New: Add support for handling device pixel ratio

[tonilastre]

The following PR adds support for automatic and manual handling of devicePixelRatio. More information about devicePixelRatio can be found here: https://developer.mozilla.org/en-US/docs/Web/API/Window/devicePixelRatio

There are two modes: Automatic and Manual.

Automatic devicePixelRatio handler (default)
The default behavior is the automatic handler of the devicePixelRatio value and changes (e.g. user drags a view from one display to another with a different DPR value). The automatic handler is turned on when the settings value render.devicePixelRatio equals to null.

Manual devicePixelRatio handler
If you want to manually handle the devicePixelRatio values, just set the settings value render.devicePixelRatio to a numeric DPR value. Orb will stop listening for DPR changes then.

This fixes issue #19.

[AlexIchenskiy]

Nitpicking, but is newDprValue !== previousDprValue necessary here? It seems it's always true because newDprValue is a number while previousDprValue is not. On the other hand, !isNumber(previousDprValue) can be removed to allow users to change the DPR value more than once, but it does not seem like a real use case.

[tonilastre]

Yep you are right, newDrpValue !== previousDprValue can be removed, but not the other check.

This is removing automatic observer for DPR. You can see on line 87 that it checks if settings doesn't have DPR, it will start automatic observer that checked for DPR from the browser.

So these lines 137 and 143 are for:

• 137: Stop the automatic observer - this can happen only if previousDPR was not a number, and the new value is defined
• 142: Start the observer again - this can happen only if previousDRP was a number, and the new value is null (this enables users to remove manual DPR handling).

Users can still change DPR manually which happens on line 127.

[AlexIchenskiy]

Nitpicking, but it would be nice to add a check for window.devicePixelRatio being null or undefined, just in case of older browsers that do not support this. I think using || 1 will do the job.

[tonilastre]

Not nitpicking, but it's a valid bug. Great catch.

[AlexIchenskiy]

Looks good to me now!