spiral-shell.clj

; === Spiral Shell ===
;
; A logarithmic spiral shell, like a snail or nautilus.
;
; The shell is built by lofting a circle along a helical path
; that expands as it spirals. The cross-section grows with each
; revolution, mimicking the natural growth pattern of mollusks.
; A noisy displacement adds organic surface texture.
;
; The key insight is using loft-n with a shape-fn that scales
; the cross-section proportionally to position along the path,
; combined with a helical path generated by arc-h + vertical lift.
;
; Demonstrates:
; - arc-h for helical paths (horizontal arcs + vertical offset)
; - loft-n with combined shape-fns (tapered + noisy)
; - Parametric spirals with growth ratio
; - Organic surface detail with procedural noise
;
; Try changing:
; - n-turns for more or fewer spiral revolutions
; - growth for how quickly the shell expands
; - tilt for the cone angle of the spiral
; - noise amplitude/scale for surface texture

(def n-turns 3)
(def steps-per-turn 48)
(def total-steps (* n-turns steps-per-turn))
(def initial-radius 3)
(def growth 2.8)        ; radius multiplier over full spiral
(def spiral-radius 15)  ; radius of the helical path
(def tilt 25)           ; cone angle in degrees

; The helical path: spiraling outward and upward
(def helix
  (path
    (resolution :n steps-per-turn)
    (tv tilt)
    (dotimes [i total-steps]
      (let [t (/ i total-steps)
            r (* spiral-radius (+ 1.0 (* t (- growth 1.0))))]
        (arc-h r (/ 360 steps-per-turn))))))

; Shell: loft a growing, slightly bumpy circle along the helix
(def shell
  (loft-n total-steps
    (-> (circle initial-radius 24)
        (tapered :to growth)
        (noisy :amplitude 0.3 :scale 5 :octaves 2))
    (follow-path helix)))

(register shell shell)