Comment by HughParry

7 hours ago

I wonder why the firefox CSS rendering engine prefers to smooth out. Looks like a dramatically different implementation, but maybe that's just because it's an edge case of rendering

9 comments

HughParry

Reply
chrismorgan  35 minutes ago

Stroke expansion is a complex topic, with more than one reasonable result (subjective preferences), and a whole lot of corner cases and incorrect answers.

Firefox has chosen to expand based on distance at all points, which is one of the reasonable answers and probably the most general one; a cusp then expands to a curve.

The others have chosen to retain cusps, which can be a reasonable answer and I believe is a lot cheaper to compute; but degenerate cases abound as you expand past the feature size (distances between nodes), so that by the fourth red ring it’s obviously incorrect.

Box shadows are another case where expansion occurs: the fourth length parameter, spread distance. If the corner is a cusp, the shadow corner will be a cusp. If it’s rounded, the shadow corner will be rounded. See https://drafts.csswg.org/css-backgrounds/#shadow-shape for some helpful diagrams. A sneaky trick: .1px border-radius means the box still looks square, but the expanded shadow will curve. Sometimes useful. But back on the original content of the article—if you use a font with microscopic curves instead of cusp nodes, Chromium/Safari will look more like Firefox.

myfonj  11 minutes ago

Ran into this discrepancy myself. On top that, what seemed also odd to me were the "dots" (tittle, period, semicolon) where oversized becomes hollow in the middle, like it cancels out itself. No other shape I've tried did that. And browsers surprisingly agreed on this.

Made few shots and playground for that back then: https://x.com/myfonj/status/1870178380831732160

zokier  5 hours ago

While I don't entirely love the rounding effect of firefox, I feel Chrome interpretation is just wrong in creating spurious spikes. Intuitively for the asterisk shape I'd expect the outline to go towards a plain hexagon, something that neither browser accomplishes.

EMM_386  2 hours ago

I think Firefox applies more aggressive subpixel rendering and path smoothing before stroking. It resamples the glyph outline path at a higher precision level before handing it to the stroke algorithm.

voidUpdate  5 hours ago

firefox looks like an SDF (shortest distance to the object), I'm not sure what the chrome one is...

  • danbruc  5 hours ago

    I would assume they are just drawing the outline, not performing any distance calculations, and the differences are just a result of different linejoin choices. [1]

    [1] https://www.w3.org/TR/fill-stroke-3/#stroke-linejoin

    • voidUpdate  3 hours ago

      I'd imagine that at some point during the text rendering process, they have to generate an SDF of the text they want to render (it's what I did when I wanted to manually render text anyway). If they do, then they can generate the extra text-width lines basically for free, just fill everything with distance less than the property.

      I may be entirely wrong though, I don't know in detail how browsers render stuff