More SDF precision

[memononen]

For good quality, the distance scale has to be at least 32, that does leaves very narrow SDF band around the glyph.

Add support for e.g. uint16 texture so that there's wider bad, which can be used for effects (outline, shadow, etc).

Not sure how to handle color + SDF. Maybe separate SDF or higher 64bit rgba format.

[pjako]

There are also two other option to improve text rendering quality (among may other for sure):
MSDF -> with the downside that all color channels are used so you have to separate the color for emoji on textures

Improve sdf rendering itself (I have not tried that myself yet):
https://acko.net/blog/subpixel-distance-transform/

[memononen]

The SDF algorithm has based on "Anti-aliased Euclidean distance transform" (Gustavson & al), and is very similar to the one from Acko article. It calculates sub-pixel positions around the outline and the propagates those.

MSDF is too slow for runtime unfortunately. It requires to calculate boolean operations of the overlapping shapes, and the distance calculation is really slow. We're talking about 100-1000x slower.

My thinking of the quality is that:

1. we have regular AA rendering for those who need to go fast or want simple rendering
2. SDF who want to have scalable fonts
3. and one day there will be GPU rendering version

This post was more about the "reach" if distance values around the glyph boundary. With 8bpp, we only get a narrow bad of 6-8 pixels of distance values around the glyph. If you wanted to do outline effect, that is enough for maybe 3 pixel outline (the SDF glyphs get often scaled down). Having more bits, we should be able to have very wider narrow band.