That said, I'm obviously really excited about this project. :) I feel strongly that it's the right from-scratch, modern approach for painting Web content. Happy to answer any questions.
There was one screenshot of Firefox included but it seemed to cherry pick the longest paint and didn't offer any explanation of how to compare it or which Servo+Webrender numbers to compare it to.
Servo uses the same painting backend as Firefox does: Moz2D (also known as Azure). Moz2D is itself an abstraction layer over Cairo, Skia, Core Graphics, and Direct2D. So comparing against current Servo is actually a good way to compare against Firefox and Chrome in CPU painting mode: it's using the same painting backend as both of those browsers and eliminates any noise that results from layout differences.
The most important thing to note is that the overall approach is quite different from Skia-GL (Ganesh). Skia is largely an immediate mode API (with a few retained-mode-style optimizations available with SkPictures, but the overall approach is immediate). WebRender (preliminary name), however, is a fully retained mode API and has no immediate mode at all, allowing it to focus on aggressive optimizations like "strength-reducing" clipping regions and Z-buffering opaque content for improved batching. This is a tradeoff, and it'd be easy to construct pathological cases in which one API or the other performs better. What we need to find out is which wins on real-world content, and while our early results are promising (and intuitively it seems highly probable that a retained mode API will win for CSS and the DOM), there's a lot more investigation that needs to happen before it'll be a slam-dunk case.
Out of curiosity, given that both Cairo and Skia run on all platforms Firefox does and have GPU-accelerated backends, why abstract over more than one of them rather than picking one and optimizing it for all platforms?
Switching to only GPU I think implies the need for at least a reference GPU backend such as mesa.
If not for the (very reasonable) expectation that things like "print to PDF" should produce vectors and selectable text rather than raster images of pages, you could render pages for printing using GL, too.
It could be great for other rust libraries, apps and games. None of them have subpixel rendering at the moment AFAIK and that's super easy with distance fields and real important for appearance.
Signed distance fields are great for animated text, but they also have a couple of disadvantages - they generally produce lower quality output than Freetype at small glyph sizes, and the signed distance field is more complex to generate at start, which slows down initial page rendering. Given that 99% of web pages are static, it's a harder sell. Maybe some sort of heuristic based switching would work.
Edit: signed distance field font rendering? Nice
Essentially everything but font rasterization (assuming you don't count image decode as part of painting). The major trick here is to avoid vector graphics, since you don't need a full-blown vector graphics library to paint common CSS.
> signed distance field font rendering? Nice
Note that this isn't integrated yet; it's a pile of experimental code, and I have some lingering doubts about its performance. But I would love it if we (or someone else!) can make it work!
You're saying that WebRenderer should work for faster for anything but vector graphics.
Is there a risk that it's optimizing for todays/yesterdays use cases?
But I don't really want to debate this here, as it's somewhat off-topic. And there are only so many ways to draw a button, SVG or not. WebRender is really good at drawing buttons. So there's a possibility that we could use the same technique, just extended, for SVG.
Indeed. Care to suggest one that's accurate and neutral? (In the meantime we'll take out the word "impressive".)
Congratulations on the ongoing work, too!
<nonsensationaltitleforhn>(Though this is somewhat belated--since it took 4 days, I suspect you'll never see this. I'd be interested to know if I'm wrong; please speak up in that case!)