hb-ft does not correctly scale bitmap-only fonts

[behdad]

Like NotoColorEmoji for example.

[behdad]

In the meantime, using hb-ot font funcs works. Eg. --font-funcs=ot

[behdad]

If anyone wants to attach this, here's the logic in cairo that picks up the best strike and uses that size to call FreeType, and scaling results:

https://github.com/behdad/cairo/blob/color-emoji/src/cairo-ft-font.c#L726

It's quite doable. Just a bit of head-scratching to figure out where to do it to minimize changes.

[khaledhosny]

Now that FreeType has FT_Get_Transform() (#2428), what do we need to do here?

[khaledhosny]

It seems to have gotten worse:

$ hb-view NotoColorEmoji.ttf  123 --font-funcs=ft
hb-view: Failed: invalid matrix (not invertible)

[behdad]

It seems to have gotten worse:

$ hb-view NotoColorEmoji.ttf  123 --font-funcs=ft
hb-view: Failed: invalid matrix (not invertible)

Weird. I don't remember any changes that would trigger that.

Let me try to tackle this.

[behdad]

This is very peculiar. My system hb-view doesn't have the change of behavior whereas if I compile the same version (4.0.0) I get the invalid matrix error. With same system freetype and cairo.

[behdad]

The error message is from cairo FWIW.

[behdad]

I almost have a fix here: #3726