That of course depends on the implementation. The point is not the game or the UI ignoring DPI scaling or browser zoom, in fact you would want to support that.

That of course depends on the implementation. The point is not the game or the UI ignoring DPI scaling or browser zoom, in fact you would want to support that. The point is, that you cannot do so on a pixel perfect-level across the board, because the widely supported way to do so, DevicePixelRatio, is just that: a ratio with precision issues under certain combinations of screen dpi and browser zoom. The browser can do pixel perfect rendering, it has to for sharp text. But in WebGL there is no reliable way to get the coordinates to do so as well. Browser specific ways to do so exist, but using standard APIs doesn't work browser zooms like 130% or DPI scales like 1.25 in combination with certain resolutions.