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Comment by nh2 | Hacker News Reader

I don't think so. This is just what happens when you redraw the screen.

Doing it 30x more frequent than needed costs more, no matter if it's only 1 pixel.

This problem is not isolated to me or to just one machine. Check out the chromium bug about the tab loading spinner, for example. It is a "simple" spinner as well.

Or the Zed editor, which spams screen redraws even when nothing changes at all, so it has high GPU usage for still picture.

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It should not cost a visible fraction of CPU/GPU to update a little sprite even at 30fps.

But it does. The GPU rerenders your entire screen with all its pixels, even if you change only one. The only thing you can do to avoid that is to not ask the GPU to render a frame. For that you need to reduce FPS.

You need a fairly modern laptop to change the screen refresh rate like you're describing. Older laptops do 60Hz (or whatever) refreshes at all times, they can't change refresh rates like that. The compositor should only paint relevant pixels on the screen.

I'm sure that some spinners are horrible and peg the CPU, but unless your machine is older than ~2018 there is something wrong with your setup if spinners (and not intense operations behind them) cause your battery to suffer.

I'm not describing anything about screen refresh rates, which I'm pretty sure are 60 Hz on my laptop even when the CPU+GPU are at 0% and don't draw anything. Compute != monitor refresh.

Compositing is fast and energy efficient. The screen should not be doing a full refresh of the entire display for an isolated change.

Did I totally miss how damage tracking has gone out of fashion, or what do you base this on?

The damage tracking doesn't seem to be effective at reducing the computational cost. Measurement:

Opening https://nh2.me/low-fps-spinners/smooth-spinner.html it doesn't matter if I zoom the spinner to 25% or 500%: Despite the 400x difference in pixels redrawn, the "GPU Process" CPU usage in the "Browser" tab of the Chromium Shift+Esc task manager is equally high.

It only scales down the cost when reducing the FPS.

I am also mystified at how far things have fallen.

I miss the 1 update per second animations of ye olden times, even if it would be ugly as sin in a modern product.

I'm on mobile so I'm not able to check, but can the will-change and contain attributes reduce the cost?

Avoiding unnecessary browser repaint of the rest of the page is a basic technique and often already done correctly. If people don't do that, it's just ultra-bad.

But do really have the CPU/GPU go idle, you need to not use them; the only solution to that is to show still images, aka reduce FPS.

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