make the default scene a bit more interesting

glsl/raymarching.js

  return length(pos) - 1.0;
}
float sphere(vec3 pos, float size) {
  return length(pos) - size;
}
float udBox( vec3 p, vec3 b ) {
  return length(max(abs(p)-b,0.0));
}
float pMod1(inout float p, float size) {
  float halfsize = size * 0.5;
  float c = floor((p + halfsize)/size);
  pMod1(pos.x, offset.x);
  pMod1(pos.y, offset.y);
  pMod1(pos.z, offset.z + sin(iGlobalTime));
  return sphere(pos);
  //return sphere(pos);
  return min(sphere(vec3(pos.x, pos.y - 0.5, pos.z), 0.75),
             udBox(pos, vec3(1.0, 0.3, 1.0)));
}
mat3 setCamera( in vec3 ro, in vec3 ta, float cr ) {