NFR: Add the Eyepiece View mode.

[halxinate]

Please add the Eyepiece View mode. So you could naturally add an EP FOV overlay and all the required new controls for that FOV arbitrary rotation and mirroring to simulate the telescopic view exactly as in the real thing. I don't remember honestly, but I believe you have something like that in the desktop version as a plugin already. Such a mode, besides its educational and practical values, could also drastically improve the performance of redrawing (within just a small(ish) region of the chart so the web app would behave smoother on sluggish internet browsers.