JS1k: The JavaScript code golfing competition

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/* The Plundering Sailsman
 *
 * 1024 byte game featuring timed navigation challenges in a procedurally
 * generated archipelago.
 *
 * Notes:
 *
 *    It had to fit in 1024 bytes after packing, so expect tortured syntax and
 *    repetition for compression.
 *
 *    Unreserved globals with a static literal value are removed and their
 *    values put in-place by the build script to save variables. The rest are
 *    assigned single character names.
 *
 *    A C preprocessor is used to inline the random number generator.
 *
 */

SEA = 0
LAND = 1
CONTOUR = 2

COIN = "💰"
RUN = "🏃"
SAIL = "⛵"
HOME = "🏡"

/* 31 is a recurring constant.
 */
MARGIN = 31
FRAME_INTERVAL = 31

/* Dimensions are chosen for their compact literal representations.
 */
W = 1e3
H = 6e2
AREA = 6e5
AREA_MUL_4 = 24e5

// The working terrain which serves as the terrain map and an ImageData.
terrain = Array(AREA);
image = c.getImageData(0,0,W,H);

// The "a" is there to make the CSS parse
c.font = "31px a"

// g initialised outside the loop helps compression.
repeat=(a,r,g,s)=> { g=0; for(;g<r;) a(g++); }

// Returns the grid index of some possibly non-integer coordinates (a,r)=(x,y)
index=(a,r,g,s)=>W*(r|0)+a|0

// Gets grid value of some coordinates or 0 (SEA) if out-of-bounds.
get=(a,r,g,s)=>+terrain[index(a,r)]

/* The maps need a seedable random number generator. This is a Lehmer LCG with
 * prime modulus 2^31-1 and a small multiplier to save space. In JS you could
 * write the modulus shorter as ~1e25 but it doesn't help in this case because
 * 31 and -1 get compressed.
 */
RNG_M = 2**31-1
RNG_A = 95
#define urand() ((rng_state=RNG_A*rng_state%RNG_M)/RNG_M)
#define irand(x) ((rng_state=RNG_A*rng_state%RNG_M)%x)

// map generation
generate_map=(a,r,g,s)=>{

  rng_state = map_id = a||1;

  terrain.fill(LAND)

  // s plots a pixel if it's within the margin
  s=(a,r,g,s)=>
      a>MARGIN
      &&a+MARGIN<W
      &&r>MARGIN
      &&r+MARGIN<H
      &&(terrain[index(a,r)]=CONTOUR);

  // generate pseudorandom coastline contours
  repeat(i=>{
    a = urand()
    Y=y=urand()*H
    X=x=urand()*W

    repeat(i=>{
      a += urand()+urand()+urand()-1.5 // approx normal angle peturbation
      r = urand()**4 * 31 + 3          // exponential random step

      x += Math.sin(a) * r,
      y += Math.cos(a) * r

      // stroke the line from X,Y to x,y
      g = Math.hypot(u=X-x,v=Y-y)
      X = x
      Y = y
      repeat(i=>s(x+u/g*i,y+v/g*i),g);
    },95)
  },31);

  // flood the perimeter with sea
  s = [u=1]
  v=i=>terrain[i]==1&&(terrain[s[u++]=i]=0);
  for(;u;
    g = s[--u],
    v(g+1),
    v(g-1),
    v(g+W),
    v(g-W));

  // filter out the contours, leaving just sea and land
  repeat(i=>terrain[i]-CONTOUR ? r=terrain[i] : terrain[i]=r,7e5);

  // map the terrain through a palette into the ImageData
  repeat(i=>image.data[i]="05786738"[terrain[i>>2]*4+i%4]*31,AREA_MUL_4);

  // scatter the gameplay objects on appropriate terrain
  random_point=i=>{for(;get(x=irand(W),y=irand(H))-i;);}
  objects = [];
  u=0;
  s=(a,r,g,s)=>(random_point(a),objects[u++]={x,y,r});
  repeat(i=>s(LAND, COIN),9);
  s(LAND, HOME);
  player=s(t=LAND, RUN);
  goal=s(LAND,'');

  // initialise game state
  running = score = time = u = v = 0

}

setInterval(i=>{

  // draw the map background
  c.putImageData(image, 0, 0);

  // game step
  if(running) {

    time += 31;

    // apply terrain-specific friction and impulse towards the goal
    r = Math.hypot(x=goal.x-player.x,y=goal.y-player.y)
    u = x / r * (t?1:.3) + (t?.6:.97) * u;
    v = y / r * (t?1:.3) + (t?.6:.97) * v;

    // update player x/y and terrain
    g = get(player.x+=u, player.y+=v);

    // kill velocity if transitioning from sea <-> land
    if(g^t)u=v=0;

    // set the player image based on its terrain
    player.r = (t=g) ? RUN : SAIL;

    // trace the route (knocks out the alpha component to show the white bg)
    image.data[3+index(player.x, player.y)*4]=0;
  }

  objects.map(i=>{

    // check for proximity to the player (coins and home)
    if(Math.hypot(player.x-i.x, player.y-i.y)<31 & t==LAND) {

      if(i.r == COIN)
        ++score,
        i.r='';

      if(i.r == HOME & score>8)
        running=0,
        goal.r=player.r='';
    }

    // draw object
    c.fillText(i.r, i.x - 17, i.y)
  })

  // draw the map status
  c.fillText(`<🔄> #${map_id} ⌛${time/1e3}`,6,MARGIN)

}, FRAME_INTERVAL)

// start level on click if paused, and operate a minimal UI
onclick=(a,r,g,s)=>{

  // start game loop on click if it's not already running
  running=running|!time

  // move the goal the the mouse coords
  goal.x = a.clientX
  goal.y = a.clientY
  goal.r = "❌"

  // treat the upper corner as 3 buttons which adjust the map seed by -1 / 0 / +1
  goal.y<MARGIN && goal.x<95 && generate_map(map_id-1+goal.x/31|0);
}

generate_map()