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Comment by thechao | Hacker News Reader

GPUs derive most of their parallelism from emitting rows of related “quads” (the smallest unit of the screen that supports a difference operator). 2D graphics are “chatty” in window sizes that are more like 5–10 units in diameter. It’s hell on HW perf. To make things worse, 2D applications usually want submillisecond latency. A GPU driver/hw stack will struggle to get latency below 1–2ms. When there’s lots of multipass rendering (which is a thing 2D also wants a lot of), latency can to 10+ ms.

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Well said, thanks. It's also a goal of this work to do compositing inside the "fine rasterizer" compute kernel, to avoid multipass as much as possible. Of course, in the general case for stuff like blur that's hard, but that's one reason why I've been working on special cases like blurred rounded rectangles, which I can render pretty much at lightspeed. (It's not integrated into the current code but would be quite easy)

What does latency have to do with 2D? Are you suggesting UI toolkits are writing GPU commands synchronously? You should fill display list, fire it and forget about GPU until the next update.

Pen drawing for UIs. The ideal case is to update a small portion of the screen at about 240hz, to provide a good simulation of pen/pencil feedback. Really, your latency envelope should be on the order of the propagation of sound through the barrel of the marking device, but screens don’t update that fast.

Surely >95% of screens out there right now are running at 60Hz, so 240Hz "pen drawing" is pretty niche and not a priority?

And >95% of screens don’t support pen drawing.

I expect a screen that supports or is designed for pen drawing to be somewhat more likely to be above 60Hz. All of these things are niche things that not many care about, but in any case, it’d be nice to be able to do better. And like with Formula 1 race cars, benefits from high-end techniques tend to trickle down to other more mainstream targets in time.

You are probably thinking https://www.youtube.com/watch?v=vOvQCPLkPt4

Bottleneck is in the input layer. While using a desktop computer look at the mouse cursor, now move the mouse - hardware accelerated 2D graphics, imperceptible latency.

Low latency thru orthogonal multiplexing https://www.youtube.com/watch?v=t1VcC9_yhc0

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