use "canvas"
use "std"

w = 800  h = 600
window("Animate line", w, h)

// Крайние точки линии
x1 = rand(w)  y1 = rand(h)
x2 = rand(w)  y2 = rand(h)

// Направление движения
d1x = rand()  d1y = -rand()
d2x = rand()  d2y = rand()

// Очищаем экран
color(rand(#FFFFFF))
frect(0,0,w,h)

hue = 0
run = 1
while run {
  if checkhoriz(x1) d1x = -d1x
  if checkhoriz(x2) d2x = -d2x
  if checkvert(y1) d1y = -d1y
  if checkvert(y2) d2y = -d2y
  
  x1 = x1 + d1x  x2 = x2 + d2x
  y1 = y1 + d1y  y2 = y2 + d2y

  hue = hue + 0.0001
  if (hue >= 1) hue = 0
  sethsbcolor(hue)
  line(x1, y1, x2, y2)
  repaint()
  sleep(10)
  if keypressed() == VK_ESCAPE run = 0
}

def checkhoriz(px) return (px >= w || px < 0)
def checkvert(py)  return (py >= h || py < 0)

def floor(v) return v - v % 1

def sethsbcolor(h1) {
  qr = h1 * 6 // временно для расчёта
  hueindex = floor(qr) % 6
  f = qr - floor(qr)
  
  if hueindex == 0  color(255, f*255, 0)
  else if hueindex == 1  color(255 - f*255, 255, 0)
  else if hueindex == 2  color(0, 255, f*255)
  else if hueindex == 3  color(0, 255-f*255, 255)
  else if hueindex == 4  color(f*255, 0, 255)
  else if hueindex == 5  color(255, 0, 255-f*255)
}