19 for bug 1475205

Copy bug description https://bugreports.qt.io/browse/QTBUG-47547 and paste here.

if developer specifies font family with Non-Regular style, potential risk to encounter Chinese characters are missing in some cases .
E.g

import QtQuick 2.4
import QtQuick.Controls 1.3

ApplicationWindow {
    visible: true
    width: 1280
    height: 800

    Text {
        anchors.centerIn: parent
        text: "系统设置"
        font.family: "Ubuntu"
        font.pixelSize: 69;
        font.weight: Font.Light
    }
}

Regarding the code snippets above.
For Chinese characters, QFontDatabase will use fallback font family("Droid Sans Fallback") with "Light" style when add font Glyph.
 since QFontDatabase checks if default style(Regular) of fallback font family "Droid Sans Fallback" is same as font style specified in qml(Font.Light). And QFontDatabase::isSmoothlyScalable will return false in such a case, which results in scene graph will
use QSGDefaultGlyphNode when createGlyphNode is called. Issue happens.

However If scene graph doesn't prefer NativeGlyphNode and create GlyphNode based on Distance Field technique. It works fine.
https://drive.google.com/open?id=0B2H9ECPSSfqIMzhvU1hPUWNlWnc

Need to only check styleKey when foundry->styles == specified style
Will see feedback from Qt guys.
Thanks.

PS: more test cases and patch can be found on https://bugreports.qt.io/browse/QTBUG-47547
Also I think we can override bool QBasicFontDatabase::fontsAlwaysScalable() method in qlinuxfbfontdatabase.cpp under qtbase/src/plugins/platforms/ for platform independent purpose.