Baseline font offset calculation changed between versions?

[gpatrut-matica]

Hello everyone,

We've been using ImageSharp for quite a while now, we even bought the commercial license and we've had no isseus so far, but recently we've had to update all the packages (previous versions were Fonts 1.0.0-beta19, Drawing 1.0.0-beta15 and ImageSharp 3.0.1). In our use case we had to draw some text at a specified x and y position with its baseline as the vertical position. In the old version, we did this by simply calculating a small offest to apply to the text options like this:

var yVariation = (float)(-font.FontMetrics.Descender + font.FontMetrics.LineGap) / font.FontMetrics.UnitsPerEm * font.Size; adjustedTextOrigin.Y += yVariation;

which worked fine when doing

canvas.Mutate(x => { x .SetDrawingTransform(rotationMatrix) .DrawText(drawingOptions, textOptions, Content, brush, new Pen(Color.Transparent, 1)); });
which produced the following result, the green cross signs the desired origin, after the offest is applied.

But after updating to the latests versions (Fonts 2.1.2, ImageSharp 3.1.6, Drawing 2.1.5) all the offsets are now wrong and the text is no longer correctly aligned.

This is how we do it in the latest version and the result

var yVariation = (double)(-font.FontMetrics.VerticalMetrics.Descender + font.FontMetrics.VerticalMetrics.LineGap) / font.FontMetrics.UnitsPerEm * font.Size; adjustedTextOrigin.Y += (float)yVariation;

Now, my first guess is that perhaps there have been some API changes that I've missed, in which case I would love if anyone could point me on what I'm doing wrong. Thanks.

[JimBobSquarePants]

Vertical metrics are used for laying out vertical text and are often different to the horizontal ones. Could you try the Horizontal metrics and report back? They should be unchanged.

[gpatrut-matica]

Sure, tried by changing everything to horizontal and still no helping it.

var yVariation = (double)(-font.FontMetrics.HorizontalMetrics.Descender + font.FontMetrics.HorizontalMetrics.LineGap) / font.FontMetrics.UnitsPerEm * font.Size;

At first I also thought it could be somehow related to the rotation matrix, but removing "SetDrawingTransform" does not help.

[JimBobSquarePants]

Ok, if you can post some more detail and the font I’ll have a look in the morning.

[gpatrut-matica]

Hi, I did a bit of more testing. Surely there's no issue with the metrics themselves as comparing the 2 between the versions nothing has changed, nor is anything wrong with the calculation itself as they both produce the same Y offest in the end.

I'm mainly using 2 fonts, OCRB and Arial Bold, but the issue is present in any font I'm using.

The only thing that I've done on my end is also changing the "TextOptions", from the method DrawText which I changed into a "RichTextOptions", but even then, the text options themselves were not doing much in the first place

RichTextOptions textOptions = new(font) { Origin = origin, HorizontalAlignment = SixLabors.Fonts.HorizontalAlignment.Left, VerticalAlignment = SixLabors.Fonts.VerticalAlignment.Bottom, };

Please let me know your thoughts on the matter!