I know that this thread is quite old, but I figured that I could share my experiences anyway. Frowm what I have gathered I believe this option I actually overrides the browser's "device pixel ratio". scaling the project to pixel ratio: 1.
For those who do not know how pixel ratio works I will try to explain it as simple as possible. Today many mobile phones have really high pixel density. The LG G3 has a resolution of 2560x1440 on a 5" display. If webpages were viewed with the pixelratio of 1, meaning that normal 12px text would be rendered as 12px. that would make it super tiny and unreadable. Instead a pixel ratio is assigned to browser/device in order to scale it according to the ratio. LG G3 has a pixel ratio of 3, meaning that 12px text will actually be rendered as 36px, same scaling will be carried out on pictures and web-elements.
The tricky thing with construct is that the canvas is assigned to the "windows size", let say you use 1024x768px on the project. The LG G3 will scale the canvas 3x, even though it will still be rendered in the full screen size, resulting in a resolution of 341x256.... Making the whole game look very low res.
I could be wrong with technicalities, but this is my experience of the option.
The trouble I'm having is that I can't actually achieve decent frame rates on the LG G3 with the "use high DPI display"-option set to yes. The only way is to have one or two layers, which is very different from the 12 layers I am currently using.
I would actually love to have this option within the game's graphics option, But I'm guessing that is pretty much impossible as it changes the way the canvas is initialized? Any ideas would be of great help though! Otherwise I need to create a new thread about that in the future.
Excelente explicação, me ajudou muito, Obrigado...