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CSS px is an Angular Measurement

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Re: CSS px is an Angular Measurement

#51

Post by jonah »

modeless wrote: post #43
nwatson wrote: post #40

Earlier quoted context omitted.

A curved display (let's say, spherical) centered approximately at the "primary" observer's eyeballs whose pixel elements all subtend equal solid angles would (a) lead to weird unintuitive and hard-to-program-for locations in their most natural expressions the further you wandered from the center-horizontal or center-vertical row/column of pixels; (b) make it very hard to those whose eyeballs aren't smack-dab in the c…

I agree that a spherical display the size of a monitor or TV would be unweildy; however a head-mounted display with a large field of view would work best if it was curved.

Well, if you want to program for a spherical display there's the 30 foot diameter AlloSphere: http://www.allosphere.ucsb.edu/

Re: CSS px is an Angular Measurement

#52

Post by alexchamberlain »

bzbarsky wrote: post #44
javajosh wrote: post #17

This is one of the more important Hacker News submissions I've seen in a long time. It seems that there is, potentially, a fundamental disconnect between what "px" is supposed to mean and what it means in practice . Given the incredible importance of the web, particularly the front-end of the web, and the extraordinary increases in screen resolution (today the iPhone 4 and iPad 3, tomorrow most computers), it's very…

High-resolution devices (that includes iPhone 4 and iPad 3, but also every single printer anyone's used in the last 5+ years) are exactly why the spec says what it says. The only other option was to not have a "px" unit in the spec at all. I mean, think about it. Say you have a 600dpi printer. Take a typical web page that sets its body element to be 1000px wide, because the person writing it was using a 96dpi display…

A pixel is the smallest controllable dot on a screen. The spec shouldn't have changed the definition of this, but introduced a new unit instead. Personally, I'd have both!

Re: CSS px is an Angular Measurement

#53

Post by JoshTriplett »

wmf wrote: post #49
JoshTriplett wrote: post #30

Earlier quoted context omitted.

And people would have quickly learned to not use "pixel" unless they really mean "pixel".

You never really mean pixel, so I guess you're arguing for the removal of the px unit completely. (bzbarsky explained this better: http://news.ycombinator.com/item?id=3697227 ) Then designers would start asking for a unit that is resolution-independent but always an integer multiple of pixels — essentially px under a different name. The px unit is really useful, but maybe it should have had a different name; it's too…

On the rare occasions where I say "px" rather than some scalable unit, I really do mean pixel. For example, I might use px to specify the width of an element that needs to have exactly the same width as an img tag.

Re: CSS px is an Angular Measurement

#54

Post by nitrogen »

JoshTriplett wrote: post #53
wmf wrote: post #49

Earlier quoted context omitted.

You never really mean pixel, so I guess you're arguing for the removal of the px unit completely. (bzbarsky explained this better: http://news.ycombinator.com/item?id=3697227 ) Then designers would start asking for a unit that is resolution-independent but always an integer multiple of pixels — essentially px under a different name. The px unit is really useful, but maybe it should have had a different name; it's too…

On the rare occasions where I say "px" rather than some scalable unit, I really do mean pixel . For example, I might use px to specify the width of an element that needs to have exactly the same width as an img tag.

On devices where 1px != 1 device pixel, images should be scaled by the same proportion as the px unit. So, if you set an img to 150px wide, and a div below it to 150px wide, they will be the same width, even if 150px == 300 pixels. I'd be happy to learn of any browsers where that is not the case.

Re: CSS px is an Angular Measurement

#55

Post by jonah »

bzbarsky wrote: post #44
javajosh wrote: post #17

This is one of the more important Hacker News submissions I've seen in a long time. It seems that there is, potentially, a fundamental disconnect between what "px" is supposed to mean and what it means in practice . Given the incredible importance of the web, particularly the front-end of the web, and the extraordinary increases in screen resolution (today the iPhone 4 and iPad 3, tomorrow most computers), it's very…

High-resolution devices (that includes iPhone 4 and iPad 3, but also every single printer anyone's used in the last 5+ years) are exactly why the spec says what it says. The only other option was to not have a "px" unit in the spec at all. I mean, think about it. Say you have a 600dpi printer. Take a typical web page that sets its body element to be 1000px wide, because the person writing it was using a 96dpi display…

Confusion between px and dpi are common for people who haven't done work for both screen and print:

Screens are more accurately measured in PPI (pixels per inch) while the smallest elements a printer can produce (more akin to each of the 8 bit sub-pixels on a screen) are measured in DPI (dots per inch). Since ink is 1 bit more smaller elements (dots) are needed in some sort of dithered pattern to represent grays and colors.

Using halftone screening [1] the image elements are called lines and so a 600dpi printer is capable of producing 85–105 LPI (lines per inch)[2].

The lines per inch of print are more analogous to the pixels per inch of a screen than dots per inch are.

So, that 96ppi LCD and the 600dpi printer have around the same information density for practical purposes.

[1] http://en.wikipedia.org/wiki/Halftone [2] http://en.wikipedia.org/wiki/Halftone#Resolution_of_halftone...

Re: CSS px is an Angular Measurement

#56

Post by Produce »

gwillen wrote: post #27
crazygringo wrote: post #16

Earlier quoted context omitted.

That's actually a very good point, don't know why you're being downvoted.

I find it interesting that I was downvoted to the negatives, then you posted this reply, and then I got upvoted to the top. I wonder what the causation is there. I suspect I know why I was downvoted; I used unnecessary emotive language ("dumb") and didn't explain my point clearly. Most of the rest of the commenters were focused on one part of the article's point, which is very relevant -- the idea that a pixel is no…

>I find it interesting that I was downvoted to the negatives, then you posted this reply, and then I got upvoted to the top. I wonder what the causation is there.

Take this as a sign that HN is going the way of Digg and Reddit, may they rest in peace.

As for the mechanism of action, I think it has to do with people having the need to feel special. The crowd does A, a lonely voice suggests B and people jump on the bandwagon to be different. In other words, it's a mild and misplaced rebellion against the status quo. I've seen this happen countless times on social news sites and it seems to be one of the glitches of the human brain. Follow the white rabbit...

Re: CSS px is an Angular Measurement

#57

Post by JoshTriplett »

nitrogen wrote: post #54
JoshTriplett wrote: post #53

Earlier quoted context omitted.

On the rare occasions where I say "px" rather than some scalable unit, I really do mean pixel . For example, I might use px to specify the width of an element that needs to have exactly the same width as an img tag.

On devices where 1px != 1 device pixel, images should be scaled by the same proportion as the px unit. So, if you set an img to 150px wide, and a div below it to 150px wide, they will be the same width, even if 150px == 300 pixels. I'd be happy to learn of any browsers where that is not the case.

If I wanted an image scaled, I'd give it a size in em or similar, not in px.

Re: CSS px is an Angular Measurement

#58

Post by JoshTriplett »

gwillen wrote: post #41
ars wrote: post #38

Earlier quoted context omitted.

http://blog.notifo.com/notifo

Oh dear. Thanks for the heads-up; this is sort of unfortunate since (as far as I know) HN doesn't provide any other way to be notified of comment replies.

Try http://hnnotify.com/ ; it works perfectly.

Re: CSS px is an Angular Measurement

#59

Post by nitrogen »

JoshTriplett wrote: post #57
nitrogen wrote: post #54

Earlier quoted context omitted.

On devices where 1px != 1 device pixel, images should be scaled by the same proportion as the px unit. So, if you set an img to 150px wide, and a div below it to 150px wide, they will be the same width, even if 150px == 300 pixels. I'd be happy to learn of any browsers where that is not the case.

If I wanted an image scaled, I'd give it a size in em or similar, not in px.

HTML is a text markup language, not a device interface language. CSS is a page layout language. HTML and CSS are designed for optimum user control as well as designer flexibility. You assume you're designing for one type of device. Designers before you have assumed 96dpi for web pages. The W3C realize these assumptions, realize that the user may want to use a different type of device, and thus define px in terms of DPI.

As others have mentioned, if a user prints a web page on a 1200dpi printer, your 960px fixed layout is 4/5ths of an inch wide. Your users would not be pleased. Under the device-centric interpretation of px, you'd have to provide a medium-specific style sheet for every possible type of output device. Designers would not be pleased.

Maybe you're trying to use HTML+CSS as a rendering target for a general purpose widget library like Gtk+. In that case, I can understand your frustration.

Re: CSS px is an Angular Measurement

#60

Post by bzbarsky »

alexchamberlain wrote: post #52
bzbarsky wrote: post #44

Earlier quoted context omitted.

High-resolution devices (that includes iPhone 4 and iPad 3, but also every single printer anyone's used in the last 5+ years) are exactly why the spec says what it says. The only other option was to not have a "px" unit in the spec at all. I mean, think about it. Say you have a 600dpi printer. Take a typical web page that sets its body element to be 1000px wide, because the person writing it was using a 96dpi display…

A pixel is the smallest controllable dot on a screen. The spec shouldn't have changed the definition of this, but introduced a new unit instead. Personally, I'd have both!

Everyone was already using the existing "px" unit because UAs had shipped it. Would you have preferred that every single web page broke on high-res devices (so that no manufacturer would ever introduce any high-res devices to the market) to the status quo?

What would you have used the "device pixel" unit for, exactly?

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