I checked the specification in detail. IMO, instead of mixing pixel computation with viewport, it would be better to keep them separate. Let viewport deal with the following descriptors -

Content developer can develop web page on one display - decide the layout of contents and define pixel property as proposed. Then the contents would layout on any other display and UA same as he has envisioned on the reference display.

Sender : Prashant Kisanrao Nevase<prashant.n@samsung.com> Senior Chief Engineer/SRI-Bangalore-Advanced Web/Samsung Electronics

Title : Re: Re: [dip] Proposal for display size and density independent pixel.

1. https://drafts.csswg.org/css-device-adapt/ does not specify how the pixel computation should be done. As I referred Android chrome browser source code, it has different device scale factor than iphone would consider. So this loses the similarity expected. So even though web page specifies viewport meta, there might be different web pages needed to support different platforms having same display size.

2. Display size is not taken. Viewport meta property implementations consider only display densities. Display size also plays important role along with display density. As per current browser implementations, following case is not solved by viewport meta property.

This proposal is regarding to have similar lengths as proportional to display screen. e.g. If 100 pixels measures 1 inch on one device having display size 5 inches, then on same size display of any resolution, it should measure 1 inch. If display size is 10 inches, then 100 pixels should measure 2 inches (proportionally).

On May 25, 2016, at 12:19, Prashant Kisanrao Nevase <prashant.n@samsung.com> wrote:

Dear CSS Working Group,

There are many displays for different devices available for rendering the contents. e.g. big screens, projected screens, TVs, computer monitors, tablets, IVI displays, phablets, phones, wearables, etc. These displays have different sizes and different resolutions and number of pixels or dots per inch (display pixel density or simply called display density) varies for different displays. Due to this writing the contents which will work across different displays seamlessly or with less modification has become difficult and content developer has to consider many different displays e.g. different contents for mobile devices, desktop monitors, etc.

I want to propose "pixel", making it independent of "display size" and "display densities". Many mobile platforms (Android, iOS, WinMo, Tizen, etc.) support display density independent pixel, but display size (pixels measured diagonally) is not taken care any of the platform. Hence contents rendered gets occupied differently on different displays. Also desktop platforms do not support this. So web page opened on 12 inches display looks different than it opened on 21 inches display.

Making this css standard will help web pages render with similar layout on any display.

It proposes having new meta name "pixel" as given below -

<meta name="pixel" content="baseline-density=640;" ></div>

Then pixel scale factor for computing DIP (display independent pixel) is as given below -

device_baseline_density = baseline_density / display_size;
pixel_scale_factor = dots_per_inch / device_baseline_density;

where

baseline_density = Value of baseline-density property [input from web page]
display_size = Display size in inches (measured diagonally) [taken from platform]
device_baseline_density = Baseline density for the target display on which web page is to be rendered. [output]
dots_per_inch = Number of pixels per inch on the target display. [taken from platform]
pixel_scale_factor = Scale factor for pixel for target display [output]

By multiplying the css pixel by pixel scale factor, we get similar layouts for the contents.

For more details, kindly have a look at
https://github.com/prashant-samsung/dip/

~ Prashant Nevase

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