I am using VirtualBox under Ubuntu Linux, and a Mac OSX (Mountain Lion) as guest OS.
For me, the full resolution started working when I did all of the following:
- Install MultiBeast 4, making sure that the system boots from the virtual hard disk rather than from any booting CD. I followed the instructions here:
http://www.macbreaker.com/2012/07/mountain-lion-virtualbox.html
However, at the end of the procedure I did not have the full resolution, which for me must be 1920x1080x32.
- In the virtual machine, edit these PLIST files,
sudo pico /Extra/com.apple.boot.plist/Library/Preferences/SystemConfiguration/com.apple.Boot.plist
In this file, inside <dict>...</dict>, insert:
<key>Graphics Mode</key>
<string>1920x1080x32</string>
<key>Kernel Flags</key>
<string>"Graphics Mode"="1920x1080x32"</string>
sudo pico /Extra/com.chameleon.Boot.plist
In this file, inside <dict>...</dict>, insert:
<key>GraphicsEnabler</key>
<string>y</string>
<key>Graphics Mode</key>
<string>1920x1080x32</string>
<key>Kernel Flags</key>
<string>npci=0x3000 darkwake=0 "Graphics Mode"="1920x1080x32"</string>
I noticed that I already had some "kernel flags", so I just added another one for "Graphics Mode". Also note that "Graphics Mode" has a space inside it.
Shutdown the virtual machine and do the commands
vboxmanage setextradata "MAC OS X" "CustomVideoMode1" "1360x768x32" vboxmanage setextradata "MAC OS X" "GUI/CustomVideoMode1" "1360x768x32 VBoxManage setextradata MountLion VBoxInternal2/EfiGopMode 3
After this, the virtual machine boots with full resolution.
Now, this might be overkill, and the result could be achieved perhaps with fewer options, but I tried various things until it started working.