This generates clouds in the DayNight.shader
if you change ctime to -ctime they go the opposite way.
vec3 cloud2(float cloudheight,float scale)
{
vec2 p=vec2(vp.zx/(vp.y))*cloudheight;
vec3 c = vec3(.0, .0, .2);
c.rgb += vec3(.6, .6, .8) * cloud(p*.3+ctime*.0002,scale)*.5;
c.gbr += vec3(.8, .8, 1.) * cloud(p*.2+ctime*.0002,scale)*.1;
c.grb += vec3(1., 1., 1.) * cloud(p*.1+ctime*.0002,scale)*1.;
return c.rrr;
}