// TRIANGLE FIELD — a `for` loop grows, rotates, and recolours one motif.
seed 42

fabric "woven

// --- triangle field ---
let numTriangles = 40  // [8:1:50] number of triangles
let startSize = 6      // [2:0.5:12] first triangle size, mm
let growFactor = 1.1   // [1.02:0.01:1.2] size multiplier per triangle
let rotationStep = 13  // [1:1:45] rotation step, degrees

def drawTriangle(cx, cy, size, angle) [
  // Convert the three polar corners into x/y points around the centre.
  let x0 = cx + size * sin(angle)
  let y0 = cy - size * cos(angle)
  let x1 = cx + size * sin(angle + 120)
  let y1 = cy - size * cos(angle + 120)
  let x2 = cx + size * sin(angle + 240)
  let y2 = cy - size * cos(angle + 240)
  // Lift before moving so separate triangles are not joined by thread.
  moveto x0 y0
  down
  setxy x1 y1
  setxy x2 y2
  setxy x0 y0
  up
  trim
]

let colorList = [1, 2, 3, 4, 5, 6]

for i = 0 to numTriangles - 1 [
  // `i` starts at zero, so it is handy for a growing sequence and list index.
  let size = startSize * pow(growFactor, i)
  let angle = rotationStep * i
  let c = colorList[i % len(colorList)]
  color c
  let stitch = 1.5 + i * 0.1
  stitchlen stitch
  // Keep the largest triangles inside the hoop.
  if size <= 44 [
    drawTriangle(0, 0, size, angle)
  ]
]