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Comment by katastic | Hacker News Reader

> That requires much higher throughput, which causes much of the added latency on the display end.

That's not all the reason. More pixels pushed would only increase latency if the CPU/memory/etc wasn't faster than the older computers.

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People demand 60fps, so systems prioritize throughput over latency. See all the layer-based systems like coreanimation.

Most old console and arcade games ran at 60fps without any abstraction layers. 60fps is the bare minimum, not a special requirement. You can already buy 240Hz monitors.

Sure, but they pushed way fewer pixels with way fewer colors.

The main benefit of layer-based systems is latency, not throughput. Prerendered layer contents give you lower latency (and more consistent latency, which is usually more important perceptually) when scrolling, because you only have to adjust the positions of layers.

Fast scrolling of prerendered layers is what I mean with throughput. You can move layers around quickly as long as their contents don't need rerendering.

Yeah, this is actually a super-complicated tradeoff. Whether layers are a win or not is largely a function of how much of the screen can be cached in the layer and how much needs to be re-rendered, so in the scrolling use case a function of how fast you're scrolling, and of course how long it takes to re-render the content. Once your scroll speed exceeds the rate at which new content can be rendered, the experience degrades.

My conclusion is that if being able to re-render the content consistently in under one frame time is feasible, it's a win over layers. Fortunately, this is possible if you're willing to write fast code to render on the GPU.

There's a lot more complexity to this based on whether compositor latency is optional. Generally if you go fullscreen you can bypass the compositor. This is feasible for games but much less so for terminals and editors. I think that in some cases on Windows a swapchain can be promoted to a hardware overlay, and there you also get the opportunity to save one frame of latency. I think we'll see more of this in the future.

I'll write about this in more detail (with measurements) soon.

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