Rendering: VSFilter/GDI draws underline/strikethrough using clockwise-wound rectangles

[rcombs]

Screenshots

VSFilter examples:

(Gandhi Sans)

(Gandhi Sans on top, Arial below)

Description of the issue

We can see here that the portions of the strikethrough line that overlap with text are inverted to transparent. This is because GDI implements underline and strikethrough by adding clockwise-wound boxes to the glyphs, meaning that counterclockwise-wound fonts (like Gandhi Sans) will generally have a 0 net winding count at those overlap points.

libass version

218dace

Is it a regression?

Nope

ASS Sample

{\fnGandhi Sans\u1\s1}TEST TEXT

https://www.fontsquirrel.com/fonts/gandhi-sans

Special Fonts

I uploaded or linked to the required font

System Information

(Not OS-specific)

Log

N/A

Additional info

I honestly don't think we need to emulate this behavior; I just think we should document it somewhere.