Cocos2dx Device::getDpi() confusion on android


I am trying to get the device ppi but it looks like on android it’s wrong.

I tried a nexus 4 which has 318 ppi but when I do getDpi it returns 320.
I tried Samsung galaxy s7 and it returned 640 but it’s suppose to be 577.

It seems to work fine on ios…

Also I think it’s miss leading that it’s called getDpi for actually getting the ppi?


Can you tell me why you are doing this? In 4 years, I haven’t used this once, nor come across anyone that has.


To get the diagonal screen size in inches


Does getting the height and width not work for your needs?


Can you get the width and height in inches? If so that would be enough. But even so I think getDpi should work. Maybe even renamed Ppi if that was the original intension. I see a few topics about this but it always seems to get forgotten about.

But I don’t think they realize also that it’s not accurate for android


I can check to see what getDpi() is doing and what it should do.

Edit: issue created:


Thank you! :smiley:


@ericb365, I checked the getDPI interface, and it returns correct on different devices.
DPI means Dots per inch, PPI means Pixels per inch.
Currently, Device::getDPI is returning correct result.
Do you wanna a new API for getting PPI ?


Yes a ppi api would be nice


Before we add a new interface called Device::getPPI, you could make one by yourself using following code:

        DisplayMetrics dm = new DisplayMetrics();
        Display d = getWindowManager().getDefaultDisplay();
        } else {

        double x = Math.pow(dm.widthPixels / dm.xdpi, 2);
        double y = Math.pow(dm.heightPixels / dm.ydpi, 2);

        double screenInches = Math.sqrt(x + y);
        Log.d("cjh", "Screen inches : " + screenInches);
        double ppi = Math.sqrt(dm.widthPixels * dm.widthPixels + dm.heightPixels * dm.heightPixels) / screenInches;
        Log.d("cjh", "dpi: " + dm.densityDpi + ", ppi: " + ppi);


Okay nice this works! It’s a little bit off but good enough for what I need it for. So with @dumganhar code, a Samsung galaxy s7 returns 576.6554669457003 ppi and a nexus 4 returns ppi of 319.0206090553892.

The s7 is suppose to be 577 but we can round that.
The nexus 4 is suppose to be 318 but it’s not a huge deal.

Thanks @dumganhar :slight_smile: