Bouncing Balls - Coders

-- Bouncing Balls Animation
-- by @beezing

abs = math.abs
sin = math.sin
cos = math.cos
sqrt = math.sqrt
random = math.random

function rectangle(x, y, width, height)
  move(x, y)
  draw(x+width, y)
  draw(x+width, y+height)
  draw(x, y+height)
  draw(x, y)
end

function circle(x, y, radius)
  move(x+radius, y)
  for i = 0, 3.14*2 + 0.1, 0.1 do
    draw(x + radius*cos(i), y + radius*sin(i))
  end
end

function moveBall(ball, wall)
  -- calculate movement borders
  minX = wall.x + ball.sz + 2
  maxX = wall.width - ball.sz + 2
  minY = wall.y + ball.sz + 2
  maxY = wall.height - ball.sz + 2

  -- check ball for borders
  if ball.x <= minX then newX = minX
    elseif ball.x >= maxX then newX = maxX
      else newX = ball.x end
  if ball.y <= minY then newY = minY
    elseif ball.y >= maxY then newY = maxY
      else newY = ball.y end

  -- check ball for collision
  hitX = (ball.x <= minX) or (ball.x >= maxX)
  hitY = (ball.y <= minY) or (ball.y >= maxY)

  return hitX, hitY, newX, newY
end

-- define wall
wall = {}
wall.x = 4
wall.y = 24
wall.width  = 312 --312 --760 --312
wall.height = 740 --388 --760 --740

-- define animation constants
ballCount = 5
minSize   = 10
maxSize   = 50
maxSpeed  = 50
slowRate  = 0.1
infinite  = false

-- create balls
balls = {}
for i = 1, ballCount do
  -- randomly create ball
  ball = {}
  ball.sz = random(minSize, maxSize)
  ball.x  = random(wall.width -2*ball.sz) + ball.sz
  ball.y  = random(wall.height-2*ball.sz) + ball.sz
  ball.dx = random(-maxSpeed, maxSpeed)
  ball.dy = random(-maxSpeed, maxSpeed)
  ball.r  = random(192)
  ball.g  = random(192)
  ball.b  = random(192)
  balls[i] = ball
end

-- animate bouncing balls
stopAll = 1
while stopAll > 0 do
  disableScreenRefresh()

  -- draw wall
  clear()
  setcolor(0,0,0)
  rectangle(wall.x, wall.y, wall.width, wall.height)

  -- animate balls
  for i = 1, #balls do
    -- draw ball at its current position
    setcolor(balls[i].r, balls[i].g, balls[i].b)
    circle(balls[i].x, balls[i].y, balls[i].sz)

    -- move ball to its next position based on its speed
    balls[i].x = balls[i].x + balls[i].dx
    balls[i].y = balls[i].y + balls[i].dy

    -- check ball's movement for collision with the wall
    hX, hY, balls[i].x, balls[i].y = moveBall(balls[i], wall)

    -- bounce ball if it hits the wall
    if hX then balls[i].dx = -balls[i].dx end
    if hY then balls[i].dy = -balls[i].dy end
  end

  if not infinite then
    -- slow down animation
    stopAll = 0
    for i = 1, #balls do
      -- calculate deacceleration
      a  = balls[i].dy * balls[i].dy
      b  = balls[i].dx * balls[i].dx
      c  = sqrt(a+b)
      c_ = c-slowRate
      b_ = abs(balls[i].dx) - abs((balls[i].dx * c_)/c)
      a_ = abs(balls[i].dy) - abs((balls[i].dy * c_)/c)

      -- deaccelerate ball speed
      if balls[i].dx < 0 then
        balls[i].dx = balls[i].dx + b_
      elseif balls[i].dx > 0 then
        balls[i].dx = balls[i].dx - b_ end
      if balls[i].dy < 0 then
        balls[i].dy = balls[i].dy + a_
      elseif balls[i].dy > 0 then
        balls[i].dy = balls[i].dy - a_ end

      -- check for remaining movement based on velocity
      if abs(c_) >= slowRate then
        stopAll = stopAll + abs(c_)
      end
    end
    -- stop if sum of velocity is less then slowing rate
    if stopAll < slowRate then stopAll = 0 end
  end

  enableScreenRefresh()
end