How to determine the BaseLine of a FormattedText object?

Question

For the internal logics of a custom control, I would like to know how the BaseLine property of a FortmattedText object depends on the FontSize, the FontFamily.LineSpacing and the LineHeight properties. Is it possible to give a general formula for that?

thanks,
Rutger.

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Rutger Koperdraad.

Answer 1

The Baseline property is the distance from the
top of the font characters to the baseline as a fraction of the font size. For a
FontFamily object based on Times New Roman, for
example, the Baseline property is approximately
0.91. Multiply that by the font size of 144 and you get 131.

The FontFamily class also includes a property
named LineSpacing, which is the suggested value to use for
spacing successive lines of text as a fraction of the font size. LineSpacing is typically greater than 1 because the
em size of a font is the approximate distance between the tops of the ascenders
and the bottom of the descenders. Line spacing must also account for capital
letters than contain diacritical marks.

Applications = Code + Markup: A Guide to the Microsoft® Windows® Presentation Foundation

By Charles Petzold Chapter 29

Answer 2

Thanks, Xperiandri.

Actually, I found the precise formulas after some trial and error. If the LineHeight property of the FormattedText object is not set, the BaseLine property is determined by the font size and the BaseLine property of the font family

       FormattedText.BaseLine = FontFamily.BaseLine * FontSize

If the LineHeight property of the FormattedText is set, the formula changes to

       FormattedText.BaseLine = FontFamily.BaseLine * LineHeight / FontFamily.LineSpacing

The first formula can be derived from the second by substituting the default line height (FontFamily.LineSpacing * FontSize).

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Rutger Koperdraad.