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CSS px is an Angular Measurement

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Re: CSS px is an Angular Measurement

#11

Post by mikeklaas »

colanderman wrote: post #9
tlb wrote: post #6

Earlier quoted context omitted.

That includes me. Making a pixel not be a pixel is surely one of the great pooch-screws of modern standards. 'pt' existed to be resolution-independent.

I'm not a web designer. Can you explain to me why it's important to be able to position/size something to exactly N pixels, rather than to exactly kN pixels (where k is some integer decided by the browser implementor)?

The biggest reason is that most css properties ignore fractional px values—you can't draw a .5px border, for instance.

Re: CSS px is an Angular Measurement

#13

Post by tlb »

colanderman wrote: post #9
tlb wrote: post #6

Earlier quoted context omitted.

That includes me. Making a pixel not be a pixel is surely one of the great pooch-screws of modern standards. 'pt' existed to be resolution-independent.

I'm not a web designer. Can you explain to me why it's important to be able to position/size something to exactly N pixels, rather than to exactly kN pixels (where k is some integer decided by the browser implementor)?

Images and and use actual pixels. It's hard to make things look right when you don't have the same unit in CSS.

Re: CSS px is an Angular Measurement

#14

Post by evincarofautumn »

mikeklaas wrote: post #11
colanderman wrote: post #9

Earlier quoted context omitted.

I'm not a web designer. Can you explain to me why it's important to be able to position/size something to exactly N pixels, rather than to exactly kN pixels (where k is some integer decided by the browser implementor)?

The biggest reason is that most css properties ignore fractional px values—you can't draw a .5px border, for instance.

Which is absurd, because antialiasing exists for that very reason. I should be able to render a single-pixel-thick vertical line between two columns of display pixels, and get two columns of display pixels at 50% (apparent) brightness. Subpixel rendering would be even better.

Re: CSS px is an Angular Measurement

#15

Post by yonran »

Not only is the definition of pixel unexpected, but 1in is now defined to be 96px in CSS 2.1, because this was the default in Windows for so many years. In retrospect, given whole page zoom from Opera and high-resolution displays from Apple, probably CSS shouldn't have had units named "in" and "px" at all but instead should have had a single unit like SVG.

Re: CSS px is an Angular Measurement

#16

Post by crazygringo »

gwillen wrote: post #5

This is dumb. The fact that one pixel subtends a particular visual angle does not imply that N pixels subtend N times that angle. It should be very plain to anybody implementing or using a rendering engine that pixels are intended to be linearly additive. This implies that N pixels will subtend less than N times the angle one pixel subtends. On a flat screen, this is normal and expected, because a pixel further from…

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

Re: CSS px is an Angular Measurement

#17

Post by javajosh »

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 important to resolve this discrepancy.

Personally, I'm disgusted at the W3C standard. It's a great idea to have an angular measure (really great) but to call it a "pixel" is horrible. A pixel is the smallest controllable dot on a physical display, and nothing else. Call it an "aixle" abbreviated "ax" and short for "angular pixel" but don't overload the term "pixel".

Re: CSS px is an Angular Measurement

#18

Post by wmf »

tlb wrote: post #13
colanderman wrote: post #9

Earlier quoted context omitted.

I'm not a web designer. Can you explain to me why it's important to be able to position/size something to exactly N pixels, rather than to exactly kN pixels (where k is some integer decided by the browser implementor)?

Images and and use actual pixels. It's hard to make things look right when you don't have the same unit in CSS.

Maybe I'm misunderstanding, but I don't think this is correct; the browser should scale everything. See http://joubert.posterous.com/crisp-html-5-canvas-text-on-mob... for example.

Re: CSS px is an Angular Measurement

#19

Post by ned »

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…

I'm afraid this boat has long sailed. The "pixel" term is in the CSS 2.1 Spec. It's set in stone.

Personally I've made peace with it. I say either "CSS pixels" or "device pixels", depending on what I want to express.

And although the high resolution screens have only made the difference between the two more visible, it was there since Opera featured full pages zoom many years ago, and when Mobile Safari introduced the "viewport" meta-tag in 2007.

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