smokestack.lua

----- parameters -----

base = 12:: int_slider("Bottom", 3, 48)
top = 8:: int_slider("Top", 3, 48)
height = 50:: int_slider("Height", 1, 500)
block_w = 3:: float_slider("Block Width", 0.2, 10, 0.2)
block_d = 1:: float_slider("Block Depth", 0.2, 10, 0.2)
block_h = 1:: float_slider("Block Height", 0.2, 10, 0.2)

rotate = 0 :: float_slider("Rotate", 0, 360, 10)
offset_frac = 0.5 :: float_slider("Offset", 0, 1, 0.1)

tighten = false:: toggle("Tighten")

----------------------

c = col()
c.dim = vec(block_w,block_h,block_d)

function subtends(_c, _r)
 return (2*math.atan((_c.dim.x/2)/(_r - _c.dim.z/2)))
end

function radius_to(_c, _n)
 return (_c.dim.z/2 + c.dim.x/2/math.tan(2*math.pi/_n/2))
end

function circle(_c, _angle, _r, _y)
 local blocks = math.floor(2*math.pi/subtends(_c, _r))
 local alpha = 2*math.pi/blocks

 for i=1,blocks do
  local t = _angle + (i-1.5)*alpha

  if tighten then
   _r = radius_to(_c, blocks)
  end

  local x = _r*math.cos(t)
  local z = _r*math.sin(t)

  local b = brk(_c)
  b.pos = vec(x, _y, z)
  b.rot.y = -math.deg(t) + 90
 end
end

r_base = radius_to(c, base)
r_top = radius_to(c, top)
offset = 0

function scale_by(_i, _imin, _imax, _min, _max)
 if _imin == _imax then
  return _min
 end
 return _min + (_i - _imin)/(_imax - _imin)*(_max - _min)
end

for i=1,height do
 local y = c.dim.y*(i-0.5)
 local r = scale_by(i,1,height, r_base, r_top)

 offset = offset + math.rad(rotate) + offset_frac*subtends(c, r)
 circle(c, offset, r, y)
end

randomize_colors()