Since composite becomes famous the desktop-cube was one of the top showcase-effects.
Right now they are a few popular composite-manager out there. One of them is kwin from the KDE desktop enviroment. kwin also supports the cube-effect alongside with alot of other effects.
Today i'll show you how to personalize this cube a bit, so that you have your own image at the top and botton of the cube. Usually there is a nice KDE-logo, but you'll see how it would look like with a gentoo-logo :) To make that possible on your system you first need the gentoo png image which you can get from here: image
Afterwards i suggest you to make a backup of the original KDE-image:
cp /usr/share/apps/kwin/cubecap.png /usr/share/apps/kwin/cubecap.png.bak
Then you can copy/move the new image into the above folder. Be sure that you change the filename to "cubecap.png".
cp ~/gentoo_logo.png /usr/share/apps/kwin/cubecap.png
After a restart of kwin the result would look like this: