Don't animate height

https://www.granola.ai/blog/dont-animate-height

by birdculture • 1 year ago

460 268 1 year ago

granola.ai

andrewstuart• 1 year ago

I seem to recall reading that Chrome has height transition optimizations coming.

jtangelder• 1 year ago

Wondering what the performance of a simple animated gif would be, instead of the composite layer transformations.

nightpool• 1 year ago

GIFs historically were pretty unoptimized from a display perspective (as anyone with a moderately-active Tumblr dashboard could tell you), so I wouldn't be surprised if it was worse.

xp8417• 1 year ago

I disagree. The height of a DOM element is much more expensive to recompute as this article shows than a single element which gets frames swapped out with static images. The latter can be guaranteed to never impact any other part of the document. The end result of either is that the pixels in the animated area need to be recomputed, and end result which will be the same for both, but a GIF will have no further impact on anything else whereas resizing DOM elements has side effects that have to be constantly updated and checked for which scale with the number of sprites you're animating (unlike the GIF bitmap which is gonna be 'flat rate').

Likewise, for a tiny animation, having the frames of the GIF in memory and blitting them onto the screen in sequence sounds like orders of magnitude less CPU/GPU than performing all the ridiculous math-based transforms over and over again.

The Tumblr example is not instructive here because those were frequently many many frames, very colorful (often photos), and/or large in dimensions, taking up a ton of memory which was probably the main problem causing our browsers to choke. This would be none of those things.

evan_• 1 year ago

Or if you need to actually control it, an SVG or <canvas> based animation

dylan6047• 1 year ago

If the bars are not related to actual data and are purely just pre-canned animation, the gif would just come with additional file size for a one time cached type of download. If the bars do need to be animated to real-time data coming in, then the gif would not be the right fit for that need.

threetonesun2• 1 year ago

Can't imagine anyone is deriving much information value from a visualizer with 3 bars. Apple Music has a similar animation and it will start bouncing when you click play, while the music is clearly downloading and there's no sound.

xp8417• 1 year ago

I've almost never seen these tiny icons to have any actual useful information being conveyed (meaning they are tracking amplitude or pitch). They're usually purely decorative, or boolean in function, meaning you can see they're flat if you are completely silent or they're bouncing around if not silent.

You can have 2 GIFs for "silent" and "sound happening" if one cares to truly indicate if it's picking up sound / playing sound, and switch between them. Will be 1000x simpler and 99% fewer lines of code to maintain forever.

norskeld• 1 year ago

Personally, I'd be annoyed by both the resource-consuming animations and the blurry GIFs/canvas. Infisical does use the latter (canvas) for icons in their UI, and I somewhat hate it. I'd rather look at crisp, but static icons.

jasonjmcghee2• 1 year ago

Canvas should never be blurry. If it is, something is doing a bilinear upscale. I'd guess someone forgot to take the scale factor of your display into account.

Or there are images being used in the canvas, which would defeat the purpose for the use case you described.

zahlman• 1 year ago

... Why does a "note-taking app" have an "audio volume visualizer"???

Edit: kinda funny how I asked what I thought was a reasonable question and expressed entirely understandable confusion; got an upvote almost right away; then got multiple downvotes after people answered the question — as if it somehow suddenly became obvious why I should have expected such a feature a priori.

samgutentag• 1 year ago

The product makes notes from the transciptions, so this animation isnt wildly off base to have

satvikpendem• 1 year ago

Transcribed voice notes

trafnar• 1 year ago

Their app listens to your calls and transcribes things. I think this visualizer helps indicate when it is actively listening.

Levitating5• 1 year ago

So why does it need to be animated, a color indication could've worked just as well. Or the stop button right next to it...

h1fra• 1 year ago

dumb question: would putting the parent div in absolute positioning solve the compositing?

Eric_WVGG4• 1 year ago

It already was. The whole point of this is that any height change is part of an expensive phase of the rendering pipeline.

HWR_143• 1 year ago

What amazes me is that so much a M2 Mac's resources would be used to render a website even if it rendered everything from scratch. There is almost no graphic content compared to a video game produced decades ago, and they would easily render a frame in 1/2 the time on decades old hardware

hombre_fatal• 1 year ago

Well, raw graphical content is the easy part.

A live layout tree that has to be repainted and composited yet intersect with arbitrary layers like an accessibility tree and what would naively be N:N style calculations is completely different architecture.

Consider examples where people toy with the concept of replacing the DOM with a canvas but basic things like text selection don't even work anymore.

zuhsetaqi• 1 year ago

Keep in mind that the percentage in Activity Monitor is 100 % per core, so a 10 core CPU can go up to 1000 % usage. So 60 % means 60 % of a single core not of the whole CPU.

pohuing• 12 months ago

And it's sensitive to dynamic scaling as well, isn't it? So it's possibly not 60% of a core at max clock, but maybe of a core clocked to 800mhz or something.

I fell for that shallow analysis myself once when I noticed just how apparently bad the gpu usage was for a big of animation in a web page, until I noticed my 30% load gpu still drew as much wattage as it did on idle.

socalgal23• 12 months ago

Videos game rarely do any complex dynamic layout. That is where all the time is going

JakeSc• 1 year ago

Great writeup. With LLMs doing an increasing amount of the coding now, it would be great for the browser or development environment to have built-in validations that enforce good performance. The coding agent (or human) would get direct, immediate feedback at development time that there's a performance threshold violation, at development time.

paulirish• 1 year ago

We're working on this within Chrome DevTools, similar to an MCP server with the signals you're describing.

alterom• 1 year ago

So, after all the optimization, they're using 6% of the CPU to display what amounts to a tiny animated GIF that 1990s PCs would have no problem with.

But it's vector graphics!, you might say. Yeah, like Flash, which ran fine on Pentium II, with plenty CPU cycles to spare.

Pardon me, and I don't say it lightly, but... WTF?!

smallpipe• 1 year ago

Yeah author congratulating themselves at the end because their note app is only using hundreds of millions of cycles every seconds, to do essentially nothing...

another_one_112• 1 year ago

I do miss flash, but we shall not forget that the performance boost came from low level access to the system (which made it a security risk).

Dylan16807• 1 year ago

I strongly doubt its ability to render a fast rounded rectangle needed that.

bob1029• 1 year ago

I would also suggest looking into the following in this case:

https://developer.mozilla.org/en-US/docs/Web/CSS/contain

https://developer.mozilla.org/en-US/docs/Web/CSS/will-change

There are hints you can provide to the browser that may have an impact in scenarios where you are animating layout properties.

bijection• 1 year ago

I was just starting a comment on this but you beat me to it! I believe

  contain: strict;

on the parent element would have been sufficient here.

webstrand• 1 year ago

I tested `contain: strict` on their color changing SVG and didn't see any difference. Profiler says it's still doing layout.

spankalee2• 1 year ago

CSS contain has made so many performance "truths" obsolete, but so few developers realize it. I've seen massive efforts to do things like port text editors to WebGL where rasterizing text is a huge pain where putting `contain: content` on the individual elements in the DOM version would have delivered most of the perf improvements.

Browser rendering engines are now sophisticated GPU-accelerated compositors. Absolute positioning with contain: strict removes basically all CSS layout from the perf equation, and you don't have to write your own compositor or line-layout! `* {contain: content}` and flex/grid gets you the good parts of HTML and very good performance.

dylan6047• 1 year ago

"What is Granola spending those cycles on? It's an Electron app"

Yup. Matches my experience with pretty much every Electron app. Great that the dev tracked it down, but every Electron app is a waste of...electrons

bitpush2• 1 year ago

Might be worth getting off of that high horse. You are not being very smart by saying 'akctually electron bad'.

You know what else was a waste of electrons? Your comment, and my reply.

dylan6047• 1 year ago

Your reply was not necessary though. Every electron app uses more of my computer's resources than when I use the same service through the web browser.

ASalazarMX2• 1 year ago

You could have a very, very long exchange of wasted electrons here to be in the scale of an Electron app starting up.

jasonjmcghee2• 1 year ago

Seems like a great use case for a tiny canvas instead.

Eric_WVGG4• 1 year ago

My head is sort of reeling from this. If height animations are that expensive today, imagine how expensive (and still commonplace) they were twenty years ago.

I fortunately quit animating height quite a long time ago in favor of similar transform techniques, but… wow, still crazy to learn the magnitude of this common operation.

moritzwarhier• 1 year ago

It's really simple. Don't animate layout, especially if your DOM is huge.

If your element floats absolutely positioned outside the layout flow, animating height would not be a problem.

And if the browser facilities for animating height/max-height, especially to/from auto, get better, it surely will become more common.

Right now, I wouldn't call it common. It's a common requirement, but only until you start to consider layout.

Fwiw, animating margin and padding is possible and has the capability to cause the same amount of jank as animating height.

Eric_WVGG4• 1 year ago

You can animate an absolute positioned div without it obviously altering what a normal person would call "the layout." That's not simple unless one is willing to dig very deeply into the how web browser rendering works. And really still not simple. Otherwise this article wouldn't have been written.

hbn2• 1 year ago

The heart of the issue isn't that animating height is expensive, it's the downstream effect of that animation repeatedly changing the page's layout and forcing redraws.

cvoss• 1 year ago

But it wasn't expensive twenty years ago. Twenty years ago people actually knew how to efficiently use their limited computational resources.

Eric_WVGG4• 1 year ago

so it wasn't expensive because people didn't do it? They did.

perilunar• 12 months ago

I actually did quite a bit of browser animation 20+ years ago. The trick was (as mentioned elsewhere on this page) to only animate absolutely positioned elements. Even back in the version 4 browsers you could animate hundreds of divs at 20+ fps on a decent computer (with JS of course — CSS animation didn't exist yet).

Liftyee• 1 year ago

This helped explain why my PC uses so many resources "with just a few webpages open". I didn't realise that graphical updates that seem so simple could be so resource-intensive.

dvt• 1 year ago

Is it just me, or have a lot of modern startups lost the plot? Imagine doing all this work for an element of your app which has nothing to do with its feature set. No one cares (certainly no customer) about an audio visualizer bar animation.

The post is also riddled with all kinds of misunderstandings, as well. For example, the authoritative language used to describe the differences between layout/painting/compositing is just simply untrue generally speaking (though it might be w.r.t. Electron/Chromium). The W3C does not care how you implement your rendering engine, and even bringing up the spec betrays a misunderstanding of how these things work.

In typical fashion, we see yet another grandiose blog post about fixing a "perf issue" for your hipster new startup that is essentially notepad.exe. Who funds this shit?

woodpanel• 1 year ago

This was my thinking, too.

Why distract users with giving an auxiliary feature so much prominence? Why wasn’t a GIF enough? Or just an SVG that consists of 3 frames?

Spending this much time on fixing this bug was worthwhile (at least it created a HN front page article) but the solution was not. 6% CPU usage is horrible.

xp8417• 1 year ago

Here's the part that makes me confused/angry: this is a flat style icon with maybe 4 or 8 colors displayed on a static flat green background. I could have built this 25 years ago with a single GIF with about 6 frames, that was a couple of kilobytes and would be performant on the (relative) potato computers we had then. With CSS you can easily make that GIF a background image and position it correctly in the <button> or whatever. Do it at 2x and scale it for retina sharpness.

But modern "web designers" feel the need to spend how long carefully crafting that CSS animation which adds dozens of lines of code to the codebase and burns a ton of CPU...why? Just because you can, I assume? The same reason the same people use embedded <svg> documents inside the HTML for simple icons like "edit pencil" or "close", wasting bandwidth instead of at least putting them into asset files that can be cached.

Frontend web "advancements" of the last 10-15 years, at least the way they are used, are mostly cancer in my opinion. I will allow for the usefulness of display: flex, and that's about it.

nawgz• 1 year ago

Yes you're right, most users LOVE barebones and classic websites, that's why HN is so popular and Reddit hardly has any users.

For that matter, do we really need colors? Just ship it with browser default styles.

seemaze• 1 year ago

Exactly this! I wish the entire web was easier to read on my e-ink device.

LastMuel• 1 year ago

I hear your snark, but Reddit isn't exactly a beauty contest winner.

xp8417• 1 year ago

I think it's funny that you think sites can't be attractive unless they include many megabytes of complex JS and CSS on every page. Craigslist lasted and was dominant a whole extra generation of the Web until Facebook Marketplace unseated it without even bothering with colors and certainly no animations. And FBM didn't win on clever animations and React UI complexity, it just won based on the fact that it was easier to detect Nigerian scammers since you can see when the buyer's FB account was created and a few other cues. Users don't care how clever your programmatic animations are. They hate how slow your site is. Look how much Jira sucks now. It's more sluggish on an M4 Pro than it was on my Core i5 in 2013 because of how much frontend bloat they've added in the meantime.

filleduchaos• 1 year ago

This seems like a rather knee-jerk response to someone arguing that they can build the same UI with less.

jakubmazanec• 1 year ago

GIFs don't scale well (including 2x version is not enough); with CSS (and SVG) you get crisp graphics at any scale. And of course you can use asset SVG files that are cached [1].

[1] https://developer.mozilla.org/en-US/docs/Web/SVG/Reference/E...

xp8417• 1 year ago

Citation needed for 'GIFs don't scale well' (in terms of dimensions. They certainly don't scale well when abused as idiotic versions of videos.)

Is this the frontend developer's version of "Postgres doesn't scale. Mongo is Webscale"?

Here's a 640x640 GIF. Scales just fine for me, to half-size or to 100px. I'm using a "Retina" screen. https://cdn-icons-gif.flaticon.com/6172/6172533.gif

panic• 1 year ago

Won’t the GIF also burn a ton of CPU? I’m not convinced it would actually be more performant than sliding textures around.

xp8417• 1 year ago

Try it yourself.

Here is a 640x640 gif: https://cdn-icons-gif.flaticon.com/6172/6172533.gif

That tab is using 4-5% CPU on my M1 Pro, and I also have a "GPU process" in my task manager, which is showing about 8% in the "CPU" column when it's onscreen. So, no, using a 64x64 GIF (1/100th the area of my example) you'd need to do this animation would absolutely not use any significant CPU or GPU. Which is why those worked very effectively to animate small icons with zero lag on the potato computers we had in 2000.

MITSardine3• 1 year ago

The app taking "only" 6% of a $3k laptop's CPU to show two lines of text and a little 2D animation also gave me pause, but maybe this is just how it is. Still I wonder how people were squeezing pacman out of prehistoric machines, and we're using an 80's supercomputer worth of CPU power (not that far given they were in the ~ 1 GFLOP range) to animate three green bars today.

xp8417• 1 year ago

They actually knew how to code back then. I fancy myself someone who cares about performance and take a great effort to not do wasteful stupidity like those CSS animations for a decorative element, but compared to 80s programmers, I'm actually a complete fraud, because I do everything in interpreted languages that do 10,000 things behind the scenes for every line of code I write. I could never make an Atari computer or NES work.

There are of course a few who do, they all either work on embedded systems or making homebrew for retro computers. So much respect for that level of skill!

DamonHD5• 12 months ago

That may be 6% of the lowest clock speed of an efficiency core, as I suspected when I saw a similar figure for a very tame CSS animation on my MBA M1. In the end I capped the duration of the animation to cap resource use unconditionally.

sampullman2• 1 year ago

Why the embedded SVG hate? A simple icon should be just a few hundred bytes, is reusable, and styleable with CSS. It's not the right fit 100% of the time, but I think it's a very nice feature to have.

zdragnar2• 1 year ago

They're generally static documents that could be served independently, and thus cached, like an image.

Many times, though, they're served up inline in the JavaScript code that templates the html, and thus is cached less aggressively, especially if the FE is deployed frequently.

ajkjk5• 1 year ago

This contempt is misplaced. It is obviously better in one sense to generate an animation on the fly using a short program instead of encoded its literal pixels in a much larger amount of data even after compression.

The ecosystem has largely moved towards that abstraction because it scales better for virtually every purpose, particularly for rendering in different formats.

Now web developers are brought up inside the abstraction and so don't even think to go outside of it by default. Which would be fine, except that the abstraction isn't designed very well: the browser is massively underpowered at building applications in an foolproof way. Part of that is historical cruft and part of it is (imo) a lack of vision--there should have been a (not-backwards-compatible) replacement for html/js/css years ago which solves its fundamental abstraction problems.

But anyway the present is still much better than the past. You must be nostalgic for the era when all monitors were the same size and websites weren't expected to do anything without reloading the page.

bobthepanda2• 1 year ago

The problem is that everyone (browsers + developers) need to agree on a replacement, which is notoriously hard to do. Chrome got laughed out of the room with Dart/Flutter.

beejiu2• 1 year ago

An engineer could build that much faster than it would take to build an animated GIF in an editor. (For a start, it's a much more complex animation than 6 frames.)

xp8417• 12 months ago

Does it need to be more than 6 frames to serve its purpose? It's 3 wiggling bars to be stuck into a 1/4 inch spot inside a button to serve a purpose of communicating a boolean state (sound happening or not?). The artist who actually designed that probably spent an hour plus getting it just right, wasting a ton of time before the engineer even wrote the "clever" GPU-destroying CSS, and then he had to rewrite the second version after discovering how resource-wasteful the first version was.

pixl972• 1 year ago

Embedded doesn't require a new tcp connection to the server and can be a speed up depending on a number of factors.

xp8417• 12 months ago

An icon served from an <img> is going to be served from browser cache (disk or even RAM) after the very first time it's encountered. Unless you're building something designed to be used for one visit ever (maybe a promotional landing page?) it's better to have a few more requests (HTTP2 especially makes this a non-issue anyway) and have a cache full of assets than to make your dynamic webpages bloated.

deathanatos5• 1 year ago

I could have built this 25 years ago with a single GIF with about 6 frames, that was a couple of kilobytes and would be performant on the (relative) potato computers we had then. […] But modern "web designers" feel the need to spend how long carefully crafting that CSS animation which adds dozens of lines of code to the codebase and burns a ton of CPU...why? Just because you can, I assume?

The animation (which is not suppose to be constant/static) conveys whether audio is being picked up by the application. I.e., it's VU meter.

efilife2• 1 year ago

Hey, grammar police here. The animation is supposeD, like in "watcheD" not "watche".

Its meter, not "it's". Its means possession, it's is a contraction that means "it is"

xp8417• 12 months ago

I can't use the app in question, but I haven't seen any proof it doesn't just "dance when receiving audio". If it tracks amplitude and pitch, I'd still say it's overengineered, since in practice no one can discern anything useful except 2 or maybe 3 states (silent, quiet, not quiet).

verall• 1 year ago

Is it possible to restrict this as a user? Like to force webpages to use under a certain amount of render/paint time/resources or else just break so that one dumb tab doesn't use up all my battery? Then I can opt-in to greater resources usage if it's a webpage I actually care about.

I've seen the "This webpage is using alot of resources" popup before but I don't think it would happen in this case.

Because honestly I think this is horrifying. I would rather it switch from grey to red "recording" dot than use even the 6% the author decided was "fixed". In 99% of cases I do not care at all about the "artistic vision" of the UI designer and in the other 1% of cases (say an in-browser game or some useful data-viz) I could choose to allow the tab to go crazy with my resources.

mrob2• 1 year ago

Your browser should allow you to override all CSS on the web. Here's how I disable CSS animations in Firefox:

https://news.ycombinator.com/item?id=33223080

nothrabannosir• 12 months ago

This is a level too deep. I don’t want to dictate what a website can and can’t do to limit resource usage; I just want to limit resource usage.

Sure, noodling with content blockers has its own advantages, but for this particular case they cut at the wrong abstraction matter.

dleeftink• 1 year ago

A bookmarklet that injects custom CSS and selects all/certain items and applies the `contain: content` and `content-visibility: auto;` rules could do to trick.

Additionally, the pseudo `:empty { display: none; }` selector may get you additional mileage.

crazygringo2• 1 year ago

Seriously. It seems pretty reasonable to allow a web page a total amount of processing that is something like 100% CPU or GPU for 5 seconds. (E.g. can be 25% for 20 seconds.) And beyond that it gets throttled to 3% CPU cumulative max for however long it's been open so far.

And make that the default for popular browsers, so sites are forced to be efficient or else be super super janky and stuttering. And allow a permission for unrestricted processing that things like WebGPU demos or games can ask for.

HWR_143• 1 year ago

100% of the CPU for 5 seconds seems unreasonably long for a random webpage.

hafeoz• 12 months ago

Firefox already has a monitor module that AFAIU tracks UI stalls and prompts the user to stop the website if it hangs for a long period [1]. It probably can be further developed to also track resource consumption and show a warning if some threshold is reached.

[1] https://searchfox.org/mozilla-central/source/browser/modules...

londons_explore• 1 year ago

ChromeOS has logic that restricts background tabs to 1% CPU use I think.

rayiner3• 1 year ago

They should put in something that allows users to electroshock web designers for wasting their battery.

thway15269037• 1 year ago

I don't think combined energy output of every power station on Earth would be enough after we have Electron apps for so long. (edit: typo)

orhmeh09• 1 year ago

Yes, with StopTheMadness https://underpassapp.com/StopTheMadness/

It works on Safari, Chrome, and Firefox, but you must buy it.

barrkel• 1 year ago

It only works on Apple though it looks like.

socalgal23• 1 year ago

How about just not using that site?

edoceo• 12 months ago

I wish. But some sites we are stuck with. EG: bank, HR App, etc.

gronglo2• 12 months ago

In 99% of cases I do not care at all about the "artistic vision" of the UI designer and in the other 1% of cases (say an in-browser game or some useful data-viz) I could choose to allow the tab to go crazy with my resources.

I'm with you 100%. Although I'd go one step further and say CSS just isn't needed at all, and should be removed from all browsers. Same goes for WebGL (if you want to play a game, download Steam).

This would fix all of your issues and save an unbelievable amount of energy across the planet. Unfortunately people like us are a dying breed!

groundcontr01• 12 months ago

No css at all is pretty extreme, but I'd be on board with disabling css animations

7bit• 12 months ago

You can disable CSS in your browser. The fact that you even complain about this tells me that you didn't didable, yet you damned it to be removed. Pretty hypocritical of you.

vanschelven• 12 months ago

To take matters in my own hand I wrote "tabdouse", a tiny kill-at-high-cpu script: https://www.bugsink.com/blog/tabdouse/

Quite unreliable and more a joke than anything, of course...

schiffern• 12 months ago

Probably too late, but uBlock Origin can disable animations (technically fast-forwards to the end, less likely to break the page) for all websites. In the Settings > My Filters tab, add:

  !Disable CSS animations globally
  *,com##*, ::before, ::after :style(animation-timing-function: step-start !important;transition-timing-function: step-start !important)

Text shadows and filters are also pretty heavy CSS properties:

  !Disable text shadow globally
  *,com##*, ::before, ::after :style(text-shadow: none !important)

  !Disable image filters globally
  *,com##*, ::before, ::after :style(filter: none !important)

Even disabling rounded corners can improve perf (and I think it looks better):

  !Disable rounded corners globally
  *,com##*, ::before, ::after :style(border-radius: 0px !important)

Varelion3• 1 year ago

It seems beyond absurd to me, that this tiny animation should be costing as much as 6% of CPU.

There has to be more optimal ways to do this.

MITSardine3• 1 year ago

So, the CRAY-2 built in 1985 was rated at 1.9 GFLOPS. The M2 the author uses seems to be benchmarked at around 6GFLOPs per core [1]. So this 6% of the author's CPU (assuming charitably this is a single core) corresponds to about 20% of the mid 80's peak supercomputer capacity.

People were already using those computers for applications that go slightly beyond animating 5 x 3 green little bars up and down at the time...

I understand dev time cost > CPU time cost (for the company that hires the developpers anyways) but aren't things getting a little out of hand?

Even without comparing to an 80's supercomputer, what if someone with a 15 years old laptop tries to use their app? What will those 6% CPU on the dev's shiny M2 MBP become?

[1] https://boinc.bakerlab.org/rosetta/cpu_list.php

utopman• 1 year ago

This.

I did not find other comments like this in this thread.

6% M2 cpu (even single core) is a huge computing budget for such a small feature.

At this point I don't really understand why OP seems happy with this result (sorry).

I think even a naive canvas implementation can really and quite easily cut most of this computing budget.

Also, a pure css animated thing should use mostly gpu in a right DOM implementation. I think some issues remains in this result.

Maybe OP displays it's app on a 240hz external screen which makes browser compute DOM animation at 240 fps requiring slighly more compute in a passive way (4o-mini suggests this, I am not sure browser works like this)

I remember too much of my pentium 1 166Mhz let run entire age of empires 2 game in 1997

makeitdouble2• 1 year ago

I assume 6% is for the whole page.

That's still a lot for a single page IMHO, but it seems that service is doing resource expensive things in the first place.

khalic• 1 year ago

Yeah it really helps knowing CSS when doing frontend dev...

exiguus• 1 year ago

I'm not 100% convinced. Likely because the article doesn't show the difference between animations that are announced with 'will-change' and/or elements that are animated with position absolute. Also, it looks related to the browser and there was no evidence that this is also a issue in FF or Chrome.

deepsun2• 1 year ago

Just wrap it in a container with fixed height and "overflow: hidden".

Now the layout engine knows that it doesn't need to recalculate positions of elements outside that wrapper, and it's much faster.

By the way, the same trick was speeding up large <table> rendering back in the day. As long as you know the size of your rows or columns ahead of time, which kinda defeats the purpose of <table>.

liuliu• 1 year ago

Thank you! This is what I am looking for in HN comments. Layout engine cannot be that stupid per the article. I guess it is not once you give it enough hint.

codeptualize• 1 year ago

This is the answer. I thought this was fairly common knowledge, height is animated quite often (think dropdowns), no need for the over complications.

alexchantavy• 1 year ago

Is there a good way to learn techniques like this from first principles other than trying to become an employed frontend dev?

brokencode• 1 year ago

Usually you try to build something, realize it’s slow, then do a combination of searching for possible solutions, trying them, and profiling again and again to gain this knowledge.

Experience is the best teacher.

notatoad2• 1 year ago

not really. the web is 30+ years of fixes, shortcuts, compatibility hacks, tech industry politics, and other assorted mistakes.

the "first principles" to understand it all is the complete set of mailing list archives of the WhatWG, plus the archives of the bug trackers of all the major browsers.

RumourRider4• 1 year ago

You need to think about what the browser is actually doing when it displays a web page. You need to think about what happens when you type the URL in and what the browser is doing conceptually.

If you have any experience programming 2D graphics with SDL this will help you to understand what is happening as well.

There is an old school talk by Nikolas Zakas on JavaScript Performance from 2009 which while some of it is out of date now due to improvements in Browser engines, the fundamental ideas are still the same.

https://www.youtube.com/watch?v=mHtdZgou0qU

If you skip to the 35 minute mark he speaks about reflow specifically. Generally I still use many of these techniques when writing vanilla JS (which is unfortunately rare these days). There are other talks where he talks about many other performance specific topics.

Obviously none of this is as good as real world experience of dealing with a thorny issue.

eviks• 12 months ago

Not sure, but if CSS first principle is parent sets width going down to children, but sets height going up from children, then you could see how children changing its height leads to layout recalc all the way up.

So the you need to fix that height /remove resize, then google on which technique to use?

dsego• 12 months ago

Understanding the document's flow layout, block and inline elements and build on top of that.

legitster• 1 year ago

As an old-school webguy, fixes like this article make me sad.

The average front-end person these days has so little respect for the DOM and then gets mystified about why the McMaster-Carr website is so good despite being build with ancient practices.

sema4hacker• 12 months ago

I just went to the McMaster-Carr home page and right-clicked for "View Page Source". There's a LOT of code there.

dotancohen3• 12 months ago

A few years ago a client that I hadn't spoken to in half a decade called me to thank me. He wanted to update his website to work with tablets, checked before calling me, and realized that his website just simply worked. Being the caveman that I am, I wrote the damn thing using the simplest CSS possible. Simple equals compatibility in this field.

bartread• 12 months ago

Well, and especially because the “fixed” version is still - if I’ve read correctly - consuming 12% CPU before any user interaction on a page that’s otherwise substantially a plain or possibly RTFish text editor.

How is that considered acceptable? It’s still going to drain the battery faster than is justified, even if at a somewhat reduced rate from the pre-fixed case.

The acceptable range would be something like 0 - 1% when no interactions are taking place.

I’d still deploy the fix in the article as an interim solution - better is after all better - but I wouldn’t stop there.

Front-end web devs need to have more respect for power consumption and battery life (proxies by CPU and GPU usage).

atiedebee• 12 months ago

huh, that was probably the least infuriating filter I have encountered in a while.

It's frustrating how just changing a filtering option will reload the entire web page on most websites.

bfgeek• 1 year ago

This likely more effective quite a few years ago, but not particularly important today.

Changing height typically only shifts elements, and browser engines typically wont relayout them due to position changes.

"overflow: clip" is also much more lightweight than "overflow: hidden"

spankalee2• 12 months ago

`contain: strict` is much better than `overflow: hidden` for this case, and implies `overflow: hidden`.

bobbylarrybobby• 12 months ago

https://developer.mozilla.org/en-US/docs/Web/CSS/contain

Yes, looks like this property isn't just a hack, but was designed with exactly the performance considerations laid out in the article in mind. Animating height is only expensive when the element’s height affects layout, which it doesn't have to!

dotancohen3• 12 months ago

  > Just wrap it in a container with fixed height and "overflow: hidden".

That's a fix for a webdev who cares, not a fix for a browser vendor as GP was alluding to.

fiddlerwoaroof• 12 months ago

I don't understand how you'd fix this, in general, for the browser: the browser can't just assume certain animations will never affect layout.

troupo7• 12 months ago

Translation: just make a completely different functionality and effect than what was originally intended because the DOM can only handle static content, barely.

kadoban2• 12 months ago

The suggested change wouldn't affect functionality or the effect. It just tells the browser that there's a thing around the changing part with a fixed size that can't possibly change layout of anything around it, to the user it's invisible.

tristor• 1 year ago

Man, I hate what the web has become in 2025. There is absolutely no respect from frontend developers for their users. It's obscene the amount of wasted CPU cycles, energy, battery life, bandwidth, and time we have in aggregate due to horrible frontend development practices.

DamonHD5• 1 year ago

Not just front-end!

https://www.earth.org.uk/RSS-efficiency.html

mpliax• 1 year ago

What is Granola spending those cycles on? It's an Electron app

He could had stopped there.

endemic• 1 year ago

ironic that the benefit of using web tech (platform abstractions) can be totally negated by such a small footgun, which then requires insane knowledge of the browser rendering pipeline to solve

Sharlin2• 1 year ago

One problem is that this is supposedly considered insane esoteric knowledge, when the concept of reflows, and why and when they're triggered, ought to be fairly basic knowledge to every reasonably experienced frontend coder. Up there with "O(n^2) may bite you in the ass". But we've decided that optimizing SEO or conversion rates or whatever is much more important than optimizing rendering.

jbeninger• 1 year ago

I think there's a bit of an "everybody knows that" [1] phenomenon when it comes to knowledge like this. Devs come from different backgrounds and work on different types of projects. There are 10000 things you expected to know to be an expert, and all of us are continually learning.

[1] https://xkcd.com/1053/

Etheryte• 1 year ago

None of this should be esoteric knowledge if you work with web technologies for a living. Animations, box shadows and blurs have a very long history of performance issues. Similarly, standard tools easily highlight the issue, as shown in the article.

makeitdouble2• 1 year ago

insane knowledge of the browser rendering pipeline to solve

Saying it having not much of that knowledge myself: it's reasonable to sometimes need platform knowledge to make intricate things (here a realtime animation) behave efficiently.

That's the same for game engines, native rendering, flash animations etc. There will always be edge cases, building enough stuff you'll hit them, and if you care about doing it right it will require knowledge to overcome the issues.

awkward• 1 year ago

This looks like a clever implementation of a useful feature. I enjoyed that the developer was able to link the streaming audio API to a useful visualizer, recognize problems with his approach, debug issues in that visualizer, and find a clever solution using graphics fundamentals like masking.

I'm less than impressed with the general consensus that he's somehow negligent for launching a feature that needed a fix, or that users don't want or need feedback about audio connectivity, or that the poster did something much better sometime back in `02.

rectang• 1 year ago

I read this article because just last week I set up CSS height transitions to show/hide divs in a form which displays conditional content (based on radio button selection). "Why shouldn't I do this?", I thought.

It looks like the point of this article is that you should avoid continuous animation for CPU performance reasons. These performance reasons are probably inconsequential for occasional transitions.

For many of us in the target demographic of "people who animate height", the scary title of this article is misleading.

DamonHD5• 1 year ago

I created a little CSS-pulsing 'live' button and give it a fixed number of cycles of pulsing to cap worst-case resource consumption. But it took me a while to work out that that was the right thing to do!

Quarrelsome• 1 year ago

Instead, we can create the illusion of a changing height by using two rectangles, applying translate to each.

Its a very clever solution and props to the engineer, but this being the fix makes me truly despair at where we are as an industry around web UI. That html and css won despite these sorts of counter-intuitive horrors.

UI layers that make me feel good reflect intent. I can take an image and write some code to darken that image (any image) and show that to the end user. It makes sense. However, in html+css I have to introduce a third element, another rectangle, slap it infront, paint it entirely black and set its opacity to something low. Sure, it works the same but it just feels so conceptually ugly.

andoando• 1 year ago

I had a similar problem trying to animate a book flipping pages. At the half way point I had to update the text to show the backside and update the back pages.

However no matter what I did, I could not get the update to sync correctly with the page being exactly half way. There's probably a solution but I just gave up

lelandfe• 1 year ago

It’s literally the sliding doors technique from, uh, two decades ago https://alistapart.com/article/slidingdoors/

ryandrake• 12 months ago

It's like building a space station with sticks and rocks.

russellbeattie• 1 year ago

I'm not sure how it's implemented on the JS side, but I can imagine the CSS getting a lot of updates per second as the voice level changes, constantly interrupting the current animation.

Might be worth it to buffer the input until animationEnd() event fires. That might reduce the amount of calculations and redrawing that needs to be done.

Or the CSS engine is robust enough to handle continual updates and this won't solve a thing. I'd have to test it.

rayiner3• 1 year ago

Why do browsers even allow this shit. I was trying out a scheduling app the other day, and it was using 3% of CPU just sitting there doing nothing. That’s a Pentium 1 level of computing power to do jack shit.

pharrington• 1 year ago

You can animate height without forcing a relayout, as long as the element is out of the document flow.

Saris2• 1 year ago

Why are the bars on a little button animated in the first place? I don't get it.

deathanatos5• 1 year ago

This looks like a very typical audio recording UI element. The bars are animated to the volume of the recorded audio. Helps the user see that the application is picking up their mic.

It's a digital analog of a VU meter on a mixing console, though the UI has morphed over time. (Like that the lines vertically centered, vs. being on aligned bottom like you might see on a real-world meter.)

Saris2• 1 year ago

Man at that point why not make it bigger and put a proper dB scale on it, at least it would be useful then.

Levitating5• 1 year ago

Except that it's not an actual meter, it's just a fake animation.

calypso• 1 year ago

You’re still okay with wasting 6% CPU and 1% gpu time on a simple note taking app?

ASalazarMX2• 1 year ago

In my wimpy work Virtual Desktop, this page eats 25-40% of my CPU just by scrolling up or down after fully loading. It's a severely limited VDI, I agree, but this performance is crazy for what is functionally a static page.

It certainly doesn't give me confidence in using their app, given this landing page can become as heavy as GMail while doing nothing. How optimized is their electron app? Is the iOS version as heavy? Are they OK with wasting all this energy for nothing?

forrestthewoods• 1 year ago

It's an Electron app

The worst modern invention. HTML/CSS is so bloody awful at rendering user interfaces. We should if at least contained it, if not killed it outright. But instead it’s a contagion that has spread far and wide.

How the hell does the optimized version use 6% of CPU? It should render at roughly 5000 frames per second.

What a tragic state of affairs we live in.

Ken_At_EM• 1 year ago

The final CPU/GPU usage is still totally unacceptable.

irrational• 1 year ago

Wouldn’t the real fix be to use an animated gif?

echoangle• 1 year ago

I think the idea is to have the animation respond to the actual volume in realtime. The animation property is only so that the 10 updates per second get interpolated according to the framerate, I think. The real solution would be to remove the gimmicky animation and show a red circle.

65• 1 year ago

This article doesn't apply to every single use case and should not be taken purely at face value.

A few week ago I needed to animate height for a banner like message that appeared in the layout (e.g. it was not absolutely positioned) once a user clicked a button. This banner message would cause a layout shift no matter what because its height was being added to the layout and shifting the elements underneath it down. Thus, to mitigate a jumpy layout, making the height animate made the layout shift easier on the eyes.

And before you say "well design it differently" - I didn't design this.

tomaskafka• 1 year ago

How about we create tools that don't consume 5+ % of user's CPU (and keep it busy, not allowing it to sleep, decreasing battery life significantly) when idling or doing some background work?

Levitating5• 1 year ago

Does a note taking app need such an animation if apparently it's that easy to accidentally drain the users battery?

The UI of this app literally only has a piece of text, a button and this animated indicator. To render this it needs an entire chromium browser loaded into memory, and still it has performance issues.

I will always prefer software written in native graphics toolkits. I understand the benefits of using electron but the only electron based software I've ever liked was vscode.

throw14082020• 1 year ago

I think there's a typo?

Less expensive are paint properties. A paint property does trigger layout, but it does repaint a layer, and then re-composites.

It doesn't trigger a layout step?

emmanueloga_• 1 year ago

Not just height, anything that causes continuous repaints can become expensive. Search for "jank free" to find more resources on the subject, or check this oldish website [1].

1: http://jankfree.org/

woah• 1 year ago

On my M2 MacBook, the renderer process is now using 6% CPU

Damn, is this 6% of the whole CPU?!

rkwz• 12 months ago

CSS animations can sometimes cause weird performance issues or even crashes. 10 years back, animating box-shadow caused browsers to crash for our some of users by consuming a lot of memory: https://www.sheshbabu.com/posts/my-binary-search-debugging-s...

syngrog66• 12 months ago

I love all things perf but stopped reading pretty early once I saw enough foundation mistakes (after which all else is folly anyway, haha):

1. making a note-taking app in 2025: 1st mistake. cuz well solved space with great existing tools/options going back to the 80s/90s

2. as a GUI

3. with animations (in a note taking app?!)

4. in a browser

userbinator• 12 months ago

Don't animate

There, I fixed it. I have a custom CSS that kills all animations whenever I'm forced to use a "modern" browser, and it definitely tames the web.

farzd• 12 months ago

I recently created a voice notes app in react-native / expo. And I have a waveform that updates according to the multimeter (audio input)

From my first try, I immediately had the performance monitor visible because I knew this could be RAM intensive.

I iterated a few times until I settled on SKIA and boy, the performance was night and day.

fitsumbelay• 12 months ago

Excellent dive that covers a bunch of stuff, thanks for this. The brevity, tho. Masterful and very appreciated

seabass• 12 months ago

I’d be interested to see the performance of the same visualizer in a canvas or animated svg instead. Forcing these animations through the dom seems a little absurd to me, but I’ve been surprised by web performance before.

torginus2• 12 months ago

Did throw together a quick SVG example - on my computer, a dummy page with just this animation spends 1ms rendering, so basically a solved issue - and cleanly.

bandrami• 12 months ago

Is the information conveyed by this animation actually useful?

kookamamie• 12 months ago

On my M2 MacBook, the renderer process is now using 6% CPU

Looking at the animation, I'd wager it's still way too much CPU use for what it is.

HellDunkel• 12 months ago

The fact that this little animation can have such heavy performance impact tells us one thing: CSS design is flawed. That‘s it. That‘s the whole story.

raincole• 12 months ago

It really isn't.

How can the browser know if an arbitrary animation can change an element's height? I'll bet 10 bucks this is equivalent to halting problem.

Unless you 1) don't support full SVG spec or 2) separate SVG elements from the layout completely, it's not a problem that is solvable by browser. The developers need to wrap their animation in a fixed size element and it's very reasonable to expect them to do so.

Plus, the CSS spec doesn't prevent browser vendors from optimizing this specific use case if it's really that needed.

(Of course in the case of this simple web app in OP, the correct solution is to not use animation at all.)

unsupp0rted• 12 months ago

On my M2 MacBook, the renderer process is now using 6% CPU (down from 15%), and the GPU process is now using 6% CPU and less than 1% GPU (down from 25% and 20%)

Ouch. All of this for a tiny visualizer animation.

Maro• 12 months ago

Cool article!

On my M2 MacBook, the renderer process is now using 6% CPU (down from 15%), and the GPU process is now using 6% CPU and less than 1% GPU (down from 25% and 20%).

This still feels way too much compute for a tiny animation updating a couple times a second.

paulmooreparks• 12 months ago

On my M2 MacBook, the renderer process is now using 6% CPU (down from 15%), and the GPU process is now using 6% CPU and less than 1% GPU (down from 25% and 20%).

Wait, this is supposed to be an improvement? 6% CPU for a lame animation?

peanut-walrus• 12 months ago

Ok, but we can all agree that even 6% constant CPU usage is way too high for a note-taking app, right?

DamonHD5• 12 months ago

That may be 6% of the lowest clock speed of one slow/efficiency core. Still far too much, but maybe a little less extreme than it appears.

imcotton• 12 months ago

Does anyone have the courage to perform a similar inspection on the Cloudflare homepage like the author did? On my M4 Mac mini, Safari lagged with single-digit frames per second (FPS), which scared me so much that I had to close the page as quickly as possible.

monster_truck• 12 months ago

An alternative solution to this is to place the height animated objects inside of containers with a static vertical size that is equal to the maximum height of the animation

amelius• 12 months ago

This is why I do everything on a canvas nowadays.

torginus2• 12 months ago

My personal call would be to use SVG for this - you can do CSS animations there just fine without triggering layout. Not a frontend expert but don't see why that wouldn't work.

soulchild37• 12 months ago

The lesson should be don't use Electron, animating height in AppKit has no problem

astura• 12 months ago

On my M2 MacBook, the renderer process is now using 6% CPU (down from 15%), and the GPU process is now using 6% CPU and less than 1% GPU (down from 25% and 20%).

I honestly can't imagine typing this out and patting myself on the back rather than thinking "wtf am I doing? It's 2025, I have a high end laptop, and this is a note taking app. The total resource utilization should be close to zero."

Modern devs are fucking hogs.

naikrovek2• 12 months ago

here's an idea - don't animate anything on a webpage.

Just. Don't.

NO ONE needs animation to convey information, unless that information is an animation, such as in an educational context, where interactive things demonstrate what is being taught.

I don't need to see your widget spin in 3d while I scroll down the page. I really don't. I don't even want to see that.

Web pages are slow because people make them slow. Stop making them slow.

Cthulhu_• 12 months ago

Previous discussions / submissions: https://hn.algolia.com/?query=Don%27t%20animate%20height

peterisza• 12 months ago

So good to see a developer who actually cares about resources. Thank you!

I usually develop my apps on a 1300 MHz single-core Intel Atom mini PC from 10 years ago. When something like this goes wrong, the app becomes unusable and I immediately notice it.

Don't animate height

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