Although the stereoscopic illusion is cubic, it applies to any shape, object or scene, not just a “cube”.
This is a good thing, since monitors, TV’s and movie theater screens are usually rectangular. 
From “Flat” to “Cubic”.
Back to square one with the Stereoscopic Cubic Illusion.
A 45 degree Z-axis rotation of a square, followed by a 45 degree Z-axis rotation of a rectangle.
The 45 degree Z-axis rotations of this square and cube introduces very close to 3.3% (1/30) Stereoscopic Net Deviation, which is the only amount of depth that can produce a perfectly cubic stereoscopic illusion, viewable with any horizontal field of view (from any seat).
Watch this video in 2D or 3D by clicking on the “3D” button under the video and selecting your options, e.g., “Turn off 3D”.
If you are using red/cyan anaglyph glasses, be sure to select “Red/Cyan” then “Optimized (Dubois)”.