Boli of Bugs — Optical Illusion

Boli of Bugs is an optical illusion by Japanese psychologist Akiyoshi Kitaoka. A static checkerboard of green-and-white squares with small rotated inner squares appears to ripple or warp — even though every tile is perfectly regular.

How it is built

• Outer squares — an N×N grid of SWTwoTonedSquare instances using pattern n=3 (opposite corner quadrant squares). Default colors: dark green base + white corner squares.
• Inner squares — up to four small SWTwoTonedSquare diamonds (n=3, rotated 45°) are placed per cell:
  • Center — at the middle of every cell.
  • Right-edge middle — between each cell and its right neighbour (omitted on the last column).
  • Bottom-edge middle — between each cell and the one below (omitted on the bottom row).
  • Lower-right corner — at the junction of four cells (omitted on the bottom row and last column).
• Checkerboard swap — at even grid positions (row+col even) the inner square uses Color A as its base; at odd positions the assignment is swapped. This alternation is what creates the apparent curvature.

Controls

• Outer colors — change the two fill colors of the large tiled squares.
• Inner colors — change the two fill colors of the central diamonds.
• Background color — canvas fill color.
• Grid N×N — number of rows and columns (3–16).
• Outer / Inner size — fill fraction of each cell; inner is a fraction of outer.
• Inner base angle — starting rotation of all inner squares (45° = classic diamond look).
• Outer / Inner spin — independently rotate all outer or all inner squares in sync.

Keyboard shortcuts

• s — toggle outer spin
• i — toggle inner spin
• r — factory reset
• q — stop all animations