Android – How to calculate device pixel ratio

androidandroid-layoutcsshtml

I would like to know how the -webkit-device-pixel-ratio is calculated. I had already read this. Yet I am unable to understand it clearly.
I would also like to know if there is a list of which devices use which pixel ratio. The android website says

The Android Browser and WebView support a CSS media feature that allows you to create styles for specific screen densities—the -webkit-device-pixel-ratio CSS media feature. The value you apply to this feature should be either "0.75", "1", or "1.5", to indicate that the styles are for devices with low density, medium density, or high density screens, respectively.

but I found that we need to use -webkit-device-pixel-ratio=2 to make a web application compatible on 768 x 1280 resolution screen.

Best Answer

According to this article

http://www.html5rocks.com/en/mobile/high-dpi/

The magic number seems to be 150.

Dividing the physical ppi by the ideal ppi of 150, gives the device pixel ratio.

E.g. a device with 445ppi would have a dpr of 3 ->> 445 / 150

The simple calculation seems to hold up okay for many items on this list,

http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density

Related Solutions

Html – How to horizontally center an element

You can apply this CSS to the inner <div>:

#inner {
  width: 50%;
  margin: 0 auto;
}

Of course, you don't have to set the width to 50%. Any width less than the containing <div> will work. The margin: 0 auto is what does the actual centering.

If you are targeting Internet Explorer 8 (and later), it might be better to have this instead:

#inner {
  display: table;
  margin: 0 auto;
}

It will make the inner element center horizontally and it works without setting a specific width.

Working example here:

#inner {
  display: table;
  margin: 0 auto;
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

EDIT

With flexbox it is very easy to style the div horizontally and vertically centered.

#inner {  
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%;
  display: flex;
  justify-content: center;
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

To align the div vertically centered, use the property align-items: center.

Html – How to make a div not larger than its contents

The solution is to set your div to display: inline-block.

Best Answer

Related Solutions

Html – How to horizontally center an element

EDIT

Html – How to make a div not larger than its contents

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