Godel Escher Bach QR Code shadow cube
by SashimiTabernacleChoir, published
The shadow of this cube in different directions gives QR codes pointing to the Wikipedia articles for Kurt Godel, M.C. Escher, and J.S. Bach respectively. Also a pretty challenging print test. Note that QR codes cannot be read in mirror image, so only 3 of the 6 possible cube orientations cast a readable shadow.
Notes. This was generated using a reduced-url QR code generator, a paint program to connect disconnected sections, Inkscape to convert to dxf, and OpenScad to extrude, rotate, and intersect the 3 images. OpenScad rendering took almost 30 minutes on a fast computer.
QR codes are fortunately very forgiving of fairly large modifications due to their built-in parity and redundancy schemes, and I verified readability of the images up through the dxf stage. (Although I got pretty close to the limit on one image, and my camera QR scanner had to rescan a few times to get a read.)
This is a complex image. To get a readable shadow your light source will need to be pretty far away to get a flat pass through. Perhaps someday I'll do a version with transformed geometry, matching specific close-up point sources.
If you can't get it to print cleanly enough to read, hey, claim it's a Borg Cube and gift it to your Trekkie friends.
Best to print this in black; then you may be able to get a QR scanner read looking directly at faces rather than shadows.