This picture changes between two different pictures when you look at it. Your mind oscillates between seeing the central vertex facing outwards or inwards. The two images you may see are: - a small cube sitting in a corner (outwards) - a large cube with a small cube cut out of it (inwards) You may also be able to see a third image of a small cube projecting out in front of a large cube.
This is a 3D Pen project. Rather than just drawing the picture, I wrote a program to draw it (seen as a small cube sitting in a corner). The project defines the back 3 faces of the large cube and the front 3 faces of the small cube in 3D. The project then rotates the cubes in 3D and projects them onto the 2D screen. Made by me ... I mean ... who else would use this 3D method to draw this illusion.
