4 ms·

Thanks for writing these updates, Raph - back in 2019, your early piet-gpu blog posts helped to reignite my interest in 2D rendering. I recently learned that yo

Thanks for writing these updates, Raph - back in 2019, your early piet-gpu blog posts helped to reignite my interest in 2D rendering. I recently learned that you also invented Cairo's trapezoidal-coverage algorithm, which was my original introduction to anti-aliased 2D rendering ten years ago! Over the last few weeks, this interest has finally spiralled into an attempt to develop a renderer of my own. I've come up with a design which seems promising, but I do have one question for which I haven't yet found a good answer: It seems to be common wisdom that 16xMSAA has unacceptable quality for 2D rendering. In practice, though, I'm struggling to find any test-cases where I can differentiate 16xMSAA from 256-shade analytical AA with the naked eye. The only exception has been fine strokes (e.g. downscaled text, or the whiskers on this Ghostscript tiger [0]), which tend to "shimmer" or "sparkle" as they move. Does MSAA have any other common failure modes that I should be aware of? [0]: https://threejs.org/examples/webgl_loader_svg.html https://threejs.org/examples/webgl_loader_svg.html

raphlinus 5y ago
Thanks for your response! I write these blog posts for you and others to understand the technology better. I didn't invent the Cairo trapezoidal algorithm, I think that was mostly Carl Worth, maybe Keith Packard, but I certainly did do one of the earliest analytical area algorithms in the free software space, which I know inspired other work. It's been quite a ride, I went back and looked at my early work[1], and thought it was impressive that I could render the tiger in 1.5s. Now I'm seeing times in the 300µs range on discrete graphics cards. 16xMSAA is pretty good, and I would say is definitely good enough for most vector art. I consider it not quite good enough for text scaling, and anything less than 16x not acceptable. Desktop cards shouldn't have much trouble with it, but mobile devices might not be capable of it or able to deliver adequate performance. Of course the upside of MSAA is that it's much easier to solve conflation artifacts, so I imagine we'll end up with some variant of it in additional to the analytical AA; and the latter will continue to be used for almost all glyph rendering. [1]: https://www.levien.com/svg/ https://www.levien.com/svg/

raphlinus 5y ago

Thanks for your response! I write these blog posts for you and others to understand the technology better. I didn't invent the Cairo trapezoidal algorithm, I think that was mostly Carl Worth, maybe Keith Packard, but I certainly did do one of the earliest analytical area algorithms in the free software space, which I know inspired other work. It's been quite a ride, I went back and looked at my early work[1], and thought it was impressive that I could render the tiger in 1.5s. Now I'm seeing times in the 300µs range on discrete graphics cards. 16xMSAA is pretty good, and I would say is definitely good enough for most vector art. I consider it not quite good enough for text scaling, and anything less than 16x not acceptable. Desktop cards shouldn't have much trouble with it, but mobile devices might not be capable of it or able to deliver adequate performance. Of course the upside of MSAA is that it's much easier to solve conflation artifacts, so I imagine we'll end up with some variant of it in additional to the analytical AA; and the latter will continue to be used for almost all glyph rendering. [1]: https://www.levien.com/svg/ https://www.levien.com/svg/