XCB: Completely bad font rendering when text changed in QML Text item using TTF font via FontLoader and some specific properties were provided

When text in Qml Text is changed during normal program run (after all Component.onCompletes) and some specific properties are provided – completely wrong font rendering happens. (see image I enclosed as attachment)

• Place DejaVuSansMono.ttf from http://dejavu-fonts.org/wiki/Main_Page next to qtbug44279.qml (or move QML file into dejavu-fonts-ttf-2.34/ttf and run from there)

To reproduce bug two Qml Text elements are at least needed. Moreover these Text items must have all three specific properties filled:

1. renderType = Text.NativeRendering
2. font.pixelSize
3. font.family

As for 2. (pixelSize) my investigation confirmed that pixelSize must be at same value in at least two Texts in order to observe bug and additionally must have value below 10

As for 3. (family) for now I managed to reproduce bug only on DejaVuSans font familly (I tested a few of them: you can get it e.g. from: http://dejavu-fonts.org/wiki/Main_Page)

I have also observed that setting antialiasing to false in any of these two Texts preserves from bug occur too.

I discovered that issue in fairly big Qml project but I managed to make minimal example (.ttf font file next to .qml file needed):

import QtQuick 2.4
import QtQuick.Controls 1.2

Rectangle {
    width: 100
    height: 100
    color: "lightgrey"

    FontLoader {
        id: fontLoader
        source: "DejaVuSansMono.ttf"
    }

    Column {
        anchors.top: parent.top
        anchors.horizontalCenter: parent.horizontalCenter

        Button {
            text: "Show BUG!"
            onClicked: text2.text = "This is a bug!"
        }

        Text {
            id: text1
            renderType: Text.NativeRendering
            font.pixelSize: 10
            font.family: fontLoader.name
            text: "text"
        }
        Text {
            id: text2
            renderType: Text.NativeRendering
            font.pixelSize: 10
            font.family: fontLoader.name
            text: "!"
        }
    }
}