uniform float u_Time;
uniform sampler2D u_Tex0;
varying vec2 v_TexCoord;
uniform vec2 u_WalkOffset;

float rainLayer(vec2 uv, float scale, float ttime)
{
  float w = smoothstep(1., 0., -uv.y * (scale / 5.));
  if (w < .1) return 0.0;

  uv += ttime * 0.5 / scale;
  uv.y += ttime * 2.5 / scale;
  uv.x += sin(uv.y + ttime * .10) / scale;
  uv *= 1.2 * scale;
  vec2 s = floor(uv), f = fract(uv), p;

  float k = 3.0;
  float d = 0.0;

  p = .5 + .35 * sin(11. * fract(sin((s + p + scale) * mat2(7, 3, 6, 5)) * 5.)) - f;

  d = length(p);
  k = min(d, k);
  k = smoothstep(0., k, sin(f.x + f.y) * 0.01);
  return k * w;
}

void main(void)
{
  vec4 Game = texture2D(u_Tex0, v_TexCoord);
  vec2 uv = ((gl_FragCoord.xy) * 2.5) / 200. + vec2(u_WalkOffset.x, u_WalkOffset.y);

  float ttime = mod(u_Time * 1.0, 1000.);

  uv.x -= (uv.y) * 0.9;
  uv.y += 1.0;
  uv.y = dot(uv * 0.055, uv * 0.125);

  float rain = (0.0);

  rain += rainLayer(uv, 2.0, ttime);
  rain += rainLayer(uv, 3.0, ttime);
  rain += rainLayer(uv, 4.0, ttime);

  float opacity = 0.6;
  gl_FragColor = vec4(Game + rain * opacity);
}