I am using Harfbuzz and Freetype to render text. In Korean, when there is some English text in some vertical text, it should be rendered horizontally then rotated 90 degrees. Like this:

Proper Rendering

So, to try to accomplish this I have shaped two pieces of text with Harfbuzz. One vertical, and one horizontal. Then, I have rotated the horizontal text by 90 degrees. This is what I get:

What I get

You can see the problem is that the horizontal text isn’t in line with the vertical text. This is because the vertical text has a negative x_offset so that the characters all line up perfectly. If I ignore the x_offset this is what I get:

Ignoring x offset

So now the two line segments are properly aligned, but of course now the vertical text is incorrect because I’ve ignored the x_offset.

If I could reverse the direction of the x_offset then the result would be what I want. Unfortunately I don’t know if there’s a property of the freetype font or something in harfbuzz that corresponds to the width I would need to do the x_offset in the opposite direction.

I’m probably just missing something simple, but does anyone know how I can do this?