ludic/examples/snake.ludic

# ============================================================================
# snake.ludic — a small, complete game in Ludic. No sprites or assets: every
# pixel is drawn from primitives. Build: bin/x app examples/snake.ludic
#
# It shows the everyday shape of a Ludic game: an ECS for the moving parts (one
# entity per snake segment), named program state for the rest, and a Render
# handler that paints the frame with the Screen API and named colors.
# ============================================================================
program Snake {

  property Pos { x: int = 0, y: int = 0 }
  property Seg { order: int = 0 }              # 0 = head, 1.. = body toward the tail

  const GRID_W:    int = 20                     # playfield, in tiles
  const GRID_H:    int = 15
  const TILE:      int = 16                     # pixels per tile

  const DIR_UP:    int = 0
  const DIR_DOWN:  int = 1
  const DIR_LEFT:  int = 2
  const DIR_RIGHT: int = 3

  const MODE_PLAY: int = 0
  const MODE_OVER: int = 1

  # ---- the game's whole state, named ----------------------------------------
  var direction: int = DIR_RIGHT
  var length:    int = 3
  var tick:      int = 0
  var food_x:    int = 14
  var food_y:    int = 7
  var mode:      int = MODE_PLAY
  var score:     int = 0
  var ate:       int = 0                        # did the head reach the food this step?
  var tail_x:    int = 0                        # where the tail sat before it moved (grow here)
  var tail_y:    int = 0
  var acked:     int = 0                        # game-over key must be released before restart

  # ---- custom shades this game uses (values the named palette doesn't carry) -
  const SHADE_BG:      int = 0x0d1020           # backdrop behind the board
  const SHADE_TILE_A:  int = 0x141a2e           # checkerboard, light square
  const SHADE_TILE_B:  int = 0x10162a           # checkerboard, dark square
  const SHADE_FOOD:    int = 0xe0405a
  const SHADE_BODY:    int = 0x40c060
  const SHADE_HEAD:    int = 0x9dffb0
  const SHADE_SCORE:   int = 0xffe060
  const SHADE_OVER:    int = 0xff5555

  function reset(unused: int) -> int {
    for (p, s) in query [Pos, Seg] { despawn self() }
    spawn S0 { Seg { order: 0 };  Pos { x: 10, y: 7 } }
    spawn S1 { Seg { order: 1 };  Pos { x: 9,  y: 7 } }
    spawn S2 { Seg { order: 2 };  Pos { x: 8,  y: 7 } }
    direction = DIR_RIGHT
    length = 3
    tick = 0
    mode = MODE_PLAY
    score = 0
    food_x = 14
    food_y = 7
    return 0
  }

  handler Boot phase Start { reset(0) }

  handler Input phase Input {
    let k = Input.key()
    if mode == MODE_PLAY {
      if k == 'w' { if direction != DIR_DOWN  { direction = DIR_UP } }
      if k == 's' { if direction != DIR_UP    { direction = DIR_DOWN } }
      if k == 'a' { if direction != DIR_RIGHT { direction = DIR_LEFT } }
      if k == 'd' { if direction != DIR_LEFT  { direction = DIR_RIGHT } }
    }
    if mode == MODE_OVER {
      if k == 0 { acked = 1 }
      if k != 0 { if acked == 1 { reset(0) } }
    }
  }

  handler Move phase Update {
    if mode == MODE_PLAY {
      tick = tick + 1
      if tick >= 6 {
        tick = 0
        # remember the tail cell, then drag every segment onto the one ahead of it
        for (pt, stg) in query [Pos, Seg] {
          if stg.order == length - 1 { tail_x = pt.x;  tail_y = pt.y }
        }
        for step in 0 .. length {
          let i = length - 1 - step
          if i >= 1 {
            for (pa, sa) in query [Pos, Seg] {
              if sa.order == i {
                for (pb, sb) in query [Pos, Seg] {
                  if sb.order == i - 1 { pa.x = pb.x;  pa.y = pb.y }
                }
              }
            }
          }
        }
        # move the head, check the walls, check the food
        ate = 0
        for (ph, sh) in query [Pos, Seg] {
          if sh.order == 0 {
            if direction == DIR_UP    { ph.y = ph.y - 1 }
            if direction == DIR_DOWN  { ph.y = ph.y + 1 }
            if direction == DIR_LEFT  { ph.x = ph.x - 1 }
            if direction == DIR_RIGHT { ph.x = ph.x + 1 }
            if ph.x < 0       { mode = MODE_OVER }
            if ph.x >= GRID_W { mode = MODE_OVER }
            if ph.y < 0       { mode = MODE_OVER }
            if ph.y >= GRID_H { mode = MODE_OVER }
            if ph.x == food_x { if ph.y == food_y { ate = 1 } }
          }
        }
        # self-collision: head onto any body segment
        for (ph, sh) in query [Pos, Seg] {
          if sh.order == 0 {
            for (pb, sb) in query [Pos, Seg] {
              if sb.order > 0 {
                if pb.x == ph.x { if pb.y == ph.y { mode = MODE_OVER } }
              }
            }
          }
        }
        if ate == 1 {
          score = score + 1
          spawn Body { Seg { order: length };  Pos { x: tail_x, y: tail_y } }
          length = length + 1
          food_x = Random.range(low: 0, high: GRID_W - 1)
          food_y = Random.range(low: 0, high: GRID_H - 1)
        }
      }
    }
  }

  handler Draw phase Render {
    Screen.clear(SHADE_BG)
    # checkerboard field
    for gy in 0 .. GRID_H {
      for gx in 0 .. GRID_W {
        var tile_color = SHADE_TILE_A
        if (gx + gy) % 2 == 0 { tile_color = SHADE_TILE_B }
        Screen.fill_rectangle(x: gx * TILE, y: gy * TILE, width: TILE, height: TILE, color: tile_color)
      }
    }
    # food, inset a few pixels inside its tile
    Screen.fill_rectangle(x: food_x * TILE + 3, y: food_y * TILE + 3, width: TILE - 6, height: TILE - 6, color: SHADE_FOOD)
    # every snake segment, straight from the ECS
    for (p, s) in query [Pos, Seg] {
      var seg_color = SHADE_BODY
      if s.order == 0 { seg_color = SHADE_HEAD }           # the head is brighter
      Screen.fill_rectangle(x: p.x * TILE + 1, y: p.y * TILE + 1, width: TILE - 2, height: TILE - 2, color: seg_color)
    }
    Screen.draw_text(x: 6, y: 4, text: "SCORE", color: Color.White, scale: 1)
    Screen.draw_number(x: 52, y: 4, value: score, color: SHADE_SCORE, scale: 1)
    if mode == MODE_OVER {
      Screen.draw_text(x: 112, y: 104, text: "GAME OVER", color: SHADE_OVER, scale: 2)
      Screen.draw_text(x: 84, y: 140, text: "PRESS ANY KEY", color: Color.White, scale: 1)
    }
    Screen.show()
  }
}