-- Cubic bezier on love2d
-- c key : draw control line on/off

-- References
-- http://hakuhin.jp/as/curve.html

function get_cubic_bezier_point(p0x, p0y, v0x, v0y, v1x, v1y, p1x, p1y, t)
  local q = 1.0 - t
  local u0 = q * q * q
  local u1 = 3.0 * t * q * q
  local u2 = 3.0 * t * t * q
  local u3 = t * t * t
  local ox = u0 * p0x + u1 * v0x + u2 * v1x + u3 * p1x
  local oy = u0 * p0y + u1 * v0y + u2 * v1y + u3 * p1y
  return ox, oy
end

function love.load()
  love.graphics.setDefaultFilter("nearest", "nearest")

  img = love.graphics.newImage("circle02_64x64_take1_05_5bit32col_edit.png")

  scrw = love.graphics.getWidth()
  scrh = love.graphics.getHeight()
  bx = scrw * 0.95
  by = scrh / 2

  ctrl_points = {
    {100, 200},
    {scrw * 0.3, scrh * 0.1},
    {scrw * 0.6, scrh * 0.9},
    {bx, by}
  }

  points = {}

  ang = 0

  draw_ctrl_points = false
end

function love.update(dt)
  ang = ang + 180 * dt

  -- set control points
  mx, my = love.mouse.getPosition()
  ctrl_points[1][1] = mx
  ctrl_points[1][2] = my

  local a0 = math.sin(math.rad(ang))
  local a1 = math.sin(math.rad(ang * 0.6))

  -- ctrl_points[2][1] = mx + (bx - mx) * 0.3
  ctrl_points[2][2] = scrh * (a0 * 0.5 + 0.5)

  -- ctrl_points[3][1] = mx + (bx - mx) * 0.6
  ctrl_points[3][2] = scrh * (a1 * 0.7 + 0.5)

  -- get cubic bezier points
  local interpolate = 40
  local spd = 1.0 / interpolate
  local p0x, p0y, v0x, v0y, v1x, v1y, p1x, p1y
  p0x = ctrl_points[1][1]
  p0y = ctrl_points[1][2]
  v0x = ctrl_points[2][1]
  v0y = ctrl_points[2][2]
  v1x = ctrl_points[3][1]
  v1y = ctrl_points[3][2]
  p1x = ctrl_points[4][1]
  p1y = ctrl_points[4][2]

  points = {}
  local t, x, y
  for t = 0, 1.0, spd do
    x, y = get_cubic_bezier_point(p0x, p0y, v0x, v0y, v1x, v1y, p1x, p1y, t)
    points[#points + 1] = {x, y}
  end
  t = 1.0
  x, y = get_cubic_bezier_point(p0x, p0y, v0x, v0y, v1x, v1y, p1x, p1y, t)
  points[#points + 1] = {x, y}
end

function love.draw()
  -- fill window background
  love.graphics.clear(0.2, 0.5, 0.6, 1.0)

  -- draw arm
  local ox, oy = img:getWidth() / 2, img:getHeight() / 2
  love.graphics.setColor(1.0, 1.0, 1.0, 1.0)
  for i = #points, 1, -1 do
    local px = points[i][1]
    local py = points[i][2]
    love.graphics.draw(img, px, py, 0, 1.0, 1.0, ox, oy)
  end

  -- draw control points line
  if draw_ctrl_points then
    love.graphics.setColor(1.0, 1.0, 1.0, 0.7)
    love.graphics.line(
      ctrl_points[1][1],
      ctrl_points[1][2],
      ctrl_points[2][1],
      ctrl_points[2][2],
      ctrl_points[3][1],
      ctrl_points[3][2],
      ctrl_points[4][1],
      ctrl_points[4][2]
    )
    for i = 1, 4 do
      local px, py
      px = ctrl_points[i][1]
      py = ctrl_points[i][2]
      love.graphics.circle("line", px, py, 16)
    end
  end

  -- draw FPS
  love.graphics.setColor(1.0, 1.0, 1.0, 1.0)
  love.graphics.print("FPS: " .. tostring(love.timer.getFPS()), 2, 2)
  love.graphics.print("C key : Draw control points", 2, 20)
end

function love.keypressed(key, isrepeat)
  if key == "escape" then
    -- ESC key to exit
    love.event.quit()
  elseif key == "c" then
    draw_ctrl_points = not (draw_ctrl_points)
  end
end