Fullscreen under Linux Ubuntu 12.04 LTS has large black borders. The actual c64 screen is small. I only have XrandR as a 'FullScreen Device'. None of the resolutions help. On the web, some report seing VidMode, but I do not.
Compiled trunk on 2014-10-25 with the following options:
configure --enable-gnomeui3 --enable-debug --enable-debug-code --enable-memmap --prefix="<some dir="">"</some>
At startup, this is the only relevant logs I find:
X11: GTK version compiled with: 3.4 (xf86 ext:yes cairo:yes pango:yes VTE:no hwscale:no fullscreen:yes ui-threads:no)
XRandR: XRandR reports current display: 1920x1080@50
hwscale:no
that is your problem - you need gtkglext for hardware scaling, which again is not available for gtk3 yet. omit the --enable-gnomeui3 from configure and it should work.