🕷️ Procedural Spider

▶ Play the live demo · by @majidmanzarpour

A self-stabilizing procedural spider you can walk over any terrain. Eight legs solved with closed-form inverse kinematics, a gait that improvises its own footfalls, and a body that leans into slopes, walls, and overhangs — with no animation clips, no skeleton rig, and no physics engine. Just math, every frame. Built with Three.js.

Drag the sliders, drive it around, watch the legs find their own footing. It's strangely calming.

✨ Features

• Analytic IK legs — each leg is solved with a two-bone closed-form solver (hip → knee → foot). No baked animation, no IK iterations to converge: one formula, exact, every frame.
• Improvised gait — feet are planted in the world, not on the body. When the body outruns a foot, that leg lifts, arcs to a fresh foothold, and plants. Step timing is an alternating-gait state machine, so the walk re-times itself naturally as you speed up, slow down, or turn.
• Terrain that's a function, not a mesh — the ground is a closed-form height field, so the spider can sample the exact height and normal at any point. That's what makes foot placement and body alignment rock-solid.
• Climbs walls & overhangs — the body's up-vector blends toward the surface normal under it, so the spider tilts onto inclines and clings to steep faces instead of clipping or sliding.
• A body that bends — two segments (cephalothorax + abdomen) joined at a flexible pedicel, so the abdomen folds at the waist: it hangs down on a wall, droops over a crest, and sags under its own weight. The spider flexes like a real spider, not a rigid blob. (Toggle: BODY FLEX.)
• Knee-swivel collision avoidance — each leg searches a fan of knee orientations and picks the one that keeps the limb out of the ground and obstacles (tunable live).
• Live tuning panel — speed, ride height, step height, gait rate, turn rate, stride, and the knee-swivel search, all adjustable while it walks.
• Tiny & dependency-light — ~1,200 lines across 8 modules, with three as the only runtime dependency. Runs at hundreds of FPS.
• Desktop & touch — WASD + mouse, or an on-screen joystick on phones/tablets.

🎮 Controls

| Action | Desktop | To