Fonts not rendered with subpixel antialiasing

[gordonbrander]

Here's a screenshot of text rendered in Servo. (I've used a loupe app to magnify the text so you can see the antialiasing pixels). The text is rendered without sub-pixel antialiasing.

Here's the same page rendered in Firefox. Fonts are rendered with sub-pixel antialiasing.

You can see a significant difference in the resulting text. The text in Servo appears "thin" and weak, whereas text in Firefox, Safari and Chrome has a rounder, fatter feel.

cc @metajack

[yump]

I don't think it's just a lack of subpixel AA. That shouldn't make a difference to the weight of the font. Either the greyscale AA renderer is not gamma correct, or it's using (eugh!) hinting.

[cbrewster]

Possibly fixed by #11103?

[raphlinus]

There's definitely RGB subpixel rendering present in the Firefox screenshot. It also looks like there's anemic gamma in the Servo screenshot. (Many people consider adjusting gamma to be linear-intensity to be "correct" but I disagree with that). It doesn't look like there's a problem with over-hinting, but it's hard to say for sure.

See btw https://www.freetype.org/freetype2/docs/text-rendering-general.html for a little more background on gamma and subpixel AA.

[notriddle]

Note that I have grayscale AA turned on everywhere. Servo's doing something else wrong, my guess is it's doing anti-aliasing twice or it's simply grabbing an overly-thin font.

[jonathandturner]

I'm also seeing this. When the browserhtml startup screen is resized, you can lose the expected anti-aliasing on the fonts.

At some sizes (closer to expected):

At other sizes (notices how font rendering loses aliasing/parts of the font render):

[nox]

I cannot reproduce this anymore.