Firefox simply ignores height declarations that resolve to a value greater than exactly 17895697px. What’s this value? Just a smidgeon under 2³⁰ sixtieths of a pixel, which is Firefox’s layout unit. (It’s the last integer before 2³⁰ sixtieths, which is 17,895,697.06̅ pixels, 4⁄60 more.) I presume Firefox is using a 32-bit signed integer, and reserving another bit for something else, maybe overflow control.
Five years ago, Firefox would ignore any CSS declarations resolving like that, but somewhere along the way it changed so that most things now clamp instead, matching WebKit-heritage behaviour. But height is not acting like that, to my surprise (I though it was).
WebKit-heritage browsers use a 1⁄64 pixel layout unit instead. Viewed in that light, the 2²⁵ − 1 pixels is actually 2³¹ − 1 layout units, a less-surprising number.
No. Everyone has always used fixed-point numbers for layout, see my comment for further details.
Now SVG… try defining a view box up where float precision drops, and interesting things happen.
AnotherGoodName · 19m ago
But it's specifically 25bits not 24?
As in n+1 == n once you go past 2^24 on a float and here they are at 2^25-1. So it doesn't quite make sense as a reason to me.
There's a post above that browsers divide pixels into 1/64th of a unit which accounts for 6bits which puts this limit at precisely that of a signed 32bit integer. This makes much much more sense than the significand of a float.
chriseing · 55m ago
The correct answer. In particular, up to 2 ^ 24 the float32 behaves like a regular integer, which can be important in some cases. Above that value, the integer starts to have missing values, and strange int behavior such as (n+1)+1 not equal to (n+2)
yosefk · 49m ago
But why are 32b floats relevant? JS, the language famously representing ints as floats, uses 64b floats. Who puts ints into 32b floats and cares about precision loss?
bobmcnamara · 17m ago
Plenty of embedded GPUs do coordinates that way. But I doubt they're running browsers.
matthewmacleod · 36m ago
Layout engines are not implemented in Javascript.
maxloh · 1h ago
Blink, Chrome's rendering engine, was forked from WebKit (Safari) in 2013.
Since WebKit already supported the infinity value at the time of the fork [0], it's highly probable that they share the same underlying code. This would explain their similar behavior.
And actually I’d be quite surprised if the infinity keyword is even relevant here; I would expect the same results if you changed each calc(infinity * 1px) to 9999999999999999px. Firefox (and, if you go far enough back, IE) will still ignore overly large height declarations, and WebKit-heritage browsers will clamp it.
maxloh · 1h ago
Thanks for the clarification. However, the number is likely encoded in binary format, which is why you're seeing 2²⁵ in the article.
calibas · 1h ago
What's the actual use case for "infinity" in CSS?
szatkus · 34m ago
According to the spec:
These constants are defined mostly to make serialization of infinite/NaN values simpler and more obvious, but can be used to indicate a "largest possible value", since an infinite value gets clamped to the allowed range. It’s rare for this to be reasonable, but when it is, using infinity is clearer in its intent than just putting an enormous number in one’s stylesheet.
jdauriemma · 1h ago
Final boss of z-index
azangru · 39m ago
Isn't the final boss of z-index the top layer?
Rendello · 1h ago
What about `infinity + 1`? ;)
dole · 50m ago
z-index = i_love_you;
PaulDavisThe1st · 51m ago
Cantor has entered the chat.
stronglikedan · 24m ago
Selling pixels at a dollar each to make an Infinity Dollar Website™.
adamwathan · 48m ago
We use it in Tailwind CSS v4 for pill-shaped borders:
...as opposed to what everyone has done historically, which is pick some arbitrary huge value like:
.rounded-full {
border-radius: 9999px;
}
No real practical benefit, just satisfyingly more "correct".
RoryH · 1h ago
This article triggered flashbacks to 20 years ago and using all sorts of crazy CSS to hack the browser to do what you needed it to. Nowadays CSS is (usually) a remarkable land of sanity in comparison.
Brajeshwar · 1h ago
It was also a fun time to interview. Can you write a CSS snippet that will make a box red in IE5, Blue in IE6+, and is Yellow in Firefox but black in Netscape? CSS these days is no longer an adventure — they just tend to work.
ge96 · 47m ago
I always grab the CSS reset
Also the purple story
echelon · 1h ago
> came across a toot
> For the sake of my aching skullmeats
> My skullmeats did not thank me for this
> I hear you asking.
> Maybe if I give my whimpering neurons a rest
> I’d be much happier if someone just explained it to me; bonus points if their name is Clarissa.
> my gray matter needs a rest and possibly a pressure washing
There is a software engineering equivalent of the "theater kids" meme, and this is it. There's an abundance of exuberance in this writing.
I'm glad we have such diversity in perspective. It's a nice change from the usual terseness, though I'm not sure I could read in this style for an extended period.
allears · 20m ago
Totally refreshing to me. Imagine -- a techie who doesn't take himself too seriously!
baggy_trough · 45m ago
"skullmeats" definitely made me wince.
nine_k · 2m ago
The interaural nerve node.
breckognize · 1h ago
Kinda related - our product, rowzero.io, is a browser-based spreadsheet with a 2 billion row limit. We initially built the client as anyone would, using a div per cell. We tried to use an off-screen div to take advantage of the browser's native scrollbars but ran into document height limits. Firefox's was 6M pixels iirc. The solution was to do rendering in canvas and draw the scrollbars ourselves.
chrismorgan · 20m ago
Firefox’s limit is 17,895,697 pixels. Others have a limit less than twice as high, so given you’re aiming for a value way higher than that, it’s not a browser-specific issue, except insofar as Firefox ignores rather than clamping, so you have to detect Firefox and clamp it manually.
In Fastmail’s case (see my top-level comment), making the end of a ridiculously large mailbox inaccessible was considered acceptable. In a spreadsheet, that’s probably not so, so you need to do something different. But frankly I think you needed to use a custom scrollbar anyway, as a linear scrollbar will be useless for almost all documents for anything except returning to the top.
Rendering the content, however, to a canvas is not particularly necessary: make a 4 million pixel square area, hide its scrollbars, render the outermost million pixels of all edges at their edge, and where you’re anywhere in the middle (e.g. 1.7 billion rows in), render starting at 2 million pixels, and if the user scrolls a million pixels in any direction, recentre (potentially disrupting scrolling inertia, but that’s about it). That’s basically perfect, allowing native rendering and scrolling interaction, meaning better behaviour and lower latency.
zwnow · 1h ago
Is it completely client side? Why does it have a 2 billion row limit? Where are the limitations coming from?
mmastrac · 1h ago
Do you even need to have one scroll pixel == one screen pixel (or even one scroll pixel == one spreadsheet row)? At the point of 2 billion rows, the scrollbar really falls apart and just jumping to an approximation of the correct location in the document is all anyone can hope for.
Five years ago, Firefox would ignore any CSS declarations resolving like that, but somewhere along the way it changed so that most things now clamp instead, matching WebKit-heritage behaviour. But height is not acting like that, to my surprise (I though it was).
WebKit-heritage browsers use a 1⁄64 pixel layout unit instead. Viewed in that light, the 2²⁵ − 1 pixels is actually 2³¹ − 1 layout units, a less-surprising number.
IE had the same behaviour as Firefox used to, but with a much lower limit, 10,737,418.23 pixels (2³⁰ − 1 hundredth pixels), which was low enough to realistically cause problems for Fastmail, all you needed was about 200,000 messages in a mailbox. I’ve written about that more a few times, https://news.ycombinator.com/item?id=42347382, https://news.ycombinator.com/item?id=34299569, https://news.ycombinator.com/item?id=32010160.
Typo, the last browser in this sentence should be "Chrome", right?
Now SVG… try defining a view box up where float precision drops, and interesting things happen.
As in n+1 == n once you go past 2^24 on a float and here they are at 2^25-1. So it doesn't quite make sense as a reason to me.
There's a post above that browsers divide pixels into 1/64th of a unit which accounts for 6bits which puts this limit at precisely that of a signed 32bit integer. This makes much much more sense than the significand of a float.
Since WebKit already supported the infinity value at the time of the fork [0], it's highly probable that they share the same underlying code. This would explain their similar behavior.
[0]: https://caniuse.com/?search=infinity
And actually I’d be quite surprised if the infinity keyword is even relevant here; I would expect the same results if you changed each calc(infinity * 1px) to 9999999999999999px. Firefox (and, if you go far enough back, IE) will still ignore overly large height declarations, and WebKit-heritage browsers will clamp it.
These constants are defined mostly to make serialization of infinite/NaN values simpler and more obvious, but can be used to indicate a "largest possible value", since an infinite value gets clamped to the allowed range. It’s rare for this to be reasonable, but when it is, using infinity is clearer in its intent than just putting an enormous number in one’s stylesheet.
> For the sake of my aching skullmeats
> My skullmeats did not thank me for this
> I hear you asking.
> Maybe if I give my whimpering neurons a rest
> I’d be much happier if someone just explained it to me; bonus points if their name is Clarissa.
> my gray matter needs a rest and possibly a pressure washing
There is a software engineering equivalent of the "theater kids" meme, and this is it. There's an abundance of exuberance in this writing.
I'm glad we have such diversity in perspective. It's a nice change from the usual terseness, though I'm not sure I could read in this style for an extended period.
In Fastmail’s case (see my top-level comment), making the end of a ridiculously large mailbox inaccessible was considered acceptable. In a spreadsheet, that’s probably not so, so you need to do something different. But frankly I think you needed to use a custom scrollbar anyway, as a linear scrollbar will be useless for almost all documents for anything except returning to the top.
Rendering the content, however, to a canvas is not particularly necessary: make a 4 million pixel square area, hide its scrollbars, render the outermost million pixels of all edges at their edge, and where you’re anywhere in the middle (e.g. 1.7 billion rows in), render starting at 2 million pixels, and if the user scrolls a million pixels in any direction, recentre (potentially disrupting scrolling inertia, but that’s about it). That’s basically perfect, allowing native rendering and scrolling interaction, meaning better behaviour and lower latency.