Comment 1 for bug 1620911

The client API has all the information required to do this now - the ID of the output their surface is on, the current display mode, the current display orientation, and the physical size of the outputs.

(In hindsight, I think having the DPI in the SurfaceOutputEvent is a minor mistake - the value that clients should care about is scale - which they can't calculate themselves - not DPI, which they can. And don't use, because they're using scale ☺)

My expectation is that exactly zero clients would use the proposed API, and any client that did is not blocked on us providing this API.