Simple spiral GLSL shader

main.s

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
   vec2 mpos = iMouse.xy / iResolution.xy;
   vec2 pos = fragCoord.xy / iResolution.xy;
 
   const float R = 1.5;

   vec2 kpos = pos - mpos;
   float r = length (kpos);
   float phi = atan (kpos.y, kpos.x);

   phi += 100.0 * r/R + 10.0*iGlobalTime;
//   phi += 1.0 * R/r + 10.0*iGlobalTime;

   kpos = r * vec2 (cos (phi), sin (phi));
   if (r <= R) {
//        vec2 tex = mpos + kpos / (1.0);
        vec2 tex = mpos + kpos / (2.0 * R);

        fragColor = texture2D (iChannel0, tex);
   } else {
        fragColor = texture2D (iChannel0, pos);
   }
}