code: function init(ctx) {
    if (glEnums == null) {
      glEnums = { };
      for (var propertyName in ctx) {
        if (typeof ctx[propertyName] == 'number') {
          glEnums[ctx[propertyName]] = propertyName;
        }
      }
    }
  }
docs: Initializes this module. Safe to call more than once.
  @param {!WebGLRenderingContext} ctx A WebGL context. If
  you have more than one context it doesn't matter which one
  you pass in, it is only used to pull out constants.