// ============================================================
// split bar — a horizontal bar cut by a virtual line between
// two draggable control points. Each side sews in its own
// thread, with its own fill style.
// ============================================================

seed 7
fabric 'woven'

// --- Cut line ---
let cut_a = [13.7, 37.6]    // [xy]
let cut_b = [-13.7, -37.6]  // [xy]

// --- Bar ---
let bar_w = 75                // [30:90]
let bar_h = 30                // [6:40]

// @preset Classic 20 : cut_a=[13.7,37.6], cut_b=[-13.7,-37.6]
// @preset Vertical   : cut_a=[0,40], cut_b=[0,-40]
// @preset Slash      : cut_a=[32,20], cut_b=[-32,-20]

// keep the line defined even if both handles land on one spot
if vdist(cut_a, cut_b) < 1 [ cut_b = vadd(cut_a, [ 0, -2 ]) ]

// the bar as a region (rectangle, closing segment implicit)
let hw = bar_w / 2
let hh = bar_h / 2
let bar = [ [ -hw, -hh ], [ hw, -hh ], [ hw, hh ], [ -hw, hh ] ]

// a big rectangle covering one side of the infinite line a->b:
// stretch the segment 200 mm past each end, then sweep it
// 200 mm sideways — plenty to swallow the whole field
def halfmask(a, b) [
  let d  = vnorm(vsub(b, a))          // along the line
  let nv = vrot(d, 90)                // off to one side
  let a2 = vsub(a, vscale(d, 200))
  let b2 = vadd(b, vscale(d, 200))
  return [ a2, b2, vadd(b2, vscale(nv, 200)), vadd(a2, vscale(nv, 200)) ]
]

let mask     = halfmask(cut_a, cut_b)
let side_one = clippaths(bar, mask, 'intersect')     // list of regions
let side_two = clippaths(bar, mask, 'difference')

if len(side_one) == 0 or len(side_two) == 0 [
  print('note: the cut line misses the bar — one side is empty')
]

// inset each piece 0.4 mm (so the two colours never overlap and a
// thin fabric channel marks the cut), then tatami-fill it.
// Park the needle ON the data before opening the fill.
def sewside(pieces) [
  for piece in pieces [
    for ring in offsetpath(piece, -0.4) [
      let rr = resample(ring, 1.5)
      up setpos(rr[0]) down
      beginfill sewpath(rr) endfill
      trim
    ]
  ]
]

// both fills key off the cut direction, so the texture
// follows the handles as you drag them
let cut_deg = vheading(vsub(cut_a, cut_b))

// side one: dense solid fill, rows parallel to the cut (thread 1)
color 1
fillangle cut_deg
fillspacing 0.8
filllen 0
sewside(side_one)

// side two: open hatch, rows across the cut (thread 2)
color 4
fillangle(cut_deg * -1)
fillspacing 0.8
filllen 3
sewside(side_two)