[whatwg] Features for responsive Web design

[Florian Rivoal]

On Thu, 09 Aug 2012 11:29:17 +0200, Kornel Lesiński <kornel at geekhood.net>  
wrote:

> On 8 sie 2012, at 12:57, "Florian Rivoal" <florianr at opera.com> wrote:
>
>>>> Is there a good reason to believe that * will be something other than  
>>>> a
>>>> power of two?
>>>>
>>>> That is, could we just optimize the *x syntax away and specify that  
>>>> the
>>>> first option is 1x, the second is 2x, the third is 4x, etc.?
>>
>> If you look at mobile phones, there are a bunch of existing devices with
>> 1.5 device pixel per css pixel, and also some with 2.25, so I don't
>> think we can assume only powers of 2 will be used.
>
> Pixel-perfect design for non-integer scaling ratios is very hard. To  
> have evenly thin lines (1 device pixel wide) on such screens you have to  
> use fractional CSS pixel sizes, and fractions need to be different for  
> different scaling ratios.
>
> I don't think anybody will take advantage of that. IMHO non-integer  
> ratios are a mistake that can/will be corrected.

I wasn't debating whether or not shipping a device with a 1.5 pixel
ratio is the best decision, but answering: "Is there a good reason
to believe that will be something other than a power of two?"

The fact that it has happened seems a pretty good reason to believe
that it may happen.

> Fractional ratios have proven to be unnecessary: on desktops 1x CSS  
> pixel changed from 72dpi (CRT) to 130dpi on notebook screens, but we  
> haven't got fractional scaling ratios along the way. Variability in  
> screen sizes and actual DPI has been accepted. The same can happen with  
> 1.5x-2.5x screens: pretend they all are 2x, vary CSS pixel width/height,  
> accept physical size of CSS pixel will be slightly different.
>
> For example the 2.25 ratio doesn't make sense to me. 12.5% increase in  
> screen density is going to be imperceptible. A better solution would be  
> to use the crisp 2x ratio and have bigger screen area (in CSS pixels).

A ratio of 2.25 on 720 physical pixel device gives a viewport width of 320
css pixels. 320 pixels is the same as the iPhone, and being identical to
that helps with site compatibility.

I am not convinced that using 2.25 was the best decision, but it has
some justifications, and has happened, so I don't think it is reasonable
to bake in some assumptions in the spec (only powers of 2) when we
know that they don't match reality.

  - Florian