Calculation of FontFamily.Baseline in WPF

Question

Hi,
I'm trying to reproduce in WPF the behavior of a Silverlight TextBlock, but the baseLineOffset is giving me problems.
The formula used by Silverlight looks quite easy:
max height of the characters in the font (aka Win Ascent) / Units per em * font size.
For example the Arial font have a Win Ascent of 1854 and is defined at 2048 units per em. So for a FontSize of 1 I get
1 * 1854 /2048 = 0.9053
But in WPF for the Arial font the FontFamily.Baseline is 0.9217
"Magically" in WPF the Arial font have an Ascent of 0.9053, but it doesn't work for all fonts. For example I'm often using a font called Tina Black.
In Silverlight it's BaseLineOffset is calculated as 1 * 800 / 1000 = 0.8
In WPF the FontFamily.Baseline is 0.8 also but the Ascent is 0.921875
Another example with the font "Salsbury" :
In Silverlight it's BaseLineOffset is calculated as 1 * 957 / 1000 = 0.957
In WPF the FontFamily.Baseline is 0.9706 and the Ascent is 0.921875
So my question is : What is the formula to calculate FontFamily.Baseline in WPF and/or calculate the BaseLineOffset found in Silvrlight ?
Thanks for your help.

Answer 1

Hello Sovitec,
Since .NET is now open source we can search for the result from this site:
http://referencesource.microsoft.com/
So when searching for FontFamily.Baseline
We can see this property:
/// <summary>
/// Distance from character cell top to English baseline relative to em size.
/// </summary>
public double Baseline
get
return FirstFontFamily.BaselineDesign;
set
VerifyMutable().SetBaseline(value);
And for BaselineDesign, we can see some related code and I think you can take them as your reference, for example:
/// <summary>
/// Distance from character cell top to English baseline relative to em size.
/// </summary>
public double Baseline(double emSize, double toReal, double pixelsPerDip, TextFormattingMode textFormattingMode)
if (textFormattingMode == TextFormattingMode.Ideal)
return ((IFontFamily)this).BaselineDesign * emSize;
else
// If the composite font has a pre specified Baseline then we respect it in calculating the
// baseline but we round it since Compatible metrics are pixel aligned.
if (_fontInfo.Baseline != 0)
return Math.Round(_fontInfo.Baseline * emSize);
// If the composite font has no specifed Baseline then we get the compatible font metrics of the
// first fontfamily in the composite font.
else
return GetFirstFontFamily().Baseline(emSize, toReal, pixelsPerDip, textFormattingMode);
http://referencesource.microsoft.com/#PresentationCore/Core/CSharp/MS/Internal/Shaping/CompositeFontFamily.cs,177
But actually I think you may interested in the formula about FormattedText.Baseline:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/4ea51d1b-84fb-42d3-ada3-afb776bd38d9/how-to-determine-the-baseline-of-a-formattedtext-object?forum=wpf
Best regards,
Barry
We are trying to better understand customer views on social support experience, so your participation in this interview project would be greatly appreciated if you have time. Thanks for helping make community forums a great place.
Click
HERE to participate the survey.