Breakout Pico-8

breakout-8.lua

function _init()
  cls()
  ball_x = 10
  ball_dx = 2
  ball_y = 20
  ball_dy = 2
  ball_r = 2

  pad_x = 52
  pad_y = 120
  pad_dx = 0
  pad_dy = 0
  pad_w = 24
  pad_h = 3
end

function _update()
  local buttpressed = false
  local next_x, nexty

  if btn(0) then
    --left
    buttpressed = true
    pad_dx = -5
  end

  if btn(1) then
    --right
    buttpressed = true
    pad_dx = 5
  end

  if not(buttpressed) then
    pad_dx = pad_dx / 2
  end

  pad_x += pad_dx

  next_x = ball_x + ball_dx
  nexty = ball_y + ball_dy

  if nextx > 127 or nextx < 0 then
    nextx = mid(0,nextx,127)
    ball_dx = -ball_dx
    sfx(0)
  end
  if nexty > 127 or nexty < 0 then
    nexty = mid(0,nexty,127)
    ball_dy =- ball_dy
    sfx(0)
  end
  if ball_box(nextx, nexty, pad_x, pad_y, pad_w, pad_h) then
    if deflx_ballbox(ball_x, ball_y, ball_dx, ball_dy, pad_x, pad_y, pad_w, pad_h) then
      ball_dx =- ball_dx
    else
      ball_dy =- ball_dy
    end
    sfx(1)
  end

  ball_x = nextx
  ball_y = nexty
end

function _draw()
  cls()
  rectfill(0, 0, 127, 127, 1)
  circfill(ball_x, ball_y, ball_r, 10)
  rectfill(pad_x, pad_y, pad_x + pad_w, pad_y + pad_h, 7)
end

function ball_box(bx, by, box_x, box_y, box_w, box_h)
  if by-ball_r > box_y+box_h then
    return false
  end
  if by+ball_r < box_y then
    return false
  end
  if bx-ball_r > box_x+box_w then
    return false
  end
  if bx+ball_r < box_x then
    return false
  end
  return true
end

function deflx_ballbox(bx, by, bdx, bdy, tx, ty, tw, th)
  -- calculate wether to deflect the ball
  -- horizontally or vertically when it hits a box
  if bdx == 0 then
    -- moving vertically
    return false
  elseif bdy == 0 then
    -- moving horizontally
    return true
  else
    -- moving diagonally
    -- calculate slope
    local slp = bdy / bdx
    local cx, cy
    -- check variants
    if slp > 0 and bdx > 0 then
      -- moving down right
      cx = tx - bx
      cy = ty - by
      if cx <= 0 then
        return false
      elseif cy / cx < slp then
        return true
      else
        return false
      end
    elseif slp < 0 and bdx > 0 then
      -- moving up right
      cx = tx - bx
      cy = ty + th - by
      if cx <= 0 then
        return false
      elseif cy / cx < slp then
        return false
      else
        return true
      end
    elseif slp > 0 and bdx < 0 then
      -- moving left up
      cx = tx + tw - bx
      cy = ty + th - by
      if cx >= 0 then
        return false
      elseif cy / cx > slp then
        return false
      else
        return true
      end
    else
      -- moving left down
      cx = tx + tw -bx
      cy = ty - by
      if cx >= 0 then
        return false
      elseif cy / cx < slp then
        return false
      else
        return true
      end
    end
  end
  return false
end