Howto edit source code VirtualBox 5.0.16 so that high resolution virtual desktop will scroll when mouse near window

http://stackoverflow.com/questions/36011878/howto-edit-source-code-virtualbox-5-0-16-so-that-high-resolution-virtual-desktop

Using VirtualBox 5.0.16 and WinXP, my computer (1280x800p) can have 3840x1024p virtual desktop. But the virtual desktop is with scrollbar vertical and horizontal.

What I want is: No problem with those scroll bar, but it would be very nice to have virtual desktop that can automatically scroll to the right when my mouse go to the right perimeter (and all direction right, left, up and down).

Anyone know what code to be revised in the VirtualBox Source Code? (what is the filename, where, and what is the code)