When displaying PDFs in "One Page" mode, it would be very convenient to have an option that ensures that the zoom level is automatically adjusted such that the displayed page fills the available window/display area as much as possible. In particular in full-screen mode, I think this would even be a good default.
Use case: when I use xournal to show PDF presentation slides in full-screen mode, it should not be necessary to manually adjust the zoom to the most useful size, to show exactly one full page as large as possible. When displaying a 4:3 slide on a 16:9 screen, the "Page Width" toolbar button will cut off the top and botton of the page, and there is currently no "Page height" or (better) "Page fit" button that gets me quickly to the right zoom level. Rather than just doing a one-off adjustment of the zoom factor, ideally "Page fit" and "Page width" should be modes that automatically adjust the zoom each time the window size changes. Similar functions are offered by other PDF viewers, such as acroread or okular (but those lack the excellent drawing functions of xournal).
Ok. In the meantime, note that "Page height" is an option in the zoom
dialog box (the next-to-last button on the first toolbar).