Comment 142 for bug 150930

xserver-xorg.postinst no longer sets up xserver-xorg/config/display/modes; instead, the X server deals with mode configuration at run-time. This means that usplash.postinst no longer has anywhere to get the correct modes.

In the desktop CD case, we can cope with this since we have a running X display, and can use xdpyinfo to fish the current screen dimensions out of that (although we may also have to restrict them to valid VESA modes). Unfortunately we can't do anything about the alternate install CD case, since an X server hasn't been started at the point when usplash is configured (well, we could perhaps do X -probeonly along the same lines as xresprobe, but that feels risky at this point).

I think the best option is to have usplash.postinst use xdpyinfo to fetch screen dimensions if DISPLAY is set. That way you at least have the option of reconfiguring usplash within a running X display if it picks the wrong values, and it keeps package-specific logic out of ubiquity. It won't be pretty, but is probably about the best we can do. I'll work on this.