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Comment by RyanRies | Hacker News Reader

Sorry I haven't gotten an opportunity to watch the video yet, so maybe the video addresses this, but if I may please ask... why would you want to render a webpage at several hundred FPS? Unless FPS is a multiple of your monitor's refresh rate, (i.e. vsync) it won't look good. You could use the extra time to do other background tasks instead of burning more CPU than you need to just to say you can do 1500 fps...

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> why would you want to render a webpage at several hundred FPS?

You wouldn't (and the demo shows 60 fps), the point's rendering absolutely definitely most certainly isn't a bottleneck anymore, which gives more time for

> other background tasks

or other foreground tasks like the page itself (and the ability to increase its complexity since you don't need to budget for rendering anymore), or just letting the CPU go to sleep (could help whatever browser ends up with servo tech finally compete with Safari when it comes to energy consumption).

It also gets you in a good place for VR (2 displays and 90Hz minimum IIRC from a Carmack note?) or for ever-larger displays (though that ties into the complexity thing, displays also get finer and denser on mobiles)

> Unless FPS is a multiple of your monitor's refresh rate, (i.e. vsync) it won't look good.

Well you could do that with several hundred FPS anyway, 300FPS is a multiple of 60Hz, so's 1540FPS for 140Hz.

Thank you for the clarification - makes sense.

The video shows off several web pages with complex CSS animations that run at a reasonable FPS in Servo, but run at less than 1 FPS on current browsers. These pages were created specifically for this purpose, but that's the general thrust of it: it's not so much that you _want_ your pages rendering at hundreds of FPS, but that you can get more complex things done in a reasonable FPS. It also proves that Rust code can be _fast_, which is always something that is important for systems languages.

I know much less about this aspect, but I also understand, vaguely, that there are battery savings here as well? When you can get things done quickly, you can idle the CPU again, saving power. I believe that's the thrust of it.

If you can render at several hundreds of FPS, then you certainly can render at 60FPS or whatever you need. Rendering is not always silky smooth on websites using lots of CSS; this lets you render more complicated things with very little effort at 60FPS. Of course, you won't actually be rendering at 100FPS.

(It also moves computation off the CPU, so the CPU can be used for better things)

In practice, you want more than 60 FPS for painting because restyling is frequently slow. (Also, display list construction is sometimes slow, but there's active work to dramatically improve that.)

The FPS is obtained by seeing how much GPU time was spent on a frame. They're not actually going to refresh the image on screen that fast. Higher FPS means that the GPU is not being taxed and more complex rendering is possible, or you have more time to do other tasks.

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