G'MIC Snow Animation

# Generate snow animation.
snow :
  nb_frames=400

  # Generate volumetric image of rotating snowflakes.
  shape_snowflake 300
  repeat 100 {
    f:=3+0.5*$> +resize[0] $f%,$f%,1,1,2 rotate. {lerp(0,90,$>/10)},1,0
  }
  remove[0] append z,0.5 autocrop. rescale2d. 16

  # Generate time-parameterized motion curves.
  local[] { 8,1,1,{3*1000} rand. 0,1 s c,-3 rbf $nb_frames,0,1 append c }

  # Render animation frames.
  repeat $nb_frames { f=$>
    echo[] "\r  > Frame "{$f+1}/$nb_frames
    400,400
    {1,s/3},1,1,1,"
      begin(P = I[#1,"$>"]; S = vector(#w#0*h#0*3,255));
      k3 = 3*x;
      x = P[k3]*w#-1;
      y = P[k3 + 1]*h#-1;
      r = round(lerp(0,d#0 - 1,cut(P[k3 + 2],0,1)));
      M = crop(#0,0,0,r,w#0,h#0,1);
      draw(#-1,S,x,y,0,0,w#0,h#0,1,1,0.75,M);
    " remove.
    text_outline. "Snow",0.5~,0.5~,${"font macondo,150"},3,1,255
  }
  remove[0,1]