code: function(t) {
          // return if the texture is already bound
          if (t.unit !== null) return;
          var i = this.getAvailableUnit();
          if (this.bound_textures[i]) {
              this.unbindTexture(this.bound_textures[i]);
          }
          this.bound_textures[i] = t;
          t.bind(i);
      }
docs: takes a texture object and, if it isn't associated with a unit, binds it to one