Kairiki Anto

Kairiki Anto (怪力アント), literally known as Strong Ant, is a 1990 Japanese short computer-animated film produced and directed by Takashi Fukumoto and Hitoshi Nishimura.

Synopsis
Robot figures—codenamed "Atom Ants"—ride unicycles along the top of an endless maze of walls.

Production
Filmlink International and Polygon Pictures were hired by NEC and Osaka University to create a 1-minute computer-animated film. Its directors and producers, Takashi Fukumoto and Hitoshi Nishimura, recognized the path.

Fukumoto explained: "It was the Hilbert curve. The Hilbert curve is generated by iterative steps, each producing a new curve with higher complexity. It is possible to create an image of a truly infinite Hilbert curve by evaluating a visible point on the ground surface and applying the Hilbert curve iteration in reverse. If that technique was used, then the horizon should be completely flat; however, the horizon gradually peaks about 2/3 from the left border of the image. Hence, the path is not infinite, it’s just very large. The peak is actually one corner of the square-shaped bounds of the Hilbert curve approximation and the virtual camera is located close to the opposite corner."

Nishimura replied: "Mathematically, the Hilbert curve is a path without any thickness since it is constructed out of line segments joining points on a plane. The points exist in a square-shaped grid. We chose 256×256 points, a large region which we hoped would conceal the fact that the landscape is not really infinite. To give the path thickness, each point is surrounded by a square separated by 2 other squares."

Fukumoto also stated that "the 256×256 points are covered by 766×766 squares (i.e. 256 points + 2 squares between points × 255 such regions). Each line segment spans 4 squares, crossing 3 square boundaries between the points. Each of the intersections between a line and a square boundary is the starting point of a unicyclist. The curve visits all 65536 points only once, requiring 65535 line segments. Each of those carries 3 unicyclists. The 2 terminal points also have short line segments that leave the grid, each contributing an extra unicyclist. There are 3×65535 + 2 = 196607 unicyclists in total in our animation."

He and Nishimura generated the following 2 test images using those ideas together, with Fukumoto stating that "the horizon actually looks pretty flat".

The engineers of the short film constructed a model of the unicyclist out of spheres and cylinders. What appears to be ellipsoids are actually scaled spheres. Finally, they merged the two together.

Their ray tracer is not a general purpose ray tracer. They hard coded everything into the program. Also, it’s not very optimized. It essentially uses bounded-box intersections to solve the ray intersections, but few other optimizations were applied. Fukumoto wanted 29,970 samples per pixel at 640×480 resolution (480p). Together that meant that rendering each frame took between 90 and 210 minutes. Each scene contains a loop of 60 frames repeated 5 times across 10 seconds. There are 360 unique frames in total.

To save him and Nishimura several weeks of rendering, they wrote the program such that users can launch it with command-line arguments, giving it a range of frames to generate. He and Nishimura asked the staff to help them split up the work by kicking off the application on all idle computers at their disposal primarily during several nights. They noted all contributors in the animation credits, but they left uncredited.

Fukumoto and Nishimura hired the composers Joji Yuasa, Yuji Ohno and Koji Kondo to make the music for the short film. To release the film, Fukumoto stated that it was computed on a SK3 supercomputer.

Release
Kairiki Anto was released in Japan on May 1, 1990. It was also released in Italy and the United States on August 1, 1992.