wayland: fix vertical resizing

Resizing in strictly the vertical direction has been broken forever on wayland. It's because of how the keepaspect calculation always resized with respect to the width. So if you moved the mouse strictly vertically with no change left/right, the mpv window would never change size since it just calculates with respect to the width that doesn't change. Fixing this is kind of weird and maybe someone should think of a better algorithm for preserving aspect ratio (we just multiply by the gcd basically), but whatever. You might naively try something like "resize with respect to what direction changes the most" at first, but this leads to very cludgy resizing since during a typical mouse dragging motion, it will flip constantly from "resize w/ respect to the width" and "resize w/ respect to the height". It "works" but it's really ugly and not worth it. The trick is to realize that we need to consider the resizing state as one continuous motion, choose a direction initially, stick to it throughout the entirety of the resize, and reset the relevant parameters after we finish the resize. This ensures the direction never unintuitively flips during a motion, but also allows for the strictly vertical case to still work. Might as well note it here in the commit, but mpv's resizing behavior technically violates xdg-shell. For the resizing event, "[t]he window geometry specified in the configure event is a maximum; the client cannot resize beyond it." Well, we do obviously go beyond the maximum in certain cases. For example consider resizing strictly horizontally. The width value increases from the compositor but not the height. Since mpv preserves aspect ratio by default, the height obviously must increase which will go over the prescribed bounds by the compositor. This happens before and after this commit, and I think everyone agrees is the desired behavior. With this commit, now vertical resizing works which violates xdg-shell in the same way. Before, it incidentally obeyed the protocol since it did not resize at all, but let's presume users expect the window to actually get bigger when they do a drag resize. *: https://wayland.app/protocols/xdg-shell#xdg_toplevel:enum:state:entry:resizing

DUDudemanguy committed 2 years ago