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

void main(void)
{
  vec2 halfres = u_Resolution.xy / 2.0;
  vec2 cPos = (v_TexCoord.xy + vec2(u_WalkOffset.x, u_WalkOffset.y)) * u_Resolution;

  cPos.x -= 0.5 * halfres.x * sin(u_Time / 2.0) + 0.3 * halfres.x * cos(u_Time) + halfres.x;
  cPos.y -= 0.4 * halfres.y * sin(u_Time / 5.0) + 0.3 * halfres.y * cos(u_Time) + halfres.y;
  float cLength = length(cPos);

  vec2 uv = v_TexCoord.xy + ((cPos / cLength) * sin(cLength / 30.0 - u_Time * 10.0) / 25.0) * 0.15;
  vec3 col = texture2D(u_Tex0, uv).xyz * 250.0 / cLength;

  gl_FragColor = vec4(col, 1.0);
}