CODEWITHSUNDEEP
qttextqmlqt5
Mark
Mark

Reputation: 5132

QML: binding loop when calculating Y position

Here my code:

FontLoader { id: font_bold; source: "qrc:/font/MyFont Bold.ttf" }
FontLoader { id: font_medium; source: "qrc:/font/MyFont Medium.ttf" }
FontMetrics { id: fontMetrics }

function getBaseline(fontFamily, fontPixelSize)
{
    fontMetrics.font.family = fontFamily;
    fontMetrics.font.pixelSize = fontPixelSize;
    return fontMetrics.ascent;
}

function getY(desiredY, fontFamily, fontPixelSize)
{
    return desiredY - getBaseline(fontFamily, fontPixelSize);
}

Text {
    x: 100
    y: getY(100, font.family, font.pixelSize)
    font.family: font_bold.name
    font.pixelSize: 96
    text: "foo"
}

Text {
    x: 200
    y: getY(150, font.family, font.pixelSize)
    font.family: font_medium.name
    font.pixelSize: 48
    text: "foo"
}

The goal is to calculate the actual y position from the desired one, removing the ascent offset of the current font, so the baseline will sit on the desired position.

I got this error for both lines y: getY(...):

QML QQuickText: Binding loop detected for property "y"

I don't see where is the binding loop. The y property is calculated as desired position - font ascent. Both are not related to y itself.

Upvotes: 0

Views: 210

Answers (1)

Amfasis
Amfasis

Reputation: 4208

This is because you are using the FontMetrics for both font's, changing the ascent continuously. Remember that you are binding a function to the y-position and thus every time the FontMetrics is set to another font it will trigger an update on the y-position of both Text's.

So, I propose to use two FontMetrics, one for the bold and one for the medium. 

FontMetrics { id: fontMetricsBold; font: font_bold }
FontMetrics { id: fontMetricsMedium; font: font_medium }

Text {
    x: 100
    y: 100 - fontMetricsBold.ascent
    font.family: font_bold.name
    font.pixelSize: 96
    text: "foo"
}

Text {
    x: 200
    y: 150 - fontMetricsMedium.ascent
    font.family: font_medium.name
    font.pixelSize: 48
    text: "bar"
}

Note, I don't have the fonts so I leave that as an exercise. Maybe configuring the FontMetrics has to be done differently with respect to the FontLoader.

Upvotes: 2

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