//...
float cost =0.0;
for (int cam_x = 0; cam_x < num_cams; cam_x++){
  for (int cam_y = 0; cam_y < num_cams; cam_y++){
      ivec2 cam = ivec2(cam_x,cam_y);
      vec2 cam_disp = disp * (camera-cam);
      vec3 d = color - lookup(cam, vec2(px + cam_disp)).rgb;
      cost += dot(d,d);
  }
}
//...